Doppler Direction Finder (RDF)
Don Gray
I'm sure I saw plans for one of these somewhere in last year or so. Anyone
out there know where I can find details on the construction of such a unit.
(The commercial ones are too expensive for my budget !)
8 R Q@worldnet.att.net James L. Jaeger
Don,
There is a great book on radio direction finding.
It includes many do it yourself home projects.
It is called: ''Transmitter Hunting, Radio Direction Finding
Simplified" by Joseph D. Moell, K0ov, and
Thomas N. Curlee, WB6UZZ. It is a TAB Publication.
It is available through most Ham Radio outlets.
You can also order it by calling 1-800-822-8158.
----------
Don Gray <lb...@panther.uwo.ca> wrote in article
<01bc1b6b$4255c860$0100a8c0@don>...
Jay Hennigan
Don Gray (lb...@panther.uwo.ca) wrote:
: I'm sure I saw plans for one of these somewhere in last year or so. Anyone
: out there know where I can find details on the construction of such a unit.
: (The commercial ones are too expensive for my budget !)
Plans for this and much more RDF gear can be found in the book
"Transmitter Hunting: Radio Direction Finding Simplified". The author's
web page is at http://members.aol.com/homingin/
--
-- Jay Hennigan j...@west.net --
WestNet: Internet service to Santa Barbara, Ventura and the world.
805-892-2133 805-289-1000 805-578-2121
Andy Moss
Jay Hennigan wrote:
>
> Don Gray (lb...@panther.uwo.ca) wrote:
> : I'm sure I saw plans for one of these somewhere in last year or so. Anyone
> : out there know where I can find details on the construction of such a unit.
> : (The commercial ones are too expensive for my budget !)
There are other excellent means of direction finding that are real'
cheap!
My friend and I did a lot of ham fox-hunts a couple of years ago. We
found the
"fox" every time. About half the time we found the fox before the
doppler guys
too.
Two people and two handies work like a champ.
All you need is a radio with an Smeter and two antennas.
Hold the handie flat up to your chest vertically and do a couple of
rotations.
You'll see the signal peak and null. The null means that the signal is
eminating
from behind you. I'm not sure, but I think the spine acts as a
"reflector"!
As you get closer to the source, use a rubber duckie for the wrong
band. ie: if
you are chasing 146MHz use the correct duckie until the Smeter shows no
null then
plug in a UHF stubby. Repeat the process untill you are using NO
antenna. Once you
get FSD (full scale deflection) with no antenna you should be within
visual distance.
Start beetin' the bushes!
The key is that you need two people to make this work. Reflections play
hell on VHF and
UHF signals. So you and your friend should hop out of the car and stand
20 or 30 ft apart.
When you both get readings that agree - you've got a good direction (90%
of the time anyway!).
Good luck - it's a riot!
Cheers!
--
Andy Moss
"I often fantasize about my inability to daydream....."
Brian Mileshosky, N5ZGT
Andy Moss <and...@ibm.net> wrote:
>Jay Hennigan wrote:
>>
>> Don Gray (lb...@panther.uwo.ca) wrote:
>> : I'm sure I saw plans for one of these somewhere in last year or so. Anyone
>> : out there know where I can find details on the construction of such a unit.
>> : (The commercial ones are too expensive for my budget !)
>There are other excellent means of direction finding that are real'
>cheap!
>My friend and I did a lot of ham fox-hunts a couple of years ago. We
>found the
>"fox" every time. About half the time we found the fox before the
>doppler guys
>too.
Doppler is good until you start messing with multi-path (Where the
signal is bouncing all over the place). That is when a regular beam
and radio setup might be better.
>Two people and two handies work like a champ.
>All you need is a radio with an Smeter and two antennas.
>Hold the handie flat up to your chest vertically and do a couple of
>rotations.
>You'll see the signal peak and null. The null means that the signal is
>eminating
>from behind you. I'm not sure, but I think the spine acts as a
>"reflector"!
>As you get closer to the source, use a rubber duckie for the wrong
>band. ie: if
>you are chasing 146MHz use the correct duckie until the Smeter shows no
>null then
>plug in a UHF stubby. Repeat the process untill you are using NO
>antenna. Once you
>get FSD (full scale deflection) with no antenna you should be within
>visual distance.
