Photo by Mark Fahey
Many thanks to SWLing Post contributor, Paul Evans, who shares the following video from an MIT/W1MX presentation series:
MIT Video: How antennas work
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Category Archives: How To
Guest Post: Radiofreunde NRW’s DXpedition-grade signal distribution system
Many thanks to SWLing Post contributor, Joachim von Geisau (DH4JG), for the following guest post:
Signal distribution at SWL camps: The new JK-1000 HF distributor
by Joachim von Geisau (DH4JG)
The Friends of Radio NRW – an independent group of shortwave listeners and radio amateurs in Germany – have been organizing 2-3 SWL camps per year for a number of years, where they meet as far away as possible from electrical noise in order to listen to shortwave together.
To distribute antenna signals, we have previously used an RFT AVV01 antenna distributor.
At an SWL camp there are high demands on signal distribution. Both very weak and strong signals should be distributed well, un-distorted, without noise and other interference. The signal levels are approximately between 0.2 ?V (S1) to over 5 mV (S9 + 40 dB), with a frequency range of at least from 150 kHz to 30 MHz, thus broadcast bands from LW to SW are covered, also all amateur radio bands from 160 m to 10 m.
Popular among listeners are RFT AVV01 RF distributors from the former GDR, at least 30 years old. However, the use of an AVV01 has several disadvantages: high power consumption, difficulties in getting spare parts, high upkeep with corroded contacts and the like. In addition, the transmission of the LW/MW range drops, which is a disadvantage especially for MW listeners. The NV-14 system from Rohde & Schwarz from the late 1960s has the same weaknesses.
Two years ago, the desire arose to develop a concept for the replacement of the RFT system.
The following aspects were important:
- Frequency range at least 100 kHz – 30 MHz, as linear as possible
- frequencies below or above desirable
- Running on 12 V DC or integrated noise-free power supply
- Remote power supply for active antennas
- Robust structure
- Versatility
- Hobby friendly budget
The amateur radio market offers several products for RF signal distribution (e.g., ELAD, Bonito et al.), but no solution to distribute 6-8 antennas to 10-12 receivers. It was clear from the beginning that DIY development was inevitable.
The starting point of the considerations was to integrate remote power supply for active antennas, an amplifier stage and a distribution network.
Such a distributor is able to distribute an antenna signal to several receivers; several antennas require several such distributors, which led to the decision to implement the project in plug-in technology.
With OM Frank Wornast DD3ZE (www.dd3ze.de), known e.g. for his converters, filters and the like, a well-known RF developer could be won, who took over the implementation of the concept based on the detailed specifications. OM Wornast first produced a prototype without remote power supply, which already did an excellent job of RF signal distribution.
A “hardness test” at an SWL camp showed that this distribution module easily fulfilled our requirements: Frequency range 10 kHz – 50 MHz (also usable with a few dB loss above 50 MHz). Supplemented by a switchable remote power supply and a 90V gas discharger at the antenna socket, the final PCB layout was created, representing the core of the new HF distribution system of Radio Freunde NRW
The distribution block consists of the following components:
- Input with 90V arrester & 100 kOhm MOX resistor to dissipate static interference
- Remote power supply, switchable, 10-14 V, max. 350 mA
- Amplifier stage with 14-14.5 dB
- Resistor network for distribution
The device is characterized by a very smooth frequency response and has a very low inherent noise. It offers the possibility of using levels of -120dBm with very good SNR
to process up to strong levels of up to + 14dBm. In addition, the reception on VLF is now possible, which did not work with the previous system.
The PCB is designed in a very practical way: series resistors for LEDs are integrated as well as fixing points for coaxial cables. The remote power supply can be switched separately, but can also be used permanently by means of a jumper.
With this concept, the distribution block can be used universally: use on an active or passive antenna with distribution to several receivers, by means of a step switch in front of it also for several antennas; if you leave the remote feed path unconnected, the block can also be used as a simple distributor, so it is almost universal for hobby purposes.
