Elimination of DC and Mirror signals

Also known as ADALM-PLUTO.
Jirka OK1MWW
Posts: 1
Joined: Wed Jul 21, 2021 4:20 pm

Elimination of DC and Mirror signals

#1

Unread post by Jirka OK1MWW »

I use PLUTO with SDR Console V3.0.38 as a PAN adapter for my 2 meter contests. There is always a DC in ther middle of the screen and also mirror signals are not suprest as I would expect.
for my Funcube dongle I have a special tool , where I can eliminate DC and mirror signal, but for PLUTO I did not found anthing like that. Maybe the automatic compensation is switched off, but I do not know, how to switch it on. Please help.

Jirka OK1MWW

jdow
Posts: 798
Joined: Mon Aug 10, 2020 8:17 pm

Re: Elimination of DC and Mirror signals

#2

Unread post by jdow »

With SDRC that pip in the center is most often associated with poor and ineffective gain control settings. I usually run with manual RX gain set to 32 dB with visual gain set to about -3 dB. The latter gives me a reasonably accurate level display. The former brings up incoming noise to a level that masks that central pip.

In general, the central pip comes from self-conversion of the local oscillator within the front end. This can be mitigated. And SDRC does it about as well as most tools. It is a mathematically inevitable feature of the way most systems work.

{^_^}

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Simon G4ELI
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Joined: Thu Aug 06, 2020 7:27 am
Location: Mawnan Smith
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Re: Elimination of DC and Mirror signals

#3

Unread post by Simon G4ELI »

Jirka OK1MWW wrote: Sun Jul 25, 2021 2:32 pm I use PLUTO with SDR Console V3.0.38 as a PAN adapter for my 2 meter contests. There is always a DC in ther middle of the screen and also mirror signals are not suprest as I would expect.
for my Funcube dongle I have a special tool , where I can eliminate DC and mirror signal, but for PLUTO I did not found anthing like that. Maybe the automatic compensation is switched off, but I do not know, how to switch it on. Please help.

Jirka OK1MWW
Hi,

Screenshot please and show the Radio pane in the receive DSP - this way I can see the gains. The spur and mirror is due to IQ and can usually be corrected.

I've attached a screenshot for QO-100 where Pluto is actually receiving at the LNB frequency - note the gain settings.

At 144MHz Pluto is working outside the spec. I have no spur when receiving on 144MHz.
Attachments
QO-100
QO-100
Simon Brown :shock:
www.sdr-radio.com

Do not send me direct e-mail, thank-you!

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