C-band Servo Polarity Mod

[John]

Been playing about a bit again to come up with a lighter version of my Cband -H/V * LHC/RHC servo motor driven combo unit to take some weight off the front of the dish.
Iv'e been evaluating the performance of individual units for motorised H/V only feed, fixed LNBF + AV-Comm poloriser barrel for L/R and the new lightweight version of a previous build for a H/V-LHC/RHC combo unit to hopefully just use the lighter single motorised combo unit.
To cut a long story short, the combo gives very good results and so gets the job.
A few construction pics ......

 

[Captain Jack]

If you ever feel like selling the av comm polariser, let me know.

 

[moonbase]

There are some ADL single LNB C Band feeds with polarotor listed for sale on eBay. The seller has 9 of them available but it is shipping from Canada. ADL were taken over by Viking SatCom who supply Elite Antennas (Precision) with C Band feeds. On that basis I would assume that they are a decent quality product.

ADL C-band Feedhorn Feed Horn SAPM90 C Band cband PM90

If anyone was interested it might be worth considering a small group buy to see if the shipping costs could be reduced? For offset focus dishes, the scalar ring can easily be replaced by a conical ring.


UPDATE:
I have sent a message via eBay to the seller asking about purchase of multiple units and combined shipping. I will possibly get one for myself anyway.

 

[John]

@MB , I came off that type of unit due to reduced efficiency of the signal path through the device. Granted, it along with the poloriser barrel gave me H/V - L/R from one unit along with skew control which is a good thing, but compared to more modern approach it was not as good. Ok if you had a 2.2mtr or greater as you could afford a bit of loss, but on a 1.8 or smaller you could be missing some transponders. See post 1&2 for reasons given. The pic of mine in post 2 is still sitting in the workshop doing nowt along with spare servo's, (not the poloriser barrel) doubt i will ever use it again.

 

[moonbase]

@MB , I came off that type of unit due to reduced efficiency of the signal path through the device. Granted, it along with the poloriser barrel gave me H/V - L/R from one unit along with skew control which is a good thing, but compared to more modern approach it was not as good. Ok if you had a 2.2mtr or greater as you could afford a bit of loss, but on a 1.8 or smaller you could be missing some transponders. See post 1&2 for reasons given. The pic of mine in post 2 is still sitting in the workshop doing nowt along with spare servo's, (not the poloriser barrel) doubt i will ever use it again.

John,

Many thanks for your feedback, it is very useful, more than likely saved me some money.

I noticed that you had a 2.2m Precision antenna at one point until it was very unfortunately damaged in a storm. I have a question about this type of dish if you can please help? Would a 3mm gap on a "string test" for a Precision 2.2m antenna detract much from its C Band performance? For Ka band it would have a big impact, however at the lower frequency of C band I am not sure how much impact it would have on the performance of a 2.2m Precision?

Thx

 

[John]

John,

Many thanks for your feedback, it is very useful, more than likely saved me some money.

I noticed that you had a 2.2m Precision antenna at one point until it was very unfortunately damaged in a storm. I have a question about this type of dish if you can please help? Would a 3mm gap on a "string test" for a Precision 2.2m antenna detract much from its C Band performance? For Ka band it would have a big impact, however at the lower frequency of C band I am not sure how much impact it would have on the performance of a 2.2m Precision?

Thx

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Your welcome, Re: the 2.2 .... in theory the short answer is yes but i would agree with how you described it. I think i only strung mine once and if i remember correctly it had about a two mm gap. I wasn't too much worried about it because i mainly used that dish on Cband and used a 1.2CM offset for Ku.
Now .... my 1.8 CM which i run C / Ku / Ka on had a 2mm or so string gap before i did some rear bracing and i did notice a slight performance gain on Ku & Ka after i braced the back and took out the gap, can't say i noticed any dramatic change on Cband though.
Have you got a 2.2 Precision then ?? .... i loved mine_ better than i do the 1.8CM but the CM is so much more versatile for doing multi band lnb gadgets

 

[moonbase]

Have you got a 2.2 Precision then ?? ....

Yes, I will have a Precision 2.2m antenna once I get it back here from its current location. I have already got the other bits back here that go with it, ie, the original Precision galvanised tripod ground stand with 4.75" pole and the original galvanised heavy duty polar mount for it. The dish has rear heating panels and I also have the controller box for those. However, I am not sure if I am going to install it due to the 3mm gap on the string test. I need to repeat the test with fishing rod line to get a better idea of how far it is out. The last time I string tested it I used some green garden twine so my estimate of 3mm could be open to variation.

If I thought I could pul it back into shape I would give it a go but it might not be that easy as it has the reinforcing circular steel ring around the rear periphery of the dish.

