[amsat-bb] Re: brain picking time

Edward Cole kl7uw at acsalaska.net
Tue Aug 5 22:14:25 PDT 2008


You said it well.  I forgot to mention that polarity sense will 
reverse upon reflection at the dish surface, so the feed sense should 
be Rx=RHCP; Tx=LHCP.  In other discussions about using a patch for 
eme, concern has been about sidelobe performance and high power 
rating of the patch if full QRO eme is considered.  Up to 200w it 
probably is OK.

I assumed that Bob was savy enough about microwave weak-signals to 
know that on eme a preamp is not a luxury but an absolute 
necessity.  LMR-400 would be fine for connection from the preamp to 
the receiver in the shack, if at least 15-dB net gain is left after 
the cable loss is subtracted.  More gain is desirable if the receiver 
NF is high.  A preamp of 0.3 dBNF is standard at 1296 for eme.

I have a WD5AGO two-stage preamp with 0.30dBNF and 31-dBgain bought 
from Radio Astronomy Supply.

73 Ed - KL7UW

At 05:54 PM 8/5/2008, i8cvs wrote:
>----- 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
> >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.
>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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