Category Archives: How To

Video: Homebrew AM Loop Antenna Project by Thomas Cholakov (N1SPY)

Many thanks to SWLing Post contributor, Thomas Cholakov (N1SPY), who shares his latest video explaining the operation of a simple homebrew AM loop antenna:

Click here to view on YouTube.

Brilliant video, Thomas! I love the fact you included a demonstration with your SDRplay RSP1A as well. Via the spectrum display, it’s easy to see the the loop’s bandwidth and also the gain it provides when tuned to a station.

I love your AM loop antenna as well–such a simple design and ideal for demonstrating the mechanics of a passive loop antenna since all of the components are visible. I’m willing to bet you built this antenna for less than $10. Smart design as it’s both portable and effective! Keep up the excellent work, Thomas! We look forward to all of your future videos.

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RSGB presentation on RF Interference

Digital-Frequency-DialMany thanks to SWLing Post contributor, Gary (W4EEY), who writes:

I want to recommend an excellent presentation on RF Interference from
the Radio Society of Great Britain (RSGB) Convention in 2015. The
presenter is Ian White, GM3SEK, who has a Blog website here:

https://gm3sek.com/

You can find the presentation video on YouTube here:

Click here to view on YouTube.

The presentation runs for about one hour and contains some valuable
information to help you fight noise and interference in your shack.

Thanks for the tip, Gary!

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The new Raspberry Pi 3 B+ and a number of RPi projects

Last month, on “Pi Day” (March 14, 2018) an upgraded Raspberry Pi 3 B was announced on the Raspberry Pi website. The new $35 B+ sports a few performance enhancements over the original–most notably:

  • A 1.4GHz 64-bit quad-core ARM Cortex-A53 CPU
  • Dual-band 802.11ac wireless LAN and Bluetooth 4.2
  • Faster Ethernet (Gigabit Ethernet over USB 2.0)
  • Power-over-Ethernet support (with separate PoE HAT)
  • Improved PXE network and USB mass-storage booting
  • Improved thermal management

Here’s a short promo video posted with the announcement:

Click here view on YouTube.

I immediately navigated to my favorite Raspberry Pi source–AdaFruit–and requested a notification when the new units were available to purchase. A few weeks later, I got the notification and placed an order within minutes (you see, when the Pi 3 B was first released, I hesitated a day and had to wait a few weeks for the second shipment!).

I received my RPi 3 B+ a few days ago:

I immediately attempted to put this unit into service but learned that it requires the latest firmware which was only released a week or so ago. If you have have an RPi 3 B+, here’s where to fetch the latest firmware:

NOOBS:
https://www.raspberrypi.org/downloads/noobs/
or if you want Raspbian:
https://www.raspberrypi.org/downloads/raspbian/
and install on SD per instructions here:
https://www.raspberrypi.org/documentati … /README.md

After receiving this latest Pi, I quickly realized I’ve bought a number of Raspberry Pi models over the years and currently have them in service for a variety ofc projects.  Here’s a list of all of my current Pi-powered applications:

That’s a total of seven RPi projects that are in service at time of posting!

As I mentioned earlier, I try to buy most of my Pi equipment from the amazing AdaFruit retailer–I like supporting what they do even if I pay a small premium.

But AdaFruit seems to rarely have stock in some of my favorite Pi bundle packages. If I’m buying a Raspberry Pi for a new application, I look for a package with at least a case, a 2.5 amp power supply, a 32 or 64GB MicroSD card, and two heat sinks (though I’m not certain the B+ needs a heatsink). I tend to grab this one or this one from Amazon (affiliate links).

Post readers: Have you ever used a Raspberry Pi? If so, in what sort of applications? How many do you own?  Please comment!

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Tudor demos his portable Raspberry Pi-powered AirSpy HF+

Many thanks to SWLing Post contributor, Tudor Vedeanu, who has kindly shared details about his portable Raspberry Pi system which now can run the AirSpy HF+ SDR.

Tudor writes:

I bought the RPi to use it as a Spyserver for my Airspy HF+ SDR.

