[FoxHunt] active attenuator

[Anthony Levand]

    One might consider a higher LO frequency, the output is both plus and minus,
so a 145.35, 147.35, 148.34 . . . signal will interfer with tracking a 146.34 fox
for example, with a 1 MHz offset. Not to mention the LO harmonics and paging
transmitters. Four, 8 or 10 MHz chip oscillator work well, are found easier and
are cheaper. I have used a 50 MHz offset to hunt a 220 signal on a 2 meter HT. A
by-pass switch for weak signals is a good idea, so one is not swaping connectors
on the fly. The active attenuator will also radiate a substantial signal on the
offset frequencies when near a strong transmitter.

    A 455 kc IF tranfomer and a JFET make a nice BFO when loosely coupled to the
IF strip near the ceramic filter if the FM receiver. One can really pick out weak
signals that otherwise wouldn't break squelch.

Tony
AA9CC

John Munsey wrote:

> Mike, I would like the details for this project.  Also, if you can send it
> to me in completed form I have access to Acrobat and could get it put in
> PDF format so that it would be easy to post and/or email to others.
>
> Thanks for the good work.
>
> At 07:09 PM 3/24/2002 -0800, you wrote:
> >
> >I have developed an 'improved' active attenuator for our local club.
> >It is simple to build, using one CMOS IC, a crystal, single diode mixer
> and a pot.
> >The improvement is mainly the addition of a 2 Hz oscillator gating the 1 MHz
> >oscillator.  This really helps to distinguish between an unmodulated
> signal and the
> >noise floor in an FM receiver.
> >
> >I could post it if there is much interest.
> >
> >Mike
> >WB6TMH
> >
> >
> >> >de Rick K5RIC wrote:
> >
> >>
> >> >Does anyone have any circuit updates to the Active Attenuator circuit
> from the
> >> >one in 11/92 QST? Im going to give this a try soon. Has anyone tried
> different
> >> >type diodes, or even used a double balanced mixer such as an SBL(over
> kill?). I
> >> >would also think you could use a different style oscillator such as a
> 74C04 and
> >> >a 500 K or 1M ceramic resonator. Any thoughts?
> >
> >_______________________________________________
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> >
> John Munsey,  KB3GK
> Ormond Beach, FL 32174
>
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