Just Sharing This AV-Comm Polariser + Zinwell lnbf

[John]

The last time I did any ali casting was at school, Made a tootbrush holder....

I know where to come now for my next ali toothbrush holder .... trying to visualise what that must have looked like ?.

 

[scopus]

I know where to come now for my next ali toothbrush holder .... trying to visualise what that must have looked like ?.

Long gone...but remember making a mould, then melting the Ali in a furnace then pouring it into the mould, then getting the old bastard file at it....

 

[John]

Long gone...but remember making a mould, then melting the Ali in a furnace then pouring it into the mould, then getting the old bastard file at it....

..Language

 

[pride21]

hi all well i made a copy of a AV-COMM polariser went by the measurements on the forum but when i did a test against my home made plate it had very poor results,i hoped it was going to do well,here are some pics of the end result

 

[John]

hi all well i made a copy of a AV-COMM polariser went by the measurements on the forum but when i did a test against my home made plate it had very poor results,i hoped it was going to do well,here are some pics of the end resultView attachment 99964 View attachment 99965

Ok, interesting ..... a polarising barrel should give possibly up to 2dB performance increase over any inserted slab method.
Firstly, could you re-take some more pics at various angles but use the max resolution / file size that the forum will allow (1meg, or just a knat's under) as your first pics are not of any use to see close up detail of the steps or the scalar positioning on the barrel. To me, the steps don't quite look right or it might just be the low res pics to blame. Looking back a few posts to my drawings of my original AV-Comm barrel dimensions, are yours on your home brew the same to 1/2mm or so ? and could you please do us a drawing showing your dimensions.
Iv'e just finished a barrel that is for Extended C-band use, it uses a barrel with an internal dia of 60mm and it actually works better than the standard 3.4-4.2 GHz AV-Comm barrel at 62.5mm ID, but drops off performance wise as you tune down towards 4.200 GHz.
Wim (Trust) will throw a bit more light on it i think cos he had to do a bit of tweeking on his to get it performing to it's best.
It will be nice to get to the root of your problem though matey ;)
Edit: what dish type and size ?.

 

[pride21]

hi John my dish is a Gibby 1.5cm dish the main barrel is 203mm long from the front i measured 38mm to first step then 27mm to second step,the first step is 107mm long the second step 52mm long the gap between the second steps is 48mm the only thing different is the inside diameter of the tube is 63mm the whole lenth of the tube.

 

[John]

Thanks @pride21 , i can see that it is the reflections off the foil ? on the side steps that give a false impression of their actual size etc.
Tuning these modifications to obtain maximum can be a bit of a task .... iv'e just tried yesterday for many hours, tuning a cone scalar on my homebrew polariser for Extended Cband and failed. The Titanium stepped scalar turned out to be the better match for this particular barrel with just over 1dB better performance.
Your measurements seem to check out, it might just be a matter of a bit of fine tuning on the steps thickness measurements and careful scalar to barrel throat positioning as i have found this to be pretty critical to get maximum performance.
Are your top and bottom step arrangements running true to each other etc ?.
You might fancy to try these different step thicknesses by just a temporary lash up using sticky back ali tape to fix them in position.
Remember .... No Pain--No Gain lol.

 

[pride21]

hi John the plates are facing each other with exact measurements,if i make the steps thicker would the ideal gap between the second plates close in when trust said when you go below 47.5mm signal is no good or have you tried to bring them closer with better results.

 

[John]

Ok re: Wim's testing for the top and bottom step gap
... Just wondering, what is the metal thickness you have used of the flat bar used for the top and the bottom steps, were they the same thickness for both or was there the two different thicknesses used the same as the original ADL & AV-Comm barrels ? ... i would have thought using a 63mm ID tube with the step flat bar thicknesses for both steps of 6.5mm ish ..x 2 should leave a spacing in the region of 49.2mm ish from between top and bottom steps. AV-Comm told me that they thought the barrel's were not especially too frequency fussy so i would have thought you were in the right ball park

 

[pride21]

hi John i will do a bit of testing and try different things.

 

[Trust]

Found some time (and spirit) to do some tests , not particularly about the barrel but about the feedhorn .
Test done at 5º W with my 63 mm ID barrel at the 1.2 m Echostar offset dish with the Zinwell lnb .
To find the best signal I attached a special adjustment device for setting the focal lenght .
With this device I can also adjust the barrel in the conicle feedhorn .





