Odd signal results from Zinwell- AV-COM combination

[nelson_b]

Hi
I,v been playing with C band Zinwell- AV-COM combination on the 2.4 c.m. offset (without sub reflector) and comparing the results to the current setup on the 1.8 c.m. offset .

Started at 1 west with the two receivable transponders AFN 4175 R 28000 and BBC 3985 R 9764
2.4 cm -AFN 4175 R 28000 is good at 9.4 db ... 1.8 cm showing 7.4 db
the difference being about what i would expect from a larger dish.

2.4 cm - BBC 3985 R 9764 is a borderline lock at 3.8 db .. 1.8 cm is showing 6.5 db
i can improve things on this t.p on the 2.4 by rotating the l.n.b 180 degrees and get around 5 .0 db
not the 8 - 9 db i was expecting ?..... thinking i might have a faulty Zinwell l.n.b. i swapped it for another one , with identical results.
if i remove Zinwell- AV-COM combination and replace it with my trusty BSC 421 C band l.n.b. and vipersan style T plate, i get a decent 8.6 db from the bbc t.p. on the 2.4 cm

Moving over to 10 East to compare t.p results ... in general the transponders i can receive there are 1.5 d.b. up on the 2.4 c.m compared to the 1.8 c.m apart from 3721 L 1124
which gives me 7.9 d.b (locked) on the 1.8 c.m. and 0.0 d.b. on the 2.4 c.m. no matter how i skew the Zinwell l.n.b,s

Has anyone else had weak or missing signals with the Zinwell- AV-COM combination?
i cant believe i have two identically faulty Zinwells ?

Anyone got any thoughts on what is happening here ?

 

[scopus]

Hmmmm, perhaps they just don't like your 2.4 Nelson...lol

 

[s-band]

My first Z was unconditionally unstable. It manifest itself as a comb on the LO. That's confusing as signal strengths could be ok but there's no hope of demodulating anything.

The replacement Z was stable but I could see big noise peaks on the IF dependant on the input match. That suggests it is on the edge but OK. It is possible to get it to go unstable with a gross mis-match (a bit of metal in front of it). Perhaps your is being picky about the match presented by the polariser at certain positions? I can't see how the dish would change the match much though.

 

[blademedia]

Hi nelson, You could be locked onto a side lobe, try some more tweaking and try again.

 

[John]

... just checked here on my 2.2 Elite & Zinwell/AV-Com barrel nelson & locking ok with C/N averaging 9.8dB. Not checked the other freq yet, will have a look now

 

[John]

... just checked here on my 2.2 Elite & Zinwell/AV-Com barrel nelson & locking ok with C/N averaging 9.8dB. Not checked the other freq yet, will have a look now

... 4175 R is at 9.1dB at the mo on the 2.2.
Off now to have a look at 10°East

 

[John]

... 10° East, Quest Tv @ 3722 L. sr 1125 is 9.4dB at the mo on the 2.2 Elite nelson

 

[blademedia]

Are you using the same STB as nelson John, some boxes give high readings compared to others, I think you both have the cigarette packet.

 

[nelson_b]

Thanks for the reply,s folks ....

Further playing around this evening confirms that the Zinwells are not happy with certain frequencies on this dish setup ?
tried a number of other l.n.b,s on the AV-COM tonight at frequency 3895 R 9764
all were way better than the zinwell

BSC421 ... 7.5 db
ESX241 ... 8.2 db
Titanium ... 6.9 d.b.
Pauxis ... 7.3 d.b.

Had a look at 10 east too with the ESX241 and got a result at 3721 L 1124 .. 8.6 d.b.
so for circular the ESX241 looks to be the one for C band with AV-COM on this dish?

"Typical" as its the worst of the lot for linear at Paksat 38 E ...

the best one - would you believe, for C band linear with the AV-COM .....
is the Zinwell l.o.l

so there goes any chance of a one C band l.n.b setup + motorized skew on the 2.4

 

[John]

Are you using the same STB as nelson John, some boxes give high readings compared to others, I think you both have the cigarette packet.

Took my readings off EBSPro & Promax analyser, both gave same reading. There's def something amiss somewhere.

 

[blademedia]

Have you tried the LNB on the 1.8 nelson, that should answer a few questions, ive experienced the same thing in KU band I was locked on a side lobe in my case.

 

[nelson_b]

Have you tried the LNB on the 1.8 nelson, that should answer a few questions, ive experienced the same thing in KU band I was locked on a side lobe in my case.

Not with the AV-COM ... i use a Zinwell + conical feed on the 1.8 ..
(5 degrees offset) for " linear" as it gives the best results of any l.n.b. that i,v tried in that position on that dish .

