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SDRplay as satellite downlink receiver?

Discussion in 'Satellite and Space Communications' started by WD9EWK, Aug 24, 2015.

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  1. WD9EWK

    WD9EWK Ham Member QRZ Page


    Has anyone on here used an SDRPlay RSP as a downlink receiver when working amateur satellites?

    I ordered one last month, and it has worked fine with a laptop running Windows 7 Professional. At the time I received mine, I had Windows 8.1 on my 8- and 10-inch tablets. I could install the Windows API and the plugins for HDSDR and SDR Sharp, but the SDRplay wasn't recognized by those programs. When I upgraded my tablets to Windows 10, I tried reinstalling the API and plugins. Until today, it still would not work. An API update released earlier today (v1.5.0) has resolved the issues with the SDRplay and Windows tablets.

    I have not used my SDRplay when working satellites yet, waiting to get it working with my tablets. I think this should work like the FUNcube Dongle Pro+ I have been using as a downlink receiver for some time. The SDRplay has front-end filtering, and a much wider receive bandwidth, than the FUNcube Dongle Pro+. The SDRplay can work with an input bandwidth up to 8 MHz. On the tablets, the default 1.566 MHz input bandwidth seems to be the most I can use without overloading the tablets. This bandwidth is fine for the tablets, and I plan to reduce the bandwidth to 200 or 300 kHz when I use it to work our satellites.

    The SDRplay is retailing at US$ 149 from the SDRplay web site - about US$ 50 less than the FUNcube Dongle Pro+. The SDRplay is a small box, larger than the FUNcube Dongle Pro+. I want to run some tests to see which of these devices draws more power over the USB connection. This may not be an issue for some, but could be an issue when using a laptop or tablet in the field. Especially for some tablets with a single micro USB port, which can be used only for one purpose at a time - charging the internal battery, or (with a USB On-The-Go cable) using a USB device like these.

    K2NCC and KC4LE like this.
  2. WD9EWK

    WD9EWK Ham Member QRZ Page


    I just tried working an AO-73 pass this evening with the SDRplay RSP as my downlink receiver, transmitting with an FT-817ND at 5 watts, and both connected through a diplexer to my Elk log periodic antenna. The SDRplay was connected via USB cables (one cable that is normally used with USB printers, and an On-The-Go cable) to my HP Stream 8 tablet with Windows 10 and HDSDR. I had no problems hearing the downlink, but could not get myself lined up to work stations. Good copy of the 145.935 MHz (+/-) telemetry beacon, and I heard a few stations like K6FW, W5CBF, and a couple of others. I was able to transmit without interfering with the SDRplay or shutting it down until I stop my transmissions (this is, unfortunately, a common thing with the RTL-SDR dongles that lack front-end filtering).

    I reduced the bandwidth the SDRplay used from the default 1.536 MHz to just 200 kHz. This is as close as I could get to the FUNcube Dongle Pro+ maximum bandwidth of 192 kHz, and not make the traces in the waterfall seem tiny on the tablet's screen. I had a Belkin Rockstar audio splitter connected to the tablet, feeding audio to my Heil Traveler headset/mic and Sony audio recorder. I had HDSDR record the RF it was receiving from the SDRplay, writing it to a large WAV file (about 280 MB for 9 minutes, recording the 200 kHz bandwidth centered on 145.925 MHz). I have previously found that trying to make HDSDR record both RF and AF bogs down the tablets. The Sony recorder gives me what I heard (and - normally - worked), and the RF recording has the passband, telemetry beacon, and anything else around the frequencies used by the satellite. I can always make new audio recordings based on what was in the RF recording.

    I may tinker with settings, to see if I can increase the signal strength in HDSDR. I might try opening the bandwidth a little more, but I won't go back to 1.536 MHz bandwidth. Anything more than 1.536 MHz bandwidth seems to be too much for the tablet. I can go to the full 8 MHz bandwidth with my Dell Inspiron 14R laptop with an Intel Core i3 CPU and 6 GB RAM, but for working satellites the 200 kHz bandwidth should be sufficient.

