[FoxHunt] Active attenuators

[Marvin Johnston]

With the permission of Joe Moell, I put together a "kit" of his offset
attenuator as shown on http://members.aol.com/joek0ov/offatten.html. The
quotes are there because the board itself is fully assembled and tested.
However it needs to have the battery leads (9V) and antenna leads
connected to complete the unit. Depending on the enclosure, a switch
would be a nice thing to have, but it is also easy to leave the battery
connector outside the enclosure and just plug it in as necessary. A
diode should probably also be added since connecting the battery
backwards can do serious damage to the regulator and CMOS oscillator :).
The board itself is about 3/4" x 1 1/4" and is mostly surface mount
components, hence the assembled unit :).

I purposely did not offer it as a completed unit because 1) different
needs require a different enclosure (take a look at the enclosures at
the bottom of the HomingIn page) and connectors, and 2) some radios use
BNC connections while others require an SMA connector. The offset
attenuator itself was offered as a complete unit because 1) some people
have trouble working with surface mount components, and 2) it was
offered at the last Southwestern Division Convention attenna workshop
and I needed to make sure that everyone could complete the tape measure
beam and offset attenuator in the 2 hour time limit.

It uses a DIP CMOS Crystal Oscillator at either 2 MHz or 4 MHz (some
older radios cannot tune out-of-band) so it can easily be changed if
necessary. The specs talk about a 25 ma current draw, but the ones I've
built only draw about 8 ma.

To use the unit in a plastic enclosure such as the "C" fitting on the
tape measure beam at the bottom of the HomingIn web page, some
"machining" of the plastic would be required (the threaded portion of
the pot is somewhat less than 1/8") or a differnt pot would need to be
used.

The cost is $12.00 for the assembled offset attenuator and 9V battery
connector, or the PC board itself is available for $3.00. The parts are
all available from DigiKey and probably run around $7.00 or so in single
quantity. As you might have guessed, this was not meant to be a
for-profit project, but rather to provide an inexpensive way to get new
people involved in transmitter hunting ... or from my standpoint, ARDF
:).

Marvin, KE6HTS


Ernie Howard wrote:
> 
> One of our new local hunters is interested in purchasing assembled
> active offset attenuators. Does anyone here know a source?
> 
> Ernie W8EH