Many thanks to SWLing Post contributor, Alexander (DL4NO), who writes:
A Message from Germany: Growing Disaster Preparedness favours Ham Radio
For a long time most radio amateurs in Germany found themselves in the defensive: Building regulations, combined with EMC standards, heavily restrict antenna possibilities. Neighbors fear “dangerous” radiation, often going to court without any legal reasons. Emergency services got a much improved digital communication systems (TETRA), removing many of the artificial borders where they sometimes used ham radio to build bridges.
This could be quite different, as you can see in Austria. If radio amateurs organize a congress about emergency traffic, even the federal government and the Austrian army send competent representatives.
But the political turmoil and the connected energy crisis change attitudes in quite some branches of administrations:
The county of Ebersberg, east of Munich, is well known for its initiatives. Recently they invited the regional chapter of DARC, our German ham radio society, to discuss the build-up of a resilient data net for the county. In normal times, this data net could be used as part of HAMNET, our part of 44net. The county and towns would help to get access to suitable positions, including power supply. Some of the stations, for example on town halls, might be dormant most of the time. But as soon as power goes out, local radio amateurs are to activate the emergency net. The first application is to be VoIP, i.e. a independent phone service.
The county of Freising, a few km to the north, is also interested in working together with radio amateurs. We are just building a task force for this.
These activities are quite different from traditional emergency traffic. The most important difference: We work as enablers, not as radio officers. Our task will be to maintain the system, make it operational in case of an emergency, and introduce the officials to its use.
This is critical as we do not have enough radio amateurs to get the messages, send them over our system, and hand them down to the respective officer: Multply 2 radio amateurs by 3 shifts per day by a new crew every second day by the number of sites.
And in normal times, we can enjoy a much improved HAMNET coverage. Until now, most radio amateurs only had to access 44net through VPNs over the Internet.
As I’ve mentioned in past articles, I believe taking some precautions against EMPs is important. While I feel that an intentional nuclear EMP is unlikely, our local star can cause even more damage to an even larger portion of our planet if it decides to cause a solar storm like the Carrington Event.
Many thanks to SWLing Post contributor, Jock Elliott, who shares the following guest post:
The Crisis Radio
By Jock Elliott, KB2GOM
Sooner or later, it will happen to you. What’s ‘it’? Short answer: a crisis.
It could be as simple as you wake in the morning to find the power is out; you don’t know how long it has been out, and you don’t know when it is coming back. It might be a weather event: a blizzard, a sandstorm, a tornado, a derecho, a hurricane. It might be a geologic event like a tsunami, earthquake, or even volcanic activity. As recent events have shown, it could even be a war or a revolution.
When normal life is disrupted, and uncertainty is perched on your shoulder like a vulture, you will want to know what’s going on, and your usual means of getting information – telephone, smart phone, internet device – may also be disrupted.
When that happens, radio can come to your rescue. Your local FM or AM (medium wave) station may be on the air, providing vital information to your community, or NOAA Weather Radio may be providing hazard information. In extreme cases, shortwave radio may be beaming information to your area when all else fails.
So I have a couple of very specific recommendations.
First, make sure that your household has a “crisis radio.” By that I mean one that will receive your local AM and FM broadcasters as well as shortwave radio, and, if you live in the US or Canada, NOAA Weather Radio. If you can afford it, I recommend getting a crisis radio that has single sideband capability (SSB) so that you have the ability to intercept ham radio communications, which might be another source of information.
Toward that end, I can heartily recommend the CCrane Skywave SSB radio. (Let’s be clear: I have no commercial connection with CCrane; I get nothing from them for making this recommendation, I purchased my Skywave SSB with my own money.) It has AM, FM, Shortwave, Weather, VHF, Aviation and SSB Bands. It is very small, measuring just 4.8″ W x 3″ H x 1″ D and weighing just 6 ounces without batteries. It will run for over 50 hours on a couple of AA batteries and comes with CC Earbuds, SkyWave SSB Carry Case, and CC SW Reel Antenna which boost sensitivity for shortwave and ham radio listening.
It is a crisis radio that you can stick in your pocket, backpack, purse or briefcase for deployment when the need arises or you simply want to listen to some radio programming. Further, you don’t have to be an expert to operate the CCrane Skywave SSB. Thanks to the Automatic Tuning System, just select the band you want to listen to, press and hold the ATS button for two seconds, and the Skywave SSB will automatically search for stations in that band (AM, FM, Shortwave, etc.) and store those stations in the memory banks for that band. You can later check those memories to hear what programming those stations are broadcasting.
Second, and this is important, if you listen to shortwave radio at all, take the time to let the stations know. Drop them a postcard; shoot them an email, do whatever you can to inform them you are listening, and you value their transmissions.
Why? Because we all want those stations to be there if and when the next crisis happens. And if your local AM or FM station provides special programming to the community a weather event or geologic emergency, for the same reason, be sure to let them know how much you appreciate their efforts.
As a fire captain observed a couple of years after the North Ridge earthquake in California: “You cannot be over-prepared for communications in an emergency.”
I entitled this review an “Everyman” review because, while I am far from “normal” (just ask any of my friends!), I am not a hard-core SWL. I am a hard-core amateur radio operator perhaps, but only for the last decade(+). I have been casually listening to shortwave radio for about 50 yrs. So, my perspective on this radio comes from someone who cut his teeth on a Realistic DX-160 (still love those radios!), progressing through various desktop and portable radios, to three of my current favorites, the FRG-7, the Sangean 909X2, and the Sony 7600GR. Of course, this doesn’t count some vintage WWII-era radios and earlier, but they are favorites for other reasons.
Now, the purpose of this little reflection on equipment is to say all radios have their place in the pantheon of shortwave radios, and no one radio “does it all.” The Tecsun radio, I believe, fills a very specific niche in the radio world, and it is excellent for those purposes. It does not, however, rival other radios whose goals are different, such as ones designed around sound fidelity, digital signal processing, SDR capability etc.
