What's your favorite cheap RDF 2m antenna
Anonymous User
cannot afford to invest much more in ham radio for awhile :-( So, the
header says it all. What inexpensive 2m RDF antennas and/or techniques
have you successfully utilized.
These are beginners' hunts, where the fox will be stationary, with not
nasty tricks like switching polarization. The average terrain is fairly
hilly, from about 300 to 800 or more feet above sea level.
Thanks in advance for your suggestions and 73 DE N1QNK
Jim
glock glock
larry wall dont kill the president
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Milton D. Miller II
2 element cubical quads with an attenuator box of some sort
(capable of at least 60db). The support materials vary from wood
to pvc pipe to ...., the elements are copper wire ranging from 14
or so (have to support 4 sides) to 6 gauge (supported at only 2
points). The dimensions are in the Antenna Hunter's Handbook.
PS: If anyone in the greater Austin area is interested, you can
contact me for more information. We can always use more
T-hunters!
milton
--
Milton Miller KB5TKF mil...@bga.com
Mont Pierce
Anonymous User <nob...@soda.berkeley.edu> wrote:
>I have a couple of fox hunts coming up in the near future, but I really
>cannot afford to invest much more in ham radio for awhile :-( So, the
>header says it all. What inexpensive 2m RDF antennas and/or techniques
>have you successfully utilized.
>
>These are beginners' hunts, where the fox will be stationary, with not
>nasty tricks like switching polarization. The average terrain is fairly
>hilly, from about 300 to 800 or more feet above sea level.
First of all, the most important bearing could be the first one from
the starting point. If the signal is too weak for you to receive on
an HT then see if there are some others that don't mind sharing their
initial readings with you. Most of them won't mind, since they usually
compare their readings with others anyway.
For the rest of the hunt you can probably get my by just using your
rubber ducky. Some have had great success by placing their HT inside
a shielded tube. By inserting the HT into the tube at different depths
it acts as an attenuator.
With your HT and rubber ducky you need to use the body fade technique.
Basically you hold the HT up very close to your chest and then watch
the S-meter as you turn in a circle. What your looking for is the
deepest null that you can find, which is caused by your body blocking
the signal, hence the name body fade.
If you are too close, or the signal is too strong, then the body fade
won't work without some help. This is where the shielded tube comes in
handy. Otherwise, here are two other tricks to attenuate the signal
so you can find the null: 1) tune slightly off frequency; 2)
completely remove the antenna, if no signal is received then set the
antenna onto the HT lightly trying not to let the center conductor
touch, if you succeed it will capacitively couple and dramatically
weaken in incoming signal. I've successfully found the fox whenever
I've used this method and I know another hunter that soley uses this
method all the time (and always finds the fox).
Another great technicue I always use to tell if I'm getting close to the
transmitter is to listen on the 3rd harmonic. Normally at the starting
point I'll hook my 440 HT to a magmount, tune it to the 3rd harmonic,
and turn the volume up all the way. When it gets enough signal to break
squelch then I know that I'm within 100 yards of the signal. I then use
a 440 6 element beam (it's less then 3 feet long and easy to handle) and
my 440 HT to close in on the fox.
If you want to make a 2m beam for fox hunts, there was a great design
here just a few days ago which used a Radio Shack FM beam as the base.
One element removed, connecting wires between elements removed, and the
remaining elements trimed to 2m frequency. When I bought my RS FM beam
the price was $16.xx + tax. I did one other mod besides the ones
listed, I swapped the element with the feedline screws with the element
that is used for 2m driven element. Just drilled the pop rivets out and
use a long screw to remount the element. Also, the mod instructions
said to totally remove one of the element. If you need the design, I
can repost it. I plan on posting my comments in a couple of days after
I get a chance to try it out.
73 & happy hunting,
km6wt
Ed Bathgate
have you successfully utilized.
I have seen (not personally used) - a df system that used 2 switched antennas
(audio freq oscillator - square waves - 2 phases and diode switching for 2
antennas with equal length feed lines)
| |
| | < short dipoles equal lengths, (but not resonant!)
=======[]======
| [] |
| | |
|
< coax from osc/diode switcher to receiver.
This thing supposedly works by phase sense difference between the 2 antennas.
It works with the fm phase discriminator, giving no tone when signal is
equidistant from both antennas (broadside), max tone if it is inline.
It is bi-directional but its claimed to be accurate to a few degrees.
I have also seen this design commercially for about $75+.
Method 2, only heard this from 1 person not sure if its accurate...
Put a bnc in the bottom of a large coffee type can, coax to ht, put rubber
duck on bnc inside of coffee can with top open.
Supposed to be a 2m "flashlight" with no polarization sensitivity.
I have a huge 10lb apple sauce can I intend to try this with.... Why not, can't
hurt. Worst it could do is provide an omni pattern with gain (fat chance).
Yagi antennas may not be good in close proximity unless you have an attenuator.
Even at a distance I have found a lot of multipath & reflections playing with
Modified radio shack fm > 2m beam.
73
Ed N3SDO
Bill Northup
: What inexpensive 2m RDF antennas and/or techniques
: have you successfully utilized.
:
: I have seen (not personally used) - a df system that used 2 switched antennas
: (audio freq oscillator - square waves - 2 phases and diode switching for 2
: antennas with equal length feed lines)
:
:
:
: | |
: | | < short dipoles equal lengths, (but not resonant!)
: =======[]======
: | [] |
: | | |
: |
: < coax from osc/diode switcher to receiver.
:
: This thing supposedly works by phase sense difference between the 2 antennas.
: It works with the fm phase discriminator, giving no tone when signal is
: equidistant from both antennas (broadside), max tone if it is inline.
: It is bi-directional but its claimed to be accurate to a few degrees.
: I have also seen this design commercially for about $75+.
[things removed]
:
: 73
:
: Ed N3SDO
I have been using three methods that seem to work.
1) Using a handy finder circuit which does the antenna switching described
above. To start with I use a dual dipole antenna (shown above) with
the dipoles tuned for the frequency that is being used. For the
dipoles I use two sets of RS TV rabbit eats because they are easy
to tune. After the initial bearings I remove the cross rod and dipoles
and hook up a single dipole (rabbit ears) and use this for additional
bearings after I have started moving around.
2) In addition to direction I like to have signal strength information. To
quickly adjust the antenna gain I have the a radio shack cable that
sticks on the windshield and connects to the HT. I start using the
rubberduck antenna, then move to 3", 2" and 1" paper clips. When I
reach full scale signals with the 1" paper clip I get ~ S2 with no
antenna.
3) Body fade, it works a lot better than most people would expect.
--
--
Bill Northup PHONE: (508) 460-2085
Stratus Computer Inc. INTERNET: nor...@sw.stratus.com
55 Fairbanks Boulevard Packet: N1QPR@WA1PHY.#EMS.MA.USA.NA
Marlboro, MA 01752 Amateur Radio: N1QPR