BATC Forum

I was using my LEO Bodnar GPS reference to do this, I took out one 27MHz crystal from an octagon dual PLL LNB and fed in the 27MHz directly. It works well but it would be nice to have it all integrated so you just send up 10MHz along with 12V. None of this 22kHz or 18V rubbish.

I have a few commercial PLL LNBs that do just that. I bought 3 at Newbury, two of them worked, one didn't. The problem with these is they are up at the top of the band ~11/12 GHz IFs so unsuited to EsHail Sat.

Mike

If you wanted to be very clever you could do it all in software if we are talking about the NB bent pipe.

I assume the German ground station is going to use a GPS locked reference for the
beacon so on receive you could correct the error in software.

Alternatively generate a very low signal at your end using the 10 MHz into a multiplier
and again do it in software. A little GNURadio project

G4GUO wrote: ↑

Sat Sep 29, 2018 9:11 am

If you wanted to be very clever you could do it all in software if we are talking about the NB bent pipe.

I assume the German ground station is going to use a GPS locked reference for the
beacon so on receive you could correct the error in software.

Alternatively generate a very low signal at your end using the 10 MHz into a multiplier
and again do it in software. A little GNURadio project

Nice of you to offer!

I think it has already been done a few years ago. (can't find the link though)

Just wondering about the Octogon OTLSO LNBs..they are, I assume, designed for offset fed dishes...how well will they perform in the middle of a prime focus one?
thanks
Graham G3VZV

Is it possible to tell if you have the old or new version of the OTLSO, without taking the screws out? Is the metalwork different?

Brian

G3VZV wrote: ↑

Tue Oct 09, 2018 12:47 pm

Just wondering about the Octogon OTLSO LNBs..they are, I assume, designed for offset fed dishes...how well will they perform in the middle of a prime focus one?
thanks
Graham G3VZV

Hi Graham,
as long as the prime focus has an f/D of 0.6-0.7 (typical for offset dishes) the feed cannot tell the difference as the perceived opening angle is the same. Most primes however, are lower in f/D which means you underilluminate the reflector and waste a few dB of gain. That said, as you aim for optimizing G/T at the end of the day, you might be still ok as the too-large reflector will better shield the LNB from rear side thermal noise.

73s Achim

Brian

If you are referring to how do you tell the difference between the "single 25MHz xtal" v "two 27MHz xtal" versions without undoing the screws. the 25MHz version only has one housing, on the top. The 27MHz version has two, one on top , one underneath, see enclosed picture in which the 25MHz xtal version is on the right, which also shows my BNC connector conversion

Dave
G4FRE

Thanks Dave. I wonder if anyone has done any comparative performance tests on 3cm between the two versions?

Brian

G3VZV wrote: ↑

Tue Oct 09, 2018 12:47 pm

Just wondering about the Octogon OTLSO LNBs..they are, I assume, designed for offset fed dishes...how well will they perform in the middle of a prime focus one?
thanks
Graham G3VZV

As discussed, the chances are your prime focus dish has a lower F/D. A value of 0.3 - 0.4 would by typical. This means the LNB will under-illuminate the dish. How much depends on the pattern but what matters is the area of dish illuminated so a first guess approximation would be the ratio of F/D is about 2:1 so its going to mean you are illuminating only the dish in that ratio, a 2m dish has the gain of a 1m dish -6dB. But not as simple as the LNB may well have a bit wider pattern to allow for alignment and ensuring the small dish is fully utilised. Also an under-illumined dish may be quieter - not seeing the ground behind it. I would say 3-6 dB loss.

An easy fix it to hacksaw off some or all of the LNB horn to widen it's beamwidth.