SDRplay as satellite downlink receiver?

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

ad: L-HROutlet
ad: l-rl
ad: abrind-2
ad: L-MFJ
ad: Left-3
ad: L-Geochron
ad: Left-2
ad: l-BCInc
  1. W5SAT

    W5SAT Ham Member QRZ Page

    Good news and bad news from today's experimenting. Good news is that there is no real desense on UHF from transmitting on VHF. I did not test using the same antenna and a diplexer (such as an Elk fed by diplexer and 2 radios). I tested this with 2 yagis (VHF and UHF) separated by about 3 feet from same radio. Also, I tested transmit on my ground plane which is about 12 feet from the Yagis. Very, very minor rise in noise floor when transmitting - maybe 1 dB or so.

    Bad news - Tonight while testing SO-50 downlink (heard you on there Patrick) I noticed a HUGE rise in my noise floor when orienting my Elk horizontally... Hmmm what could that be??? Pointed my antenna around and found noise was strongest in the direction of South Mountain. For those not familiar with South Mountain, that's where most of the TV transmitters are. Set my bandwidth to 8 Mhz and tuned around and sure enough there were ATSC (8VSB modulation for those that may nit pick) carriers starting at channel 15 (476 to 482 Mhz) and up. So having a pile of TV stations (which transmit horizontal polarity) putting out up to 1,000,000 watts each is not a good thing to have around. Basically, when orientating the Elk antenna horizontal and pointing int he general direction of the TV transmitters is raising the noise floor to unusable levels on 420 Mhz and above. Bummer there wasn't one more filter in there for 450 Mhz and up.

    BTW, the UK uses the same general range of frequencies for it's UHF TV broadcasts - seems like they would have thought to filter those out the way they did with the FM (well 60 to 120 Mhz, close enough).
  2. WD9EWK

    WD9EWK Ham Member QRZ Page

    This is good. You would probably see similar results if you used your Elk through a diplexer like I've been doing.

    I must be far enough away from the South Mountain transmitter site, and possibly with some hills between my house and that site, where I haven't had the pleasure of experiencing that. Or maybe having a diplexer always in line with my Elk makes a difference in filtering/blocking the ATSC signals in the UHF TV band above 470 MHz. I can try that from the back yard, pointing southwest with my Elk oriented horizontally.

    By comparison, the FUNcube Dongle Pro+ has a SAW filter centered on 435 MHz and a separate (non-SAW) bandpass filter for 410-875 MHz. Here's a block diagram from Howard Long's (G6LVB) presentation on that dongle at the 2012 AMSAT Symposium, showing (among other items) the front-end filtering it uses in its RF path from the antenna to the USB port going to a computer:


    With the band switching in the FUNcube Dongle Pro+, it is able to use the SAW filters for the 2m and 70cm ham bands, and the "normal" bandpass filtering for other portions around those bands. I'm not sure we'll see the same thing implemented in the SDRplay, as it was not made as a 2m/70cm satellite downlink receiver that happens to cover much more spectrum than those two bands.

    Maybe it's not as much of an issue with DVB broadcasts vs. ATSC. I don't know. That might be a good question to pose on the SDRplay community forum, so the SDRplay developers can chime in with their thoughts - unless someone from Europe sees this thread, and can post their thoughts here on how well the SDRplay performs on/around the 70cm ham band and their UHF TV transmitters.

  3. W5SAT

    W5SAT Ham Member QRZ Page

    After reading your comment about the noise hump yesterday before the SO-50 pass, It got me wondering about the fact that I was using Low IF mode. I'll re-test later and see if a difference between the IF modes. I don't want to rush to judgement on this issue just yet now that I have more food for thought.

    I have a regular 2m/440 diplexer and one for 23cm that cuts off below about 700 Mhz that I may play with as well to see of they offer any filtering advantages. Like I said, more testing before I make a judgement call on this. That's half the fun....
    WD9EWK likes this.
  4. WD9EWK

    WD9EWK Ham Member QRZ Page


    I didn't scribble this earlier... but last night on a western SO-50 pass, I was out in the yard again working with the SDRplay. I used the same setup as before, pairing the SDRplay and tablet with my Wouxun KG-UV9D HT and an external speaker/mic. Since last night's setup mirrored what I used before, I won't post the photos in this message. I did add a photo of my back yard thermometer, taken a few minutes before that pass, along with the photos of my radio/tablet setup. That's visible at:

    I worked 6 stations on that pass, mostly near the west coast with one in Calgary and another in Louisiana near the end of the pass. Other than trees that block my view between north and northwest where the downlink signal was weaker than when I was pointing around that tree. HDSDR's AFC did a decent job, but I had to do more adjusting while the satellite was behind the tree.

    If I could find a tablet that didn't have a glossy screen yet supported Windows 10, I could end up with a viable setup that I can work when I'm outside during the day. I expect that I'll have some HTs that will do full-duplex with the upcoming Fox-1 satellites, but an SDR downlink receiver has advantages even on the single-channel satellites.

  5. WD9EWK

    WD9EWK Ham Member QRZ Page

    That would be useful information, to see if your setup matches what I tried last night. I've been more concerned with finding a setup that works satellites, and now I need to venture out of that small comfort zone and try other settings on the SDRplay to see if I can use it with Low IF, reduce/eliminate the spike in the center of the passband, and still work satellites.

