[FoxHunt] Attenuator

Sun, 21 Apr 2002 10:42:08 -0700

My friend Tony has built a sniffer around the Analog Devices
Logrithmic amplifier chip. Here is his report...

   "This week I finished my new sniffer with the AD 8307. It
is
the best I have ever used. I combined the 8307 and a ticker
that goes up
in tone with more RF. It starts to tick at -107 dbw and has
70 db dynamic range to the high tone. I then can switch in
30 and 35 db
attenuators to numb it  60 db. The lost 5 db is some kind of
leakage. (marginal shielding)   I think I did the
measurements correctly.    I can stand in my yard and key a
repeater 10 miles away and it
will start to tick when pointed in that direction. With the
switches in, -60db, I can DF my repeater, 80 watts at 25
feet."

I suggested to Tony that he replace the toggle switches with
relays and use bypass feedthroughs for the wires to get
better shielding. He is working on numbing down the 8307 as
well. It is one hot chip It takes almost no support parts
and has a 90 dB dynamic range if you can figure out how to
get them all.

Anthony Levand wrote:
> 
> If one has a standard type of in line attenuator, it could be adapted to make an
> active stepped attenuator. This would be easy to do.
> 
> Tony
> AA9CC
> 
> Clay Melhorn wrote:
> 
> > 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
> >
> > _______________________________________________
> > FoxHunt mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/foxhunt
> 
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