 

[John]

Yes, I will have a Precision 2.2m antenna once I get it back here from its current location. I have already got the other bits back here that go with it, ie, the original Precision galvanised tripod ground stand with 4.75" pole and the original galvanised heavy duty polar mount for it. The dish has rear heating panels and I also have the controller box for those. However, I am not sure if I am going to install it due to the 3mm gap on the string test. I need to repeat the test with fishing rod line to get a better idea of how far it is out. The last time I string tested it I used some green garden twine so my estimate of 3mm could be open to variation.

If I thought I could pul it back into shape I would give it a go but it might not be that easy as it has the reinforcing circular steel ring around the rear periphery of the dish.

reinforcing circular steel ring around the rear periphery of the dish.

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That strong outer ring though could be a bonus to you as an attachment point x 4 back to the rear central circular tube ??.... might work, never tried it though.

 

[John]

.... Anybody that is into C band projects and does not mind waiting for six to seven days or so can order these single feeds from our Chinese supplier friends for a fraction of the costs from elsewhere.
This pair was £30 all in.

 

[Captain Jack]

Hey John, I have some newbie questions on this. I have a Chaparral Corotor II thingamajib but... will that give me a better performance having a corotor choosing the polarity (very 80's!) than a bog-standard Titanium LNB in linear?

Also, another one... I would like to have a better reception of circular polarity. At the moment I am using a @pride21/@dx qwer plate, which works OK but feel that I am missing out on a dB or two here and there. The obvious choice is an AV-Comm barrel with a Tit LNB stuck in there but can I do anything with the above corotor to merge it into a both linear and circular solution? Not that I really need it because of LNB rotator but...

My really weak understanding is what a corotor is capable of (other than selecting polarity mechanically and adjusting skew) - especially with regards to circular polarity.

 

[Captain Jack]

Further - am I correct in thinking that with a corotor, rotating the AV Comm barrel at 90 degrees relative to the probes will convert it to linear and 45 degrees to circular?

 

[John]

Hey John, I have some newbie questions on this. I have a Chaparral Corotor II thingamajib but... will that give me a better performance having a corotor choosing the polarity (very 80's!) than a bog-standard Titanium LNB in linear?

Also, another one... I would like to have a better reception of circular polarity. At the moment I am using a @pride21/@dx qwer plate, which works OK but feel that I am missing out on a dB or two here and there. The obvious choice is an AV-Comm barrel with a Tit LNB stuck in there but can I do anything with the above corotor to merge it into a both linear and circular solution? Not that I really need it because of LNB rotator but...

My really weak understanding is what a corotor is capable of (other than selecting polarity mechanically and adjusting skew) - especially with regards to circular polarity.

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Bare with me CJ, iv'e got some answers but they are accompanied by pics that are in other threads somewhere .... errr, no there not, they are in post 2 onwards in this thread.
Basically the signal transfer / path from the mouth of the cband feed, onto the rotating pick-up probe, transfered passively through the transfer chamber, through a right angle bend if it has one and then finally making it to the pickup probe on the attached lnb is fairly lossy ..... we can't afford that, as you know, on our piddly little dishes if it's the weak hard to get TP's we are after. I gained around 3dB from dumping the old school polorotor to going to the shortest signal path route possible, which again is shown in the early posts. There is nothing extra than changing the polarity on the old school polorotor unless you can get hold of one that has the built in poloriser barrel, (rare as hens teeth) then you add the possibility of going H-V-LHC-RHC with more effeciency than using a plate but still having the signal losses as described before. Extracting the last tiny drop of signal/performance 'aint easy going .... takes a lot of blood sweat and tears (ask VS), and some will say it's just not worth the hassle which is fair enough. Easiest solution is to go up to 2.4mtr and upwards dishes ...... in our dreams for most of us.
Re: using Tit's or any lnbf with whatever pol plate is a fairly easy and quick painless solution that give's good results but again it's a bit of a compromise and for 90% of the signals coming in is a good choice .... snag is , it's that other difficult 10% that will be the problem.
My favourite motto's ?? .... "No pain-No Gain" & "Where there's a will, there's a way" ..... never let me down for 80% of the time.
Sorry i can't be of any more use Alex , I'm still on a learning curve here myself ... which prompt's another fav saying--"Your never too old to learn"

 

[John]

Further - am I correct in thinking that with a corotor, rotating the AV Comm barrel at 90 degrees relative to the probes will convert it to linear and 45 degrees to circular?

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No, the poloriser barrel stops in a permanent position, it's the physical orientation of the probe determined by the servo motor that gets you the polarity shift. My old one used to run as follows-- probe (as in the last pic) vertical for V sigs, probe horizontal for H sigs, probe at 45deg for L circular & the opposite 45deg for R circular

 

[John]

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No, the poloriser barrel stops in a permanent position, it's the physical orientation of the probe determined by the servo motor that gets you the polarity shift. My old one used to run as follows-- probe (as in the last pic) vertical for V sigs, probe horizontal for H sigs, probe at 45deg for L circular & the opposite 45deg for R circular

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I should also say that another point to mention on the old school polorotor is the ability to adjust skew which can be very beneficial.