My main radio listening location is a small house located on a hill outside the city and there is no power grid there (it’s a radio heaven!), so everything has to run on batteries and consume as little power as possible.

My first tests showed that the Raspberry Pi works very well as a Spyserver: the CPU usage stays below 40% and the power consumption is low enough to allow it to run for several hours on a regular USB power bank. If I add a 4G internet connection there I could leave the Spyserver running and connect to it remotely from home.

Then I wondered if the Raspberry Pi would be powerful enough to run a SDR client app. All I needed was a portable screen so I bought the official 7” touchscreen for the RPi.

I installed Gqrx, which offers support for the Airspy HF+. I’m happy to say it works better than I expected, even though Gqrx wasn’t designed to work on such a small screen. The CPU usage is higher than in Spyserver mode (70-80%) but the performance is good. Using a 13000 mAh power bank I get about 3.5 hours of radio listening.

I made a video showing how it works:

Click here to view on YouTube.

This is fantastic, Tudor. Thanks for taking the time to put together a video for us. I’ve just ordered the latest Raspberry Pi 3 (Model B+). It has slightly more horsepower than the previous Pi3. Tudor, you’ve inspired me to grab the 7″ touch display as well and try my hand at running the AirSpy HF+ portable.

I’m not sure if the Raspberry Pi 3 will be able to record spectrum without hiccups, but it’s certainly worth a try.

As you tweak your system, please keep us in the loop!

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Backpack Shack 2.0: an update from the field

Finished Backpack Loop 2.0 and accessories assembled together

Many thanks to SWLing Post contributor, TomL, who shares the following update about his homebrew Backpack Shack 2.0 portable loop antenna:


Quick Field update

by TomL

This is just a quick Field Update for my Backpack Shack 2.0 antenna. It is not the most powerful antenna but in the right location it can be useful, especially with using an SDR. It was used during February in two Forest Preserve (County Park) locations outdoors and once from my usual Grocery Store parking lot!

Field Recordings

Please excuse some of the computer generated noises (caused by a slow CPU) as well as some audio connector problems on a couple of recordings.

Each Time is in UTC and Frequency in kHz. Where can you hear unique programming like these samples except Shortwave Radio??? Enjoy!

VOA, @03:00 on 6080 kHz in English from Sao Tome towards Africa (backside of their antenna, opposite of my location)

China Radio Int’l, @23:00 on 9415 kHz in Vietnamese from Beijing (not sure if this traveled around Antarctica to get to me or a backside of their antenna over the North Pole?)

WHR, @15:59 on 9965 kHz in Korean from T8WH Palau

Mighty KBC, @01:48 on 6150 kHz in English from Nauen Germany (announcer sound effects included!)

Voice of Greece, @20:34 on 9420 kHz in Greek from Avlis (unique stylized Greek music, INTERESTING artistic expression)

Vatican Radio, @20:27 on 9660 kHz in English from Vatican City to Africa

WINB, @21:30 on 9610 kHz in English from Red Lion, PA USA (a FUN song about promoting Radio listening!)

And my favorite Government-run authentic folk music station of Mexico, tiny 1KW XEPPM @04:17 on 6185 kHz with clear station ID

I will be working on a larger version of this antenna to transport in my car as well as a small VHF loop antenna for the outside deck for Air/Police/Weather scanning.

Hope to report sometime this Spring.


Thank you so much for the update, Tom! It looks to me like you’re having an amazing time with you homebrew loop in the field! 

As always, keep us in the loop! (Yeah…bad pun, I know!)

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Vintage Radio: How to read a logging scale

Many thanks to SWLing Post contributor, Charlie Liberto (W4MEC) for the following guest post:


Vintage receiver frequency counter…sort of

by Charlie Liberto (W4MEC)

You probably know what a log book is, and maybe a logarithm, but do you know what a ‘Logging Scale’ was meant for? If you are a modern SWL’er, and have a receiver built in the last 40 years or so, you probably don’t have that mysterious 0 to 100 range on your dial, as shown at the top of the picture of the Hallicrafters S20-R main dial, and you may not have a dial at all, peering without question at a digital display of your received frequency.

