R: [TowerTalk] coax and phasing

[Maurizio Panicara]

Lane,

you can use the RG8X but check its velocity factor and if a 50 Ohm line
will be the right line impedance. I don't think so, if you want to avoid
extra and unnecessary matching complications.
The 3/4 feed method, beeing this lenght a quarter wave multiple, leads to
the typical quarter wave impedance transformation and has to be taken
in account.
A 1/2 wave spacing has not a tight mutual coupling and if you plan to feed
the verticals in phase (no other effective chances at 1/2 spacing than a
broadside bidirectional pattern) everything is symmetrical and there
are not problems to force phase.
If the above is what you want and the antennas are first matched to 50 Ohm,
two 3/4 wave lenghts of 75 Ohm lines are what you need to get directly and
again 50 Ohm when lines are paralleled, with no other complications.
If the antennas are anything else than 50 Ohm, to get 50 Ohm at their
parallel, other lines (impedance) than 50 Ohm ones have to be used.
The method mentioned by N5AR and contained in the ARRL antenna book
is a triky useful one when a 90 degree (or better, odd values) shifts
between
antennas have to be developed (end fire, small spacings).
I don't think this is your case.

73,
Mauri I4JMY


-----Messaggio Originale-----
Da: dan hearn <dhearn@ix.netcom.com>
A: <zeitler@ibm.net>; <towertalk@contesting.com>
Data invio: luned́ 13 settembre 1999 7.30
Oggetto: Re: [TowerTalk] coax and phasing


>
> RG8X is OK for the individual phasing lines. Each handles 1/2 of your
> power output. Do you plan to switch directivity 90 deg. by connecting
> the verticals either in phhase or 180 deg out of phase? Its easy to do
> as shown in the ARRL ant book. When the two feed lines are connected
> together, the termination on your feed line to the xmtr will be lower
> than 50 ohms. Some circuits for changing directivity use an L matching
> network at the paralleling point to get 50 ohm feed Z. 73, Dan, N5AR
>
> zeitler@ibm.net wrote:
> >
> > When phasing a pair of verticals a 1/2 wave apart and forcing equal
currents
> > by using two 3/4 wave 50 ohm coaxes to a T connector does it matter if
RG8X
> > for the 3/4 wave portions is used if the freq is 20 meters or is their
too
> > much loss, even on 20? I have Rg-214 but the 8X is so much easier to
use.
> >
> > Lane
> > Ku7i
> >








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