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Old 26th Nov 2023, 10:09 pm   #1
Cruisin Marine
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Default Doppler DF Unit wanted

Fancy a play with a Doppler unit as I have never used one.
After a cheap Doppler unit, preferably with 16 LED display.

All I ask is some documentation to save tracing the cct out.

I can build one for about £50 if not.
Not too bothered about the antennas as I can build that part.

Whilst on the subject, am I right in thinking they only work with FM signals, not AM?
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Old 27th Nov 2023, 12:45 am   #2
Radio Wrangler
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Default Re: Doppler DF Unit wanted

Ah, I can see where you got confused.

The rotation of a doppler direction finder antenna CREATES FM on the signal, whatever that signal may be. So you need an FM receiver to recover the doppler-created FM. The audio from your FM receiver is compared with the rotation (switching) of the antennae in phase and the result is the heading of the signal.

With this setup around an FM receiver, you can DF AM CW SSB SSTV whatever signals.

OK the FM receiver won't recover the audio if the incoming signal is anything other than FM, but it will give you the direction!

David
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Old 27th Nov 2023, 12:53 am   #3
Cruisin Marine
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Default Re: Doppler DF Unit wanted

Thanks David, that misconception I had has been cleared up now. Cheers.
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Old 27th Nov 2023, 10:00 pm   #4
g4wim_tim
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Default Re: Doppler DF Unit wanted

Here's a link to a schematic - I built a design similar to this design in the early 80's and it worked quite well but not as good as my DSP version as published in RadCom.
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Old 28th Nov 2023, 2:49 am   #5
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Default Re: Doppler DF Unit wanted

The 'Dopplescant' article in the American 'Ham Radio' magazine. Contains a serious warning about his car accident while staring at the display. Use a co-pilot if mobile!

David
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Old 28th Nov 2023, 12:40 pm   #6
Julesomega
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Default Re: Doppler DF Unit wanted

The linked article seems to be about ultrasonic DF, despite the site being called 'Radio Direction Finding PA8W'. I have a few 10GHz doppler radar waveguide modules if anyone is looking for one
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Old 28th Nov 2023, 3:20 pm   #7
Cruisin Marine
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Default Re: Doppler DF Unit wanted

Here's a link to a schematic - I built a design similar to this design in the early 80's and it worked quite well but not as good as my DSP version as published in RadCom.

Many thanks for that Tim. I shall have a go at that design, it is an impressive 32 LED design giving about 5 degrees resolution, so very nice.

I notice it says avoid NXP chips in the case of the 1st 4051? I guees the designer had problems.
The matrix driving the LED indication looks clever at first glance.
All good stuff, many thanks

PS: I will have a co-pilot.
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Old 28th Nov 2023, 3:54 pm   #8
G6Tanuki
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Default Re: Doppler DF Unit wanted

DATONG electronics did a doppler DF system in the 70s and early 80s. Four quarter wave magmount antennas connected to a box by equal length feeders, the box had a sucker to stick it in the centre of your car roof.

The circuit and operating instructions are available if you do a quick Google.
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