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mute on transmit

Posted: Wed Sep 04, 2019 9:58 pm
by k1tod
I have a RTL-SDR and am using Sharp. I am a Ham and am using this on HF. Everything is up and running but I am trying to figure out how to completely mute the audio from the dongle and computer when I transmit on a separate transceiver. I have it set up so the antenna connection to the dongle is disconnected and grounded during transmit but I still get a full audio hiss from the computer during transmit. Is there a way to mute this audio? If not it is basically useless to me because I can not have this audio noise present when transmitting. Thanks, Todd K1TOD

Re: mute on transmit

Posted: Thu Sep 05, 2019 12:40 pm
by k1tod
I guess what I am looking for is a way to auto mute the RTL-SDR and or computer audio during transmit. Thanks, Todd

Re: mute on transmit

Posted: Thu Sep 05, 2019 4:37 pm
by snn47
How much power do you transmitt and on which bands do you have problems?

Have you considered that it is direct RF getting directly into your setup somehwere after you muted the audio that is generating the hiss?

I know in todays totally solid state envrionment it is an old fashioned advise, but have you considered using a relais driven by your tx to mute/disconnect the audio or speaker, or at whatever stage the hiss is generated? In case standard relais are to slow there are always the much faster reed-relais.

vy 73
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Re: mute on transmit

Posted: Thu Sep 05, 2019 7:47 pm
by k1tod
Thanks for the reply. It is not an RF problem I am having. I am talking about the white noise coming from the computer speaker when the RTL-SDR antenna is disconnected and its antenna connection is grounded by a T/R relay like the MFJ-1708B. I can actually disconnect the antenna from the dongle and then ground the antenna input on the dongle and I still get loud white noise (without any transmission) like when you listen to an HF receiver with no antenna connected. I thought maybe there was a setting in the software or a software add on that would auto mute the dongle when I transmitted. If not I will use an external speaker on the laptop and use a relay to disconnect it when I key the transmitter. Any advice or suggestions are appreciated. 73, Todd K1TOD

Re: mute on transmit

Posted: Fri Sep 06, 2019 3:36 pm
by hotpaw2
Software squelch that cuts out the demodulator and/or output to the OS audio driver when the IQ spectrum is high and flat would work. I've experimented with that in some of my SDR software experiments, and it seems to work.