This is a good technique, but a radio hooked up to an attenuator and
beam or quad is better. Use a compass and map, too. That way you can
plot the signal (Draw a line from where you are to the other side of
the map in the direction of the signal. ). Don't forget to calculate
in your declination! HI. Do this 3 or 4 times, and where the lines
all intersect, is the area of where the transmitter most likely is.
>The key is that you need two people to make this work. Reflections play
>hell on VHF and
>UHF signals. So you and your friend should hop out of the car and stand
>20 or 30 ft apart.
>When you both get readings that agree - you've got a good direction (90%
>of the time anyway!).
Actually, one person can do everything very easily. But it is fun
with two people. Reflections DO play hell on these signals. Our
T-Hunting group here in Albuquerque bounce signals off of any of the
mountains in sight. For some reason the best signal is towards that
mountain...
Two rules in T-Hunting: ASSUME NOTHING and NEVER TRUST A T-HUNTER.
>Good luck - it's a riot!
I can't agree more! For more information on T-Hunting, please visit
the site below. This is my group's site and is one of the absolute
best around. The URL is:
http://www.swcp.com/~ab5p
73,
Brian, N5ZGT
_________________________________________________________________________
Boy Scouts of America Amateur Radio - N5ZGT
Eagle Scout (12-6-96) ARRL QRP: NorCal# 1700 QRP-L# 580 AK/QRP # 125
JASM - Troop 41 Author of Worldradio's "Youth Forum" Column
Albuquerque, N.M. Packet: N5ZGT @ KC5IZT.ALBQ.NM.USA.NOAM
O.A. Lodge 66 <-W-W-W-<< Internet: n5...@swcp.com
_________________________________________________________________________
Andy Moss
Brian Mileshosky, N5ZGT wrote:
>
> Andy Moss <and...@ibm.net> wrote:
>
> >Jay Hennigan wrote:
> >>
> >> Don Gray (lb...@panther.uwo.ca) wrote:
> >> : I'm sure I saw plans for one of these somewhere in last year or so. Anyone
> >> : out there know where I can find details on the construction of such a unit.
> >> : (The commercial ones are too expensive for my budget !)
>
> >There are other excellent means of direction finding that are real'
> >cheap!
>
> >My friend and I did a lot of ham fox-hunts a couple of years ago. We
> >found the
> >"fox" every time. About half the time we found the fox before the
> >doppler guys
> >too.
>
> Doppler is good until you start messing with multi-path (Where the
> signal is bouncing all over the place). That is when a regular beam
> and radio setup might be better.
Other problems I've found with doppler units: When you are really close
- or the transmitter is very strong,
the pin diodes get swamped, the coaxial cable starts to leak and the
reading becomes useless. Also, the
audio that drives the doppler can't be common with the speaker of the
receiver otherwise noise in the
car will skew the readings badly.
> >Two people and two handies work like a champ.
>
> >All you need is a radio with an Smeter and two antennas.
> >Hold the handie flat up to your chest vertically and do a couple of
> >rotations.
> >You'll see the signal peak and null. The null means that the signal is
> >eminating
> >from behind you. I'm not sure, but I think the spine acts as a
> >"reflector"!
>
> >As you get closer to the source, use a rubber duckie for the wrong
> >band. ie: if
> >you are chasing 146MHz use the correct duckie until the Smeter shows no
> >null then
> >plug in a UHF stubby. Repeat the process untill you are using NO
> >antenna. Once you
> >get FSD (full scale deflection) with no antenna you should be within
> >visual distance.
>
> This is a good technique, but a radio hooked up to an attenuator and
> beam or quad is better. Use a compass and map, too. That way you can
> plot the signal (Draw a line from where you are to the other side of
> the map in the direction of the signal. ). Don't forget to calculate
> in your declination! HI. Do this 3 or 4 times, and where the lines
> all intersect, is the area of where the transmitter most likely is.
