Archived from groups: alt.video.satellite.mpeg-dvb (
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"Gary Tait" <classicsat@yahoo.cominvalid> wrote in message
news:vjsdg09e7snpest3lak60d0nksm8m7rugf@4ax.com...
> On Mon, 26 Jul 2004 22:19:38 -0400, Web Williams
> <Doncha@WishuKnew.com> wrote:
>
> >Right frequency, wrong polarization. They're circular,
> >and you want linear.
> >
> >-Web
>
> The polarisation is the easy part. Just yank out the dielectric plate
> or the wedge. The frequency 550 Mhz higher for DBS, so it will take
> some work to bring that down.
I believe the Ku10750 LO is spaced 500Mhz lower than the DBS/DSS 11250 LO.
It's possible to do a partial band conversion without much effort. The lnbf
(DSS) I choose for the experiment had a metal back plate held in place by
screws. Once inside I retuned the DRO by adjusting the LO set-screw. There
was sufficient range to allow me to lower the LO frequency by over 250 Mhz..
I choose 208Mhz because it provided the highest reading on my IF signal
testing meter connected inline at the lnbf. Further lowering the LO brought
more transponders into the 950 -1450 window, but at a sacrifice of IF signal
level and decreased quality overall. So 208Mhz was optimum without
modifying any RF circuitry. Six transponders (offset by 208Mhz) were
located on a blind search. The polarity was found to be reversed with the
lnbf mounted normally -- turning it 90 degrees would solve that problem.
Keep in mind that I am receiving Americas (Telstar) 5 transmissions using a
21-22" Dishnet 500 dish, significantly smaller than a standard 1 meter Ku
dish. Here are my results from west central Wisconsin on a clear day:
Tr27 12177 V--12385 H Mhz--quality 35% locked
Tr26 12152 H--12359 V Mhz--quality 20% locked
Tr25 12144 V--12353 H Mhz--marginal
Tr24 12122 H--12330 V Mhz--"
Tr23 12115 V--12322 H Mhz--"
Obviously the signal would be well in the green using a larger dish designed
for Ku reception. But this test proved it's possible to easily modify (5
minutes) an DBS lnbf to test KU reception on a small DBS dish with very
little work and no special tools. Of course, without a spectrum analyzer or
frequency counter, the blind search function made it quick and simple to
locate unknown shifted transponder IF frequencies. Also, it should be noted
that 15% of the lnbf scaler ring is missing due to another experiment in the
past where a modification was needed to fix a co-feed spacing problem. I
was using co-feeding 5 lnbf's on a Primestar dish where two adjacent
satellites were only 4 degrees apart. Some scaler had to be trimmed. DSS
lnbf''s don't fully illuminate the horizontally oval Primestar dish surface
anyway, so precision numbers don't really apply here. In the end it all
worked fine. Reinstalling the lnbf (with some of the scaler ring missing)
on it's original matching DSS offset dish probably diminished the gain due
to a distortion in the feed to dish illumination, but again, in the end it
worked surprisingly well - even with an added handicap.
-Dan
/www.adventistsat.com
fNNc.14130$BU4.772741@news20.bellglobal.com...
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