[FoxHunt] Moded ELTS

[Gerald boyd]

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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