[amsat-bb] Re: brain picking time
w7lrd at comcast.net
Tue Aug 5 22:39:03 PDT 2008
Ed and all
Many thanks for the information from many of you. I realize I will need a preamp. For now I will be content to see what I can hear. As you can guess once I can copy signals I will want to join in. That will require at very least mounting the amp at the antenna and a sequencer. I have seen W0LMD' web site as well as several others. I want to start out slow, before I "lose it".
73 Bob W7LRD
"if this were easy, everyone would be doing it"
-------------- Original message --------------
From: Edward Cole <kl7uw at acsalaska.net>
> 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"
> >To: ; "AMSAT-BB"
> >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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