 

[Captain Jack]

2.4 cm -AFN 4175 R 28000 is good at 9.4 db ... 1.8 cm showing 7.4 db
2.4 cm - BBC 3985 R 9764 is a borderline lock at 3.8 db .. 1.8 cm is showing 6.5 db

So, one thing that's definitely apparent (and it's not limited to Zin or 1W) is that different polarities require nudging of the dish. If I maximise AFN, I get 7.6dB but BBC is only 5.0dB. However, if I maximise on BBC at 6.7dB, I only get 7.2dB on AFN (F15 readings).

I don't know if this is limited to circular polarisation or C band but perhaps you need to physically move the dish a little between L and R? Another thought is that maybe the LNB isn't at correct focus, since you had to remove the sub-reflector (unless that's where the LNB is supposed to go?)...

 

[John]

So, one thing that's definitely apparent (and it's not limited to Zin or 1W) is that different polarities require nudging of the dish. If I maximise AFN, I get 7.6dB but BBC is only 5.0dB. However, if I maximise on BBC at 6.7dB, I only get 7.2dB on AFN (F15 readings).

I don't know if this is limited to circular polarisation or C band but perhaps you need to physically move the dish a little between L and R? Another thought is that maybe the LNB isn't at correct focus, since you had to remove the sub-reflector (unless that's where the LNB is supposed to go?)...

The last point you made CJ also crossed my mind as well. @nelson_b, can you take a quick pic showing how you have mounted the combo on the 2.4 lnb support arms please

 

[nelson_b]

The last point you made CJ also crossed my mind as well. @nelson_b, can you take a quick pic showing how you have mounted the combo on the 2.4 lnb support arms please

Hi John ...
Been out on the mountains all day today ...
its only a makeshift arrangement but it is solid ... will take some pics later ... i,v tinkered around extensively in the past few weeks to find the sweet spot .. mainly at 38 E as the few channels that i can get there are some of the hardest t.p.s to get, and hold a lock on for me here .. and i though i was doing ok ... til i started exploring some of the circular transponders l.o.l.

 

[nelson_b]

So, one thing that's definitely apparent (and it's not limited to Zin or 1W) is that different polarities require nudging of the dish. If I maximise AFN, I get 7.6dB but BBC is only 5.0dB. However, if I maximise on BBC at 6.7dB, I only get 7.2dB on AFN (F15 readings).

I don't know if this is limited to circular polarisation or C band but perhaps you need to physically move the dish a little between L and R? Another thought is that maybe the LNB isn't at correct focus, since you had to remove the sub-reflector (unless that's where the LNB is supposed to go?)...

Hi C.J.
Yes this dish .. as with the 1.8 requires a little nudging to maximise signals between the transponders at 1 west ... but it does not matter how much i re position the dish the Zinwell has issues with those certain frequencies on the 2.4 .. there may well be more that i,v not noticed yet ..... if i replace the Zinwell with the ESX241 those issues that i,v noticed disappear and i get a decent signal .... i will be trying the Zinwell/ AV-COM on the 1.8 at some point to see if the issues are present on that dish .... i,v had similar issues in k/u with c.m. feeds and C120 l.n.b,s on the 1.8 ... and just ended up fitting a twin black ultra and no longer had a problem ....

 

[nelson_b]

Hi -
Managed a few pics before the rain came last night ... as you can see the temporary support is made of timber with a coat of alum primer

here,s how the dish normally looks with the sub


I was hoping that i might be able to end up with an arrangement like i have on the 1.8

(which i,v been very happy with) but with just the one C band l.n.b + the AV-COM with a motorised skew
Most C band results have been good so far ... apart from the issues i found with the Zinwell /AV-COM setup,
My attempts to get good results from this dish in k/u without the sub have not been as good and i didn,t get anything better than on the 1.8 (mostly it was around equal ) when i spent an afternoon on it some weeks ago .... maybe the feedhorns i tried will only work properly through the sub reflector on this 2.4 c.m dish and that is how it will have to be .... not enough spare time to play with sat things so far this year... progress has been slow

 

[John]

... nelson, just looking at your lnb assembly, not 100% sure if it's in the right area. Never had any doings with a 2.4 CM offset so could be wrong. Does this picture off the net showing measurements of a 2.4 without sub reflector help you establish if your in the right ball park with yours.

Edit: Looking at it a bit closer i'm not 100% sure it's a CM as we know it with the joint running horizontal, the one in the pic seems to have a vertical joint
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[nelson_b]

Hi -
Thanks for the pic with measurements on ... its the first time i,v played with a 2.4 offset dish .... it may well be that the angle of the bottom arm on my dish needs to be different without a sub reflector? .. when i set up my l.n.b support i was working on the basis of the l.n.b probes being at the same spot as the central point of the sub reflector ... which indeed seems to work .. as any deviation from this point looses signal ... but its all quite experimental as this dish is supposed to use the sub reflector .. i wonder if its the same dish mould for both types of 2.4 .. (the one in the pic looks like a one piece) and just the arm support system is the difference ?

 

[Captain Jack]

@Feedsat_DXer ? Do you know if the arms are the same or different between the Gregorian and non-Gregorian varieties?

Pretty sure the mould will be the same.