Getting TP 3646 R with 8.2 dB
When I took away the conicle feedhorn , signal dropped to 5.2 dB
By moving the barrel with lnb 16 mm closer to the dish , signal increased to 5.7 dB



To get the best signal (7.5 d with the conicle scale I had to move the barrel and lnb 33 mm more to the dish .
Removing the plastic cover did bring the signal to 7.7 dB

So the focal lenght difference for max. signal between using feedhorn or scale is 49 mm at my setup .

Pulling back the Zinwell just one mm , signal was dropping , what would happen when it could deeper into the barrel ?
Making the Zinwell shorter would give me the answer but I did'nt do that (yet)
Later I changed the Zinwell for a Panorama lnb which performed allready a little better (locked on 3 TP's more )
Shortened that one with 5 mm and signal increased with 0.5 dB .
Being reckless , cut away another 5 mm but that failed , no progress , less signal .
Still wondering what would happen by shortening the Zinwell .

 

[John]

Found some time (and spirit) to do some tests , not particularly about the barrel but about the feedhorn .
Test done at 5º W with my 63 mm ID barrel at the 1.2 m Echostar offset dish with the Zinwell lnb .
To find the best signal I attached a special adjustment device for setting the focal lenght .
With this device I can also adjust the barrel in the conicle feedhorn .

View attachment 101185

View attachment 101177

Getting TP 3646 R with 8.2 dB
When I took away the conicle feedhorn , signal dropped to 5.2 dB
By moving the barrel with lnb 16 mm closer to the dish , signal increased to 5.7 dB

View attachment 101178

To get the best signal (7.5 d with the conicle scale I had to move the barrel and lnb 33 mm more to the dish .
Removing the plastic cover did bring the signal to 7.7 dB

So the focal lenght difference for max. signal between using feedhorn or scale is 49 mm at my setup .

Pulling back the Zinwell just one mm , signal was dropping , what would happen when it could deeper into the barrel ?
Making the Zinwell shorter would give me the answer but I did'nt do that (yet)
Later I changed the Zinwell for a Panorama lnb which performed allready a little better (locked on 3 TP's more )
Shortened that one with 5 mm and signal increased with 0.5 dB .
Being reckless , cut away another 5 mm but that failed , no progress , less signal .
Still wondering what would happen by shortening the Zinwell .

Woah, WoW .... haven't read the text and description yet, can't take my eye's off the pictures !.

 

[aceb]

Crunch time! Mum is off to Sydney on Wednesday for a month so before I commit what's the verdict on this combo? Direct comparisons over the ESX241 or Tit PLL, plate directly into a scalar would be most useful as that's my current set up.

 

[scopus]

Best combination for me...

 

[John]

.... Same here, for Cband iv'e tried various combinations of lnb / lnbf/ cone scalars / stepped scalars/ different feeds / dielectric plates / Co-rotors + servo etc etc and this has been the best performing set-up iv'e used after careful setup to the CM 1.8 offset dish. The additional skew mod is a performance bonus as well if looking at different birds scattered across the arc.
So .... no regrets here ;)

 

[aceb]

Well that's ordered, I'll order a servo later and knock up a manual controller for it. Is there a link to one of the Latvian cone scalars that's mentioned a few pages back, I can't find any info on them and wonder if there are any suitable for PF dishes?

 

[John]

Well that's ordered, I'll order a servo later and knock up a manual controller for it. Is there a link to one of the Latvian cone scalars that's mentioned a few pages back, I can't find any info on them and wonder if there are any suitable for PF dishes?

Cone link here .... Extra cone with Cap for С-band (65 mm), improves reception quality by 8-25% | eBay

Generally used on Offsets, never tried one on a PF .... might be worth popping one on just to see exactly how it fairs

 

[aceb]

I've messaged the seller, will see what he says.

 

[Trust]

improves reception quality by 8-25% ?????
Maybe in case you used first a bare lnb , but not when you use a conicle scalaring .
See the test I made at posting # 251
5º West TP 3646 R signal with :
Conicle scaling feedhorn 8.2 dB
Cone scale with plastic cover 7.5 dB
Cone scale without cover 7.7 dB

 

[John]

Due to really not very nice outside working conditions, decided to tidy up the appearance of the servo skew / polarity controller today making it look a bit tidier on the desk