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Author Topic: doppler frequency selectivity  (Read 5566 times)

KC0QNB

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doppler frequency selectivity
« on: June 07, 2008, 06:42:28 AM »

I have searched around the net but could not find a good answer. I have an interest in doing some RDF. The way I understand it a separate receiver is used in the activity
and the Doppler (Roanoke and Montreal type) units work by finding the signal and then indicate the relative direction of that signal on a display.
Now the question I have how does the Doppler system "know" that the signal it is indicating is the right one?
In my area all the public safety agencies and a lot of businesses use VHF and if the unit is not selective in frequency it could "lock" on any of those signals and lead the user astray.
73 Ryan
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WB6BYU

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doppler frequency selectivity
« Reply #1 on: June 07, 2008, 04:15:11 PM »

You use a regular 2m receiver attached to the doppler - it can be the
receiver in your mobile rig, HT, scanner, etc.  The selectivity is the same
as for normal ham 2m use.  The doppler will indicate a direction based
on the signal it is receiving, whether it is the one you are trying to find
or not.  So you have to be listening to the audio to know what it is
hearing.  (I think some dopplers include an audio output with the doppler
tone notched out of it.)

KC0QNB

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doppler frequency selectivity
« Reply #2 on: June 07, 2008, 05:06:22 PM »

OK thanks
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WB6BYU

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doppler frequency selectivity
« Reply #3 on: June 07, 2008, 05:45:25 PM »

On re-reading my comments I may not have been clear:  you set the
receiver frequency just as you would for any other 2m signal.  The
doppler doesn't do a frequency search, it simply responds to whatever
signal it hears on the frequncy the receiver is tuned to.

N6DMR

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doppler frequency selectivity
« Reply #4 on: August 08, 2008, 07:47:32 PM »

Here's a good link that shows the connections of a pic based doppler PicoDopp.  The link takes you to the hook up diagram and build instruction page.  You'll see that the HT audio and the data from the antennas are both ported to the doppler.

http://www.silcom.com/~pelican2/PicoDopp/COMPLETION.html

Duane
N6DMR
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