Hello Nigel,
I'm as mystified as you are, but I would be surprised if a generic driver would do that sort of pre-emphasis processing (I could be wrong).
Have you tried simply listening to the audio coming from your sound card (without going through Quisk)?? I'm wondering if the raw sound might give a clue as to the origin of the bump.? Perhaps try comparing the sound from your Line2 USB with your UFO202?
Good luck!
-- Ben, AC2YD --
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On 12/3/22 21:42, Nigel Johnson MIEEE via groups.io wrote:
OK, I brought the box with the softrock 40 ensemble and raspberry pi down from the roof and hooked it up to the service monitor.? ?I can clearly see there are no images of any signal that I inject at normal levels playing with it around 7.12 MHz.? The only way I can see images is if I turn the service monitor's attenuator way up beyond any signals that I would ever receive, hundreds of mV of signal. It clearly shows and demodulates AM with a few uV of RF. When I had it up on the roof I could clearly demodulate WWV, CHU, some broadcast stations and 40m CW signals, so I know it is working.
The noise level at the edges of the screen is sitting at around -80 dBm, but there is still this mountain rising by 30dB in the noise floor +/- 10 kHz from the VFO (on 40m)
Right now I think I am in need of somebody who can help me debug the linux driver.? I originally tested this setup with a Behringer UFO202 USB sound card (which uses a TI chip), but when I built it into a small box to put up on the roof I bought a Behrigner Line2 USB for the size, which uses a C-Media chip.? That is when the mountain appeared.
I cannot see anywhere that the driver is named to differentiate what chip it is expecting, it is just called snd_usb_audio.? I perceive that there is something in the driver that is pre-emphasizing the lower frequencies.? There is very little info on the C-Media web site, they obviously are oriented to just supplying chips to board makers.
Is there anybody in this group that has experience with linux drivers?
73 de Nigel ve3id