What this radio does do is present a very capable radio in an ultra-small package, designed to fit easily for travel and for survival/emergency situations, or for armchair operation. That middle one may surprise you, so allow me to explain.
I have a previous model of this radio (GP-5/SSB still available) sold by CountyComm, which was modified from Tecsun’s stock production PL-365, to have features suitable for government use. This has become a rather popular radio for preppers because of those modifications. The idea behind this radio as a compact piece of kit for government embassy people was to have something which could be easily concealable, operated with one hand, and have a wide range of reception capabilities. Of course, good reception of shortwave, AM, and FM bands was considered a must. You can look at the CountryComm website to find out specific features of the modified units if interested, as that radio, or the PL-365, are not the subject of this review.
While not a real “prepper” myself, I was intrigued by the AM broadcast reception capabilities due to the plug-in ferrite antenna, and also liked the idea of the small footprint. In actual use I found the radio to be quite versatile, a good performer, but rather awkward to use as there was no quick way to get to specific frequencies, unless already programmed into a memory location. With no direct keyboard entry on the GP-5, going to random locations to channel surf was, for me, frankly a bit annoying.
Enter the PL-368 which boasts a direct keyboard entry! Yes!! This one feature has taken the radio to a new level of performance which makes it a joy to use in this reviewer’s humble opinion. (Full disclosure, the unit I received for this review was provided by ANON-CO, and is the latest model after the recent firmware update incorporated by Tecsun. However, I have no other connection to ANON-CO or Tecsun, and my willingness to do the review is purely based on my previous purchase and experience with the CountyComm model.)
Despite having an unusual number of stormy days and nights here in the Midwestern U.S. recently, I have managed to enjoy some very productive listening opportunities with this little radio. For example, being an amateur radio operator, I appreciate the ability to listen in on the amateur frequencies now an again, and the recent ARRL Field Day afforded me the opportunity to really test out the radio’s USB/LSB reception capabilities, and its ability to dig out signals on a really crowded band. I was quite impressed both with its DSP and bandwidth capabilities and the reasonable clarity of the audio when tuning in various signals. Does it have the richness of audio that my Sangean 909X2 has? No, of course not. The speaker is much smaller in the PL-368, but it was quite listenable. Likewise, listening to various nets on 80 meters was quite acceptable with the built-in antenna, where noise and local interference are common gremlins on any radio.
For shortwave stations I found the radio to be quite sensitive just using the built-in antenna, which is key to portable listening. If I have to attach an external antenna, my mobility becomes limited, and I might as well just listen to one of my desktop radios. Some reception examples include: NHK World Radio 9560, Helliniki Radiophonia Voice of Greece 9420, WRMI relay of KSKO 89.5’s Paul Walker from McGrath Alaska on 7780 (beamed to east coast U.S., as well as on 7730 beamed to west coast, Hawaii, and South Pacific).
Of course, reception of CRI, Radio Havana Cuba, and numerous religious broadcasts were heard on all the usual places. I also listened to WWV signals at various locations, my go-to initial band reception check, as well as listening to HF aircraft broadcasts, military planes training on 11175 (USB), and maritime weather broadcasts. While I did not try digital mode reception such as FT8 with WSJT-X from the headphone jack, I have no doubt I would have been able to monitor these stations on various bands easily as the signals were immediately recognizable. The same holds true for CW reception.
For a thoughtful, in-depth review of many technical aspects of this radio Dan Robinson has written an excellent piece on the PL-368, along with an updated review of the latest firmware’s effect on the radio. One aspect worth mentioning in my experience with this radio is that, unlike Dan, I did not find an issue with changing sensitivity when touching/holding the radio versus the radio standing on its own. Your mileage may vary, of course, so this goes in the “for what it’s worth” category. Maybe this issue has been resolved in later production runs? Or maybe my capacitance is running low and I need more electrolytes<grin>!
Like Dan, I found the SYNC detection of USB/LSB to be marginal at best, mostly making the signals harder to hear. On the upside, standard reception was quite good, and I did not experience significant fading most of the time.
Below are some of the hidden keyboard functions as listed, provided by Anna of ANON-CO, but I wanted to mention a feature I have either forgotten when using my GP5 CountyComm model, or which has been added (sorry, I don’t have access to the GP5 right now as it is packed away due to a recent move in progress). When “speed tuning” as I call it (turning the tuning dial quickly) with the “step” selected to the smallest increment on SW, what starts as increments of 10Hz will jump to 50Hz at a time after a few moments. This helps in trying to quickly latch on to a signal when increments of 10 are not necessary. The tuning will revert to 10Hz units when stopped for a few seconds.
Now for some undocumented features:
Switch between internal ferrite rod and whip on AM (MW & LW)
Select the MW or LW band.
Press and hold key ‘3’ for about 2 seconds.
When the display briefly shows “CH-5” this means that the device is set to MW/LW reception using the telescopic antenna. The display shows MW (or LW) and SW on the left side of the screen.
When the display briefly shows “CH-A” this means that the device is set to MW/LW reception using the internal ferrite antenna. The display shows only MW (or LW) on the left side of the screen.
Adjusting the maximum volume level
Select the frequency band, then press and hold key ‘7’ for 2 seconds until a number is displayed. At this moment, rotate the [ TUNING ] knob to adjust and press the key ‘7’ again to save and exit.
In power-off mode, press and hold [ VF/VM ] for 0.5 seconds until all characters on the display are shown, then wait a few seconds until the firmware version is briefly displayed in the middle of the display.
Extend SW-range for European setting (1621-29999 kHz)
In power-off mode, press and hold the [ 3 ] key to set the MW tuning steps to 9kHz.
