Airborne DF

[ccwillwerth]

Hi All,

I am fitting my homebuilt with instruments and radios, and wanted to add a
Direction Finder. I wanted a doppler type, but with small antennas in a 4
point aray with a small dimension or distance between the antennas. Am I
really far out of reason, or is this an achievable goal?

Charlie

[UltraJohn]

ccwillwerth wrote:

> Hi All,
>
> I am fitting my homebuilt with instruments and radios, and wanted to add a
> Direction Finder. I wanted a doppler type, but with small antennas in a 4
> point aray with a small dimension or distance between the antennas. Am I
> really far out of reason, or is this an achievable goal?
>
> Charlie

Hi Charlie
There are many kits out there that will do this. Here is one.
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=DDF1
Of note is most require an FM receiver and aviation uses AM signals.
Although the transmitted signal doesn't need to be FM it can be SSB CW AM
or FM but it might be hard to get a receiver that will receive using FM on
the aviation band. Although if you can get schematics of your receiver you
should be able to modify it for FM reception (add a coax connection to one
of the many FM demodulators kits (I think this Ramsey company has one) just
make sure they both use the same IF) I wouldn't try this with your active
aircraft receiver.
John

[ccwillwerth]

Thanks John, but the ramsey units require huge antennas and to great a
spread between them. I have looked at them on several occassion, but can't
see how I could make them work.

Charlie
"UltraJohn" > wrote in message
ink.net...
> ccwillwerth wrote:
>
>> Hi All,
>>
>> I am fitting my homebuilt with instruments and radios, and wanted to add
>> a
>> Direction Finder. I wanted a doppler type, but with small antennas in a
>> 4
>> point aray with a small dimension or distance between the antennas. Am I
>> really far out of reason, or is this an achievable goal?
>>
>> Charlie
>
> Hi Charlie
> There are many kits out there that will do this. Here is one.
> http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=DDF1
> Of note is most require an FM receiver and aviation uses AM signals.
> Although the transmitted signal doesn't need to be FM it can be SSB CW AM
> or FM but it might be hard to get a receiver that will receive using FM on
> the aviation band. Although if you can get schematics of your receiver you
> should be able to modify it for FM reception (add a coax connection to one
> of the many FM demodulators kits (I think this Ramsey company has one)
> just
> make sure they both use the same IF) I wouldn't try this with your active
> aircraft receiver.
> John
>

[UltraJohn]

ccwillwerth wrote:

> Thanks John, but the ramsey units require huge antennas and to great a
> spread between them. I have looked at them on several occassion, but
> can't see how I could make them work.
>
> Charlie
Actually Charlie you can use an electrically shortened antenna and the
spacing for them is only 1 1/2 to 2 feet so it should not be a huge
problem. The below link is another site with a df kit the link actually
goes to the antenna page which is quite interesting.
John

http://www.silcom.com/~pelican2/MINI_INTRO.html

[COLIN LAMB]

Doppler sometimes does not work well if there are reflections - but the
aircraft has an advantage over ground vehicles so it could have a better
success rate. Because the signal is line of sight, you can reduce the
length of the antenna and still have an adequate signal, although you will
have a reduced range. Rubber ducks can be used, although flexing can affect
directivity.

Another option is to install a number of directional antennas and switch
between them. The aircraft has an advantage in that it can be rotated
fairly easily. With a good signal indicator, you could home in on the
hunted signal. I have one of the Ramsay Dopplers and normally use it on the
ground for Search and Rescue. We search in rugged terrain and I have not
found it as useful as a directional antenna.

Years ago a friend of mine built a Doppler to use in a hidden transmitter
hunt. Soon after the start, he realized it was not working, but he had left
all of his other direction finding gear at home. He got his handy talkie
with rubber duck out and drove around finding the strongest signal. He
would drive behind buildings to determine directivity - since the building
would make the signal weakest if it was directly in the path. He was first
to arrive at the hidden transmitter, proving that it is the operator rather
than the equipment that is key in direction finding.

Colin

[ccwillwerth]

Thanks Colin,

I like the Picco Doppler Mini Antenna of the system John sent info on. I
could bury it in the wooden wing with dual band rubber duck antennas. The
problem is that once it is in, access would be difficult to accomplish. I
will be covering the wing during the summer. I gusee I could try it out
before then. Thanks for the input.

Charlie

"COLIN LAMB" > wrote in message
nk.net...
> Doppler sometimes does not work well if there are reflections - but the
> aircraft has an advantage over ground vehicles so it could have a better
> success rate. Because the signal is line of sight, you can reduce the
> length of the antenna and still have an adequate signal, although you will
> have a reduced range. Rubber ducks can be used, although flexing can
> affect directivity.
>
> Another option is to install a number of directional antennas and switch
> between them. The aircraft has an advantage in that it can be rotated
> fairly easily. With a good signal indicator, you could home in on the
> hunted signal. I have one of the Ramsay Dopplers and normally use it on
> the ground for Search and Rescue. We search in rugged terrain and I have
> not found it as useful as a directional antenna.
>
> Years ago a friend of mine built a Doppler to use in a hidden transmitter
> hunt. Soon after the start, he realized it was not working, but he had
> left all of his other direction finding gear at home. He got his handy
> talkie with rubber duck out and drove around finding the strongest signal.
> He would drive behind buildings to determine directivity - since the
> building would make the signal weakest if it was directly in the path. He
> was first to arrive at the hidden transmitter, proving that it is the
> operator rather than the equipment that is key in direction finding.
>
> Colin
>

[Morgans]

"ccwillwerth" > wrote

> I like the Picco Doppler Mini Antenna of the system John sent info on. I
> could bury it in the wooden wing with dual band rubber duck antennas. The
> problem is that once it is in, access would be difficult to accomplish. I
> will be covering the wing during the summer. I gusee I could try it out
> before then. Thanks for the input.

A few extra access panels could make things much better, no?
--
Jim in NC

[ccwillwerth]

Hi Jim, Yes, I will have the panels, but when you try to pull a 9" diameter
object through a 4" hole, something groans. I want to build the device, and
make the electronic antenna rotor in a box small enough to get through the
hole. If the antennas are mounted to the groundplane via BNC or something,
I will be able to try different versions, but the groundplane will have to
be permanent.

Charlie
"Morgans" > wrote in message
...
>
> "ccwillwerth" > wrote
>
>> I like the Picco Doppler Mini Antenna of the system John sent info on. I
>> could bury it in the wooden wing with dual band rubber duck antennas.
>> The problem is that once it is in, access would be difficult to
>> accomplish. I will be covering the wing during the summer. I gusee I
>> could try it out before then. Thanks for the input.
>
> A few extra access panels could make things much better, no?
> --
> Jim in NC