Setting frequency by the remote control protocol problem

[Oleksandr]

Hello, everyone. If I set the frequency with the mouse on the screen, then everything is fine. When I give the command F 14450000, the frequency is set, but with a offset relative to the center by 432 kHz. Why is it so and how to set the frequency without offset?
And why is the maximum sensitivity only in the 200kHz band? I use Sdrplay and in SDRUno for Windows, I see a band up to 10MHz

[Robin Gape]

1) The remote control protocol does not allow for remote setting of the hardware offset frequency. There is a gap in the capability noted in https://github.com/gqrx-sdr/gqrx/blob/master/resources/remote-control.txt.

2) The hardware offset frequency, shown as 432 kHz in the screenshot, may be freely set by the user, to any value within the SDR's sampling passband. [A hardware offset is necessary to deal with certain hardware which otherwise shows a spurious peak around 0 Hz due to a DC offset in the signal chain. This effect is present on some, but not all, SDR hardware.]

3) The maximum sensitivity question needs some further clarification.

73

Robin, G8DQX

[Oleksandr]

Helo, Robin.

Thanks for the answer.

1) OK. 

2) Yes, I can change the offset frequency to any value and to zero too, but only with the mouse on the GQRX screen. But even this offset frequency is set to 0, and I send "F 14450000" command, the offset jumps to 432kHz. And I can not return it to 0
3) it is a reason of my previous questions. I don't know why, but the maximal sensitivity of my system (SDRplay + GQRX) is only in 200kHz part of the band.  When I send the "F 14450000" command, the system tuned behind the border of this part, and I can only receive the nearest power signals. If I use the same SDRPlay with windows SDRuno I can see all band 2, 4, or 10 MHz without such strong maximum. Now I try to use another SDR soft to be shure. I have the RTL-SDR dongle, but GQRX does not work with it (in Windows this dongle works all right)

неділя, 9 листопада 2025 р. о 19:03:05 UTC+2 Robin Gape пише:

[Oleksandr]

I found the way to solve my problem. It is described there:  https://osmocom.org/issues/5448  and there: https://github.com/gqrx-sdr/gqrx/issues/970.  

"RSP1 supports 8 fixed bandwidths: 0.2, 0.3, 0.6, 1.536, 5, 6, 7, 8 Mhz. Any other value interprets as invalid and defaults to 0.2MHz"

I tried to change the bandwidth to different values, but I set 1, 2, 0.5MHz, and could not think to set so strange digits 0.3 or 1.536. And really, bandwidth 1.5 or 1.6  gives the minimal  0.2MHz. And 1.536 works correctly. 5, 6, 8 work too.

Also, I tried to use RTL-SDR v4 and Hack-RF to find out where the cause of the problem is..  The RTL dongle worked, but the frequency swam for 100kHz and more.  HackRF worked without any problem with GQRX. But it has worse sensitivity than my SDRplay

Thanks for the answer. Now I can continue to experiment with SDR and Raspberry and don't need to control the hardware frequency anymore.

понеділок, 10 листопада 2025 р. о 13:25:10 UTC+2 Oleksandr пише: