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G0FTD > WANTED 24.09.04 23:14l 51 Lines 2119 Bytes #999 (0) @ WW
BID : 9B7082G0FTD
Read: GUEST
Subj: Re: 70MHz Horizontal - oops
Path: DB0FHN<DB0RGB<DB0SL<DB0FSG<IN3TRX<IW3AQL<I4UKI<IK5CKL<IZ0AWG<IK1ZNW<
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Sent: 040924/2017Z @:GB7SXE.#38.GBR.EU #:6313 [Hastings] FBB7.00i $:9B7082G0FTD
From: G0FTD@GB7SXE.#38.GBR.EU
To : WANTED@WW
PA2RHB wrote:-
> With Andy, G0FTD, I agree that a horizontal antenna for 4m, mounted just
> 30cm over a groundplane, gives 'not much' lowish-angle radiation. Exactly
> where the -3dB point does not change the fact that it is too high. I must
> have been thinking of repeaters on high buildings along the streets ;-)
> (horizontally polarized? oh, well)
>
> I quite liked the idea of a vertical wire down the middle of the
> windscreen, coupling energy into the car body for it to radiate. Some
> horizontal radiation will show up too, but not much directly fore-aft.
>
> Coupling your RF into the rear window heater is interesting too. I would
> guess that the losses would be higher though.
This *can* be a complicated subject but I will try to keep it simple.
Performance of both systems of car body coupling can work extremely well
with the performance of a dipole if time is taken to produce a good system
and experiment. The experimentation does require dedication though.
Every vehicle will have it's own problems and differences because the
harness or loom wiring is different in every model and this effects
the exact configuration of such rear heater systems.
Also the earthing system can change when things like the handbrake or foot
brake is applied because of complicated rf earth loops etc.
However do not let this put you off attempting such systems - they are
superb
in the real world when a little time is taken to make them.
Actually the radiation pattern is quite good for both vertical and
horizontal, with slight degradation in vertical mode.
However BOTH radiations patterns are like the horizontal dipole "figure 8"
pattern except that the vertical pattern is shifted by 90ø compared to
the horizontal pattern.
I have measured this with professional equipment maybe 100,000 times ;-)
If there is sufficient interest maybe I will scan my paper measurements and
send them on packet - but as you know REAL technical discussion on packet
is futile. There are too many time wasters who only make hot air ;-)
Regards - Andy
them on packet
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