Your method sounds a little more cut and dried. I've tried
triangulation
but when you're in a hurry it's a time-waster. You get to know how
close you are
using two guys and two radios. The entire group I was with were all
really
good. None of them used any sort of plotting though.
Driving a fast car helps too!
> >The key is that you need two people to make this work. Reflections play
> >hell on VHF and
> >UHF signals. So you and your friend should hop out of the car and stand
> >20 or 30 ft apart.
> >When you both get readings that agree - you've got a good direction (90%
> >of the time anyway!).
>
> Actually, one person can do everything very easily. But it is fun
> with two people. Reflections DO play hell on these signals. Our
> T-Hunting group here in Albuquerque bounce signals off of any of the
> mountains in sight. For some reason the best signal is towards that
> mountain...
> Two rules in T-Hunting: ASSUME NOTHING and NEVER TRUST A T-HUNTER.
Ahhh! Those mountains probably make things a little trickier than the
flat
terrain around here! <G>
>
> >Good luck - it's a riot!
>
> I can't agree more! For more information on T-Hunting, please visit
> the site below. This is my group's site and is one of the absolute
> best around. The URL is:
> http://www.swcp.com/~ab5p
>
> 73,
> Brian, N5ZGT
>
>
> _________________________________________________________________________
> Boy Scouts of America Amateur Radio - N5ZGT
> Eagle Scout (12-6-96) ARRL QRP: NorCal# 1700 QRP-L# 580 AK/QRP # 125
> JASM - Troop 41 Author of Worldradio's "Youth Forum" Column
> Albuquerque, N.M. Packet: N5ZGT @ KC5IZT.ALBQ.NM.USA.NOAM
> O.A. Lodge 66 <-W-W-W-<< Internet: n5...@swcp.com
> _________________________________________________________________________
--
Bruce Hawkins
Brian Mileshosky, N5ZGT wrote:
>
> Andy Moss <and...@ibm.net> wrote:
>
> >Jay Hennigan wrote:
> >>
> >> Don Gray (lb...@panther.uwo.ca) wrote:
> >> : I'm sure I saw plans for one of these somewhere in last year or so. Anyone
> >> : out there know where I can find details on the construction of such a unit.
> >> : (The commercial ones are too expensive for my budget !)
>
> >There are other excellent means of direction finding that are real'
> >cheap!
>
> >My friend and I did a lot of ham fox-hunts a couple of years ago. We
> >found the
> >"fox" every time. About half the time we found the fox before the
> >doppler guys
> >too.
>
> Doppler is good until you start messing with multi-path (Where the
> signal is bouncing all over the place). That is when a regular beam
> and radio setup might be better.
>
>
> >All you need is a radio with an Smeter and two antennas.
> >Hold the handie flat up to your chest vertically and do a couple of
> >rotations.
> >You'll see the signal peak and null. The null means that the signal is
> >eminating
> >from behind you. I'm not sure, but I think the spine acts as a
> >"reflector"!
>
> >As you get closer to the source, use a rubber duckie for the wrong
> >band. ie: if
> >you are chasing 146MHz use the correct duckie until the Smeter shows no
> >null then
> >plug in a UHF stubby. Repeat the process untill you are using NO
> >antenna. Once you
> >get FSD (full scale deflection) with no antenna you should be within
> >visual distance.
>
> This is a good technique, but a radio hooked up to an attenuator and
> beam or quad is better. Use a compass and map, too. That way you can
> plot the signal (Draw a line from where you are to the other side of
> the map in the direction of the signal. ). Don't forget to calculate
> in your declination! HI. Do this 3 or 4 times, and where the lines
> all intersect, is the area of where the transmitter most likely is.
>
> >hell on VHF and
> >UHF signals. So you and your friend should hop out of the car and stand
> >20 or 30 ft apart.
> >When you both get readings that agree - you've got a good direction (90%
> >of the time anyway!).
>
> Actually, one person can do everything very easily. But it is fun
> with two people. Reflections DO play hell on these signals. Our
> T-Hunting group here in Albuquerque bounce signals off of any of the
> mountains in sight. For some reason the best signal is towards that
> mountain...
> Two rules in T-Hunting: ASSUME NOTHING and NEVER TRUST A T-HUNTER.
