[amsat-bb] Re: brain picking time

i8cvs domenico.i8cvs at tin.it
Tue Aug 5 18:54:23 PDT 2008

----- Original Message -----
From: "Edward Cole" <kl7uw at acsalaska.net>
To: <w7lrd at comcast.net>; "AMSAT-BB" <AMSAT-BB at AMSAT.Org>
Sent: Tuesday, August 05, 2008 8:24 AM
Subject: [amsat-bb] Re: brain picking time

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
>73 Bob W7LRD

> Bob,
> Is your patch feed circular polar?  EME on 1296 is RHCP in transmit
> and LHCP in receive.

Hi Ed, KL7UW

It is best to specify to Bob that on 1296 MHz the dish in transmit must
radiate RHCP in direction of the moon so that the patch or any other
feed must radiate LCHP in direction of the surface of the dish.

> The switch of polarity sense is due to the fact
> that reflection at the moon reverses the sense of polarization.

So that on receiving the wave coming from the moon is received LHCP
over the surface of the dish but the dish reverse by reflection the signal
in direction of the feed that must be made RHCP polarized on receiving.

In addition a TVRO dish works well with a patch feed if the F/D ratio of
the dish is ranging from 0.35 to 0.45

> might be difficult to achieve with a patch feed.

W0LMD make a patch feed for RHCP and LHCP but never I tested it

Since the target of Bob is to see if he is able to only "hear" EME signals
at 1296 MHz without to complicate his life I suggest at the very beginning
to build only a patch feed RHCP polarized.

To receive a 1296 EME signal with a 12 foot TVRO and a IC-1271A
it is strictly necessary to connect directly to the patch connector a low
noise preamplifier with a NF in the order of 0.5 dB 

Since the gain of a low noise EME preamplifier for 1296 MHz is 
in the order of 30 dB or more then  50 feet of LMR400 connected from
the output of the preamplifier up to the input of the IC-1271A will not
deteriorate the overall NF of the system that will be only a little bit
higher than 0.5 dB   

> 73 Ed - KL7UW

73" de

i8CVS Domenico

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