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Re: AO40 U Uplink antenna/power needed



>From: "Don Woodward" <dbwoodw@abraxis.com>
>What type of antenna would be good for the UHF uplink?
>
>I've got a 6 element Yagi laying around, or do I need something like M2's
>436CP42? If I go with the 436CP42, will I be able to get by with 5-10 watts?
>What kind of power would I need with the 6 element yagi?
>
>Any recommendations on other antenna choices?

Don,

You are likely to get all sorts of recommendations ;-)  Here's my
experience using an M2-436CP42:

I have an FT-847 which is able to output up to 44w [measured at 435 MHz on
cw into a Bird/load].  Initially, I ran power up thru about 50-foot of RG-8
coax with about 3 dB loss, so the maximum power I got to the antenna was,
lets say 25w.  That was more power than I needed most of the time.  On
particularly good passes [ones with low squint angle, high elevation angles
away from trees, and moderate-to-low activity] I usually ran around 15-25w
output...meaning I had about 8-15w into the antenna.  But at times it took
full power to produce an adequate downlink signal [to my ears].  So I was
running an EiRP of 320 to 1000w, since my antenna has a gain of ~16 dBic.
LEILA doesn't like the upper end of that power range, though.

My guess is that you should be able to do well with 25w and a 13 dBi
antenna...that translates as 500w EiRP.  There will be times that will not
exactly be enough...but most of the time I think you will do fine.  If your
antenna produces circular polarization you have an additional 3 dB
advantage in your uplink.

A 6-element yagi has maybe 10 dBi gain, so you'll need corresponding more
power.  5-10w will not do well most of the time.  Since you have the
antenna and apparently 10w, why not try it  and see how well you hear
yourself?  My guess you will decide on some combination of antenna and
power that is higher.  I think a 50w transmitter and a M2-436CP30 would
make a good combination if you have low-loss coax like Belden-9913 or Times
LMR-400.

I have upgraded my 435 MHz uplink capability by installing a 55w "brick" PA
on the roof under the antenna running about 15-foot of RG-8 to the antenna
[with a measured loss of 10%] so I get up to 50w into the antenna [when I
need it].  So now I usually operate around 15-30w into the 436CP42 [EiRP
from 600-1200w].

Ed

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