Tag 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).

Spread the radio love

US Army Training Film: Circuit Testing and Signal Generators (1951)

Many thanks to SWLing Post contributor, Jarno de Haan, who shares this US Army Training Film about circuit testing via YouTube. If you own vintage radio gear, you should check this out:

Click here to view on YouTube.

Spread the radio love

Tecsun PL-660: A simple hack to scan the air band

Many thanks to SWLing Post contributor, Bruce F, who writes:

HI Thomas, I thought I would put this idea out to your site – in case it isn’t already there. It’s a brilliant solution to the apparent lack of a working Air Band scan function on the Tecsun PL-660.  Note – I did not come up with this idea, but came across it in a Yahoo group.

It IS possible to scan the Air Band on the PL660, as long as you have picked out WHICH Air Band frequencies are in use in your area. There are websites which list these frequencies for each airport:

Here’s how to set up the PL-660:

  1. Pick an empty page in the Memory.
  2. Put in a shortwave frequency in the first empty space; the “00” slot.
  3. Then fill in the succeeding spaces on that page with the Air Band frequencies you’ve chosen.
  4. Now go back to the “00” slot and hold down the scan button.

Works on my set!

What a cool trick!  I’ve lent my PL-660 to a friend, but as soon as I get it back, I’ll also try this trick by setting up a page dedicated to my local aviation frequencies!

Thanks, Bruce!

Spread the radio love

Making a FlightAware ADS-B feeder with a Raspberry Pi 3 and RTL-SDR dongle

It’s been nearly a year since I acquired both the RTL-SDR (above) and Rasperry Pi 3 (below)r.

Remember when I made a plea for Pi 3 projects just last year––?

Although many of you suggested some great projects, I never actually got around to doing any of them. Now, don’t get me wrong––I wanted to, of course, but simply got involved with reviews, NPOTA, two months of travel…and, well, life.

Then, last week at the Winter SWL Fest, a common theme emerged in both presentations and discussions:  the numerous applications of the super-cheap, and thus super-ubiquitous, RTL-SDR dongle. In their engaging presentations, both Dan Srebnick and Mark Fahey––SWLing Post contributors and good friends––focused on the power of the RTL-SDR, expounding upon some simple, inexpensive applications in their forums. It was inspiring. Also, buddy Eddie Muro showed me just how easily an ADS-B receiver could be set up using an Android phone.

Back to the Pi. Though I was already aware the Pi 3 and RTL-SDR could be united to make an ADS-B receiver, watching Mark Fahey talk about how simply one could feed the FlightAware network with ADS-B data finally hooked me.  Why not, indeed? Here was fun to be had!

Mark preparing to woo his captive audience at the Winter SWL Fest!

I couldn’t get the idea out of my head, so Tuesday, the day following my return, I set the afternoon aside.  I rolled up my sleeves, and with my long-neglected Pi 3 and RTL-SDR, got ready to cook up a flight sensor.

I figured I was probably missing a component or two, and fully expected the process to be complicated, but decided I wouldn’t let this deter me. And guess what? I was wrong on both counts!

FlightAware ADS-B feeder recipe

Ingredients:

If you only plan to use this SDR and antenna as an ADS-B feeder, you might go for the FlightAware Dongle and 1090 MHz antenna combo.

Directions:

Note: I used this excellent PiAware ADS-B feeder tutorial to build my system–it’s detailed and doesn’t make the lofty assumption that you actually understand formatting cards, building disk images, and/or editing config text files.

Directions below are a highly distilled version of that tutorial. If you’re new to all of this, as I was, follow these directions instead of the above tutorial. Be aware that the directions assume you’re using the Pi 3 and a Windows PC to burn the image file.

