Rx sensitivity measurements for DVB-S2 and DVB-T

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G4WIM
Posts: 379
Joined: Thu Jan 29, 2015 8:36 pm

Rx sensitivity measurements for DVB-S2 and DVB-T

Post by G4WIM » Wed May 19, 2021 7:10 pm

Following my attempts to work Rob M0DTS I thought I'd make some rx system measurements for DVB_S2 and DVB-T on 437 and 1315MHz,

I was using 250kS and FEC 1/2 for both DVB-T and DVB-S2 with a LIme as the source at a level of -31dBm output followed by precision switched attenuators giving me confidence in levels down to at least -127dBm. Running the Lime ast a low level helps signal leakage issues.

Both my 437 and 1315Mhz have high performance helical or interdigital filters directly on the antenna inputs - adding about 0.3dB extra loss.

The 23cm Rx uses a gasfet LNA whereas the 437MHz rx uses a PGA103. The gasfet measures a NF of just under 1dB whereas the PGA103 measures just over 1.1dB.

Taking into account the rest of the rx chains both systems have a noise figure close to 2dB - not brilliant but adequate.

I found the got the same results sensistivity wise on both bands - as might be expected as the noise figures are similar

On both bands I could reliably decode both DVB-S2 and DVB-T down to -117dBm.

DVB-S2 took about about 0.5dB more to intially capture whereas DVB-T took 2dB more (and about 30 seconds) - but once locked both rx's would work down to -117dBm and hold the signals without dropping.

Looking at the signals on SDR Sharp at -117dBm they were about 6dB above noise floor.

I was wondering if anyone else had tried measuring their rx thresholds and how they compare to mine ?

Using Knucker for DBT-T and Winterhill for DVB-S2

FYI I suspect the reason I couldn't rx Rob M0DTS was due to a very strong signal out of band on 443MHz blocking my 437MHz rx - the antenna filter has significantly reduced this blocker hopefully down to a level where it's no longer a problem, in band blockers are something else !!

73 Tim

radiogareth
Posts: 1215
Joined: Wed Jan 06, 2016 9:46 am

Re: Rx sensitivity measurements for DVB-S2 and DVB-T

Post by radiogareth » Thu May 20, 2021 6:53 am

Interesting stuff Tim. Whilst I definitely don't have pro-level gear I have been testing across the shack on 5.66GHz. All a bit of a lash-up at the moment but it works. I found similar results from looking at 'what managed a decode' with a SDR and came up with similar - about +4-6dB above the noise floor would work fine. Having a SDR on-board certainly helps as it takes out the guesswork.
I think I need more gain for the Minitiouner (+11dB Amsat filtered preamp on 2m) whereas the Knucker has better 'ears' (?eyes??) anyway.
Gareth

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