How about a Chapparal C-Band OMT with "studs"?

[paulvr]

Hi,

I have an opportunity to buy a secondhand Chapparal OMT feed for C-Band with two 17 K LNB's that is meant to be used for linear C-Band reception. So horizontal and vertical.

However, I live in Europe where just about all C-Band satellites of interest to me broadcast in circular mode, LHCP and RHCP.

At present I use a very good CalAmp feed that was recommended here as being superior to the Chapparal feed and a Norsat C-Band LNB type 8515, again, recommended to me here.

The disadvantage is of course that I need to use an old analog Echostar receiver to change polarizations, the advantage is that I can use the skewing option for the most perfect signal. But it sure would be attractive if I no longer needed to skew or change polarity manually.

Now I don't know how this is seen in publications from the USA, but here lately people use what's called a "studs" solution als an alternative to using a dialectricum like I do to get circular polarized signals. But it seems to me that using a dialectricum on a fixed OMT with two LNB's wouldn't work.

Normally this solution is carried out rather rudimentarily by sticking a plastic bottle with studs at exactly calculated positions into the feed. However, the person who figured this out old me that although theoretically this should also work with a dual LNB OMT like this (the seller speaks of a Bull OMT but I don't find this back in that context) he also told me that he is not aware that anyone ever was able to apply this studs-solution succesfully in such a system, that he only knows it to work in a regular feed.

Can anyone tell me what's wisdom? An extra complication is that the guy wants to sell the OMT without the matching scalar rings because he wants to use those himself for another project. I know of two types of Chapparal scalar rings (one type had deeper rings than the other) which of course complicates the issue even further for me.

Should I risk it and buy, or should I not mess with a good working system and accept that polarity is something that I juist have to do manually with a separate contraption? Or is there such a thing as a dual C-Band LNB system that's made for circular and linear polarization? What's wisdom in this matter, I hate to buy gear for good money that ends up in the trash can or tool box...

 

[SatPhreak]

There is a feed horn I've seen before that does circular and linear but I don't remember what brand it is. You can try using a teflon block in the feed horn. Most of the the cband lnbf's sold over here come with a teflon slab that goes into the feed at 45 degrees to the probes and turns the lnbf from linear polarity into circular polarity.

 

[paulvr]

Dear Satphreak,

Thanks for your response. However, finding a C-Band feedhorn with a teflon dialectricum isn't the question, I own several of those. The question is if there is what to do if you want to have an OCS system, in other words a system with two LNB's using 5150 and 5750 MHz that is meant to set horizontally and vertically polarized stations in one band on your receiver EXCEPT that in our area it shouldn't be horizontal and vertical but LHCP and RHCP.

That's the question! Using a dialectricum is based upon a moving dipole in your feedhorn but an OCS system depends upon two dipoles, one horizontal and one vertical that in principle operate simultaneously. A studs system to receive both circular polarizations might work, at least in theory, but so far I found no evidence at all that it indeed has been applied succesfully anywhere.

That´s the basis of my question. Is it applied anywhere, and moreover, is it commercially available anywhere?

 

[FaT Air]

A dielectric plate will/should also work in an OMT. IIRR. Should be able to 'put it in there'. At least 'take a look see', can't (at least - don't think) hurt anything, by trying it. http://www.chaparral.net/feed-horns/dual-feed-with-dielectric-plate/
Or contact Chaparral and inquire if the 'without' can be retrofitted to 'with'.
http://www.chaparral.net/feed-horns/dual-feed/
Other than using a dielectric plate I do remember seeing some other brand that had like 4 or 6 studs between the probes and the feedhorn opening which enabled reception of circular polarization. Problem is could never find the 'math' it takes to 'figure' said studs size or placement. Wonder if it wasn't Seavy????

 

[FaT Air]

At present I use a very good CalAmp feed that was recommended here as being superior to the Chapparal feed and a Norsat C-Band LNB type 8515, again, recommended to me here.

