SDR for Frequency Deviation

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Scubadennis
Posts: 3
Joined: Wed Nov 07, 2018 5:31 pm

SDR for Frequency Deviation

Post by Scubadennis » Wed Nov 07, 2018 7:49 pm

Hello,

I just purchased an SDR to help with my Kantronics KPC-3+ modulation settings. I want to hook my radio RF directly to the SDR. I understand I need a RF Sampler. Does anyone make one for Ham bands? Is it possible to just use provided antenna to get accurate measurement from dummy load?

Scubadennis
Posts: 3
Joined: Wed Nov 07, 2018 5:31 pm

Re: SDR for Frequency Deviation

Post by Scubadennis » Tue Nov 13, 2018 3:25 pm

Any help on this?

rtlsdrblog
Site Admin
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Joined: Mon Nov 19, 2012 11:54 pm

Re: SDR for Frequency Deviation

Post by rtlsdrblog » Wed Nov 14, 2018 5:29 am

Why can't you just connect the RF output to an attenuator, then into the SDR?

Scubadennis
Posts: 3
Joined: Wed Nov 07, 2018 5:31 pm

Re: SDR for Frequency Deviation

Post by Scubadennis » Wed Nov 28, 2018 2:37 pm

Which attenuator? That is what I need do know.

rtlsdrblog
Site Admin
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Re: SDR for Frequency Deviation

Post by rtlsdrblog » Thu Nov 29, 2018 11:15 am

You need to find out what the output power of the TNC is, then use an attenuator to reduce it to something well below 10 dBm (10dBm is the max input power of the RTL-SDR).

But yes you could also just attach a dummy load to the TNC, and put the RTL-SDR with an antenna near it. That should pick up the small stray signal which should be enough to evaluate the output modulation of the TNC.

Mojoworkin
Posts: 1
Joined: Mon Dec 09, 2019 8:45 pm

Re: SDR for Frequency Deviation

Post by Mojoworkin » Mon Dec 09, 2019 9:16 pm

Antenna near the dummy load sounds like a winner to me, but I came to this thread wanting to know more about using SDR to measure deviation, so perhaps I can add on here?

So far I have found some info on how to coax this info out of an SDR with Bessell functions, and that's great - but I am so surprised that this measurement is not baked in to any of the SDR software that I've played with. I just found out about GNU Radio, and if there isn't a module that does this in GNU, maybe I can figure out how to make one, but still - all the info is right there on my screen - it just needs some math pointed at it, right?

So my actual question - Is there an SDR based deviation meter? Either standalone or built into a software suite?

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