[amsat-bb] Re: brain picking time
kl7uw at acsalaska.net
Mon Aug 4 23:24:19 PDT 2008
At 04:35 PM 8/4/2008, w7lrd at comcast.net wrote:
>Next question- which probably would be more aimed at a EME bb. I
>have a 12 foot TVRO I am building a patch feed for 1296, and feed it
>through 50 feet of LMR400 to my IC-1271A. I want to see if I am
>able to "hear" EME signals. Of course if I am able to, you can
>guess what my next effort will be. This will be a cheapie effort as
>I am only using stuff I already have. I do have a KJ6KO L band 70 watt amp.
>73 Bob W7LRD
Regarding 1296-eme: The 12-foot dish will do fine on eme and the 70w
amp will do fine as a start, especially if you use JT65C.
Is your patch feed circular polar? EME on 1296 is RHCP in transmit
and LHCP in receive. The switch of polarity sense is due to the fact
that reflection at the moon reverses the sense of polarization. This
might be difficult to achieve with a patch feed. Many eme stations
are going to the septum feed since it produces both senses of
circular polarization and eliminates the need for a high power coax
relay. See http://www.ok1dfc.com/EME/emeweb.htm for septum designs.
50-feet of LMR-400 will lose a lot of power at 1296 (2.4dB loss);
only 42w will reach the dish. You can solve this two ways: upgrade
to 1-5/8-inch hardline (61w will reach the dish) or mount the
amplifier at the dish (on the back side would work well). Then use a
10-12 foot 1/2-inch hardline to the feed so that 95% of the power
reaches the feed. Typical stations on 1296 eme run a minimum of 150w
and average 200-300w. I understand from talking with Gordy, WA6ZKY,
that a 150w amp is being developed by KJ6KO. I probably let the cat
out of the bag so my appology to Greg.
73 Ed - KL7UW
More information about the AMSAT-BB