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Problem with RSP

Posted: Wed Jul 08, 2015 10:11 am
by aether
Hello SDR guru's
I was pleasantly surprised today ...taking delivery of the sdrplay so soon. Thanks for a rapid delivery.
I subsequently downloaded and install relevant drivers etc. but have an issue with tuning?? I’m using two
machines,both AMD processers one is dual core at 3ghz the other is quad core at 3.4ghz with
windows 7 64 prof installed.
Using both HDSDR & SDR# the tuning goes erratic and all sorts of duplicated signals appear above 250 mhz.
Its not the gain that’s to high or image issues because if I tune very slowly it behaves until the frequency wont increase any more (258 MHZ ish)
If I try to go backwards or take 1 mhz steps I get the DAB signals pop up all over that band. the only way i can stop this is to restart the program.
Hope you can put me on the right track.
I have had a browse through the forum but couldn't find anything relevant.
Thanks for any suggestions.
Kind regards

Re: Problem with RSP

Posted: Wed Jul 08, 2015 12:47 pm
by Tech_Support
Hello Aether,
We will need to look into this and get back to you about the erratic tuning behaviour as this seems rather strange. Regarding the DAB images that you are seeing, I believe that we can explain that.
At HF and for frequencies between 240 MHz and 380 MHz, the RSP uses a dual conversion heterodyne architecture. For all other bands it uses a homodyne architecture. All wideband receivers are susceptible to producing spurious images that result from signals mixing with harmonics of the various local oscillators. So for example, if you were using a wideband homodyne receiver at say 30 MHz, a signal at 90 MHz could mix with the 3rd harmonic of the 30 MHz local oscillator and produce a signal 'on-channel', giving the impression that the 90 MHz signal is actually at 30 MHz. With a dual conversion heterodyne architecture, because there are two mixing stages, there are many more possibilities for spurious responses.
The way that we to deal with these responses is twofold. Firstly, we use band filters to attenuate the unwanted signals when you selecting signals well away from the unwanted ones. Secondly, we have tried to select a frequency plan to ensure that these spurious responses are well away from bands that people are likely to be most interested in.
The DAB images that you are seeing are one of these spurious mixing products and the problem is that because the spurious response occurs close to the upper edge of the DAB band the band filter gives relatively little rejection. As a consequence, if the DAB signals in your area are strong, the spurious responses will be easy to see. If this is a problem for you, you can try adding more filtering of the DAB signals at the antenna. Alternatively, we have a new API coming aimed at closing the 380 - 420 MHz 'gap'. This API works by dynamically adjusting the frequency plan and if necessary, we can investigate the feasibility of giving the user a degree of control over this to allow them to move where these spurious responses fall.

Regarding the erratic tuning behaviour, please email directly and we will attempt to get to the bottom of what you are experiencing. When you do so, please let us know what your setup is, i.e. PC configuration, CPU/speed etc and what software you are using (including version numbers)



Re: Problem with RSP

Posted: Fri Jul 10, 2015 4:22 pm
by aether
Hello Tech Support.
Thanks for the reply. I have now tried the RSP on a 3rd computer (this time a laptop Toshiba L7550) Windows 7 home prem.
And I still encounter the same problem. At 70 MHz I can increase in frequency slowly in 100khz steps until I get to about 71/72 MHz when the display jumps to DAB signals, the frequency readout does not jump to 230 MHz it reads 72.???MHz I then have to tune several hundred kHz down in freq for it to recover. The same happens at 250 ish MHz and again at 300 ish mhz. Its as though its band switching when it shouldn't.
I haven't had time to go through the entire freq range as I'm working 12hr shifts. Could this be a extIO problem or hardware issue ?
Odd that this happens on all 3 machines.
I will attempt to make a video of the issue and upload to YOUTUBE.
I'm fully aware of intermixing and images but not convinced its that. Have no issues with other dongles and devices except for the usual pager breakthrough due to poor filtering etc.
Thanks again for your support in this matter.