Select the SW band, and then press and hold the [ 5 ] key for 10 seconds to enable/disable the SW frequency extension. The starting point of the SW frequency range will become 1621 or 1711 kHz.
Some Nitpicks (There had to be some, right?!)
I wish the batteries were still standard AA units instead of the flat rechargeable unit. This is merely a personal preference, but as a radio designed for carry-anywhere usage, I like a radio to use batteries I can pick up anywhere if needed. I tend to use rechargeable AA and AAA batteries anyway, but I like knowing I can use ubiquitous alkaline batteries available at almost any store in a pinch.
I suspect the change was made to allow for more space for the direct keypad entry, and that is definitely a tradeoff I am willing to make!
On a related note, the recharging port uses the USB micro-b connector which I have found in cell phones, tablets, etc. to be a weak point as cables often seem to go bad, or the connector itself gets damaged. The larger mini-b would be my preference, but hey, again, that’s a nitpick.
Finally, the case does appear to be a little thin which makes me wonder how it might survive if dropped or knocked off a table. This is not a deal-breaker by any means, but something to consider when carrying it around or when packing it for a trip. It may survive quite well, but that’s a test I don’t want to try out just to see what happens.
For me, as a casual shortwave listener, I look for several things in a portable radio. I want true portability – if a so-called portable radio must be tethered to an external antenna to work decently, chances are I am not going to use it often – my various desktop models attached to outdoor antennas will always out-perform a portable. I also want a simplified layout of controls. I do not want to dig through menus, have be a contortionist to work the buttons/controls, or carry a manual with me to find out how to use the radio each time because the controls are confusing. I also want reasonable audio and clarity, or the ability to fine-tune a signal to minimize adjacent signals.
I find the PL-368 does for me what I want a portable to do and does it reasonably well. Is it the best portable out there? No. Is it a benchmark radio? No. But it is extremely portable, easily handled with just one hand, and its reception capabilities put it far above some other portables I have used. If you are looking for something which can easily fit into a pocket, bag, or purse, this radio is great. If you want a radio which performs well over a wide range of signals using the built-in antenna, this radio fills the bill. And if you want true USB/LSB, along with good bandwidth options in your portable, this is a great choice. Cheers!
(edit, July 23, 2021: an additional “hidden” feature to be included in the shipping version not included in this reviewed unit is an SSB calibration capability – definitely a plus! — Robert)
Many thanks to SWLing Post contributor, Kostas (SV3ORA), for sharing the following guest post which originally appeared on his radio website:
Emergency transmitter: An 8-component, high-power 40m/30m transmitter to get you quickly on the air
by Kostas (SV3ORA)
QRP is all about doing more with less. This is more than true, with the construction of this cheap, simplistic transmitter presented here. It is designed primarily as an emergency transmitter (EMTX) that can be built or serviced in the field or at any home. However, it can be used as a HAM radio transmitter as well. Do not judge by its low components count though. This transmitter is powerful, more powerful than anything the QRPers would dream of. It is just remarkable how 8 components can lead in so much output power, that lets you communicate with a big part of the world, when propagation conditions are right. It is very difficult for a circuit to match that kind of simplicity in balance with such performance.
Following my detailed instructions, the EMTX can be reproduced easily, within hours. The result is always success, this is one of the circuits that are not critical at all and a successfully working transmitter can be reproduced every time. I have built this transmitter several times, using similar components (even toroids) and it always worked. The transmitter meets the next expectations:
1. Output power (including harmonics): A few mW up to 15W (depended on transistor, crystals and voltage/current used) at 50 ohm.
2. It can drive any antenna directly, 50 ohm or higher impedance, without external tuners.
3. Bands of operation: Currently 40m, 30m
4. Mode: CW, Feld-Hell (with external switching circuit), TAP code and any other ON/OFF keying mode. AM modulation has been easily applied too.
5. Options like reverse polarity protection diode (useful in the field when testing different unknown polarities PSUs) and current meter (for easier tuning) are available.
The purpose of this transmitter is to be used primarily as an emergency transmitter. This poses several challenges that influence the design of the transmitter:
1. It must be able to be built or serviced easily in the field or at any home, with components that could be salvaged from near by electronics sources or a small electronics junk box. This means that components count should be kept very low and they must not be rare to find but commonly available parts. As a side effect cost would also be kept small, if one is to buy any component. Also, the active components must be interchangable with many other devices without the need for the design or the rest of the circuit components to be changed.
2. It must be able to operate from a very wide range of DC voltage sources and at relatively low current, so that common house power supplies could be used to supply power to it. Such devices include linear or switched mode power supplies from laptop computers, routers, printers, cell phone chargers, Christmas lights or any other device one might have available.
3. It must be capable of transmitting a powerful signal, so that communication is ensured. An emergency transmitter that is capable of a few mW of output power, might be heard locally (still useful, but there are handheld devices for that already) but isn’t going to be of much usage if it can’t be heard really far away.
4. It must be capable of loading any antenna without external equipment required. In an emergency situation, you just don’t have the luxury of building nice antennas or carrying coaxial cables and tuners. There may be even extreme cases where you can’t even carry a wire antenna and you depend on salvaging wire from sources in the field to put out a quick and dirty random wire antenna.
5. Adjustments of the transmitter should be kept minimum without the help of any external equipment and there must be indication of the correct operation of the transmitter or the antenna in the field.
This transmitter has been designed so that it can operate with any NPN BJT in place. This includes small signal RF and audio transistors and high power RF transistors like the ones used on HF amplifiers and CB radios. Despite 2sc2078 is shown in the schematic, just try any NPN BJT in place and adjust the variable capacitor accordingly. When you are in the field, you do not have the luxury of finding special types of transistors. The transmitter must operate with any transistor in hand, or salvaged from near-by equipment. Of course the power capability of the transistor (as well as the crystal current handling) will determine the maximum VCC and current that can be applied to it and hence the maximum output power of the transmitter. Some of the most powerful transistors I have used, come out of old CB radios, such as the 2sc2078, 2sc2166, 2sc1971, 2sc3133, 2sc1969 and 2sc2312. There are many others. As an example, the 2sc2078 with a 20v laptop PSU, gave 10-12W of maximum output power into a 50 ohms load.