For use on SWL camps, we decided to install them in 19 “rack-mount technology. A standard rack can thus accommodate 4 distributors and a power supply, allowing distribution of 4 antennas to 12 outputs each. An example of the installation is shown in the following picture: Parallel to the input is another BNC socket, which is connected via a C 100 nF where the input signal can be used DC-free for measurement purposes or the like. The distribution unit is installed in a transport case. The components themselves are mounted in slide-in housings which are provided with a corresponding front panel: Such front panels might be obtained from CNC manufacturers.
On the back + 12V DC must be supplied as operating voltage. For the power supply units, we opted for linear power supplies because we have made the best experience with these without interference. For a distribution unit with 4 slots, a power supply with 12V 1A is sufficient – each distribution block takes about 55 mA, an active antenna up to 150 mA, so even with “full load” a power supply with 1 A is sufficient. The distributor was tested with various well-known active and passive antennas, including a PA0RDT MiniWhip, active loops, long wires and T2FD.
Due to the wide input voltage range, the module can handle nearly any antenna. The cost for a distributor for 4 antennas amounts (depending on the version: housing, sockets, switches, power supply, etc.) to about 700-1000 €. That may seem a lot at first glance. However, taking into account that a simple 5-gang distributor from mass production costs already around 250 ¬, the cost of the distribution of 4 antennas to each up to 12 outputs are not that much. The Friends of Radio NRW use two of these distribution units for SWL camps.
If you are interested in building one, please contact the author (dh4jg@darc.de) for further information. The development history of the distribution unit is also available at www.dx-unlimited.eu.
Wow! What a beautifully engineered antenna distribution solution, Joachim! I love how you worked together to sort out all of the requirements for your system then build it for ultimate performance and flexibility. No doubt, you and your colleagues at Radiofreunde NRW posses a lot of design and engineering skills! Simply amazing and thank you for sharing your design with the radio community!
Contact Joachim for more details and check out notes and discussion at www.dx-unlimited.eu (may require registration).
Mike Ladd’s primer on decoding NAVTEX using an SDRplay SDR with SDRuno
Many thanks to SWLing Post contributor, Mike Ladd with SDRplay, who shares the following PDF primer on decoding NAVTEX with an RSP series SDR.
Click here to download “Basics to decoding NAVTEX using an RSP and SDRuno” (PDF).
Thanks for sharing this excellent guide, Mike. Without a doubt, SDRplay has some of the best documentation and primers in the world of radio. Click here to check out more.
Also, check out Mario’s post, from our archives, which discusses decoding NAVTEX, RTTY, and Sitor B.
DRM30 on a Smartphone: KTWR Shows Us The Way
Image via the KTWR Blog
Many thanks to SWLing Post contributor, Dan Van Hoy, who writes:
[Regarding the reception of DRM via smart phone,] I happened to find this KTWR Guam post about decoding DRM30 with a smart phone, app, and an RTL-SDR:
Convert Smart Phone to DRM 30 HF receiver!
We are pleased to report successful use of an SDR Dongle used to directly receive and Decode DRM 30 over HF today.
The SDR Dongle is an RTLSDR v3 type connected to an android smartphone using an OTG cable (phone or tablet must be OTG capable).
The Software used:
1. Android driver (free)
2. DRM+SDR Android App ($4.99)The Frequency of the HF broadcast is directly assigned within the DRM+ SDR app with two settings
1. Frequency in Hertz
2. RF Gain (0-512)Demonstration video showing Clean DRM decode of AAC Audio and Journaline data along with live metadata. (our signal was very strong, so only a short wire used for Antenna, DX’rs will need an appropriate Antenna)
Now anyone with a smartphone and a $20 SDR can receive DRM 30 HF broadcasts…
Restoration of a USN version of the ARC-5 command set receiver
(Source: Southgate ARC)
Gregory Charvat N8ZRY writes on Hackaday about an un-modified-since-WW2 surplus CBY-46104 receiver with dynamotor.
He writes:
I’ve been told all my life about old-timey Army/Navy surplus stores where you could buy buckets of FT-243 crystals, radio gear, gas masks, and even a Jeep boxed-up in a big wooden crate. Sadly this is no longer the case.
