[amsat-bb] Antenna separation on crossboom

[Bob Hammond]

Thanks Jean Marc.  That is exactly the answer I was seeking.  I have 2m and
70cm CP yagis with RHCP.

Bob
W7OTJ

On Sat, Dec 15, 2018 at 7:44 AM Jean Marc Momple <jean.marc.momple at gmail.com>
wrote:

> Bob,
>
> So that all may fully understand:
>
> Most LEO’s use monopoles or dipoles (on VHF/UHF) which are actually linear
> and not circular polarization, but the birds are spinning and tumbling
> therefore the polarization can be H, V or any angle. If you use H or V pole
> at the ground station the fading may be as high at 30dB therefore it is
> recommended to use circular polarization at the ground station as maximum
> fade would be around 3 dB whatever the satellite polarization may be.
>
> I suggest that you use RHCP without polarisation switch, except if you
> wish to spend some money to experiment with same. I have the possibility to
> switch polarization but it is not used at all.
>
> Hope this help.
>
> 73
>
>
> Jean Marc (3B8DU)
>
> > On Dec 15, 2018, at 1:40 AM, Mark D. Johns <mjohns+K0JM at luther.edu>
> wrote:
> >
> > On Fri, Dec 14, 2018 at 10:58 AM Bob Hammond <propgrinder at gmail.com>
> > wrote:
> >
> >>> Do you use polarity switches on your yagis?  If you do, is it worth
> > the effort?
> >
> > No and no.
> >
> > I had polarity switching on long yagis back in AO-10 & AO-13 days and it
> > was helpful. But for the LEO satellites we have now, it's rare to have a
> > fade so deep that one can't copy.
> > --
> > Mark D. Johns
> > KØJM / MØGZO / ex-9H3DJ / ex-KØMDJ
> > Brooklyn Park, MN USA   EN35hd
> > -----------------------------------------------
> > "Heaven goes by favor; if it went by merit,
> >   you would stay out and your dog would go in."
> >    ---Mark Twain
> >
> >
> >
> > Greg,
> >>
> >>
> >> 73s,
> >>
> >> Bob
> >> W7OTJ
> >>
> >> On Mon, Nov 26, 2018 at 10:08 AM Greg D <ko6th.greg at gmail.com> wrote:
> >>
> >>> That's pretty much what I did, though with different antennas.  Also
> put
> >>> the AO-40 dish on the other side of the rotor from the 23cm helix, so
> it
> >>> went 70cm, 2.4gig, rotor, 23cm, 2m.   Put things as far away from each
> >>> other as you can, without running out of crossboom.
> >>>
> >>> I was very concerned about having the 70cm beam (uplink) so close -
> >>> inches - to the 2.4 ghz dish (downlink), but it was fine.  Good input
> >>> filtering in the 2.4 ghz Khune preamp, I guess.  More recently, Mode
> L/v
> >>> on AO-92 seems ok too, with the 23cm antenna near the 2m, but I have a
> >>> lot less power on 23cm than I did with AO-40 on 70cm.
> >>>
> >>> Greg  KO6TH
> >>>
> >>>
> >>> Bob Hammond wrote:
> >>>> I'm putting the following antennas on an 8-foot fiberglass crossboom:
> >>>>
> >>>> M2 2MCP8A, 143-148 MHz C{
> >>>> Gulf Alpha 70cm 8x8 CP
> >>>> WiMo Helix 23
> >>>>
> >>>> I'm not sure how to calculate the proper spacing on the crossboom.  I
> >>>> assume the 2m antenna should go on one end and the 70cm antenna on the
> >>>> opposite end.  Can I mount the 23cm helical antenna very near the
> >> rotator
> >>>> without harm since it has the solid reflector behind the helix?
> >>>>
> >>>> Bob
> >>>> W7OTJ
> >>>> (was WL7CQX)
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> >>>
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>