[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: antenna cable routing question

Hi Greg,

Your going to get varying opinions on this one. Purists will tell you 
that letting the coax drop off the rear of the antenna is the only way
ensure that the radiation pattern remains undistorted. 

The real question is, if it does what is the impact to the link budget ?
I can tell you from experience that circular polarization for birds
you want to work isn't a significant factor. In fact you can make
a strong argument that linear polarization might be best in the long
run anyway. Consider what happens if you are configured for RHCP but
the downlink is LHCP for a period. Your down 15 to 20 dB  where
the linear antenna might be 6 dB worst case and often only 3 dB.

I never had a problem getting in the que on any of the birds you are
planning to work. I was running a CC 13B2 for 2M and a KO22 on 70 CM.
Rig is a barefoot 736R. Plenty of margin for the LEOs. If we were 
discussing A0-10/13 mode B the situation would be different.

So my recomendation is to run your coax along the boom right to the
crossboom and don't concern yourself with it. You will never know
the difference and will have alot less trouble with the system.
If you have the ability to measure return loss (or VSWR) determine
where the coax has minimal impact on the VSWR and secure it in that

One other thing. Aircom is nice coax but I will never use it outdoors
again. It is in the same league as 9913 as far as water contamination
is concerned. I used the proper connectors taped it and thought I had
everything right. After two seasons I noticed my VSWR inceased on 2M
and 70cm. It was mid January one week before the VHF sweepstakes.
Up the tower I went to remove the jumpers. Sure enough just like the
9913 I had water (frozen) in the coax. Since then LMR-400 is the only
way for me. Has been perfect since.

Good Luck

--db-- AA2GF

> Gregory Young wrote:
> Hi all:
> I have just constructed 2 new satellite antennas.. the KLM 2M-14C, and
> the 435-40CX. They are super!
> A local satellite enthusiast, who has the same antennas (except for
> the larger 2 meter version) routed his Aircom coax along the length of
> the beam, across (along actually) the fiberglass crossboom, and down
> his tower, to avoid the weight of about 12 - 15 of the Aircom cable
> dangling down from his antennas.
> He found that as long as the cable was not routed thru the driven
> elements, as the instructions suggest, all works fine.
> I would like to put the antennas up this weekend, but am undecided as
> to which way to go. His way certainly seems more structurally sound,
> but how much will the antennas' patterns be altered by this approach?
> Any thoughts?
> Thanks in advance!
> 73, Greg, KE2VW