[FoxHunt] Attenuator

[Bob]

There are radios and then there are radios. In general, the
All-mode radios have better shielding than the mobile that
are better than the hand held. I can easily do over 100 dB
with my Kenwood 9000 (including the 25 dB of the internal
attenuator) without tuning off freq.

Bob, WB6JPI

Kuon & Dale Hunt wrote:
> 
> >What are the thoughts on a good attenuator...
> 
>   Clete -
> 
>       That Radio Shack attenuator probably won't help much.
>   You will generally need more attenuation than it will provide.
> 
>   I find 60dB of attenuation is about the limit I can use with
>   most receivers before the signal picked up through the case
>   exceeds that from the antenna connector.  After that point,
>   any additional attenuation won't help.  60dB may get you
>   there if the transmitter is running low power and it isn't
>   well hidden, but I've seen receivers wimp out at a quarter
>   mile from a 25 watt transmitter - the signal was full scale
>   on the "S" meter even with the antenna disconnected.
> 
>   The solution is to use a "active attenuator" (or "offset attenuator".)
>   This is an oscillator and a mixer circuit.  The oscillator is on
>   some frequency in the MF or low HF range - say, 2 MHz.  The receiver
>   is tuned 2 MHz off from the desired signal, and the level of the
>   oscillator signal applied to the mixer is varied with a pot.
>   Because the receiver is not tuned to the transmit frequency, it is
>   much more immune to overload and pickup through the case.
>   Attenuation levels of 100dB are possible - which is usually enough
>   to sniff out a transmitter hidden in a clump of bushes
> 
>   The design on the HomingIN web site is a good start, and there are
>   others around on the net.  Personally I like to use double balanced
>   mixers in mine, but the single-diode ones are simpler and still
>   should do the job for you.
> 
>   Good luck and happy hunting!
> 
>        - Dale WB6BYU
> 
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