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Doppler DF

Started by BigMojo, February 05, 2008, 07:40:38 PM

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AirAux

#20
December 10, 2009, 08:08:05 PM
Let us know which unit you got and where and how much and how it works.  I have thought this was the way to go for a while, but didn't see much interest in it.  Thanks.

Major Lord

#21
December 11, 2009, 02:02:12 AM
My distributor sells this one as a kit for a good low cost Doppler kit.

http://byonics.com/dsp-rdf/

Major Lord
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

321EOD

#22
December 11, 2009, 02:38:33 PM
Does anyone have any feedback on using the RAMSEY DDF unit?

Has anyone successfully replaced the really poor antenna array/magnets that come with the kit?

Photos would be appreciated (especially any vehicle installs)

Thanks
Steve Schneider, Maj, CAP
Deputy Commander for Cadets (Retd!)
Thompson Valley Composite Squadron (CO-147)

a2capt

#23
December 11, 2009, 04:24:40 PM
I got a Roanoke Doppler and thought about working the antenna array I made for it, into the Ramsey one, as I decided that the Ramsey stuff would not last more than one use. If the antennas didn't depart.

Major Lord

#24
December 11, 2009, 04:28:05 PM
I tried the Ramsey kit, and found it to be less than ideal. The antenna array as provided is just plain awful, but, there is no reason you could not improve on their array with a more robust build.

Major Lord
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

♠SARKID♠

#25
March 25, 2010, 03:31:22 AM
Well I finally took my PicoDopp out for its first field test today.  I have to say that the performance is less than stellar.  It is very inaccurate on 121.5 and gives such a wide range of bearings that at a distance of even a few hundred yards its useless.  I'm going to have to tinker, talk with the creator, and figure out if its a problem with my setup or something.  I've been working on this far too long to let it go down in flames.

Major Lord

#26
March 25, 2010, 04:09:02 AM
What are you using as a receiver?

Major Lord
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

♠SARKID♠

#27
March 25, 2010, 04:11:47 AM
Quote from: Major Lord on March 25, 2010, 04:09:02 AM
What are you using as a receiver?

Major Lord

A RadioShack Pro-95 scanner.

Major Lord

#28
March 25, 2010, 04:25:23 AM
Confirming that you were able to switch the aircraft band range into the FM receive mode? If so, what kind of detection range were you getting with just the scanner alone? ( no Picodopp antenna array?)

Major Lord
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

♠SARKID♠

#29
March 25, 2010, 04:28:18 AM
Oh dear lord I'm an idiot.  I forgot to switch it into FM.  *Bangs head against desk* :-[

Major Lord

#30
March 25, 2010, 04:32:08 AM
Naaah, happens all the time with people using Dopplers on Aircraft bands. I did not have great luck with Doppler on 121.XXX, but maybe the Picodopp will work better then the commercial Marine unit, and the Ramsey, I tried. The Picodopp looks cool!

Major Lord
"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

wingnut55

#31
March 26, 2010, 03:48:18 AM
And you are using FM for what? Aircraft com and ELTs are AM,  121.775 is our practice beacon.

♠SARKID♠

#32
March 26, 2010, 03:50:49 AM
Quote from: wingnut55 on March 26, 2010, 03:48:18 AM
And you are using FM for what? Aircraft com and ELTs are AM,  121.775 is our practice beacon.

The doppler requires the receiver to be in FM to create the necessary modulation and tone.  You lose all the audio, but a carrier is a carrier and it can still be tracked in FM.

Major Lord

#33
March 26, 2010, 02:55:56 PM
You should still be able to hear the characteristic sweep tone even using FM demodulation, since there is a phase-shift modulation element to the signal as well. No signal is really AM or FM in a perfect sense, they contain aspects of multiple forms of modulation, depending on your mathematical model for viewing them. As a practical matter, you will find that you can talk to an aircraft radio with an FM ham radio operating out of band, although it won't sound good! (Note: This is against the rules-only use for emergencies!)

One of the limiting factors of a Doppler for small signal direction finding is the requirement for an FM receiver. You have to have enough signal level for FM capture, generally much more than you need for AM demodulation. The antenna array in a switched antenna system (like the Doppler) is also inherently lossy.

What are you using for a Beacon?

Major Lord

"The path of the righteous man is beset on all sides by the iniquities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."

♠SARKID♠

#34
March 26, 2010, 09:03:30 PM
I'm just using the standard pointer cadet beacon.

a2capt

#35
March 27, 2010, 06:17:37 PM
It was clippy, but when VX-150's were still usable within CAP, and when you do the wide open modification instead of just the MARS mod, you can enter anything from 100 to 200 mhz. Of course, the radio didn't tune that whole spectrum but some got fairly down into the aviation band.  So much so that they were very usable in close proximity to talk to overhead aircrews who had no FM. I had a chance to cherry pick radios after I modified a whole bunch and have a couple that work down as far as 121.395 which also makes them useful for DF'ing up close, when you need an additional piece of equipment to do hangar elimination.

At one place I used to work, they were always picking up SoCal Approach on a particular radio one part of the building. (A radio tuned to an album rock FM station for music in the tech shop), sometimes the chatter got quite  busy and someone would call me to ask what it meant. The station in question was 101.5, IMHO. Quite "far" from the nearest voice frequency of 118.000 and higher. Even the VOR's begin at 108.000, so there must have been some harmonic reasoning having to do with the exact positioning of the radio, it's antenna, the surrounding terrain and a remote station for the approach sector.

I've got a Roanoke Doppler that I've used with the output from the VX-150 as well, and had decent results with it. The hassle with that thing is the antenna array that I over-built.
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