>
>
> I can't agree more! For more information on T-Hunting, please visit
> the site below. This is my group's site and is one of the absolute
> best around. The URL is:
> http://www.swcp.com/~ab5p
>
> 73,
> Brian, N5ZGT
>
>
> _________________________________________________________________________
> Boy Scouts of America Amateur Radio - N5ZGT
> Eagle Scout (12-6-96) ARRL QRP: NorCal# 1700 QRP-L# 580 AK/QRP # 125
> JASM - Troop 41 Author of Worldradio's "Youth Forum" Column
> Albuquerque, N.M. Packet: N5ZGT @ KC5IZT.ALBQ.NM.USA.NOAM
> O.A. Lodge 66 <-W-W-W-<< Internet: n5...@swcp.com
> _________________________________________________________________________
I can't find this person who makes dopler unit kits, if u dont get
any answers, i look harder, he's an arrl oo, i cant rememer his name...
--
***********************************************************
# Bruce Hawkins,
# bhaw...@cruzio.com bhaw...@comix.santa-cruz.ca.us
# ac...@comix.santa-cruz.ca.us
# AC6DN@KI6EH.#CCA.CA.USA.NOAM (packet radio)
# 52.8-, PL 114.8 Hz; 146.79-, PL 94.8 Hz;
# 440.925+, PL 123 Hz; 1286.150-, PL 127.3 Hz
73,
AC6DN
Bruce Hawkins...
###########################################################
Richard Kendrick
Bruce Hawkins <bhaw...@cruzio.com> wrote:
>Brian Mileshosky, N5ZGT wrote:
>>
>> Andy Moss <and...@ibm.net> wrote:
>>
>> >Jay Hennigan wrote:
>> >>
>> >> Don Gray (lb...@panther.uwo.ca) wrote:
[ lotta stuff snipped ]
>Hello,
> I can't find this person who makes dopler unit kits, if u dont get
>any answers, i look harder, he's an arrl oo, i cant rememer his name...
>--
>***********************************************************
># Bruce Hawkins,
Check out Doppler Systems, P. O. Box 2780, Carefree, AZ 85377,
(602) 488-9755, (602) 488-1295 fax. They make some of the best
doppler units available.
Also, check out the book Transmitter Hunting, Radio Direction Finding
Simplified by Joseph Moell K0OV and Thomas Curlee, WB6UZZ.
Inside you'll find complete construction plans for the Roanoke
Doppler. I think a pc board and complete kit is available for this unit.
The book is published by TAB Books.
Have fun and 73,
Richard
Richard Kendrick CET N7NT (ex WA7TWI) |
Amateur Radio Extra Class | Do not adjust your mind, there
QRP #4129/G-QRP #8591/MI-QRP #M-1412 | is a fault in reality.
Mesa, AZ email: wa7...@primenet.com |
Jeff Liebermann
Brian Mileshosky, N5ZGT (n5...@swcp.com) wrote:
: Doppler is good until you start messing with multi-path (Where the
: signal is bouncing all over the place). That is when a regular beam
: and radio setup might be better.
Doppler has a bunch of other problems. This is NOT intended to
discourage anyone from using doppler, just to recognize its
limitations. Credibility check: I helped design the AN/SRD-22
doppler direction finder for Intech Inc for use by the US Coast
Guard in approx 1975.
1. A doppler DF can only display the direction of *ONE* transmitter.
If there are any other sources of signal (reflections, other xmitters,
adjacent channel junk, computer noise, synthesizer spurious signals,
harmonics of clock oscillators, ignition noise, images, etc) the
reading will be erronious. Reflections is the real killer. A
ground bounce mixed with a direct signal will yield horrible
results. (Incidentally, the reason most dopplers have rather large
antenna ground planes is to reduce ground bounce).
2. Switched doppler is susceptable to switching noise which acts
as modulation sidebands. These sidebands (harmonics of the switching
frequency) will cause strong adjacent channel signals to mangle
the bearing. The typical "Roanoak" design is highly susceptable
to this. Doppler Systems uses DGFet switches which have a much
"softer" (less rise time) switching characteristic. Intech used
a modified sine wave drive to literally modulate the PIN diodes
instead of switching. It totally eliminated the problem, but
sensitivity was reduced. PIN diode matching was very critical.