The Logging Scale on older and vintage receivers had two functions: to let you find a station you might be looking for, when you knew the frequency it would be on, and to determine the frequency of a station, but you had to have known references. How to do that on those old scales that may have had 50 kHz or even 500 kHz hash marks between whole Megahertz numbers, or in that era, KC or MC numbers? The process is fairly straight forward, but did require you to know the operating frequency of at least 2 stations on the band of interest, and the closer they were to the mystery frequency, the better.

Let’s say you are looking for WLMN that is supposed to begin its operation day on 6025 kHz. and your receiver has a mark every 250 kHz between 5 and 7 MHz, that’s pretty iffy as to setting the dial. Now, you know that station WABC is on 5500 kHz, and station GXYZ is on 6525 kHz, so, tuning in WABC you note what number the pointer on the dial is over on the logging scale, maybe it is 40. Then you tune to GXYZ and you find it on 70 on the logging scale. The known difference in frequency between WABC at 5500 kHz and GXYZ at 6525 is 1025 kHz, and the logging scale number difference is 40 to 70 or 30 divisions. Take the 1025 kHz separating your two known stations, divided by the 30 logging scale divisions and you get 34.167 kHz per division. Some more math, the station you are looking for, WLMN is on 6025 kHz, which is 525 kHz away from WABC at 5500 kHz., divide 525 kHz by the logging scale frequency versus division number of 34.167 kHz which equals approximately 16. Take that 16, add it to WABC logging scale number of 40, and you should expect to hear WLMN on logging scale 56 on the dial.

Of course you can flip this process around. If you heard WLMN, but did not know it’s frequency, the same procedure worked backwards to interpolate the logging scale 56 into kHz, added to the WABC frequency/log number, or subtracted from GXYZ numbers, and you would figure out WLMN was on 6025 kHz.

What did this process do? It ‘calibrated’ your receiver dial to known checkpoints by using known frequencies of stations, such that you had a better idea of where you were frequency wise, but it did have it’s limitations. Older receiver dials usually had the lower frequencies divisions of a band close together, and as you tuned to higher frequencies on the same band, hash marks for frequencies got farther apart, while the logging scale stayed linear. This was because builders used the simpler straight line capacitance variable capacitor for tuning, instead of the straightline wavelength or straight line frequency style which would have made the dial more linear. If you used two stations on the low end to set a logging scale reference, chances are it will be quite a bit off in the frequency versus logging scale number on the high end of the dial. So, if you could find two stations that bracketed the one you were examining, that would assure the most accuracy.

After all that, you are probably saying thank God and a lot of engineers for a digital readout.


Thank you, Charlie, for an excellent tutorial and example of using dial logging. I’ve had a number of vintage radios over the years with logging scales and it took some digging to discover how they worked. While digital radios make the process as easy as pie, vintage radios are worth the extra effort! 

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Guest Post: Listening To Pirate Radio Stations from South America

Many thanks to SWLing Post contributor, Chris Smolinski, who shares the following guest post. Note that this post has also been published on Chris’ excellent blog, Radiohobbyist.org:


 

Listening To Pirate Radio Stations from South America

by Chris Smolinski

Looking for a new DX challenge? In addition to shortwave pirate stations in the USA, and Europe (Europirates as we call them), there’s a relatively new group of pirate radio stations being heard in North America, those from South America.

It’s really only been the previous year that we’ve confirmed that there’s a significant number of pirate radio stations in South America that can be received here. Radio Pirana has been known for some time, and I believe thee were a few reports of it, and at least one other station that I cannot remember the name of, but that’s about it. For years there have been logs of very weak UNID stations heard on the 43 meter band (6800-7000 kHz), presumed to be pirates of some sort, and it is possible some of these were South American pirates.

Most of these stations use homemade transmitters, often of the “Lulu” design, with a IRF510 or similar MOSET RF final stage. That means they are generally in the 15 or 20 watt carrier range, although some are higher power. That also means that unless otherwise noted, all of these stations use AM mode, and in general the frequency is highly variable, easily varying 100 Hz or more from night to night, or even during transmissions.