The disadvantage is of course that I need to use an old analog Echostar receiver to change polarizations,

Have you looked at the ASC-1 from Titanium Satellite? ( being that the polarotor has been recommended as superior to the OMT)

 

[paulvr]

A dielectric plate will/should also work in an OMT. IIRR. Should be able to 'put it in there'. At least 'take a look see', can't (at least - don't think) hurt anything, by trying it. http://www.chaparral.net/feed-horns/dual-feed-with-dielectric-plate/
Or contact Chaparral and inquire if the 'without' can be retrofitted to 'with'.
http://www.chaparral.net/feed-horns/dual-feed/
Other than using a dielectric plate I do remember seeing some other brand that had like 4 or 6 studs between the probes and the feedhorn opening which enabled reception of circular polarization. Problem is could never find the 'math' it takes to 'figure' said studs size or placement. Wonder if it wasn't Seavy????

Hi,
Thanks for your reply. Let me give some responses:

1. Take a look or trying don't hurt are nice thoughts for after I've bought the darn thing. My prime question is if it's worth the money and if it's smart to want to change the National ADL RP1C dual hybrid mode feedhorn with a Norsat 8515 LNB for a Chapparal OMT with two 17 K eagle LNB's considering the fact that I live in an environment where linear signals are of little importance and circular are of great importance. Please note that an original Seavey or Chapparal C Band system including the factory-supplied teflon slab does take away around 2,5 dB of any linear signal. And also please note that where our experiments with stubs so far have resulted in a much lower loss in linear signals but much less gain on circular. It's a devlish choice for the moment and I have no idea what a dual C-Band LNB system will amount to, problem of course is that where systems with teflon slabs are factory supplied and tested, I know of no commercial product using stubs so all is experimentally done by hobbyists who aren't able to do any testing under lab conditions.

2. I am more than a little surprised to be referred to the Chapparal company. I was told that they had gonbe bankrupt many years ago because they weren't able to handle the switch from analog to digital. At least in Europe all of their reps had to close down as well simply because there was nothing left to sell. Did someone pick up the pieces and start a new firm under the same name, or was I misinformed about their demise?

3. To get back to the original question: my basic problem is that there are ways to get my system to turn on a USALS-interface based system but it would be so very nice if i could also use a regular receiver, any digital receiver, if only I hadn't had the problem of the 4 polarities (two linear, two circular). The owner of the Chapparal OMT (which he refers to as the Chaparral Bull) said that using a matching teflon slab had deteriorated the signal way too much. But he also mentioned using just one set (line) of stubs instead of two and that this meant that one polarity was missing but that he did that in order to not loose too much signal on other (I presume linear) signals. My experiences with stubs in my feed mentioned above is that it indeed improves linear signals a lot (only 0.4 dB loss instead of 2.5) but that you pay by getting a lot less circular polarized signals. (a loss that's more than 3 dB). I also don't know how much signal loss may occur by changing my present ADL RP1C feed back to a Chaparral feed. Buyingh something for the trashcan is not something I can easily afford.

 

[paulvr]

Have you looked at the ASC-1 from Titanium Satellite? ( being that the polarotor has been recommended as superior to the OMT)

Yes I have, I even last year considered reviewing it as I work for a range of publications but once it finally became available on the market I read about a load of problems and firmware update after update in order to cope with the problems, also read some rather negative reviews from Britain and decided that it didn't seem wirth looking at. It's getting more and more fashionable nowadays to first start selling a product and then later to start working on the operating software. I'm rather tired of this.

Same thing about their PLL based C-Band LNB. At first I decided to wait because of it's lack of bandwith, and then later I read some tests in which it appeared that they werent any better than conventional C-Band LNBF's. At least not within an environment where one uses mostly circular signals and where the frequencies used start at 3400 MHz.

Please tell me if you feel I'm wrong. It just didn't seem the best way to go.

 

[Titanium]

Paulvr,

You obviously are looking for solutions and Titanium Satellite offers some very unique solutions that perform very well. I understand that Titanium Satellite products may not be suitable for your needs. I stand by our quality products, specifications and independent testing results 100%. We continually work to improve our products based on customer testing and comments. Contrary to your statement, ASC1 firmware releases have been primarily to add function and features, not to address issues.

