C-band Servo Polarity Mod

[John]

Great job John , how do you cover it from rain ?

... A valid point Wim, i will have to devise some sort of close fitting rain guard at the latter end of the build. The bearing joint has a silicone seal at the moment but i will try and bolster that up at some point.

 

[John]

.... a bit of a crude video of situation so far here:

Need to sort out the servo motor mount next. The servo motor had to be chosen to give 135deg travel to obtain the full H/V & L/R rotation travel needed.
The ASC1 positioner that used to rotate the probe in the 'Old Boy' works fine with this servo unit.

 

[Captain Jack]

Nice job! So it's an AVComm polarizer that's the long tube?

 

[John]

Nice job! So it's an AVComm polarizer that's the long tube?

Yep that's right, i had a spare tube but had to have it modded to make it usable for this project. A friend of mine has a massive lathe that accepted the poloriser barrel and he had to skim about 1mm off the outer front edge so as to accept the conical scalar and about half a mill off the single C-band feed barrel to fit inside the roller bearing . This job is basically a 'Cut & Shut' of the back end of the old servo poloriser

 

[nelson_b]

Hi -
I,m following progress in this thread with interest .. as i,m also using a CM 1.8
I purchased a - AVComm polarizer - to experiment with at the end of last year but with one thing and another and the bad weather... have only recently had the chance to play around a little ... comparing the AVComm to the various polarising plates that i,v used on the BSc421 l.n.b. that i currently use for circular on the 1.8 CM.
regards ....

 

[Captain Jack]

I also want to get an AV Comm polariser - I also have a Chapparal corotor thing. Not sure how/if I should/can combine the two to get me the best of both worlds (L/R and H/V)?

 

[John]

Hi -
I,m following progress in this thread with interest .. as i,m also using a CM 1.8
I purchased a - AVComm polarizer - to experiment with at the end of last year but with one thing and another and the bad weather... have only recently had the chance to play around a little ... comparing the AVComm to the various polarising plates that i,v used on the BSc421 l.n.b. that i currently use for circular on the 1.8 CM.
regards ....

The manufacturers say that it's the best way of obtaining L/R circular. Iv'e found it to be good over the years.

 

[nelson_b]

The manufacturers say that it's the best way of obtaining L/R circular. Iv'e found it to be good over the years.

I,m hoping so as it was not cheap ..
I Like the way you have coupled the wave-guide and l.n.b. to the AV-Comm -- re post 17 .
part of the reason its taken me some time to get to experimenting with it , is the odd internal and external diameters of the AVComm ... its taken me a while to couple the feed and l.n.b. to it ..
and make a suitable bracket to hold it in position for testing , with scope for some adjustments .
As its new to my 1.8 setup i,m reluctant to alter the AVComm in any way till i have some experience of it.
had it on the dish briefly but had to give up due to rain showers a few days ago.

 

[nelson_b]

I also want to get an AV Comm polariser - I also have a Chapparal corotor thing. Not sure how/if I should/can combine the two to get me the best of both worlds (L/R and H/V)?

That would be a interesting/massive piece of kit sitting on the front of the dish - C.J.

 

[John]

I,m hoping so as it was not cheap ..
I Like the way you have coupled the wave-guide and l.n.b. to the AV-Comm -- re post 17 .
part of the reason its taken me some time to get to experimenting with it , is the odd internal and external diameters of the AVComm ... its taken me a while to couple the feed and l.n.b. to it ..
and make a suitable bracket to hold it in position for testing , with scope for some adjustments .
As its new to my 1.8 setup i,m reluctant to alter the AVcomm in any way till i have some experience of it.
had it on the dish briefly but had to give up due to rain showers a few days ago.

Thankfully when i bought mine, it was so long ago that i can't remember what they cost Nelson lol. The one iv'e been modding was found up in the loft the other month when i was having a ferret about lol .
To be able to use mine i had no choice but to have it machined a bit to make the bits fit at either end of it. Re: the bearing coupling bit ..... it is possible to just have the single feed part slide into the input of the poloriser barrel without the use of a bearing if you wanted to keep the costs down but the construction & joining of the two separate parts , barrel and feed, has to be spot on as to not cause any metal contact or grating. If you need any costings & supplier details for the bearings, pipe coupler, small servo motor etc, just shout up if you decide to bite the bullet.
Can you post a few pics if possible of your AV-Comm from various points, would like to see if there has been any details or dimensions changed since i bought mine many moons ago
Cheers.