Schematic of the 8 components EMTX for the 40m/30m bands. Components with gray color are optional.
This is the most uncommon part of the transmitter. You have to find the crystal for the frequency that you want to operate on. Crystals within the 40m or 30m CW segments are not that common. Further more if you operate the transmitter at high powers and currents, you will notice crystal heating and chirp on the frequency of the transmitter. The current handling capability of your crystal die inside the crystal case, will determine the chirp and the amount of crystal heating. You can still work stations with a chirpy transmitter provided that the chirp is not that high, so that it can pass through the CW filters of the receivers. However, if a small chirp annoys you or if this chirp is too much, then you have to use these vintage bigger size crystals (e.g. FT-243), that can handle more current through them. But these are even more uncommon today.
The approach I have used in my prototype, was to connect more than one HC-49U crystals of the same frequency in parallel, so that the current is shared among them. This reduced the chirp at almost unnoticeable levels, even at high output power, just if I was using a single FT-243 crystal, or even better in some cases. Again, this is optional, but if you want to minimize chirp (and crystal heating) without searching for rare vintage crystals, this is the way to go.
A bit of warning. If you notice a very high chirp when plugging in a crystal to the EMTX, you should consider this crystal as inappropriate for this transmitter, as it cannot handle the current required. If you continue to use this inappropriate crystal, you could easily crack it inside and set it useless. Don’t use these tiny HC-49S crystals, they won’t work.
The current meter:
A 1Amp (or even larger) current meter can be used to monitor the current drawn by the transmitter during key down. The recommended current operating point is anywhere between 450mA to 1A, depended on the output power (and harmonics) level you want to achieve. The current point is set by the variable capacitor. I would avoid setting the current to more than 1Amp, although it can be done. The use of the current meter is optional, but along with the incandescent bulb, will give you a nice indication of the correct tuning of the transmitter, so that you do not need to have an external RF power meter connected to the transmitter output. If you do have, then you can remove the current meter. If you don’t have a 1Amp analogue meter available, but a smaller one, you can parallel a low value power resistor across the meter. In my case, I only had a 100uA meter and I paralleled a 0.15 ohms 5W resistor across it to scale down 1Amp to 100uA, The resistor value depends on the internal meter resistance so you have to calculate this for your specific meter. When the 2sc2078 is used at 20V, 500mA in the current meter indicates around 5W of output power, 600mA indicates around 6W, 700mA 7W, 800mA 8W, 900mA 9W and 1A around 10W. So the current meter can be used as sort of power meter without the need to do any scaling on it.
The incandescent bulb:
A current meter alone, without the use of the incandescent bulb, will not give you the right indication of the operation of the transmitter. In some cases, the transmitter might be drawing current without actually generating much, or even any RF. When you are in the field you do not want to carry extra monitoring equipment with you. The incandescent bulb will light on when the transmitter oscillates. It monitors the actual RF signal, so it’s brightness changes according to the amount of RF power the transmitter produces. Along with the current meter reading, this is just what you need to know in order to set the variable capacitor properly. Note that the bulb will not lit at very low signal levels. The one used in the prototype starts to glow up from a bit less than 1W. Miniature incandescent bulbs may not be that easy to find nowadays. However, there is a good source of these, that almost anyone has in their houses. This source is the old Christmas lights. You do save old Christmas lights, don’t you? The incandescent bulb indicator as well as it’s single turn winding on the transformer, are optional components. If you have an RF power meter connected to the transmitter, you can remove these.
The protection diode is an optional component to the circuit. If you are in the field, correct polarity of a power supply may not be obvious. Without a multimeter it might me difficult to determine the correct polarity of the PSU. A power diode (I used a 6A one) will protect the transistor from blowing up in the event that reverse polarity is connected to the circuit.
The Cx and Cy:
The Cx and especially the Cy capacitors need to be of good quality. The Cy will get hot on high output power if it isn’t. In the tests, I have used homemade gimmick capacitor and even double-sided PCB as a capacitor for Cy and they all got hot at high power. Silver mica capacitors run much cooler and they do make a small difference in the output power, so I suggest to this type. Cy must be able to handle quite a lot of voltage, so silver mica type is ideal.
The variable capacitor:
The variable capacitor can be air variable or ceramic, although I prefer air variables in tis application. In any case it must be able to handle a high voltage just as the Cy.
The key directly shorts the transistor emitter to the ground, therefore it is a part of the active circuit. For this reason, I suggest the key leads to be kept as short as possible. The key must be able to handle the voltage (20v) and current (up to 1A) on its contacts, which is usually not a big deal.
The construction of the transformer is shown below step by step. Note that if you decide that you don’t need to drive higher impedance loads but just 50 ohm ones (eg. antenna tuners or 50 ohm matched antennas), you just need to wind 2t in the secondary and not 14t. You also don’t need any taps of course.
Take a piece of 32mm external diameter PVC pipe from a plumber’s shop. Alternatively, a suitable diameter pills box can be used, or any other suitable diameter plastic tube.
Cut a 4cm piece out of this tube. 4cm is the minimum length required.
Below a 4cm PVC tube has been cut in size.
Wind 16 turns of 1mm diameter enameled wire onto the PVC pipe and secure the winding in place as shown in the picture below. Notice the winding direction of the wire. This is the primary of the transformer, the one that is connected to the two capacitors. Notice that this winding is wound a bit offset to the right of the pipe.
Wrap the winding with 3 turns of PTFE tape. It can be bought at any plumber’s shop, just like the PVC pipe. The PTFE tape will help in keeping the second layer turns in place and it will provide extra insulation.
