[ARDF] Attenuators for ARDF...

[Marvin Johnston]

Joe Moell's offset attenuator works pretty well, and that is the one
that I offer as a "kit". It uses a circuit board and is all surface
mount except for the pot, diode, and oscillator.

One of the problems I've run into is saturation when close to the
transmitter. John Munsey and some others have been working on getting
better attenuation out of it, and something that he says works *very*
well is to run the oscillator on 3V instead of 5V as specified in the
datasheet. I found that by putting the attenuator in a shielded box, and
adding a 20 dB switched attenuator would allow me to almost touch an 8W
transmitter and still attenuate the signal away.

If you are after cheap, you might try that circuit without the regulator
and just run a couple of AA cells directly to it and see if it works for
you. The oscillator runs about $1.50 and the audio taper pot another
$1.50. Add in an enclosure and some BNC/SMA connectors and I don't know
how you could get by for much less than maybe $8.00 or so plus the time
to build them in quantities of 20 or so. Using a circuit board would
help reduce the time but add to the cost. My junk box could handle a
couple, but certainly not 20 without buying parts :)!

Marvin, KE6HTS



Matthew Robbins wrote:
> 
> The vibe I'm getting is that offset is cheap enough and easy enough to use.
> Furthermore, it's just more capable than a step attenuator.  It sounds
> like offset is the way to go when you have to use an off-the-shelf
> radio.
> 
> Dale: Tell me about this double balanced mixer instead of
>     a single diode.  Do you have a schematic you can send me?  (And
> the crystal set, too.)
> 
> One last question (no promises, though): I've been looking for a
> schematic of an older offset attenuator that uses one AA battery
> rather than a 9V.  Again, the impetus is to reduce the cost of, say,
> 20 units.  I realize I'm only talking about two or three dollars per
> attenuator, but I'd like to consider all the options.  Does the more
> complicated one with voltage regulator and TTL (?) oscillator offer
> advantages with stability or ease-of-manufacture (or especially cost)?
> 
> Matthew
> Cincinnati, Ohio USA
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