To capture the RF noise signature, a scope should not be the tool of choice.
You'll want to investigate using a pan adapter on an IF port or an SDR
receiver as a pan adapter. Capturing the noise signature requires spectrum
analysis and not a time analysis as is provided with an oscilloscope.
Using the speaker output is fine for recording and archiving the demodulated
noise, but I'm not clear why a scope would be of any value for that purpose.
If finding the noise and documenting the RF noise signature is the ultimate
goal, an audio recording and scope is of little help.
Here's an example of capturing a noise signature:
http://72.52.250.47/images/RF-Noise-112608.jpg
The plot above was taken with an SDR-IQ, netbook PC, and Palomar LA-1 loop
antenna. Sampling an IF port in the 8-12 MHz range is another option
offering similar results. Also, the SDR-IQ also gives you the ability to
record real-time spectrum over time to the PC hard drive for playback later
on. That's a great way to record the spectrum of the noise signature, and
have the ability to demodulate the recording for listening later on.
Paul, W9AC
----- Original Message -----
From: "RFI Services' Michael Martin" <mike@rfiservices.com>
To: "'Missouri Guy'" <n0tt1@juno.com>; <RFI@contesting.com>
Sent: Thursday, December 09, 2010 8:09 AM
Subject: Re: [RFI] Video output for a 'scope?
> Hello Charlie,
> The speaker output will work but using it will create an issue when you
> change the volume output. When you change to a comfortable level you'll
> also
> be changing the scope displayed spike level. This is why it would be
> better
> to use the record jack, if available. The output at this point won't
> change
> when the audio output level is adjusted. The spike level will rise with an
> increase in signal level as you approach the power line noise source.
>
> Michael C. Martin
> RFI Services
> 6469 Old Solomons Island Rd
> Tracys Landing, MD 20779
> www.rfiservices.com
> 240-508-3760
>
> -----Original Message-----
> From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
> Behalf Of Missouri Guy
> Sent: Wednesday, December 08, 2010 3:12 PM
> To: RFI@contesting.com
> Subject: [RFI] Video output for a 'scope?
>
> Hi Gents,
>
> I now have a portable o'scope and I want to observe the RF "signature"
> of a noise. One of my RFI books said to use a radio with a video output.
> I'm not really sure what the author meant by that.....
> is that, what I would call, the IF output (before the radio's AM
> detector)....
> or maybe it's the audio output that's been run through an integrator?
>
> I know the sweep for the 'scope should be an accurate 60hz...I'll get that
> with a special IC chip.
>
> Thanks,
> Charlie
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