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I would leave it off until you are sure everything is how you want it,
as far as the number of turns of the helix, etc. If you decide to seal
the whole ball of wax, do it on a cool and dry day, otherwise
condensation will collect inside the radome. Unless you can hermeticly
seal the radome, I would just either leave it open, or drill a couple of
drain holes to allow condensation to drain out. As I mentioned before,
it might be a good idea to mount the dish upside down for this reason as
well. Water *definitely will* affect how well things work. Signals at
these frequencies are attentuated by rain, fog, and wet leaves. If water
gets inside your connectors, you can kiss your signals goodbye as well
(ask me how I know).  Once everything is set and permanant, mold a good
heapin helping of Coax Seal or Silicone Rubber around all exposed
connectors to keep the water out. 

Regarding coax used for the downlink, I am using plain old RG 59 Foam
from the downconverter to the shack for a 75 foot run. With most
downconverting schemes, the noise figure is determined at the
downconverter or preamp, and most of the popular downconverters have
ample gain to make up for coax line loss without adversely affecting the
noise figure. It would not hurt to use RG 6 or a better coax, but I
doubt that you would see much benefit from it. 

I would save the "good" coax for your uplink antenna, especially if you
are running less than 50 watts or into a short yagi or helix, and have a
fairly long run. RG-214 has a loss of about 5 dB per 100 feet at 450
Mhz, so it would pay to use something like 9913, or even CATV Hardline
for your uplink feedline. In other words, a 100 foot run of RG 214 fed
with 35 watts at the radio will get you about 12 watts at the antenna.
If you replace that 100 foot run of 214 with 9913, you will reduce your
feedline loss to 2.6 dB, which will increase your power at the antenna
to 20 watts or so. This is the same as doubling the length of the
antenna! Of course, if you already have a long OSCAR 13 class uplink
antenna, this step might not be necessary.  

w7lrd@juno.com wrote:
> Hello
> I am a few days away from getting on AO-40.  Is it worth the effort to have a radome over the helix feeding the dish.  Does water (I live near Seattle) have an effect on the performance?  I have the origonal radome for the prime star feed assembly.  It could be fashioned to fit over the helix and sealed.  Also the down converter has an F connector, I will be feeding the DC up the coax.  Which type of coax are most of us using?  Thanks as always.
> 73...Bob...W7LRD
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