Graham E Laucht wrote:
>
> In message <339DBB9A.77B5@carib-link.net>, Ember <ember@carib-link.net>
> writes
> >I wonder whether anyone has considered a dipole made by sticking the
> >copper tape to the inside of the fuselage skin
>
> I looked at the same on Duncan's "boat" and reckoned a tape vertical up
> behind the luggage bay bulkhead might also work though it would have a
> rather disturbed radiation pattern especially in the forward direction.
And which is why I didn't suggest this location !
> Given that we need to talk to people in front of us more often than
> those we are leaving
Well, I'm not too sure about that ! I seem to spend most of my radio
time talking to the tower, which is only in front of me when I am on the
last leg !
>
> NB, Centre fed half wave antenna have a terminal impedance of 75 not
> 50ohms or 73+j42ohm to be pedanticaly exact and need a balanced feeder.
Precisely - which is why the impedance of a centre fed dipole is taken
as 72 ohms for practical purposes. BUT I suggested using the curvature
of the fuselage plus any necessary internal angle to produce a dipole
with the arms not in line - ie. a shallow "V". As in the case of the
usual quarter wave groundplane this should produce a 50 ohm match.
Yes, in theory a balanced feeder is needed and if you want to be fussy
when using coax then a balun is required at the antenna feed point - but
in practice this doesn't seem to make any discernable difference.
Martin
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