 

[John]

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No, the poloriser barrel stops in a permanent position, it's the physical orientation of the probe determined by the servo motor that gets you the polarity shift. My old one used to run as follows-- probe (as in the last pic) vertical for V sigs, probe horizontal for H sigs, probe at 45deg for L circular & the opposite 45deg for R circular

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This is the kind of thing to look out for CJ, rare and need work on them to release the barrel but should be a lot cheaper than buying a brand new barrel.
This was one i used years ago on my 2.2mtr PF.

 

[Captain Jack]

Thanks John - it's a bit of a learning curve for me. Having re-read your thread with my brain in gear, it makes a bit more sense.

So, I could do either of the following:

1) Get an AV-Comm barrel for circular, stick a Tit LNB in (or some other?) and be done with it. Will need to machined to fit standard sizes..somewhere (will your friend be able to do that?). Leave linear as is.
2) As above but convert linear to a single polarity arrangement with a servo motor - probably salvaged from Corotor II monster.
3) Merge 1 and 2 together to create a single feed to cater for all polarities - a lot of work!

Another issue I have with servo is lack of cabling for it, for which I understand you need 3 wires. Can probably steal a couple of those from my actuator, though.

John, what signal level (or rather SNR) differences do you have between the above? Especially with number 2...? Also, is there a way to automate this for each polarity? ASC1 is expensive.....

 

[John]

Thanks John - it's a bit of a learning curve for me. Having re-read your thread with my brain in gear, it makes a bit more sense.

So, I could do either of the following:

1) Get an AV-Comm barrel for circular, stick a Tit LNB in (or some other?) and be done with it. Will need to machined to fit standard sizes..somewhere (will your friend be able to do that?). Leave linear as is.
2) As above but convert linear to a single polarity arrangement with a servo motor - probably salvaged from Corotor II monster.
3) Merge 1 and 2 together to create a single feed to cater for all polarities - a lot of work!

Another issue I have with servo is lack of cabling for it, for which I understand you need 3 wires. Can probably steal a couple of those from my actuator, though.

John, what signal level (or rather SNR) differences do you have between the above? Especially with number 2...? Also, is there a way to automate this for each polarity? ASC1 is expensive.....

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Can't use the servo motor from the polorotor CJ as it's just not got enough balls to rotate anything else bigger than the piddly original probe.
The ASC1 firmware does not like a servo motor too much like the ones i'm using now on my projects ..... it makes it crash too easily and if you had filled the ASC1's data base up with channel info it lost all that as well.
A TiT + barrel will only gain you about 1dB or so extra over a TiT with just a standard or custom slab inserted but the cost difference between the two set-ups is substantial.
Also, TiTs seem to have different performance figures depending which probe is in use .... so the weak TP your after might have to be set up on the strongest performing probe which will then make it a non-conventional set-up possibly.
A TiT + barrel once set up and secured in place will only give you either LHC or RHC depending which probe is used .... to squeeze some V or H out it would require you to go outside to it and physically do a bit of reorientatation ?? of the parts which would be a b*l* ache.
My findings after weeks and weeks of trying this, that and the other, I'm running a version of your No1 just for circular but constructed to squeeze absolute maximum out of it. Ie, a single lnb / servo motor to swing the lnb from LHC to RHC. It will resolve H & V sigs by having the lnb either horizontal or vertical but the performance on H/V is about 1/2 dB down. A bit anal i know.
For H + V i use a separate set up same as above but without the barrel. This has at least 1dB or a tad more performance over any lnbf configuration i have tried and up to 3 dB better than the old school polorotor set-up. Both my systems also give me control over the important skew settings.
Very careful lnb set-up, alignment etc is required as you know, to get the absolute maximum out of the system.... for what it's worth, i set up my Cband lnb's like this, which has worked pretty well for me: ... .. ... ... Remove conical scalar and tune lnb for focus / max signal strength level either with meter or receiver display and also take note of what SNR / Quality reading you have. Carefully slide on the scalar and adjust back or forth to obtain maximum SNR + strength. It should reap a benefit.

 

[Captain Jack]

Thanks John. I am a bit disappointed with the gain you would get with the barrel on circulars without the rotor control. Hmm... I wonder if the Tit is not the best LNB for this and I should try a different one.

I think this is a bit too much for the moment! Labour-wise. Might still invest in the barrel just for kicks... expensive ones.

This is all very helpful, John so maybe when I am bored one day, I'll try this.

 

[John]

Just noticed this fella in Latvia selling these cone scalar's again for Cband use, this time with rain covers. Had one before without cover for evaluation and on my 1.8 CM i did get around 3/4dB C/N than the usual stepped cone scalar with a bit of careful tuning. Smaller and lighter as well.
Had a couple to do a bit of experimenting with as an "insert" to go inside a Titanium stepped scalar ??

 

[scopus]

Got one on the tit for the aero stuff, worked better than the convential scalar, more suited to the sub reflector on the Greg methinks