Wind 2 turns of 1mm diameter enameled wire on top of the primary winding and secure the winding in place as shown in the picture below. Notice the winding direction of the wire, as well as it’s position relative to the primary winding. This is the feedback of the transformer, the one that is connected to the collector of the transistor.
Wind 14 turns of 1mm diameter enameled wire on top of the primary winding, starting from just next to the 2 turns one and secure this winding in place as shown in the picture below. Notice the winding direction of the wire, as well as its position relative to the primary and the 2 turns windings. This is the secondary (output) of the transformer, the one that is connected to the antenna. At this point do not worry about the taps yet.
Notice in the picture below, the way the windings are secured in place onto the pipe. The wire ends are passed through the pipe using small holes and then bent towards the ends of the pipe and once more to the surface of the pipe, where the connections will be made.
Wind 1 turn of 1mm diameter enameled wire onto the pipe and secure the winding in place as shown in the picture below. Notice the winding position relative to the other windings. This 1 turn winding is placed about 1cm away from the other windings. This is the RF pick up winding, the one that is connected to the incandescent bulb.
Use a sharp cutter (knife) and carefully scrap the enamel of all the windings ends. Do not worry if you cannot scrap the enamel at the bottom side of the wire ends (that touches to the pipe). We just want enough copper exposed to make the connection.
Tin the scrapped wire ends, taking care not to overheat them much.
Now it’s time to make the taps on the secondary winding. Use a sharp cutter (knife) and very carefully scrap the enamel of the wire at the tap points (number of turns). Take much care not to scrap the enamel of the previous and the next turn from each tap point. Do not worry if you just scrap the enamel at the top of the wire (external area). We just want enough copper exposed to make the connection.
Make each tap, a bit offset from the near by taps, like shown in the pictures. This will avoid any short circuits (especially at the 4, 5 and 6 taps) and it will allow for easier connections, especially if alligator clips are used to connect to the taps.
Tin all the tap points, taking care not to overheat them.
This step is optional and it depends on how you decide to do the connections to the taps. You may solder wires directly to the tap points, but in my case I wanted to use alligator clips, so I did the next: I took a piece of a component lead and soldered it’s one end to each tap point. Then I bent the component lead to U-shape and cut it accordingly. This created nice and rigid tap points for the alligator clip.
This step is optional and it depends on how you decide to mount the transformer to your enclosure. In my case, I wanted to create three small legs for the mounting. I cut three pieces of aluminum straps and made holes at both their ends. I made three small holes onto the transformer pipe end and mounted the aluminum straps using screws. After mounting them, I shaped the straps to L-shape. Then I used three more screws to mount the transformer to the enclosure.
The completed transformer is shown in the pictures above and below. The 6 connection points at the bottom of the pipe, are the low voltage points, whereas the 2 points at the top of the pipe, are the high voltage points.
If you have built the transformer as described, the bottom connections are as follows (from left to right):
Wire end 1, connected to the incandescent bulb
Wire end 2, connected to the incandescent bulb
Wire end 3, connected to the current meter
Wire end 4, connected to the current meter
Wire end 5, connected to the GND (ground)
Wire end 6, connected to the transistor collector
The top connections are as follows (from left to right):
Wire end 1, connected to the 25pF variable capacitor and the Cy fixed.
Wire end 2, is the 14th secondary tap and it is left unconnected, or tapped to the appropriate impedance antenna.
Videos of the EMTX in operation
I have made two small videos of the EMTX in operation.
The first 13.5MB video (right click to download), shows the operation when the transmitter is set for a bit less than 10W of output power.
The second 3.5MB video (right click to download), shows the operation when the transmitter is set for about 5W of output power.
EMTX chirp analysis
Every self-exited power oscillator (and even many multi-stage designs) exhibits some amount of chirp. Chirp is mainly considered as the sudden change in frequency when the power oscillator is keyed down. Apart from chirp, there is also the longer term frequency stability that may be considered. The chirp in the EMTX is surprisingly low, if it is built properly. Hans Summers, G0UPL has performed a chirp analysis on my EMTX (PDF) and the EMTX built by VK3YE and presented on YouTube. Hans, performed the analysis from the video/audio recordings of both transmitters. I sent him two videos, one with the EMTX set for an output power of 10W and one where it is set for 5W. The chirp at worst case (10W) was about 30Hz and at 5W in the order of 10Hz or so. Being so small, the chirp is almost undetectable by the ear and it surely poses no problems when passing the tone through narrow CW filters. This is an amazing accomplishment from a transmitter so simple and so powerful.
EMTX harmonics measurement
Every unfiltered transmitter will excibit harmonics at it’s output. This means that the output waveform has some distortion in comparison to a pure sinewave. Many of the transmitters I have seen, present a very distorted output waveform and absolutely need a LPF if they are to be connected to an antenna. I can’t say that this is true for the EMTX, because surprizingly, it has low distordion, despite the high output power it can achieve. Although a LPF is always a good idea, it is not that much needed on the EMTX. However you have to use one to comply with the regulations.
The image above, shows the measurements on the output of the EMTX, when it is set closely to 10W at 50 ohms. The main carrier is exactly at 9.9W and all the harmonics are less than 50mW! Also, the harmonics, do not extend into the VHF region.
The image below, shows the measurements on the output of the EMTX, when it is set closely to 5W at 50 ohms. The main carrier is exactly at 5.17W and all the harmonics are less than 9.6mW! Again, the harmonics, do not extend into the VHF region.
These small harmonics levels aren’t going to be heard very far at all, compared to the powerful carrier. This means only one thing. A LPF, although a good practice, is not mandatory in this transmitter. But you should better use one so that you comply with the regulations.
