RonSwinden@aol.com wrote:
>
> Dear all. theorising about aerials is just about the most non consumating
> sport I have ever watched.
If you think so you should try reading one of the Ham radio texts on the subject
!
> Please can someone who really knows about such
> things tell us how long the bits of copper tape that we stick in our a/craft
> tails need to be to give us a reasonable preformance over the band that we
> operate in.
The formula for the length of a a half wave dipole in inches is 5,616 divided by
the operating frequency in MHZ so that
for my local tower frequency of 118.1 MHZ the length works out at 47.5". Cut
this in the centre and solder the centre
conductor of the coax to one side and the braid to the other. When you lay
out the antenna it is best not to have it in a
straight line but to have an included angle of about 120 degrees -this gives a
better match to the 50 ohm coax as the
characteristic impedance of a straight line dipole is 72 ohms. If the
surfaces
on which you stick the copper tape are not
flat, don't worry !
> Is it really necessary to invent a new sized wheel for every
> Europa??
NO!
>The Europa instructions recomend the use of an SWR meter to fix
> the length of the dipole then glass it in but G L comments the glass is a
> lossy? material which presumably means that the glass cover will modify the
> tuning that we did before the glassing? at which point futher tuning will be
> difficult if not immpossible.I pass.
Losses from one layer of glass (the epoxy is probably more lossy than the glass
!) will not be of consequence.
>Help somebody gimme a length that I can measure with a rule and which has a
>fair
chance of working with a
>reasonable level of efficiency.
See above !
>I'll settle for that.
You shouldn't have any trouble - getting a SWR of 1:1 is almost impossible and
cutting to length and putting in place
should be accurate enough ! I use a groundplane cut for the 2m ham band (144
MHZ) for my handheld NAv/Com and it
works well.
Best of luck !
Martin W. Berner,
26 Mayfield Road, Valsayn Park, Trinidad, The West Indies
Live Long and Prosper !
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