    Yes, it is fun to try different things out. I'm no expert on this stuff, but I get regular e-mail queries based on posting I've done on forums and mailing lists, and the article I wrote for the AMSAT Journal a few months ago. Reasonably-priced SDR receivers, cheap computers (tablets), free software, other radio-related accessories... lots of room for experimentation...

  6. W5SAT

    W5SAT Ham Member QRZ Page

    Ok, I decided I'd get on SO-50 tonight using the SDRPlay as my downlink receiver. This is connected to my 4 element yagi vertically polarized. For TX I decided to use my Kenwood TM-v71A connected to a Radio Shack VHF/UHF scanner antenna which just happens to tune up nicely for 2m and 440 TX. Basically, I was using a 1/4 wave 2m ground plane for TX.

    Anyway, the SO-50 gods were being kind to me today and allowed me to have a nice long QSO with KG6FIY in Long Beach, CA. I probably sounded like an idiot (fine, more of an idiot than usual) due to the delay in hearing myself back via the SDRPlay receiver but it worked very well. Really pleased with my results. Couldn't be happier. Yippee!!!

    I recorded the pass - well most of it, forgot to hit record right away, but anyway I have an HDSDR IF recording on my google drive at:
    File name is SO-50 20150917_030243Z_436802kHz_IF.wav

    I only recorded about 85 Khz worth of bandwidth to keep file size manageable. At the high end of the spectrum, when I transmit I can see myself bleeding into the SDRPlay. The SDRPlay is sitting right next to the Kenwood transmitting at 50 watts (into an omni antenna, don't yell at me) so some bleed is understandable but it did not affect my RX. In fact, when I TX there is virtually no movement of the noise floor which is impressive since the TX and RX antenna are only about 12 to 15 feet apart.... So - good news there.

    Finally.... In HDSDR, under Options (F7), selecting "Input Channel Calibration for RX" will effectively null the DC spike - basically the same thing SDR Sharp does - just select the "Auto" button by "Mode" in the upper right of the dialog box. Never played with this before. Works great.

    Finally (again.. but for real this time), Running EXTIO in IF Mode "Low IF" seems to work well for me and results in anywhere between a small to almost non-existent DC spike - seems to depend on which frequency range you are in how small the DC spike is... Not sure.
  7. WD9EWK

    WD9EWK Ham Member QRZ Page


    I saw that Endaf KG6FIY posted on Twitter last night that he was going to be on that pass, and he mentioned he worked you and another station. If I was doing other stuff around the house at that time, I was going to go out and join in the fun.

    I have had some successes with that option to minimize or eliminate the DC spike for other uses. I need to take another look at that for working satellites, since I still see the spike when I have used this out in the yard.

    Again, I'll have to take some time this weekend to work on this. I know the Low IF setting is supposed to minimize or eliminate the spike, so there may be other settings I have to adjust to get the desired effect.
  8. WD9EWK

    WD9EWK Ham Member QRZ Page


    Reading over some posts on the SDRplay community forum, it appears that a recent update to the SDR Sharp (SDR#) software breaks its compatibility with the SDRplay and the ExtIO DLL used with previous versions of SDR#. This is unfortunate. SDRplay is hoping to find a way to have its receiver working with newer versions of SDR Sharp once again. One thing noted in some of the posts is the fact that the developer of SDR Sharp is also part of the group producing the Airspy SDR receiver. In fact, SDRplay's forum has a message (not from someone working at SDRplay) indicating that SDRplay users should not update their SDR Sharp installations, and identifying at least 5 versions of SDR Sharp that work with the SDRplay.

    I don't use SDR Sharp for my satellite work, but have had it installed on my Windows 10 tablets and a laptop with Windows 7. There are some features I like in SDR Sharp for general listening, but have used HDSDR when working satellites. I hope there is a way to get the SDRplay working once again with current/newer versions of SDR Sharp. Otherwise, I'll use SDR Sharp with other devices, and HDSDR with all of my devices.

  9. W5SAT

    W5SAT Ham Member QRZ Page

    I'm the same way about SDR Sharp. Got some nice features and a great selection of plugins but I have found that I am using HDSDR the most lately.
  10. WD9EWK

    WD9EWK Ham Member QRZ Page

    I like how HDSDR runs on my Windows 10 tablets, using fewer resources than SDR Sharp or SDR-Radio would. I really can't use SDR-Radio on the tablets anyway, without going to a small bandwidth and turning off most of the features in the program. On a larger PC or laptop with more memory and CPU power, it's a different story...

    I saw one friend on Twitter earlier today lament the need to now use alternative software when running the SDRplay. I take that to mean he prefers SDR Sharp over HDSDR. For me, it's the direct opposite - I can still use all of my SDR receivers with HDSDR, and one of the alternative software packages no longer works with my SDRplay. I think my Win7 laptop has an older version of SDR Sharp which should support the SDRplay, so that means I have to keep it as is and never upgrade it to use the SDRplay with it - until SDRplay and/or SDR Sharp come up with support for the SDRplay with that software.

    For general listening, I have only been running SDR Sharp for one reason - SDR Sharp can decode the RDS data on broadcast FM stations. Other than dabbling with SDR-Radio, most of my SDR work is done using HDSDR. I know some claim that HDSDR is no longer supported, since the last update for it was released in November 2013. I don't know for sure if the author of HDSDR has stopped development of the software, but the HDSDR web site has continued to be updated. The HDSDR home page acknowledges that it runs on Windows 10, and I have seen updates or new receivers listed on the Hardware page of that site (i.e., HackRF - it has only had a ExtIO DLL for HDSDR since June or July).

    Back to work...

Share This Page