Electronics > Projects, Designs, and Technical Stuff

Radio Direction Finding

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steve_w:
I don't understand your antenna system are you using a rotatable loop antenna and a sense antenna or are you using 4 fixed directional antennas?

I worked on an auto ADF system that had a rotating loop antenna that was null seeking that gave you an ambigous bearing then there was the sense antenna that resolved the direction. the bearing was read from a position sensor in the rotating antenna.  this could give bearings down to +- .5 Degrees.

There is a picture of one here:
http://austradesecure.com/radschool/Vol29/Page8.htm

PA3BNX:
Hello Every Body,


My SuperSimpleSoundDoppler  (VHF and UHF)  antenna system consist of only 4 whip antenna.

They are switched on one by one so there is always just one antenna connected to the VHF Receiver.

You must receive with a FM receiver.

The FM detector in the receiver is basically a frequency to voltage device.

Remember now the doppler tone frequency of a car coming to you at
constant speed.

The tone of the motorsound  will increase en then if the car passes you it will decrease

That's the doppler Principe.

My other design I am working on is called HF Peiler.

That are two crossed loops with a sense antenna that's meant for HF.

I still do not have the HF Peiler working.

So I am working on two systems one for HF and one for VHF/UHF

Today I did work on the zerocrosdetector again.

I found that it is possible to have more acurate bearings even at the 8000 samples / sec
input soundcard mode.

Just detect where the zero cros does happen in the SCF filter array

And then take in account the amplitude values storen in the 2 adjacent array elements.
And so calculate the bearing + the right portion of the 2 element zero cross elements.

Earlyer I did just take the first element + 0.5 * zerocrossingfactor  of the two adjacent arrswitchcap elements

In basic it looks like this:

Public Function ZeroCrossDetector() as Single

'Arrswitchcap() contains all the values summed from FM audio
'at right reference frequency.

dim x as int32
dim y1 as int32
dim y2 as int32

dim j as single
dim zerocrossfactor as single
 
zerocrossfactor = 360 / ubound(arrswitchcap)

for x = 0 to ubound(arrSwitchCap) - 1

y1 = arrswitchcap(x)
y2 = arrswitchcap(x+1)

if y1 > 0 and Y2 <= 0 then
   j = math.abs(y1 / (y2 - y1))
   return  (x + j)  * zerocrossfactor   
end if

'If zerocross is between arrswitchcap(ubound(arrswitchcap) and arrswitchcap(0) then
 
y1=arrswitchcap(ubound(arrswitchcap)
y2=arrswitchcap(0)

if y1 >0 and Y2 <=0 then
   j=math.abs(y1/((y2-y1)
   return   j  * zerocrossfactor   
end if

'If not yet  found then return

Return 999  'No bearing found

End Function


I will do some hardware and software testing before I upload it to
The site of PI4WAG

PA3BNX:
Hello Every Body,

My Software:

Today I did make the waterfall display spectrum in 64 steps
instead of 32 in SoundDoppler.exe

So now the steps are 360 / 64 = 5.625 degrees and that about the
maximum precision of a pseudo-doppler-direction-finder.
It looks nice in graphics.

I was also thinking of streaming 2 channel audio over internet
So sounddoppler application can decode/save  all on distance.
Not done yet.


I have some other thoughts about building a
Radio Direction Finder hardware

Okay my software runs on a PC with GPS and supersimple sounddoppler
through the 2 channel input soundcard.

But I want something smaller (wireless)
running on a iPad or android.

and/or maybe hardware control done on an Aduino board

I think it is possible to make the sounddoppler
running on an Arduino

The Arduino:


It has to generate the 4x antenna switch (hard or softswitching) signals.
and has to decode the audio from the RX receiver audio
and then output agrelo out on the comport %BBB/Q

or maybe it can display the bearing on some leds or
a small dot matrix display ?

The RDF wants a Gps-Rx and Mapping plot possibility.

The Arduino will never have the possibility to show bearings on a map
directly.

Other things not so nice is to save the audio of the RX squelch controlled

WB6EYV Bob Simmons (PicoDopp) did already something nice with pic16f628.
That outputs Gps ($GPRMC) and Agrelo (%xxx/q) mixed on a comport.

So there is some thoughts needed to find out what I maybe will be
trying to create in software and hardware on small tabloids.

It would be very nice if the Gps was build in the iPad or android.

And a wireless connection from arduino to the iPad (infrared or bluetooth).

Just programming the arduino will be a challenge.   

It should emulate some sort of audiocard 

Also on the ipad or android must the software written.

But maybe if there exists gps software then the Arduino could
modify the $GPRMC  Course field and calculate a new CRC for $GPRMC string.
The Gps-Rx-input must be inputted in the Arduino with this method.

(My Mapping.exe and SoundDoppler.exe and gps.exe have this modified $GPRMC already) 

So lots of things to do (All much time consuming)...

Let me know if you have better ideas.

PA3BNX:
Hello Every Body,


I did gain some improvements on my SoundDoppler.exe software.

I increased the amount off bars in the waterfall from 32 to 64

so no that's 360 / 64=5.625 degrees wide bars.

It look nice.

I also made a freeze button on the SCf and Waterfall screen
To stop it from running That's nice to precisely check the graphic data.

In the back ground all software runs of course.

The next version will be SoundDopplerbAll.zip on the site of PI4WAG.

PA3BNX:
Hello every Body,

I think I got the kml logging okay now in sounddoppler.exe

So you can log to kml files with 100 records

Nice for displaying in Google-Earth.

I am right now busy with a new future in MyMapping.exe

My own RDF plot program on UI-View32 Maps.

It will not get a zoom function but a AutoTrack Smallest Map
auto track mode and a just once button to track to smallest Map.

It's again quite complicated I am already working on it for 3 days now.

But I hope I get it working soon.


I let you know wen its on the PI4WAG Site available.

That's all foo ks for now.



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