Thanks a lot, Alan!

I am getting closer to a real understanding now. It is gruesome to
have learned something as a very young HAM that does not match
what you learned at university that does not match what you have
experienced etc. I must admit I never counted the number of 1/4
wavelengths - I rarely know the cable factor and just measuring the
length of a cable with sufficient precision can be pretty hard - at
least in the Guadalahara desert with scorpions, rattlers, coral
snakes and killer bees every second.
But when the switchblade occationally is free from its defensive
duties it works fine to just cut a few inches off the cable.
I have a few snapshots of the site at
http://anakron.net

Btw. I found a very nice spread spectrum chip for 433 in Norway.
Check out http://www.bluechip.no

Kent

> >Thanks a lot for the corrections.
>
> >The fairy tale helped me, though -
> >I had super signal through from antenna 1 to antenna 2, but the
> >other way - NIL.
>
> >I then cut 17 cm off the cable and voila - it worked.
> >Any explanations ?
>
> The business of making the cable a complete number of half wavelengths long is a
> not unreasonable practice unless you have matching networks that you can
> specifically tune to take out any impedance mismatch. There will always be some
> mismatch between the feed wire and the aerial. If the cable is an odd number of
> quarter wavelengths long then this can represent a very high impedance at the
> transmitter (or receiver) end, resulting in considerable losses. If the cable is
> a complete number of half wavelengths long then the impedance will be very close
> to that at the aerial, which will almost be guaranteed to be a closer match than
> add an odd quarter wavelength different. At VHF and UHF this does become of some
> importance as the output networks at the transmitter are not normally tuneable
> to tune out any mismatch.
>
> At HF and lower, because the networks are designed for lower bandwidths and
> typically have components which are of a type that can be varied, then the
> feeder length is less critical. Also at HF it is common to have a tuneable
> component at the aerial end to get a closer match between the aerial and feeder.
> At VHF there may be an attempt at matching the aerial to the feeder, but this is
> generally a broadband match, which is not often tuneable, and is only done when
> the aerial is far off a 1/4 or 5/8 wavelength long. Do remember that an aerial
> does have a reactive impedance that also has to be tuned out by the matching
> network for best energy transfer, as well as the resistive portion of the
> impedance.
>
> In your case it sounds like the feeder was close to an odd number of quarter
> wavelengths long, and so the transmitter was working into what it saw as an open
> circuit (or significantly high impedance), and changing the feeder length
> brought it close to a half wave multiple which allowed to transmit a significant
> proportion of its energy, and so radiate a worthwhile signal strength.
>
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