3. The typical vertically polarized doppler system does not
work well with horizontally polarized signals. Building a
horizontally polarized doppler is no major challenge, but nobody
seems to have done it.
4. Doppler is sensitive to fox frequency. The doppler receiver
measures the phase shift from the antenna to the FM demodulator.
Any change in receiver system phase shift appears as a substantial
directional error. The worst error is caused by the crystal IF
filter. The phase shift from IF center to filter edge goes through
radical phase changes. An AFC (automagic frequency control) is
manditory to keep the signal in one place on the crystal filter
curve.
5. Doppler is sensitive to rotation frequency and FM demodulator
distortion. There two schools of thought here. Doppler Systems
uses about 300Hz rotation frequency. This is good for insuring
that the signal will remain in the IF bandpass (no AFC) but
results in harmonics of the 300Hz in the bandpass. These harmonics
cause bearing errors and linearity (approximation of a circle)
errors. The typical commutating audio bandpass filter will not
remove harmonics.
Intech elected to use 4.1KHz. Most of the harmonics are outside
the IF bandpass. Combined with the PIN diode modulation technique,
this yielded a very low distortion sine wave at the demodulator
and very good linearity. However, the group delay (phase shift
error) of the IF crystal filter was far worse at the edges (+/-4KHz)
than it was near the center (+/-300Hz). AFC became manditory.
It turned out that the conventional balanced multiplier FM
demodulator was also slightly sensitive to signal level. Since
the AN/SRD-22 was both an AM (121.5 aircraft) and FM (Marine
VHF band) receiver, an ALC (automagic level control) was used.
There error here is not large and can be probably be ignored.
6. Doppler is sensitive to modulation audio. The response
time of the doppler DF is totally dependent upon the Q of the
doppler tone bandpass filter. The wider the bandwidth, the
faster the DF. If you make the filter too narrow, it takes
forever to get a bearing. However, too fast and FM audio
modulation and fox tones will leak through the filter and
mangle the bearing. One favorite trick is to use a 300Hz
fox tone to mess up the Doppler Systems DF'ers.
7. Doppler antenna patterns are very sensitive to nearby
antennas and reflections. The AN/SRD-22 had to be mounted
at the very top of the mast. Unfortunately, almost every other
piece of electronics equipment wanted to be in the same place.
On the roof of a car, the AM/FM antenna and other radio antennas
create horrible errors. Nearby antennas from other hunters at
the starting point will mutilate the pattern. This is why
the DF book says (several times) that the ONLY way to get a
decent bearing is while moving. Moving tends to average out
these errors. While the error at a given location may be
severe, a few feet away might be perfectly acceptable. The
trouble is you have no idea where there is a reflection free
location. Moving while DFing is the only way.
73 Magazine carried a series of articles in the HomingIn
section based on rotating yagi and quad antenna direction
finding. This is basically an AM (signal strength) system.
The difference is that you can easily see multiple transmitters,
recognize reflections (they tend to blurr), do NOT require
an AFC, and have an easily controllable antenna pattern
(using boresight calibration). However, driving down the
freeway with a spinning 4 element quad is a great way to
attract the constabulary. Short transmissions are also
difficult to see. Equipment complexity is about the same.
Having dealt with doppler professionally and recognized its
limitations, I'm partial to a rotating antenna.
One place where a rotating antenna is far superior to doppler
is tracking a jammer. With a jammer, you have *TWO* signals
on a frequency (the person trying to talk and the jammer).
A doppler DF will yield a bogus direction because of the two
signals. A rotating antenna will show both.
I hope this helps. If there are any questions, please email.
--
# Jeff Liebermann Liebermann Design 150 Felker St #D Santa Cruz CA 95060
# 408.336.2558 voice wb6ssy@ki6eh.#cca.ca.usa.noam wb6ssy.ampr.org 44.4.18.10
# 408.699.0483 digital_pager 73557,2074 cis [don't]
# je...@comix.santa-cruz.ca.us http://www.cruzio.com/~jeffl