Many HAMs use just a watt meter to measure the output of their homebrew transmitters. This is not the proper way of doing it, because the watt meter is a non-selective meter. It will measure both the fundamental carrier and the harmonics, without being able to distinguish them. So in an unfiltered transmitter, or in a transmitter with a simple (often non measured) LPF, this way will give a totally false reading of the output power of the transmitter at the set frequency.
The proper way of accurately measuring the output power of a transmitter and the harmonics levels, is a spectrum analyzer. The FFT available in many modern oscilloscopes, having a dynamic range of approximately 50-55dB, is adequate for this purpose as well. A 50 ohms dummy load must be connected at the transmitter output and then the high impedance probe of the scope, is connected to the output of the transmitter as well. This was the way that the above measurements have been performed.
Here are some test transmissions, to determine how far one can get with such a transmitter. I have to say that there is an antenna tuner between the EMTX and my inefficient short dipole (not cut for 40m and not even matched to the coaxial). However I could still cover a distance of more than 2500Km even on the 5W setting.
A screenshot of the transmitter signal, as received on a WebSDR 2500Km away and when the EMTX is set for an output power of 10W.
Below, is a picture and an audio recording of the transmitter signal, as received on the same WebSDR and when the EMTX is set for an output power of 5W.
Pictures of the finished transmitter. You don’t have to build it that nice-looking if you don’t care.
EMTX prototype built on a breadboard. Yes it worked just fine onto a piece of wood.
This is a phenomenal project, Kostas. Thank you so much for sharing it with us. I love the simplicity of this design–truly form following function. With a little patience, anyone could build this transmitter.
My Red Oxx Micro Manager packed with a full radio field kit
Yesterday, my family packed a picnic lunch and took a drive through Madison County, North Carolina. It was an impromptu trip. Weather was forecast to be pretty miserable that afternoon, but we took the risk because we all wanted to get out of the house for a bit.
Although that morning I had no intention of performing a Parks On The Air (POTA) activation, my family was supportive of fitting in a little radio-activity, so I jumped on the opportunity!
A quick glance at the POTA map and I determined that the Sandy Mush State Game Land (K-6949) was on our travel route. Better yet, the timing worked out to be ideal for a lunch picnic and before most of the rain would move into the area.
Ready for radio adventure
I had no time to prepare, but that didn’t matter because I always have a radio kit packed, fully-charged, and ready for the field.
The Micro Manager pack easily accommodates the entire kit
This 20 year old blue stuff sack is dedicated to antenna-hanging. It holds a reel of fishing line and a weight that I use to hang my end-fed antenna in a tree or on my Jackite telescoping fiberglass pole. The sack also accommodates a 10′ coax cable.
The Elecraft KX2 transceiver, EFT Trail-Friendly Antenna, hand mic, CW paddles, C.Crane earphones, and wide variety of connectors and cables all fit in this padded Lowe Pro pack:
The advantage to having a simple, organized radio kit at the ready is that everything inside has its own dedicated space, so there’s no digging or hunting for items when I’m ready to set up and get on the air.
This level of organization also makes it easy to visually inspect the kit–missing items stand out.
Yesterday I parked our car at one of the Sandy Mush Game Land parking areas, deployed my field antenna, and was on the air in a matter of seven minutes at the most.
Technically, this should read “Activator” parking area! (A questionable inside joke for POTA folks!)
We planned for heavy rain showers, so I fed the antenna line through the back of my car so that I could operate from the passenger seat up front.
I also brought my Heil Proset – K2 Boom Headset which not only produces better transmitted audio than the KX2 hand mic, but it frees up my hands to log stations with ease. This is especially important when operating in the front seat of a car!
The great thing about the KX2 is that it’s so compact, it can sit on my clipboard as I operate the radio (although typically I have an elastic strap securing it better). Since all of the KX2 controls are top-mounted, it makes operation a breeze even in winter weather while wearing gloves.
Since I routinely use the KX2 for shortwave radio broadcast listening as well, I know I always have a radio “locked and loaded” and ready to hit the air. My 40/20/10 meter band end-fed antenna works well for the broadcast bands, as long as there is no strong local radio interference (RFI). When I’m faced with noisy conditions, I pack a mag loop antenna as well.
What’s in your radio go-kit?
Having a radio kit stocked and ready to go on a moment’s notice gives me a great sense of security, and not just for recreational ham and shortwave radio listening reasons.
Sometimes I travel in remote areas by car where I’m more than an hour away from the nearest town and where there is no mobile phone coverage.
If my car breaks down, I know I can always deploy my radio kit and get help from the ham radio community in a pinch. Herein lies the power of HF radio!
If you haven’t built a radio go-kit, I’d highly recommend doing so. Although I’m a bit of a pack geek, keep in mind that you don’t need to purchase special packs or bags for the job. Use what you already have first.
I’m plotting a detailed post about the anatomy of an HF radio field kit. In the meantime, I’m very curious how many of you in the SWLing Post community also have a radio kit at the ready–one based on a transceiver or receiver. Please comment!
Better yet, feel free to send me details and photos about your kit and I’ll share them here on the Post!
Many thanks to SWLing Post contributor, Paul, who shares a link to Letters of a Radio-Engineer to his Son by John Mills. The book, originally published in 1922, is in the public domain and shared/hosted on the Project Gutenberg website.
It is a fascinating read. Mills does a rather amazing job explaining complex electronic principles in a simple narrative form.
To give you a taste, check out Letter 3 – How a Battery Works below:
HOW A BATTERY WORKS
(This letter may be omitted on the first reading.)
My Dear Boy:
When I was a boy we used to make our own batteries for our experiments. That was before storage batteries became as widely used as they are to-day when everybody has one in the starting system of his automobile. That was also before the day of the small dry battery such as we use in pocket flash lights. The batteries which we made were like those which they used on telegraph systems, and were sometimes called “gravity” batteries. Of course, we tried several kinds and I believe I got quite a little acid around the house at one time or another. I’ll tell you about only one kind but I shall use the words “electron,” “proton,” “nucleus,” “atom,” and “molecule,” about some of which nothing was known when I was a boy.
