[FoxHunt] Moded ELTS

Wed, 27 Mar 2002 15:51:15 -0700

I often hear signals when LPER's don�t detect anything at all (no meter movement and
just has background noise).

With a low noise FET front end on the receiver a beam antenna and the CW detector my
minimum detectable signal level is way below a LPER.

That�s the advantage of doing Ham �weak signal� T-Hunts two times a month. You learn
what works and what doesn�t work very well.

I have seen LPER�s used on our T-Hunts and they do not ever win a hunt. The multpath
and week signal is the kiss of death for them.

Jerry

Bob wrote:

> I think you will find the LPER will detect and provide DF
> information just fine on an unmodulated signal and probably
> has more sensitivity than other more normal receivers
> because of it's narrow bandwidth. It's just you cant hear
> the carrier. If the needle moves, there is signal whether or
> not you hear anything.
>
> Bob, WB6JPI
>
> Gerald boyd wrote:
> >
> > My home made AM receiver brings out the 10.7 Mhz IF to a front panel BNC
> > connector. I always monitor it using a CW detector (A HF RX in CW mode) connected
> > to the monitor port. If any carrier is on frequency I know it because of the beat
> > note produced in the CW receiver. Using this setup I can detect signals that the
> > LPER can not copy.
> >
> > Sometime ago we had an ELT mission  where the ELT was not modulated and this
> > setup detected it. By the way several of the LPER guys where reporting "no
> > signal".
> >
> > Jerry
> >
> > de Rick K5RIC wrote:
> >
> > > Good work Dale,
> > >
> > > One of the major problems I have seen during actual missions is an ELT with
> > > out any modulation.
> > >
> > > I was talking to an aircrew that keep saying "No Signal."  When I asked
> > > them for a signal reading, it full scale. It was an FAA ground station with
> > > keyed TX, and no modulation.  I could hear the carrior in my mobile unit
> > > under the aircraft, about 3000 feet lower.  They swore they had no signal,
> > > until I pointed out big signal no audio.
> > >
> > > I want to set up a practice ELT with no modulation one of these days.
> > >
> > > 73
> > >
> > > rick sohl
> > > k5ric
> > > CAP West 4
> > >
> > > At 09:08 PM 3/22/02 -0800, you wrote:
> > > >>-Here in Yamhill County, Oregon, we got some old ELT beacons and
> > > >>-recrystalled them for
> > > >>-121.775......
> > > >>
> > > >>
> > > >>Great!  Go for it Dale.
> > > >>
> > > >>One thing to check is to see if your ELT is radiating strong RF on the
> > > >>second harmonic. .....
> > > >
> > > >
> > > >     We paid attention to that in the conversion.  One box has an outboard
> > > >     low pass filter with BNC connectors that goes in line with the antenna.
> > > >     In another we replaced the output circuit with a low-pass "T" network.
> > > >
> > > >     Fortunately, we have access to a spectrum analyzer, and made good use
> > > >     of it!  We have also reduced the power output a bit.
> > > >
> > > >     The ELTs we converted are probably similar to many - the modulation is
> > > >     applied in the collector lead one or two stages away from the final
> > > >     (to minimize the amount of audio power required, and perhaps to
> > > >     broaden the signal to make it easy to hear!)  An AM signal
> > > >     amplified by one or two class-C stages is going to splatter all over
> > > >     the band!  So one of the future projects will be to clean up the
> > > >     modulation and keep it within a reasonable bandwidth (+/- 10 kHz or
> > > >     so.)  Unmodified, the output at 100kHz off frequency is only down
> > > >     40dB or so, which is a big reason why 121.6 MHz didn't work well
> > > >     for a practice frequency.
> > > >
> > > >
> > > >     (While I was working on the other units, I repaired the practice
> > > >     beacon for the local CAP group.  Didn't look like it had ever
> > > >     worked since someone had put in the 121.775 MHz crystal, plus one
> > > >     transistor had blown, and the 1988 Radio Shack nicads were no
> > > >     longer in peak condition.)
> > > >
> > > >          - Dale WB6BYU
> > > >
> > > >
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