[FoxHunt] antennas for harmonic sniffing

[Steve]

I am interested, and some other CAP hunters too.
Thanks,
Steve

----- Original Message ----- 
From: "Kuon & Dale Hunt" <kuon@onlinemac.com>
To: <foxhunt@mailman.qth.net>
Sent: Sunday, January 25, 2004 12:16 PM
Subject: [FoxHunt] antennas for harmonic sniffing


> With the "DC to daylight" coverage of the newer
> hand-held receivers and transceivers, sniffing
> transmitter harmonics for close-in work can
> easily extend beyond the common 146 -> 438
> combination.
> 
> K7FM was interested in hunting ELTs, and sat
> down with a calculator to determine the options.
> It turns out that 730 MHz is a good choice:  it
> is 6 * 121.5 (actually 729 MHz) and 5 * 146 MHz.
> You can hunt both bands with the same antenna.
> 
> This sounded promising so I scaled the W4RNL "OWA"
> 6-element yagi design to 730 MHz and built one
> using PVC pipe and #8 aluminum wire.  The antenna
> is less than 11" / 28cm long.  Set out my
> ELT practice beacon and it works great!  Using
> the frequency knob as an attenuator (the ELT has
> a VERY WIDE signal - only 40dB down at 100kHz off,
> which is why the old 121.6 MHz practice frequency
> could be heard on the emergency channel) I could
> get clear bearings at 3' / 1m away.  The pattern
> is very clean, with just one peak above the noise.
> I could hear the beacon at 250 m / yards away, and
> could probably stretch it to a quarter mile ( 400m )
> line of sight.  (Maximum distance was about 100m
> when the signal passed through a building.)
> 
> Haven't tried it on 2m yet:  although odd harmonics are
> generally stronger than even ones, most 2m rigs should
> have much lower harmonic output than the ELT...
> 
> ...OK, I'm back.  The rain stopped and the temperature
> warmed up to 36F / 3C so I set out one of my 2m
> transmitters:  a Hamtronics synthesized kit at about
> 1 watt output.  I could copy the signal on 732.825 MHz
> from 400m away.  Probably could go further, but the road
> went over a hill at that point.
> 
> Receiver in both cases was a VR-500.  The minimum
> discernable signal is at least 6dB better using CW
> than AM or FM.
> 
> If there is interest maybe I can post the dimensions
> and a photo somewhere.
> 
>      - Dale WB6BYU
> 
> 
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