[FoxHunt] Attenuator

[Clay Melhorn]

Jeffrey Madore wrote:

> Has anyone tried putting steps in an active attenuator, then using the pot
> for fine adjustment between the steps?
> Just a thought.
> Jeff  K1LE

Hello Jeff and all,
To answer your question, yes I did and it's the best thing since sliced
cheese!!!
    I built a FAR oscillator circuit board recommended by Dick Arnett WB4SUV out
at Dayton 2000. (Great guy!)
Next I made a box out of double sided pc board with four sections. One section
large enough for the oscillator and associated active circuitry and three
smaller sections for the passive sections 20dB, 20dB, 10dB.
    The active attenuator is "switched in-line" like the passive sections except
it is a 3-pole, double throw switch
in that one of the poles is used to turn the power to the oscillator "on" from a
AA battery holder when the active section is switched in-line.
    All wall seams are soldered together.
The back is screwed down. (I used screw terminal lugs from a 15 amp toggle
switch and soldered them to the back side corners, held them in place with
pliers and soldered.)
The holes for passing wire through were pre drilled.
The key to making this work VERY well is to make those holes "just big enough"
for the wire to pass through.
NO MORE THAN IS NEEDED, "Make it a snug fit."
Use light gauge wire, say 22 gauge stranded or smaller.
Don't let there be "any" space between the hole wall and wire insulation.

    I use my Active / Passive attenuator with an Alinco DR-610 dual bander (with
dual vfo.)
One vfo gets set to the actual receive frequency,
The other vfo gets set to the difference (mixed) frequency.
I use the passive "only" at first when the fox signal is weak.
As I get relatively close I switch in the active attenuator and dial the signal
down in huntable range,
then I use the passive attenuator sections once again.
    All I can tell you is that it works "VERY WELL"!!!
I've built three so far.
The first did not work very well.
Upon experimentation with the very same oscillator board and passive components
in a "new box" with those snug fit holes I was telling you about I got
"FANTASTIC" results.

    My daughter Crystal W9IOU helped me out with the tests on my new toy.
This is my 16 year old that's been hunting with me since she was 12.
Actually she was 6 weeks old at her first hunt but she doesn't recall, Hi!
Crystal was in our motor home transmitting on 2 meters with 50 watts into a 1/4
wave spike antenna (at a campground.)
I was able to be 10 feet away from the antenna, switch in the active attenuator
and literally turn my 2 element quad away either direction and watch the signal
drop off to "nothing"!!! zero! nada!
Built these little jems in the summer of 2000.

    I've even experimented with the quad and an Alinco DJ-41 2 meter hand held
(One of the baby 300mW ht's)
We call them our hamfest handies...
Since it only has a telescoping antenna I leave the antenna collapsed at it's
side and run a short piece of coax connected to the output of the attenuator and
at the other end the center conductor is soldered to an alligator clip.
The Alligator clip gets attached to the tip of the collapsed antenna and taped
down as not to damage the antenna in the heat of the hunt...  Even with the
small LCD S-meter display of this baby hand held I get pretty much the same
results.

I'm inspired by this writing to take photos of my Active / Passive attenuator
and post them on the KARS web site...
I'll let the group know when I get them posted.

73' and happy hunting!!!
Clay Melhorn  N9IO
KARS Web Master
Fox Hunt coordinator
http://www.w9az.com