Edit: Just seen your post to CJ, you are right it does become a weighty bit of kit. Tomorrow i will add the servo motor to the unit and put it on some scales to get an idea of the total weight.

 

[nelson_b]

Thankfully when i bought mine, it was so long ago that i can't remember what they cost Nelson lol. The one iv'e been modding was found up in the loft the other month when i was having a ferret about lol .
To be able to use mine i had no choice but to have it machined a bit to make the bits fit at either end of it. Re: the bearing coupling bit ..... it is possible to just have the single feed part slide into the input of the poloriser barrel without the use of a bearing if you wanted to keep the costs down but the construction & joining of the two separate parts , barrel and feed, has to be spot on as to not cause any metal contact or grating. If you need any costings & supplier details for the bearings, pipe coupler, small servo motor etc, just shout up if you decide to bite the bullet.
Can you post a few pics if possible of your AV-Comm from various points, would like to see if there has been any details or dimensions changed since i bought mine many moons ago
Cheers.

Edit: Just seen your post to CJ, you are right it does become a weighty bit of kit. Tomorrow i will add the servo motor to the unit and put it on some scales to get an idea of the total weight.

The cost of the AV-Comm was almost doubled by the cost of carriage and import v.a.t ...

Thank you .... i may well get back to you at some point regarding - "costings & supplier details for the bearings, pipe coupler, small servo motor etc," if testing shows the AV-Comm to do well compared to my non standard plates
My other hobby takes up all the spare time i,v gained by retiring to part time work so it could be a while before i get to that stage ......

I will take some pics an measurements this week sometime ... looking at your pics though i t looks the same,
but you never know there may be slight changes .....

regards .....

 

[Captain Jack]

Hm, weight might be a concern. Is it worth just having AVComm on one LNB for L/R stuff and another LNB for H/V stuff? It's far less fun, of course, but less hassle? Especially as I don't have a controller to drive the servo.

 

[John]

Hm, weight might be a concern. Is it worth just having AVComm on one LNB for L/R stuff and another LNB for H/V stuff? It's far less fun, of course, but less hassle? Especially as I don't have a controller to drive the servo.

Yes agree with you CJ, it can be a headache deciding which way to go for the best that suits each individuals needs. I have done what you suggested above and it does work, see pics, it meant tho having to have the poloriser tube skimmed out front and back to make the bits fit.

Servo control can be a simple set-up and not mega expensive. Pic shows my little test set-up that i use.... cheap and cheerful off ebay, but i use my Titanium ASC1 positioner for the final set-up

Weight: Yep, another head scratcher ..... does one all in one unit that does H/V - L/R weigh the same as two separate units ?? .... decisions decisions lol

 

[scopus]

Will adding extra length to the wave guide not have a detrimental effect on signal? or have you already tried it?

 

[John]

Will adding extra length to the wave guide not have a detrimental effect on signal? or have you already tried it?

Good question, when you go onto either ADL or AVComm's web page it shows configurations like above..... can't say iv'e noticed any detrimental effects. For me, and with my dish installation being nearly 3mtrs off the ground , it's a convenience thing. Here's a pic of the commercially designed unit for H/V - L/R pol as it comes out of the factory that i used to use, as said before my little project is to bring the back end of it up to date a bit with a 'cut & shut' job to get a bit more efficient signal path into the lnb probe.

 

[John]

.... not done too much today on it .... waiting for some bits to come that will make up the coupling between the servo motor cog and the lnb cradle spindle, plus it's freezing outside !.
So knocked up the bracket that holds the servo motor, gave it a coat of primer and two top coats of finish paint. Pic shows roughly where it will sit and is at pre-paint stage.

 

[John]

Will adding extra length to the wave guide not have a detrimental effect on signal? or have you already tried it?

... This pic might be a bit more useful to people ..... This was originally used on my 2.2 Precision PF many moons ago.

 

[scopus]

... This pic might be a bit more useful to people ..... This was originally used on my 2.2 Precision PF many moons ago.

Carry on...............

 

[John]

.... a bit of paint applied to servo motor bracket

 

[RimaNTSS]

@John How do you fix servo motor in the bracket? Is it just stuck inside? Is not that little bit overkill with strength of the bracket for the motor? If you have exact drawing of needed bracket, I could try to make one out of 2mm INOX.