sdrplay duo and uhf

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fiann
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Joined: Fri Jul 19, 2019 11:36 am

sdrplay duo and uhf

Post by fiann » Fri Jul 19, 2019 7:00 pm

i have a d777 and pwk log per 140-450 mhz and still uhf is so bad my bct 15 is much better

anyone has problems on uhf to
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fiann
Posts: 3
Joined: Fri Jul 19, 2019 11:36 am

Re: sdrplay duo and uhf

Post by fiann » Sat Jul 20, 2019 6:12 pm

No 1 had te same things vhf works perfect uhf i tryed everything
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g1hbe
Posts: 493
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Location: Cheshire, UK

Re: sdrplay duo and uhf

Post by g1hbe » Sun Jul 21, 2019 8:59 am

The RSP's can suffer from DAB images on parts of the UHF band. Have you tried enabling the DAB filter?
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Andy

fiann
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Joined: Fri Jul 19, 2019 11:36 am

Re: sdrplay duo and uhf

Post by fiann » Mon Jul 22, 2019 10:06 am

Yeah i did and still uhf IT was bad reception i send IT back already
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g1hbe
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Location: Cheshire, UK

Re: sdrplay duo and uhf

Post by g1hbe » Mon Jul 22, 2019 11:06 am

That's disappointing, fiann. I often tune to around 255 MHz and listen to the South American pirates operating through the US Milcom satellites, and there's an old military satellite on 237 MHz that comes over every now and then. The reception of these on my RSP2 is just as good as it is on my other receivers.
There are some areas of the UHF band that are off-limits due to DAB images as the RSP2 does not have a DAB rejector, but reception everywhere else is excellent.
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Andy

Tech_Support
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Joined: Mon Jun 01, 2015 7:00 pm

Re: sdrplay duo and uhf

Post by Tech_Support » Mon Jul 22, 2019 11:38 am

Hello Andy,
There is a bit of a problem with scanning the Mil-Air band from with SDRuno. As you have pointed out, the architecture of the RSPs makes them vulnerable to DAB images in areas where there are strong DAB transmissions. The DAB filter implemented in the RSP1A and RSPduo has been effective in mitigating this problem, but it also creates a problem with the software scanner in its current incarnation. As you are probably aware, the software contains gain calibration tables for all RSP models and this allows both signals and the noise floor to be referred back to an equivalent value at the antenna port. When the DAB filter is enabled, it causes a noticeable change in the RF gain between 240 and 300 MHz and this throws out the calibration across that range. Because the filtering is performed after the LNA, the impact on the device NF and hence sensitivity is in fact minimal. The problematic impact of this though is the make setting a single threshold for the scanner for the entire Mil-Air band impossible. This is what we believe is causing the problem for the user above. If you set a threshold high enough to allow scanning across the 250-300 MHz range, it becomes too high for signals above 300 MHz and so the device appears to lack sensitivity because the threshold is set too high for the scanner to be able to lock onto certain signals. Of course you can manually tune to these signals, but many people understandably want to use the scanner.

We have a solution in the pipeline and as was explained to the user above, is scheduled for the next release of the software, but because we are unable to provide an immediate fix, the user in question instead chose to return their device, which is of course their right.

The solution is to use a different set of calibration values for when the DAB (and other) notch filters are enabled and this will keep the overall indicated antenna referred noise floor in-line with what the true NF actually is under all circumstances.

The scanning software is still relatively new and we are still learning about how people might use it and issues that they might have. We are constantly working to improve the software, but unfortunately, these things take time.

Sincerely

Tech_Support

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