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VK6BE > BIKE 04.05.07 14:17l 36 Lines 2100 Bytes #999 (0) @ WW
BID : F30794VK6BE
Read: GUEST DK3EL
Subj: Perambulator mobile
Path: DB0FHN<DB0FOR<DB0MRW<DK0WUE<I0TVL<N9ZZK<WA7V<KD4YAL<VK2TV
Sent: 070504/1202Z @:VK2TV.#MNC.NSW.AUS.OC #:9569 [Kempsey, QF68JX] $:F30794VK6
From: VK6BE@VK2TV.#MNC.NSW.AUS.OC
To : BIKE@WW
Yes, the title is correct. In the days when fox hunts (hidden transmitter
hunts on 144) were popular it was my turn to hide the transmitter. Some of
the foxes had devised all sorts of unusual means of tricking the hounds -
one had a rotating aerial which put heavy QSB on the signal. Another ran
the coax in the river to a site midstream. A third acted really cunning
and had two transmitters about 1 kHz apart in frequency and separated by
100 yards or so. The fox hunters, who were using AM in those days of
course, could hear a tone from the heterodyne till they got close to one
or the other of the TXs when the tone would disappear.
Again another cunning fox had a small 144 tone modulated transmitter in
his overcoat pocket and caught a bus between two bus stops about 2 miles
apart, going back and forth until someone spotted him.
My effort was to build a small 144 TX using a couple of 12AT7s, one and a
half of which was an oscillator, multiplier chain, while the other half
was a reactance modulator fed by a tone oscillator at 400 Hz. This was
very small and was mounted in a cane pram with mosquito netting over the
top. A halo antenna was mounted in the hood of the pram and a car battery
placed on the undercarriage under the pram. A couple who were friends of
mine then pushed the pram up and down a Perth street, while I stayed in
hiding. It amused me greatly to hear the tone issuing from the hunters'
cars as they went past.The "sniffers", consisting of a diode detector,
were useless because the signal was NBFM. However the receivers which were
AM picked up the tone quite well. The power was milliwatts but the signal
was clearly audible for several miles. Finally one of the hunters became
suspicious and picked up enough courgae to ask to see the "baby" amd the
game was up.
Half the fun of those fox hunts was in devising some way of providing a
fox that would defeat the efforts of the hounds. We had to build whatever
we used at that time most of the time, and solid state was almost, but not
quite, unknown.
Bob VK6BE.
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