One important caveat: Since most of these stations use relatively low power, and due to the long distances involved, signal levels are generally weak, although occasionally when conditions are excellent (especially if there’s grayline propagation), they can put in stronger signals. I am fortunate to live in a rural area with relatively low noise/RFI levels, and have several high end receivers and large antennas. My primary setup for catching these stations is a netSDR receiver and a 670 foot Sky Loop antenna. You’re going to want to use the best receiver and antenna you can for catching these stations, you’re not likely to have good (or any) results with a portable SW radio, RTL dongle, or small/indoor antenna. Also, I record the entire 43 meter band nightly on my netSDR, and then go through the recordings each morning. This lets me catch stations that may only appear for a brief period of time. That said, you can still hear them with a reasonable HF setup, although it may take persistence, checking each night, until conditions permit reception.

It’s well worth checking the Latin American Pirate logging forum on the HF Undergroundwebsite, to see what is presently being heard. The HF Underground is the best way to keep up to date with the hobbyist radio scene in general, with dedicated forums for North American PiratesEuropirates, and of course radio in general.

And for those of you into collecting QSLs – many of these stations are reliable QSLers!

In general, the easiest station to hear is Lupo Radio from Argentina. It is on the air most evenings on 6973 kHz in AM mode. At least at my location, it puts in the strongest and most reliable signal. Usually in the SIO 222 to 333 range, sometimes stronger. There are frequent IDs. I use Lupo Radio as a “beacon” to gauge how good conditions are to South America on 43 meters.

Another station that is often on the air is RCW – Radio Compañía Worldwide from Chile. They use 6925.13 kHz, and their carrier is more stable and usually on this offset frequency, which makes it easier to determine that it’s likely you’re hearing them vs a US pirate station.

New to the scene is Radio Marcopolo on 6991 kHz.

Also new to the scene is an as yet UNID pirate from South America on 6934.9 kHz. I have received them for several weeks now in the local evenings, usually starting around the 2300-0300 UTC window. They put in a respectable signal (relatively speaking), strong enough for Shazam to ID songs. They have frequent breaks in their transmission, with the carrier often going off and on many times during a broadcast. They also occasionally transmit audio test tones, and sometimes seem to relay audio from licensed stations in Argentina such as Radio El Mundo. This could be someone testing a new transmitter? A new mystery to solve!

Radio Dontri is somewhat unique in that they use USB mode, on 6955 kHz. They also send SSTV, which is sometimes easier to receive than music, and helps to verify that you’re actually hearing them, vs a US pirate on 6955. They tend to drift a lot, however, which can make decoding the SSTV transmissions challenging.

Outside the 43 meter band, there is Rádio Casa 8000 kHz. I have only received weak carriers from this station, although partly that may be because I do not frequently check for it, and it does not turn up on my overnight SDR recordings.

Radio Triunfal Evangélica is other station outside of the 43 meter band, they use the nominal frequency of 5825 kHz, often closer to 5824.9 kHz. Again I have only received a carrier from them. As the name implies, they are a religious station, affiliated with a church.

Now that we’ve talked about the pirate stations from South America, we should probably mention things you are likely to hear that are not pirates. Specifically, what we call Peskies (or Pesky as the singular), short for pescadores, the Spanish word for fishermen. Peskies generally use LSB mode, and can be heard on many frequencies in the 43 meter band, engaging in QSOs. Years ago, pirate listeners started to call these stations pescadores, since some of them were indeed fishermen, and could be heard discussing related matters. It might be better to think of most of them as freebanders/outbanders, much in the tradition of those transmitting on 11 meters. There’s a logging forum on the HFU dedicated to Peskies, if you’re interesting in learning more about them.

Occasionally they use AM mode. We’ve logged several on 6965 kHz (+/- of course), that at first were thought to be pirates. But they never transmitted music, and after some discussions with DXers in South America, it was determined that they were more properly considered peskies.


Many thanks, Chris, for sharing this excellent guest post with us! Until the Winter SWL Fest last week, I had no idea South American pirates were on the rise–what a great opportunity to catch interesting DX!

Readers, check out this and other posts on Chris’ website Radiohobbyist.org.

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