    This was my first attempt to use the SDRplay as my satellite downlink receiver. This is something I have been doing with the FUNcube Dongle Pro+ for much of this year, and a little bit of 2014. My laptop could easily handle this, but I want to make this work with my tablets. I operate portable, and the Windows tablets are better suited for my portable operating than a larger laptop. I think the SDRplay will work fine, once I get the hang of how to configure it using its HDSDR ExtIO plugin settings.

    KE0MHJ, K2NCC and KC4LE like this.
  3. W5SAT

    W5SAT Ham Member QRZ Page

    I was on that pass tonight. There was activity around 145.960 for a bit, I called CQ a couple times up around 145.970 then the QSO on 145.960 ended and I called CQ around 145.960 and had short QSO with K6FW before the transponder shut off - again - while he was talking. I thought it was supposed to stay on since it was the weekend????

    You really got me interested in the SDRPlay and I read a few reviews and it seems like the hot ticket right now for the price. I'm anxious to get your take on it's performance compared to a "real" radio.
    WD9EWK likes this.
  4. N8HM

    N8HM Premium Subscriber QRZ Page

    Per a message to the AMSAT-BB (, the command stations were not available to switch it last night over the UK. Looks like they also didn't get a chance on the morning passes today.

    Always check here for the current status of the satellite (the mode is on the left side of the page):

    By the way, all satellite operators should subscribe to the AMSAT-BB. It's an invaluable resource and after the launch of the Fox satellites, it will be the primary distribution method for information about the schedule for when the transponders will be active and open for use by hams. You can subscribe here:
    KD8ATF and WD9EWK like this.
  5. KA8NCR

    KA8NCR Ham Member QRZ Page

    That is pretty impressive for the price. Having a spectrum analyzer display of the passband is worth the price of many of the SDR options, and any of these are a far cry lighter than the 40 pounds of Hewlett-Packard love I have at my disposal. Just to see the noise floor rise and the beacon appear when the satellite comes into view is worth it, but knowing exactly where other stations happen to be as well as my own signal is quite nice. No wasting time.
    WD9EWK likes this.
  6. W5SAT

    W5SAT Ham Member QRZ Page

    Ha!!!! I knew it! Somebody is deliberately messing with me - 4 nights in a row I got cut off just when I was getting the hang of it. And you all thought I was crazy!!!

    Just to be absolutely clear, I am kidding - I'm almost certain there is no conspiracy against me - yep - almost certain.....

    Think it is time for me to subscribe to the mailing list - been meaning to do that. thanks for the reminder.
  7. WD9EWK

    WD9EWK Ham Member QRZ Page

    I think I'm going to like it.

    I have not played with the high-end SDR gear like what you see from FlexRadio. I have a few of the low-end items - RTL-SDR dongles, FUNcube Dongle Pro+, HackRF One, HackRF Blue (same as HackRF One, but produced using some different components for $100 less than HackRF One), and now the SDRplay. So far, I have only been using them as receivers - even though the HackRF One and HackRF Blue are wide-band transceivers (1 MHz up to 6 GHz, no gaps), although at milliwatt power levels. Once I have more time to work with the SDRplay, I think it will be at least as good as the FUNcube Dongle Pro+ for working satellites. Where the FUNcube dongle has front-end filtering at 2m and 70cm, the SDRplay has font-end filtering across its entire frequency range that switches on automatically based on what you're listening to.

    I tried using the SDRplay this morning to work SO-50. One problem - even in the shade, I could not see my tablet's screen well enough to work with it. I did observe that I could transmit on 145.850 MHz from another radio (I used my Wouxun KG-UV9D for that), and I could not hear or see anything that would indicate my transmitter was desensing or affecting my SDRplay/tablet combination in any way. I ended up using just the HT with my Elk log periodic to work about half of that pass, and made a QSO with W5PFG in Texas. I also heard ZF1DM in the Caymans near the end of the pass - I could have worked him, if I had a different radio out in the yard.

