Homebrew SDR Tuning Knob Unit

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This is my latest little homebrew project; a tuning knob unit for my SDRPlay RSP1A software defined radio receiver. The project was inspired by the article "Wireless Tuning Knob" in the April 2018 issue of the excellent Practical Wireless magazine.

To make an easy to use tuning knob for your SDR receiver, the PW article suggests using the inners of a cheap wireless computer mouse, removing the mouse wheel, and connecting a rotary encoder instead. Then a tuning knob can be attached to the rotary encoder's shaft, and voila!

And that's exactly what I did, except I did use a wired USB mouse, not a wireless one, as I didn't want the hassle of having to change batteries all the time. The result is shown in the photos below. It works like a charm!

ADS-B

Last edited: 27.01.2018

This is my latest high tech creation, hi. It's a little 4-leg "spider" antenna for 1090 MHz (1.090 GHz) constructed around a nice old Amphenol SO-239 chassis connector that I had lying around. Its 4 legs and top element are made from copper wire and are about 68 mm in length.

Beside being a ham radio operator, I've always been a radio hobbyist in general, and every once in a while I like to explore radio related stuff outside of the ham bands. The little spider antenna is used to receive the ADS-B signals broadcasted from aircraft on 1090 MHz. ADS-B stands for Automatic Dependent Surveillance - Broadcast. ADS-B signals are periodically (twice every second according to the YouTube movie below) broadcasted by aircraft and contain among other things the aircraft's unique ICAO identifier, the aircraft's callsign, and data provided by the GPS navigation system of the aircraft, like GPS location, altitude, heading, speed, etc. ADS-B signals enable an aircraft to be tracked in real-time by for instance air traffic control stations. Since other aircraft can also receive the ADS-B signals from ADS-B equipped aircraft surrounding them, it also provides pilots with improved situational awareness.

I use my RSP1A SDR receiver (see my last blog entry) connected to the spider antenna to receive the ADS-B signals. Special software extracts the data from the signals. This data is sent to another computer program called Virtual Radar Server (VRS) which then plots the received aircraft on a map. With the aircraft identifiers received on 1090 MHz, VRS is able to retrieve additional information for the aircraft from various online databases, including the aircraft registration or "tail number" and the current route (destination and departure airport). When you select an aircraft, VRS also shows the aircraft type and model, operator, country of registration, and when available (most of the time) even photos of the aircraft (not just a random photo of the type and model, but the actual aircraft with the registration of the selected aircraft).

It's really fun to see in real-time what's up in the airspace above you. Of course you can also use some online service like www.flightradar24.com for this, but for the radio hobbyist it's a thrill to know that the aircraft that are plotted on the map are plotted there because their ADS-B signals have been received with his own radio equipment directly over the air.
With the antenna inside the house, depending on the height I place the antenna at (ground level or attic), I've been receiving aircraft up to distances of 100 to 200 km. You can even do some DXing, trying to catch aircraft from as far away as possible and trying to beat your personal record.

The ADS-B data extracted from the signals received on 1090 MHz

The aircraft plotted in Virtual Radar Server. For the selected aircraft (the one in yellow) additional information is displayed, including route, operator, country of registration, tail number, aircraft type and model, and any available photos of the aircraft.

Below some YouTube movies explaining how to set up ADS-B with your SDRPlay RSPA1/1A/2 receiver and explaining how ADS-B works.

See also:

https://en.wikipedia.org/wiki/Automatic_dependent_surveillance_%E2%80%93_broadcast
https://discussions.flightaware.com/t/three-easy-diy-antennas-for-beginners/16348/3
http://lucsmall.com/2017/02/06/making-antennas-for-1090mhz-ads-b-aircraft-tracking/
https://en.wikipedia.org/wiki/Aircraft_registration
https://en.wikipedia.org/wiki/Aviation_call_signs
https://en.wikipedia.org/wiki/List_of_airline_codes
https://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes#ICAO_24-bit_address
https://en.wikipedia.org/wiki/List_of_airports_by_ICAO_code:_A
https://junzis.com/adb/
https://www.flightradar24.com/
https://www.sdrplay.com/docs/SDRplay_ADS-B_User_Guide.pdf

WSPR monitoring and the SDRPlay RSP1A 1 kHz - 2 GHz SDR-receiver

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The SDRPlay RSP1A "DC to Daylight" SDR receiver

The downside of the popularity of stand alone WSPR transmitters like for instance the QRP Labs U3S and the Sotabeams WSPRlite is that more and more hams in the field of WSPR have become transmit-only stations and do little WSPR monitoring or none at all. On the other hand though, if it wasn't for these neat little stand alone WSPR transmitters many radio amateurs would probably never have been active in WSPR at all. I'm one of them; it was my beloved U3S that has made a keen and active WSPR operator out of me.

But we all depend on eachother; without WSPR monitoring stations there's no use in transmitting WSPR beacons, and without transmitting stations there's no use in monitoring. It occurred to me that if you're an active user of a U3S or a WSPRlite, and you're enjoying seeing your WSPR beacons being spotted all over the world, you more or less have the obligation to do the occasional monitoring session, as a favour in return and to keep the WSPR network alive and interesting! To me, being a transmitting-only station has always felt a little selfish.

I've done the occasional monitoring sessions, but only if some special WSPR project was in progress; maritime mobile, floaters, high altitude balloons, expeditions, etc. Still a little selfish and I decided I wanted to become more active with general WSPR monitoring as well. I don't like having my transceiver powered up for longer, extended periods of time though (it occurred to me that manufacturers should build in to their transceivers an on/off switch or a sleep mode for the display to be turned off during extended monitoring sessions).
So, for this reason (and a million others) I decided to purchase the new SDRPlay RSP1A SDR receiver. The RSP1A is manufactured in the UK and receives from 1 kHz to 2 GHz, or to use a popular term, it's a "DC to Daylight" receiver. It's my first experience with a Software Defined Radio, and I must say that I'm really thrilled with all the possibilities the RSP1A brings. It's really nice to also be able to explore the VLF frequency range for instance; for the first time in my life I managed to hear the signals of time signal station DCF77 on 77.5 kHz. I'm planning on making a PA0RDT mini whip antenna to do some more serious monitoring on VLF, LF and MF, including 2200m and 630m WSPR.

My first WSPR monitoring session with the RSP1A was done on 40m and instantly the SDR receiver connected to my HyEndFed 10/20/40m wire antenna managed to pull in the 5 Watt WSPR signals of the DP0GVN beacon on Antarctica for me (earlier, reciprocally the DP0GVN receiving station already picked up my 200mW WSPR signals on 20m, see the addendum to my blog entry of January 13th). I'm really pleased with the reception of the RSP1A.

A nice interview with Jon Hudson from SDRPlay about the new RSP1A can be found here on YouTube.

I also don't like leaving my laptop powered up for extended periods of time, so in the future I might look into the possibility to do WSPR monitoring sessions with the RSP1A connected to a Raspberry Pi.