Thursday, 25 February 2016

SDRPlay

CHaving read the review of the SDRPlay in Radcom I thought that I'd buy one. Now it has arrived I needed to connect it to my TS2000X in order to monitor 23cm. I am able to do this already via my SDR-IQ and a PAT board connected to the 10.695MHz second IF.  However, I find this most unsatisfactory as the 'span' is limited to about 30kHz and it reverse tunes (LO is high).
Connecting an SDR to the TS2000X first IF (135.495MHz) turned out to be surprisingly easy as there are a number of MMCX connector test points on the 23cm module board. CN8 is a light tap (1pF) between two 135MHz tuned circuits and after the first mixer (dual gate fet). CN7 is after the 135MHz monolithic filter and first IF AGC controlled stage. I really didn't want to have the SDR connected after an AGC controlled stage as it meant high level signal level measurements would likely be wrong as the AGC activated. I was not sure whether the IF at CN8 would be clean enough. It was.

I had a short UF/L to SMA cable end jack available, purchased originally to use with a small GPS module. The cable is about 15cm long and very thing, but as this is 135MHz it doesn't really matter.
This cable turned out to be long enough and thin enough to loop around the 23cm antenna flying lead as it emerges from the TS2000x. By carefully drilling a 7mm hole in the removeable (2 screws) cable clamp plate I was able to fit the SMA bulkhead jack in place next to the cable lead. There is not quite enough room to do up the SMA nut, but a dab of superglue soon fixed that!

With this IF tap cable in place I was able to do some tests through the front end. Previously ARRL Lab had measured the TS2000X noise figure as 6dB as quoted in a QST review. From 23cm RF cable input to CN8 cable IF output I measured a very acceptable 4.1dB, consistent across the whole 1240 to 1300MHz range with a centre band gain of 14dB falling by about 1dB at either end of the range. I felt this was adequate for connecting the SDRPlay without using one of the G4HUP PAT boards, although this might be fitted at a later date. 

Checking with my spectrum analyser there were no spurious mixing signals within the 135MHz IF range down to at least 70dB below my -40dBm 1296MHz input test signal.
Using HDSDR I was able to see noise from the SDRPlay up to about 3.5MHz either side of centre band (IF) and able to zoom right into signals such as the Martlesham 23cm beacon. There is no centre (DC) spike even using the zero IF option!

If ever the SDR application teams ever get round to adding Continuum mode to this or any of the other SDR programes they will become really useful for measurements rather than just looking at signal spectrum (Spectravue does have Continuum but doesn't run on the SDRplay!)

Back to destroying 23cm preamps in the name of determining safe input levels......

Sam


3 comments:

  1. Sam, have you taken a photo of where CN8 is and what to remove to get to it?

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  2. I have the SDRPlay here also Sam, and currently use it with a 3dB splitter on the IF of my 144 to 14 MHz transverter. Using Omnirig it can track the VFO and mode of the KX3. This allows quick switching to listening on SDRPlay when there is static rain and the HDSDR RF Noise Blanker removes it so well, being wideband.
    I wouldn't hold out much hope of SDRPlay doing any software themselves, they seem to depend on third parties like SDR# who have now locked them out as they produce competing Airspy hardware. HDSDR is the best of the bunch but has not been updated for years. Then there is Simon's SDR-Radio which is in a perpetual state of flux, maybe one day it will be finished and totally useable.
    The only software that SDRPlay produce themselves is the EXTIO which allows it to be used with those few other third party programs. The hardware is pretty good, though you have to watch if you have very strong signals closes in frequency and may require additional bandpass filtering in some situations. Lacks the SAW filters of the FunCube on VHF UHF bands.
    It quickly becomes apparent that producing the hardware is only a tiny part of the solution, SDRPlay need to have an in house SDR software team to develop their own software as depending on others to supply free software isn't going to work out for them. The SDR# cat and mouse game proves that, they are left high and dry on that.

    73 David

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  3. SDRplay now provides its own software - SDRuno - based on Studio1 - you can download this from http://www.sdrplay.com/windows.html

    73, Jon G4ABQ (SDRplay)

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