[RFI] tips for finding the source of broadband mixing products

[Martin Sole]

Definitely a possibility the SDR is in overload. A 10dB attenuator on 
the front will soon show if that is the case or not. If its an SDR 
amateur radio transceiver hopefully that's built in. If you use one of 
the lower end simple direct sampling boxes like an SDR play, investment 
in a stepped attenuator and perhaps a tunable preselector are both very 
worthwhile if not vital additions.

Martin, HS0ZED



On 30/09/2019 12:24, Lee STRAHAN wrote:
>    Hi Matt,
>     It looks and sounds to me like you are simply overloading the SDR receiver and generating the spurs and noise inside it. What level of the fundamental signal is actually being applied to the SDR? I am guessing the largest pip shown is the third harmonic you refer to.
>     One way to find out is to lower the transmitter power by 10 dBm of the transmitted signal. If the spurs go down by more than 10 dBm they are most likely being generated inside the SDR receiver by simply too much signal overload. You may be chasing a ghost. If the screen shot is really the third harmonic at 14 MHz why are you transmitting on 14/3 or 4.67 MHz?
>      Any way lower the signal into the SDR and find out if the problem spurs go away. I think you are simply overloading the SDR with way too much signal.
>    Lee   K7TJR   OR
>
> -----Original Message-----
> From: RFI <rfi-bounces at contesting.com> On Behalf Of Matt NQ6N
> Sent: Sunday, September 29, 2019 7:00 PM
> To: rfi at contesting.com
> Subject: [RFI] tips for finding the source of broadband mixing products
>
> Hello,
>
> I'm noticing that the second harmonic of my transmitted signal is accompanied by all sorts of broadband noise.
>
> I am in the process of ruling out the equipment inside the shack as a cause of this noise.
>
> But I want to be prepared to begin the search outside the shack for things (wall warts, etc.) that might be generating the broadband noise when exposed to RF.
>
> What are some techniques for localizing the causes of this kind of broadband noise?
>
> A screen shot of the pan adapter and a recording of the audio of the third harmonic + noise is attached via the below link:
>
> https://www.dropbox.com/sh/2639h09dhr8qxkf/AADr4-Nl4GS7e-Cl3TKSuq5aa?dl=0
>
> Any advice would be much appreciated.
>
> 73,
> Matt NQ6N
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