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Radio Direction Finding
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PA3BNX:
Hello Every Body,


Happy New year 2014 to all.


I have been programming to get also elevation data from the
4 antenna array.

And that works because a transmitter at the horizon gives maximum dopplertoneamplitude
en if the transmitter is right above the array then there is no doppler tone left

so 0 degrees = max dopplertone and 90 degrees above  is zero dopplertone.

So I created a form with a elevation first kwadrant meter.

The slider is for the reference when the transitter is on the floor.

The amplitude diff is a sin function.

In the rim of the elevation meter is also a averaged red bug.

This should be very handy if you are hunting a balloon fox hunt.

Soon version SoundDoppler142 wil be on our sites.

Happy Foxhunting/experimenting this year.
EA4FRD:
Dear PA3BNX,

First of all thanks sincerely for your nice job. It is really great everything you are doing for the ARDF.

I have a question that maybe you can help me. My idea is using your equipment for 27MHz in the car. I have been checking your software using a PIC as square wave generator (600Hz) for creating the switching signal, and as switcher I use a Chip RF chip switcher (instead of the diodes). As antennas I use 4 mag antennas, which separation is maximum 90cm (shaping a circle of 127cm of diameter)on the roof of the car. I see(heard) the antennas swithing, and the audio switching signal coming from the Rx seems fine. However If I spin the car, I don“t see any variation on the angle of arrival, keeping all the time in the same angle.

I have been checking the circuit and everyting seems ok. I am thinking that maybe one antenna is somehow much better than the others...but I do not see that in the oscilloscope (audio signal). Do you have any solution? Did you find that before? Something else I can do is filtering (with a Switched capacitor filter) the audio signal before conecting to the PC.

Thanks for your help.

Carlos.
PA3BNX:
Hello Carlo,

If one antenna is not working it should give wrong bearings all the time.
after calibration.

Does the reference frequency read okay ?

See the menu Edit InputXY screen in SoundDoppler.exe

The upper-channel must be the reference signal about 300 to 1000 Hz orso
The lower channel must be the audio from the RX.

Also do check the sql (Squelch)
You must use a RX in FM mode ofcourse.


It happens that the referency and audio signal are changed from Left and Right
You can switch that on the soundcard hardware or use menu Edit Change left and right
in software.

Also make shure the reference frequency is the same as the doppler tone frequency heard from Rx when
signal recieved.

To check the antenna array is simple

Use a 4.5V battery with a 470 Ohm resistor on the + in series with a control line
and listen to the Rx on each antenna by just powering one control antenna switcher line.
You can easy check every antenna and cable this way.

You use a chip switcher

Important is that it leaves the not connected antenna unloaded.
Most chips I saw do terminate them with 50 ohm orso...
Thats bad because not used antenna's may not take RF energy from the rf field because of distorsion of the
wave front.
Thats why we use diodes and not switching chips.

Don't forget to ground the mag whipes very good to ground of car roof.

So maybe wrap some alufoil around the magnetic feet whipes to get more capicitya (Lower Xc) between
carroof and coax cable shield at antenna feet.


In the new versions sounddoppler 141 an 142 there is under menu Info an Antenna Array Calculator too.

Hope you get sounddoppler working okay now soon.

Does the PIC  output softswitched and overleap pulses
like our SuperSimpleSoundDoppler de Luxe does ?
(The one with 4 transistors after the 4017 chip?)


The new version SoundDoppler142aALL.zip is now on the PI4WAG site.



Succes

PA3BNX

EA4FRD:
Hello PA3BNX,

Thanks for the nice email. Currently I cannot check my development, but I will do it asap, so the antennas. I chose frequency equal to 650Hz (by the PIC aka square wave generator, which I do not filter or smoth. Therefore pure square signals to the switcher) and as far as I remember, both channels (left and right) had the same frequency. BTW, although the filtered square signal generator was still in the scope (triggered by your software), the signal coming from the Rx was moving, as it was not triggered.....is that wrong?. On the other hand I use a switcher in a chip, which put the unconnected input to 50Ohms ( I think it is the best way to avoid re-rediation). In any case I want to check the diode-switcher too with a soft switched and over-leap pulses (as you proposed)

Moreover I must re-enforce the ground of the magnetic whips.

Thanks sincerely again for the answer, and I let you know as soon I have any answer.

Regards.

Carlos.
Wolfy:
Greetings from North Carolina USA
K4GHL here, and I just wanted to say thank you for all your work (before I dive into building your stuff that is hihi)
I have read a lot of your posts, and am truly impressed with your dedication and continued support of your project!!!!!

I have built the Ramsey DDF on a breadboard, and about tore my hair out doing so (nothing like having one part left to place and having two parts left over, yeah, I missed something somewhere), so we will see how well things go with your set up :)

Just wanted to say thanks, keep up the great work!
Gary K4GHL
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