Today surplus stores only have contemporary Chinese-made boots, camping gear, and flashlights. They are bitterly disappointing except for one surplus store that I found while on vacation in the Adirondacks: Patriot of Lake George.
Read the full story at
https://hackaday.com/2019/12/12/wwii-aircraft-radio-roars-to-life-what-it-takes-to-restore-a-piece-of-history/
Video
Video description: Repair and restoration of a USN version of an ARC-5 command set receiver. This model covers 1.5-3 Mc, runs off its original dynamotor, with no internal circuit modifications. This radio is original with the exception of a small number of caps that tested bad which were re-stuffed. Build date is Feb. 42, who knows where and what this radio may have been involved in?
I’ve always wanted a functioning ARC-5 command set to accompany my BC-348-Q receiver. This article has inspired me.
Post readers: Anyone own a functioning ARC-5 (or any variants)? Please comment!
AM radio from a hand-wound coil and an oxidized British penny
Many thanks to SWLing Post contributor, Paul Evans, who shares the following video and article via Hackaday:
There’s been a spate of apocalypse related articles over the last few weeks, but when I saw an AM radio made from a hand-wound coil and an oxidized British penny, I couldn’t help but be impressed. We’ve covered foxhole radios, stereotypical radios that are cobbled together from found parts during wartime.
This example uses a variable capacitor for tuning, but that’s technically optional. All that’s really needed is a coil and something to work as a diode. Surprisingly, copper oxide is a semiconductor, and the surface oxidation on a penny is enough to form a rudimentary diode.[…]
Thanks for sharing this, Paul. I absolutely love simple receivers like this one. In the past, I’ve built several crystal radios and had great success hearing local AM broadcasters. Indeed, the very first kit I ever built was a crystal radio, then later a foxhole style receiver.
Post readers: Have you ever built a radio similar to this one that uses an oxidized penny? Please comment!
Click here to read posts from our archives that focus on crystal radios.
The NooElec Balun 1:9 v2
Many thanks to SWLing Post contributor, Grayhat, who writes:
Hi Thomas, was about to write you about some infos related to the NooElec balun when found that they now offer a v2 model:
https://www.nooelec.com/store/balun-one-nine-v2-barebones.html
The new balun has the same schematic as the previous one:
But it is slightly bigger, has a better connector for the antenna wires and (according to NooElec) uses a transformer which allows the tiny balun to work more efficiently from 0 to around 70 MHz (check out the charts found in the downloads section of this link).
The transformer used, judging from the pics, is a CoilCraft WB9-1, whose data can be found here:
https://www.coilcraft.com/wb_th.cfm
As I wrote the reason for this was the fact that a friend of mine reported that he used the (v1) balun with a Loop On Ground (LoG) Antenna !
If you look at the schematic (above) you’ll notice that there’s a “jumper” labeled R1 (zero Ohm resistor). That tiny detail is important, see, leaving the balun as is, it will work fine with a longwire, one just connects contact #1 to the antenna and #2 to a counterpoise or ground system and there he goes, BUT there’s another way to use the balun, that is, CUT the “jumper” (ok, resistor) labeled “R1”. If you cut it, the balun will become a 9:1 isolation transformer and with such a modification will work just fine with the KK5JY “LoG”
antenna: http://www.kk5jy.net/LoG/According to what my friend reported, the balun works just fine, and although probably the ferrite core used in the V1 isn’t up to par with the original one used by KK5JY, the difference isn’t so huge.
Oh, and I also suspect that the modified balun may work fine with the KK5JY simpler passive loop http://www.kk5jy.net/rx-loop/ which may be a nice antenna for restricted spaces!
I think it may be of interest to people not knowing/willing to wind their own baluns, at that point one may just need an enclosure to protect the balun and putting up a receive antenna will be as easy as 1-2-3.
Thank you for sharing this! Readers: Grayhat has been encouraging me to deploy a LoG antenna at my home and I do plan to do so in the coming months. Please comment if you use a LoG similar to the KK5JY model and what your results have been.
Thank you again for the tip, Grayhat!