[amsat-bb] Re: brain picking time

Edward Cole kl7uw at acsalaska.net
Sat Aug 9 01:05:15 PDT 2008


The problem with using a helix is that you need to switch circular 
polarity back-n-forth on eme everytime you swich from Tx to Rx.  A 
helix is usable for only one sense of circular pol and near 
impossible to switch.  Two helices would be nearly impossible to wind 
on the same common axis like your dual band helical.  I strongly urge 
you to think about using a septum feed on 1296.

73 Ed

At 11:28 PM 8/8/2008, w7lrd at comcast.net wrote:
>Hello Domenico & all
>Thanks for all the information.    The measured F/D ratio works out 
>to 0.375, therefore a patch would be appropriate.  As mentioned 
>earlier I would be content to just be able to receive EME (for 
>now).  For transmitting no doubt a different feed would be 
>needed.  Currently I am looking around for a preamp.  I built a dual 
>helix feed I am going to use on a four foot primestar off center 
>dish.  I used  to receive on AO40  (sobsob) with a 3731AA 
>downconverter.  This same system will be used for transmitting (L 
>band) on our next HEO.  Maybe by  planning and working toward the 
>next HEO will generate more intense drive by all concerned.  I can 
>mount the 70 watt amp behind the 12 foot TVRO as suggested.  Could a 
>short helix be used for receive on the big dish?  They are easier to 
>build as opposed to a patch.  All this work (fun) will help fill the 
>void untill the next HEO.  Fr om what I am reading on the BB I could 
>be at this for a long time.  Any additional information would be 
>helpfull, perhaps others can get something out of this.  I have some 
>pictures of the dish, dual helix I can send upon request.
>73 Bob W7LRD
>"if this were easy, everyone would be doing it"
>-------------- Original message --------------
>From: "i8cvs" <domenico.i8cvs at tin.it>
>Hi Bob, W7LRD
>Before to start anyting you must to know the F/D ratio of your dish 
>because this parameter will tell you if a patch as
>a feed is suitable or not for it.
>If your TVRO dish is a prime focus dish to measure the F/D ratio is 
>very easy
>Put your dish horizontal on the ground  looking up 90 degrees and 
>strain a rope passing just through the center of the mouth and 
>measure the diameter D
>Measure the depth of the dish just from the center of the mouth 
>between the rope and the bottom of the dish and call the deepth  c
>                    D 
>                          D
>F/D = -----------------              and the focal point   F 
>=    --------------   from the bottom of the dish
>                16 x 
> c                                                                  16 x c
>If   the F/D ratio is less than 0.5 then a patch can be used but if 
>F/D is greater then 0.5 then a patch is not suitable.
>By the way a patch as a feed is not used at all for EME because 
>there are type of specialized feed that are much and much better.
>If the F/D ratio is less of 0.5 then a VE4MA feed can be used and if 
>the F/D ratio is greater of 0,5 then a dual mode dish  W2IMU must be used.
>Both VE4MA and W2IMU are dual port feeds one the LHCP is used to 
>transmit and the other one the RHCP is used to receive.
>Waiting for P3E and depending of the F/D ratio of a 5 meter dish 
>that I plan to build for 1296 MHz EME I have already  built both a 
>VE4MA and a W2IMU feeds  in order to be prepared for EME in the 
>future because unfortunately the future seems to be not bright for 
>the HEO satellites.
>73" de
>i8CVS Domenico
>----- Original Message -----
>From: <mailto:w7lrd at comcast.net>w7lrd at comcast.net
>To: <mailto:kl7uw at acsalaska.net>Edward Cole ; 
><mailto:domenico.i8cvs at tin.it>i8cvs ; <mailto:AMSAT-BB at AMSAT.Org>AMSAT-BB
>Sent: Wednesday, August 06, 2008 7:39 AM
>Subject: Re: [amsat-bb] Re: brain picking time
>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>
> > Domenico,
> >
> > 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 receive r
> > 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
> > > >g u ess 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
>; ; ; ; ; & gt;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
>&g t; & gt; ;
>&g t; >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
> >
>From:    w7lrd at comcast.net
>To:    "i8cvs" <domenico.i8cvs at tin.it>, "Edward Cole" 
><kl7uw at acsalaska.net>, "AMSAT-BB" <AMSAT-BB at AMSAT.Org>
>Subject:    Re: [amsat-bb] Re: brain picking time
>Date:    Sat, 09 Aug 2008 07:17:14 +0000
>Content-Type: Multipart/mixed;
>  boundary="NextPart_Webmail_9m3u9jl4l_3405_1218266937_2"
>From:    w7lrd at comcast.net
>To:    "i8cvs" <domenico.i8cvs at tin.it>, "Edward Cole" 
><kl7uw at acsalaska.net>, "AMSAT-BB" <AMSAT-BB at AMSAT.Org>
>Subject:    Re: [amsat-bb] Re: brain picking time
>Date:    Sat, 09 Aug 2008 07:09:09 +0000
>Content-Type: Multipart/mixed;
>  boundary="NextPart_Webmail_9m3u9jl4l_27280_1218266234_2"

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