We used a straight-sided glass jar which would hold about a gallon. On the bottom we set a star shaped arrangement made of sheets of copper with a long wire soldered to it so as to reach up out of the jar. Then we poured in a solution of copper sulphate until the jar was about half full. This solution was made by dissolving in water crystals of “blue vitriol” which we bought at the drug store.
17Blue vitriol, or copper sulphate as the chemists would call it, is a substance which forms glassy blue crystals. Its molecules are formed of copper atoms, sulphur atoms, and oxygen atoms. In each molecule of it there is one atom of copper, one of sulphur and four of oxygen.
When it dissolves in water the molecules of the blue vitriol go wandering out into the spaces between the water molecules. But that isn’t all that happens or the most important thing for one who is interested in making a battery.
Each molecule is formed by six atoms, that is by six little groups of electrons playing about six little nuclei. About each nucleus there is going on a game but some of the electrons are playing in the game about their own nucleus and at the same time taking some part in the game which is going on around one of the other nuclei. That’s why the groups or atoms stay together as a molecule. When the molecules wander out into the spaces between the water molecules something happens to this complicated game.
It will be easiest to see what sort of thing happens if we talk about a molecule of ordinary table salt, for that has only two atoms in it. One atom is sodium and one is chlorine. The sodium molecule has eleven electrons playing around its nucleus. Fairly close to the nucleus there are two electrons. Then farther away there are eight more and these are having a perfect game. Then still farther away from the nucleus there is a single lonely electron.
The atom of chlorine has seventeen electrons which 18play about its nucleus. Close to the nucleus there are two. A little farther away there are eight just as there are in the sodium atom. Then still farther away there are seven.
I am going to draw a picture (Fig. 1) to show what I mean, but you must remember that these electrons are not all in the same plane as if they lay on a sheet of paper, but are scattered all around just as they would be if they were specks on a ball.
You see that the sodium atom has one lonely electron which hasn’t any play fellows and that the chlorine atom has seven in its outside circle. It appears that eight would make a much better game. Suppose that extra electron in the sodium atom goes over and plays with those in the chlorine atom so as to make eight in the outside group as I have shown Fig. 2. That will be all right as long as it doesn’t get out of sight of its own nucleus because you remember that the sodium nucleus is responsible for eleven electrons. The lonely electron of the sodium atom needn’t be lonely any more if it can persuade its nucleus to stay so close to the chlorine atom that it can play in the outer circle of the chlorine atom.
The outer circle of the chlorine atom will then have a better game, for it will have just the eight that makes a perfect game. This can happen if the chlorine atom will stay close enough to the sodium atom so that the outermost electron of the sodium atom can play in the chlorine circle. You see everything will be satisfactory if an electron can be shared by the two atoms. That can happen only if the two atoms stay together; that is, if they form a molecule. That’s why there are molecules and that’s what I meant when I spoke of the molecule as a big game played by the electrons of two or more atoms.
This molecule which is formed by a sodium atom and a chlorine atom is called a molecule of sodium chloride by chemists and a molecule of salt by most every one who eats it. Something strange happens when it dissolves. It wanders around between the water molecules and for some reason or other–we don’t know exactly why–it decides to split up again into sodium and chlorine but it can’t quite do it. The electron which joined the game about the chlorine nucleus won’t leave it. The result is that the nucleus of the sodium atom gets away but it leaves this one electron behind.
What gets away isn’t a sodium atom for it has one too few electrons; and what remains behind isn’t a chlorine atom for it has one too many electrons. We call these new groups “ions” from a Greek word which means “to go” for they do go, wandering off into the spaces between the water 20molecules. Fig. 3 gives you an idea of what happens.
You remember that in an atom there are always just as many protons as electrons. In this sodium ion which is formed when the nucleus of the sodium atom breaks away but leaves behind one planetary electron, there is then one more proton than there are electrons. Because it has an extra proton, which hasn’t any electron to associate with, we call it a plus ion or a “positive ion.” Similarly we call the chlorine ion, which has one less proton than it has electrons, a minus or “negative ion.”
Now, despite the fact that these ions broke away from each other they aren’t really satisfied. Any time that the sodium ion can find an electron to take the place of the one it lost it will welcome it. That is, the sodium ion will want to go toward places where there are extra electrons. In the same way the chlorine ion will go toward places where electrons are wanted as if it could satisfy its guilty conscience by giving up the electron which it stole from the sodium atom, or at least by giving away some other electron, for they are all alike anyway.
Sometimes a positive sodium ion and a negative chlorine ion meet in their wanderings in the solution and both get satisfied by forming a molecule 21again. Even so they don’t stay together long before they split apart and start wandering again. That’s what goes on over and over again, millions of times, when you dissolve a little salt in a glass of water.
Now we can see what happens when copper sulphate dissolves. The copper atom has twenty-nine electrons about its nucleus and all except two of these are nicely grouped for playing their games about the nucleus. Two of the electrons are rather out of the game, and are unsatisfied. They play with the electrons of the part of the molecule which is called “sulphate,” that is, the part formed by the sulphur atom and the four oxygen atoms. These five atoms of the sulphate part stay together very well and so we treat them as a group.
The sulphate group and the copper atom stay together as long as they are not in solution but when they are, they act very much like the sodium and chlorine which I just described. The molecule splits up into two ions, one positive and one negative. The positive ion is the copper part except that two of the electrons which really belong to a copper atom got left behind because the sulphate part wouldn’t give them up. The rest of the molecule is the negative ion.