Appreciate that you are a tester and reviewer and would think that you would like to test them for yourself and provide feedback and review of our products. I am not aware of any negative UK reviews. I do understand that a few users increased the circular performance by using modified dielectric inserts and we have been offered to use one awesome design in a future release! Maybe you would be kind enough to contact me and share these reviews? I invite you to contact me and share any input that you might offer to make Titanium Satellite products even better.

Thank you and best wishes for a optimal circular C-band solution!

 

[paulvr]

Paulvr,

You obviously are looking for solutions and Titanium Satellite offers some very unique solutions that perform very well. I understand that Titanium Satellite products may not be suitable for your needs. I stand by our quality products, specifications and independent testing results 100%. We continually work to improve our products based on customer testing and comments. Contrary to your statement, ASC1 firmware releases have been primarily to add function and features, not to address issues.

Appreciate that you are a tester and reviewer and would think that you would like to test them for yourself and provide feedback and review of our products. I am not aware of any negative UK reviews. I do understand that a few users increased the circular performance by using modified dielectric inserts and we have been offered to use one awesome design in a future release! Maybe you would be kind enough to contact me and share these reviews? I invite you to contact me and share any input that you might offer to make Titanium Satellite products even better.

Thank you and best wishes for a optimal circular C-band solution!

Dear Brian,
Thank you for your response, I just sent you a reply via your company address.

 

[FaT Air]

Circular C band polarizer - AVCOMM

This waveguide polariser uses integrated waveguide steps to achive polarisation conversion, achieving 2.5dB better efficiency than a dielectric plate.

Don't have a clue where they are available locally. The company looks to be Australian. 2.5db better efficiency could be HUGH.

 

[paulvr]

Circular C band polarizer - AVCOMMDon't have a clue where they are available locally. The company looks to be Australian. 2.5db better efficiency could be HUGH.

You're right, it's Australian, I am aware of this product. Some time ago an East German company took orders for this product but at that time not much was known about it and the price was nothing short of exorbitant. Perhaps as a reviewer I could have gone after this product but there must me a certain ratio between cost and value in order to be able to recommand it to any of my readers. At this point I can't remember the price that was asked but to the best of my memory it was at least double and maybe even triple that price.

Looking at the (assumed) simplicity of the product it seemed to me that if it were any good it was very likely that someone would come up with a similar idea at a more realistic price. But alas, I guess I was wrong. At least for the moment.

 

[Trust]

Circular C band polarizer - AVCOMMDon't have a clue where they are available locally. The company looks to be Australian. 2.5db better efficiency could be HUGH.

Here a posting from me from jan. 2013 at satellites.co.uk


A heavy discussion about receiving C-band on a Triax 110 cm offset dish on a dutch board , make do again some tests on C-band .
Also the fact that I have another LNB : Panorama 13º
Receiving already pictures at 20E , 2E , 5W , 11W , 40.5W
Bad performing for Hor and Vert TP's by the dielectric plate is common known .
The AV-COMM polariser would be a better (Also for Circ. TP's) but expansive option ,

looking for alternatives on several boards brought me this idea .
I took the half part of a juice bottle , burned (with my smoking iron) at both sides in a vertical line 4 holes .
In each hole i put a 4 mm aluminium rivet ( took the steel pins out) 4 rivets of 12mm and 4 of 16 mm long , sealed the outside with Tesa transparant tape .
The greater bottom reaches out and give me the opportunity to twist it for maximum result .
Testing at 5 west the signal improved at TP 4.137L (SLBC TV) with the DE plate 83/72% and now 88% signal / 79% quality
With a new scan i found 1 more channel there , all the other sat positions i still have to do .


Later I find out that a 2 x 5 rivets gave a bit more profit .

 

[beavs2112]

My prime question is if it's worth the money and if it's smart to want to change the National ADL RP1C dual hybrid mode feedhorn

was I misinformed about their demise?