    I am convinced even more that the SDRplay will be a nice option for satellite operators looking for an SDR receiver in their stations. I think the SDRplay will work as well as the FUNcube Dongle Pro+. I still like the FUNcube dongle, and will not sell mine. The FUNcube dongle still has the advantage of size over the SDRplay, plus FUNcube dongle purchases help support the FUNcube satellite project - a good thing. The recent SDRplay API update means it works fine on Windows tablets, and removes the gap in its coverage around 380-430 MHz it previously had. I will also try it on HF, to see how well it picks up signals on those bands - amateur, shortwave broadcasters, WWV/WWVH, and others.

    W5SAT likes this.
  8. WD9EWK

    WD9EWK Ham Member QRZ Page

    Even the $20 (+/-) RTL-SDR dongles can be useful as a very inexpensive spectrum analyzer, but the SDRplay has a lot more going for it than the less-expensive dongles. Last night working AO-73, I could clearly see the 20 kHz transponder in the waterfall display (that section was a lighter color than the darker background in the HDSDR waterfall display). Within that lighter portion of the waterfall, I could clearly see CW and SSB signals - including some zig-zagging CW, as someone was going up and down the transponder. The AO-73 telemetry beacon at 145.935 MHz (+/-) was also clearly visible below the transponder portion, and I could clearly hear the signals when I clicked on it. I recorded that pass with HDSDR last night, giving me something to play around with.

    "No wasting time" - very true. You see all signals on the transponder, Click on any one of them, and there you are. You only need to adjust your transmitter to line up with that spot on the downlink. Software like HDSDR can be interfaced with SatPC32, just like you would interface a "real" radio, so you should be able to set your downlink frequency in the HDSDR windows and your transmit radio (if interfaced with SatPC32) would be lined up automagically. Even without SatPC32 controlling my FT-817ND transmit radio, it takes almost no time for me to move around the transponder during a pass - once I have lined myself up initially.

    W5SAT likes this.
  9. WD9EWK

    WD9EWK Ham Member QRZ Page


    Here's a screenshot from HDSDR, as I played back the recording from last night's AO-73 pass. I recorded this in HDSDR, capturing the 200 kHz bandwidth I was receiving from the SDRplay, centered on 145.925 MHz.

    You can see the telemetry beacon around 145.935 MHz, and the 20 kHz transponder above the beacon. HDSDR shows the transponder passband in a lighter color than the rest of the waterfall, and you can see signals within that waterfall. The red/yellow in the center of the passband was a QSO in progress, around 145.960 MHz USB. At other points in this recording, I could see a CW signal going up and down through that lighter portion of the passband.

    There was a DC spike in the center of the 200 kHz passband I recorded last night - a common thing with many SDR receivers like this one, and the FUNcube Dongle Pro+. After this pass, I figured out how to eliminate that when using the SDRplay. The spike is present with the FUNcube Dongle Pro+, but I have not seen a similar option in HDSDR to reduce or eliminate the spike when using that dongle. We can avoid it, by keeping what we want to hear above or below the spike. Since I had 100 kHz above the spike with what I was interested in hearing, the spike caused me no issues.

    Once I am more comfortable in using this setup, I will try to record one of my sessions working a satellite with the FT-817/SDR combination. I can also make a recording, where I play back an HDSDR recording, to demonstrate what we can hear when working the satellites with an SDR receiver.

    KC4LE likes this.
  10. W5SAT

    W5SAT Ham Member QRZ Page

    Very nice, Patrick. The nice thing is you can record a whole chunk of RF Spectrum and listen to multiple QSOs later, or decode the telemetry later, etc... I never bothered trying to record the spectrum with my cheap RTL-SDR but maybe I should play with that aspect. Also, I never realized you had such a collection of SDRs...
    WD9EWK likes this.

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