  1. Download PiAware image7-zipSD card formatter, and the Win32 Disk Imager. Decompress all compressed files, install and note the folder locations.
  2. Register your username at FlightAware–presuming you don’t already have an account, of course.
  3. Use SD Card Formatter to format your MicroSD card.  Just make sure you’re formatting the correct drive, else you could easily wipe the wrong disk/card!
  4. Use Win32 Disk imager to write the PiAware image to your MicroSD card.
  5. If using WiFi, open Windows Explorer.  Locate text document called piaware-config on the MicroSD card, open it with a text editor, and locate the WiFi ssid and password locations. Per the config comments, edit them to match your WiFi system. Note that any special characters in both the name and password will require the use of quotation marks (again, noted in the config file comments). Save the file in the same location on the disc image.
  6. Remove the microSD card containing the PiAware image; insert it into the Pi 3.
  7. Connect the RTL-SDR or FlightAware dongle to the Raspberry Pi. Attach an appropriate antenna to the RTL-SDR. Note:  You’ll get the best results if you place the antenna outdoors with line of sight to the skies.
  8. Plug the Raspberry Pi 3 into a power source…and cross your fingers!
  9. Grab a cup of coffee, walk the dog, or listen to this 12 minute version of the BBC countdown; it could take at least this long for FlightAware to start receiving data from your ADS-B feeder.
  10. When you see this My ADS-B button in the header of FlightAware (see below), you’ll know you’re in business. Congratulations!  You can now watch the skies.

Feeding FlightAware

After my ADS-B receiver had been in operation for a while, I was very impressed with the data FlightAware was able to pull from my ADS-B feed. I was equally impressed with the number of distant aircraft I could receive with such a modest antenna––a number of them up to 135 miles from my location. Once I find a suitable outdoor location for the mag mount antenna, currently indoors, I expect the reception distance will increase significantly.

You can also connect to the live feed from your ADS-B receiver through your local network. Here’s a screenshot of my live data:

Future plans

At the moment, my ADS-B receiver is located indoors, in a south-facing window.

It works, but clearly isn’t ideal. Since the Pi 3 connects to my network via WiFi, I intend to install the full ADS-B receiver system into a small weatherproof case and mount it outside. My Pi 3 has no case, so I purchased an inexpensive one yesterday. I should be able to feed it power with an outdoor outlet…but I’m very tempted to experiment with making it solar powered.  To find out if this is a logical move, I need to observe and measure the power requirements first, and will be doing that in the next few weeks.

Meantime, I’m thoroughly enjoying watching the (amazingly busy) traffic in the skies…and the kid in me relishes it!

Thanks, Mark, for the great idea!

Have any SWLing Post readers attempted to build a solar-powered or outdoor ADS-B receiver? Please comment!

Spread the radio love

Gary’s mediumwave DX FSL antenna phasing experiment

Many thanks to SWling Post contributor, Gary DeBock, who shares the following note about his latest FSL antenna experiment:

Medium wave DX FSL antenna phasing experiment– 1593-CNR1 (Changzhou, China, in Mandarin) boosted up to strong (S9) peaks by two 5 inch “Frequent Flyer” FSL’s at 1435 UTC on February 25th in my frozen back yard in Puyallup.

Unlike other high gain MW antennas, the FSL’s can provide cumulative gain at very close inductive coupling ranges.

Click here to download and play MP3 recording.

Amazing, Gary!  Thank you for sharing this excellent bit of DX!

Click here to read more about Gary’s FSL antennas.

Spread the radio love

Raspberry Pi WiFi Radio with touch screen

For those of us who like to tinker with the Raspberry Pi, this looks like a fun weekend project.

It’s multi-step, but I believe this project could be completed by almost anyone–you wouldn’t have to be a Raspberry Pi or Python guru (code snippets can be downloaded, for example).

Here’s a short video demonstration of the finished Raspberry Pi Touchscreen WiFi Radio:

Click here to view on YouTube.

The whole project is documented on the superb AdaFruit website. 

Spread the radio love

SDRuno tutorial videos

SDRuno running the RSP2.

SDRuno running the RSP2.

Jon Hudson with SDRplay recently noted the following tutorial videos in an SDRplay discussion forum. Since I’m also trying to learn the ropes of SDRuno, I thought I’d share this here on the SWLing Post.

Jon notes:

These video guides are very helpful for newcomers to SDRuno and the RSP1 or RSP2:
RSP1: https://youtu.be/xBGHB0oMXHU

RSP2: https://youtu.be/92Ijh_NAEfc

Especially when used in conjunction with the SDRuno Cookbook from Paul and Mike: https://www.nn4f.com/SDRuno-cookbook.pdf

Spread the radio love