----- Original Message ----- From: "Edward Cole" [email protected] To: [email protected]; "AMSAT-BB" [email protected] Sent: Tuesday, August 05, 2008 8:24 AM Subject: [amsat-bb] Re: brain picking time
At 04:35 PM 8/4/2008, [email protected] 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 Seattle
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.
OK 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