[FoxHunt] Moded ELTS, active atten?

[sdonnell]

de Rick K5RIC wrote:

> Be careful attaching non LPER Antennas to your LPER DF unit.  When you are
> in the DF mode DC  power will be sent up the coax, if you have a grounded
> antenna, you my damage the LPER unit.

Hi, Thanks we are aware of this. I would sort of expect the switched DC output
on the ELPer to be currect limited to protect the drive circuitry. I havent
checked, but isnt the DC(AC) present only in DF mode? Either way, the w/ gamma
matched used on the Arrow yagi this wouldnt be an issue. Ques: has anyone seen
an ELPer mod for adding an external(larger) meter. I used to think the submini
jack on the bottom of the case was for such, but later learned it is an
earphone jack,,. Is one side of the ELPer metter connected to common/case
ground, or does  the meter "float" as Ive seen in other TDOA DF circuits? Even
still I would think this would be an easy mod to do and providea MUCH easier
way to see signal readings.. I also seem to recall a design change that
increased the damping of the meter so as to reduce some of the wild flucuations
that can occur.

We went out on a SAREX( CAP practice search) today, mostly just to check our
equipment. As its seems most of our "real" searches are done at night,,. One
thing I noticed w/ the Arrow yagi is that when I took a bearing using vertical
polarization, in a couple of instances we saw a couple of false/secondary
peaks. When we swapped to horizontal we got no falses. Is this at all typical?
When we took these readings we area about a mile or less from the target, which
we later IDd as being in a camper/van, parked directly next to a metal hanger,
so Im sure the signal was bouncing all over the place to begin w/.. Ill give it
another shot sometime when we have a beacon set in an open field, as we usually
configure them.

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?

Prior to our use of the IC-R100 as a mobile receiver, we had  an old Regency
"TurboScan". We did an "active attenuator" mod for that which cut the bias to
the RF preamp completely and the 1st mixer by half. While this was an
all-or-nothing  selection, it dropped the VHF sensitivity down to about 1,000
uV. More than once, this easily got us to within  50 ft of the beacon.  We have
a similar mod for some recent generation Uniden/RS scanners, where by lifting
one pin of the frontend converter chip w/ a diode or resistor(cant recall),
drops the VHF sensitivity by about 40db. Ill look it up if anyone is
interested.

One other trick we used to use was image reception. Back in the days when use
of IC-02ATs was common in CAP, we figured out that if you programmed in
155.300(I think), you could get 121.500 as an image. The sensitivity was very
poor, but that was the whole point. It was great for close in sniffing.. We
even did the same thing for our new NTIA-compliant Kenwood TK-280. We figured
out the LO/IF orienation an programed in a pair of channels, one for real and
one for practice ELTs. The image though, is from the 243 second harmonic. Even
w/o an S Meter on the radio, I suspect this could be a handy backup. It helps
to be sure, as some folks arent tooo pleased when they are called at 1AM to
come out to their airpalne or boat to secure the beacon,,.

Steve Donnell
WA1YKL/Abenaki 102