The copper ion is a copper atom which has lost two electrons. The sulphate ion is a combination of one sulphur atom, four oxygen atoms and two electrons which it stole from the copper atom. Just as the sodium ion is unsatisfied because in it there is one more proton than there are electrons, so the copper ion is unsatisfied. As a matter of fact it is twice 22as badly unsatisfied. It has two more protons than it has electrons. We say it has twice the “electrical charge” of the sodium ion.
Just like a sodium ion the copper ion will tend to go toward any place where there are extra electrons which it can get to satisfy its own needs. In much the same way the sulphate ion will go toward places where it can give up its two extra electrons. Sometimes, of course, as ions of these two kinds wander about between the water molecules, they meet and satisfy each other by forming a molecule of copper sulphate. But if they do they will split apart later on; that is, they will “dissociate” as we should say.
Now let’s go on with the kind of batteries I used to make as a boy. You can see that in the solution of copper sulphate at the bottom of the jar there was always present a lot of positive copper ions and of negative sulphate ions.
On top of this solution of copper sulphate I poured very carefully a weak solution of sulphuric acid. As I told you, an acid always has hydrogen in its molecules. Sulphuric acid has molecules formed by two hydrogen atoms and one of the groups which we decided to call sulphate. A better name for this acid would be hydrogen sulphate for that would imply that its molecule is the same as one of copper sulphate, except that the place of the copper is taken by two atoms of hydrogen. It takes two atoms of hydrogen because the copper atom has two lonely electrons while a hydrogen atom only has one. It takes two electrons to fill up the game which the 23electrons of the sulphate group are playing. If it can get these from a single atom, all right; but if it has to get one from each of two atoms, it will do it that way.
I remember when I mixed the sulphuric acid with water that I learned to pour the acid into the water and not the other way around. Spatterings of sulphuric acid are not good for hands or clothes. With this solution I filled the jar almost to the top and then hung over the edge a sort of a crow’s foot shape of cast zinc. The zinc reached down into the sulphuric acid solution. There was a binding post on it to which a wire could be connected. This wire and the one which came from the plate of copper at the bottom were the two terminals of the battery. We called the wire from the copper “positive” and the one from the zinc “negative.”
Now we shall see why and how the battery worked. The molecules of sulphuric acid dissociate in solution just as do those of copper sulphate. When sulphuric acid molecules split, the sulphate part goes away with two electrons which don’t belong to it and each of the hydrogen atoms goes away by itself but without its electron. We call each a “hydrogen ion” but you can see that each is a single proton.
In the two solutions are pieces of zinc and copper. Zinc is like all the rest of the metals in one way. Atoms of metals always have lonely electrons for which there doesn’t seem to be room in the game which is going on around their nuclei. Copper as we saw has two lonely electrons in each atom. Zinc 24also has two. Some metals have one and some two and some even more lonely electrons in each atom.
What happens then is this. The sulphate ions wandering around in the weak solution of sulphuric acid come along beside the zinc plate and beckon to its atoms. The sulphate ions had a great deal rather play the game called “zinc sulphate” than the game called “hydrogen sulphate.” So the zinc atoms leave their places to join with the sulphate ions. But wait a minute! The sulphate ions have two extra electrons which they kept from the hydrogen atoms. They don’t need the two lonely electrons which each zinc atom could bring and so the zinc atom leaves behind it these unnecessary electrons.
Every time a zinc atom leaves the plate it fails to take all its electrons with it. What leaves the zinc plate, therefore, to go into solution is really not a zinc atom but is a zinc ion; that is, it is the nucleus of a zinc atom and all except two of the planetary electrons.
Every time a zinc ion leaves the plate there are left behind two electrons. The plate doesn’t want them for all the rest of its atoms have just the same number of protons as of electrons. Where are they to go? We shall see in a minute.
Sometimes the zinc ions which have got into solution meet with sulphate ions and form zinc sulphate molecules. But if they do these molecules split up sooner or later into ions again. In the upper part of the liquid in the jar, therefore, there are sulphate 25ions which are negative and two kinds of positive ions, namely, the hydrogen ions and the zinc ions.
Before the zinc ions began to crowd in there were just enough hydrogen ions to go with the sulphate ions. As it is, the entrance of the zinc ions has increased the number of positive ions and now there are too many. Some of the positive ions, therefore, and particularly the hydrogen ions, because the sulphate prefers to associate with the zinc ions, can’t find enough playfellows and so go down in the jar.
Down in the bottom of the jar the hydrogen ions find more sulphate ions to play with, but that leaves the copper ions which used to play with these sulphate ions without any playmates. So the copper ions go still further down and join with the copper atoms of the copper plate. They haven’t much right to do so, for you remember that they haven’t their proper number of electrons. Each copper ion lacks two electrons of being a copper atom. Nevertheless they join the copper plate. The result is a plate of copper which has too few electrons. It needs two electrons for every copper ion which joins it.
How about the zinc plate? You remember that it has two electrons more than it needs for every zinc ion which has left it. If only the extra electrons on the negative zinc plate could get around to the positive copper plate. They can if we connect a wire from one plate to the other. Then the electrons from the zinc stream into the spaces between the atoms of the wire and push ahead of them the electrons 26which are wandering around in these spaces. At the other end an equal number of electrons leave the wire to satisfy the positive copper plate. So we have a stream of electrons in the wire, that is, a current of electricity and our battery is working.
That’s the sort of a battery I used to play with. If you understand it you can get the general idea of all batteries. Let me express it in general terms.
At the negative plate of a battery ions go into solution and electrons are left behind. At the other end of the battery positive ions are crowded out of solution and join the plate where they cause a scarcity of electrons; that is, make the plate positive. If a wire is connected between the two plates, electrons will stream through it from the negative plate to the positive; and this stream is a current of electricity.
Pl. III.–Dry Battery for Use in Audion Circuits (Courtesy of National Carbon Co., Inc.) Storage Battery (Courtesy of the Electric Storage Battery Co.).