Hi.

I am just in the throws of installing a half size G5RV in my back garden. I
am going for the "top hat" arrangement (North / South) instead of the
inverted V.

It says on the instructions with the kit that the best coaxial feeder length
to stick to is either 45 feet or 90 feet. I have 77 feet of Belden coax and
didn't really want to cut it ! How critical is the 45 feet coax length ?
If I have to cut it I will but as said, didn't really want too . Could I
just leave the 77 feet and neatly fix it around the edge of the garden, to
use up the excess, and not suffer too much loss ??

Any help will be greatly received,

Thanks.

--

Jim Burrill (Smogthemog)
M1BMW
Kiteaholic

www.jbphonetech.info


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Modeling of the G5RV shows that the best length for the Coax section
is 0 feet!
The reason is that the coax section only creates loss, depending on
the SWR at the frequency of operation. Some frequencies have higher
SWR than others.

I provide a sample G%RV antenna file with Coax definition in the demo
version of Nec2go. It is very easy to Sweep the coax length and see
the losses.

Pat W.

Jim,
Sorry, but the length of the coax is important. You
have another option (per the instructions), add another
12 feet to the 77 feet you already have.
The length of coax is specified for a purpose, it makes
up part of a circuit which does impedance transformation, and
if you change the 'value' of a circuit's component, you
're-tune' the circuit. The length is fairly critical. Maybe
not to the 'milimeter' level of accuracy, but certainly to the
'foot' level...
'Doc

PS - Are you sure the instructions said 45 feet or 90 feet?

"PatW" wrote in message
m...
Modeling of the G5RV shows that the best length for the Coax section
is 0 feet!
The reason is that the coax section only creates loss, depending on
the SWR at the frequency of operation. Some frequencies have higher
SWR than others.

That is probably the case in all antennas. Just one slight problem. HOw
does the average ham set up a station for the low bands without any feedline
? With some of the remote heads like the Icom 706 I guess that you could
mount the rig at the feed point and remote it. Still not too practical for
most .

The G5RV was designed to allow a reasonable match on some bnads if fed with
a specific ammount of feedline. YOu pick up losses but the SWR will be low
into a 50 ohm system. Did you modle the impedance of the G5RV without any
feedline ?

PatW wrote:
Modeling of the G5RV shows that the best length for the Coax section
is 0 feet!

Depends upon your definition of "best length". If "best
length" is defined as the length that provides the lowest
SWR at the source, zero is not it.
--
73, Cecil http://www.qsl.net/w5dxp



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