The owner of the Chapparal OMT (which he refers to as the Chaparral Bull) said that using a matching teflon slab had deteriorated the signal way too much.

hi paulvr. greetings from a Canadian sat hobbyist Chaparral is still in business I think,

Im my opinion it would be a waste of money replacing your CalAmp (ADL) feedhorn. There seems to be somer confusion as to what feed (omt) the seller is referring to. This one http://www.chaparral.net/feed-horns/dual-feed-with-dielectric-plate/ or the Chaparral Bullseye

the Chaparral Bullseye OMT came in 2 versions - the Bullseye 1 which is a 3 port (for polarity) 2 Cand linear & 1 linear ku that uses a rotor for h&V. http://www.satellitedish.com/cata0056.htm scroll down to see the bullseye 1

the second version is the Bullseye 2 which is 4 ports 2 - c & 2 - ku. I have one by the way. To achieve circular on a Bull 2 a dielectric slab is used.

now ADL (who made your feed for CalAmp) made a circular c band feed that used a metal 1/4 wave plate cast into the throat of the feed. http://adlfeed.com/cat_sec_1_4.htm I am not sure if they are available anymore or price.

Regards,

kevin

 

[FaT Air]

http://www.ok1dfc.com/EME/Technic/septum/sept IEEE.pdf
http://www.ok1dfc.com/EME/Technic/septum/calc.xls

 

[paulvr]

hi paulvr. greetings from a Canadian sat hobbyist Chaparral is still in business I think,

Im my opinion it would be a waste of money replacing your CalAmp (ADL) feedhorn. There seems to be somer confusion as to what feed (omt) the seller is referring to. This one http://www.chaparral.net/feed-horns/dual-feed-with-dielectric-plate/ or the Chaparral Bullseye

the Chaparral Bullseye OMT came in 2 versions - the Bullseye 1 which is a 3 port (for polarity) 2 Cand linear & 1 linear ku that uses a rotor for h&V. http://www.satellitedish.com/cata0056.htm scroll down to see the bullseye 1

the second version is the Bullseye 2 which is 4 ports 2 - c & 2 - ku. I have one by the way. To achieve circular on a Bull 2 a dielectric slab is used.

now ADL (who made your feed for CalAmp) made a circular c band feed that used a metal 1/4 wave plate cast into the throat of the feed. http://adlfeed.com/cat_sec_1_4.htm I am not sure if they are available anymore or price.

Regards,

kevin

Thank you very much for all this information, Kevin. I'll pursue the matter and let you if I get any results. The owner of the aforementioned OMT appears to be willing to come to our place so we can do some comparisons, my very good friend friend Trust who wrote the information above brought me a sample of the studs juicebottle contraption to try out (first results are a major improvement on linear signals compared to a teflon deelectricum but lesser gain on circular but this may be due to the fact that I'll have to modify it a bit so the studs-thingy can be shoved into the feed somewhat deeper. Here to I'll let you know of results once they are final.

 

[paulvr]

hi paulvr. greetings from a Canadian sat hobbyist Chaparral is still in business I think,

Im my opinion it would be a waste of money replacing your CalAmp (ADL) feedhorn. There seems to be somer confusion as to what feed (omt) the seller is referring to. This one http://www.chaparral.net/feed-horns/dual-feed-with-dielectric-plate/ or the Chaparral Bullseye

the Chaparral Bullseye OMT came in 2 versions - the Bullseye 1 which is a 3 port (for polarity) 2 Cand linear & 1 linear ku that uses a rotor for h&V. http://www.satellitedish.com/cata0056.htm scroll down to see the bullseye 1

the second version is the Bullseye 2 which is 4 ports 2 - c & 2 - ku. I have one by the way. To achieve circular on a Bull 2 a dielectric slab is used.

now ADL (who made your feed for CalAmp) made a circular c band feed that used a metal 1/4 wave plate cast into the throat of the feed. http://adlfeed.com/cat_sec_1_4.htm I am not sure if they are available anymore or price.

Regards,

kevin

Hi Kevin,

I just checked your links. It's 100% sure that the very first link is the OMT involved, so naming it "Bull" is bull, there's no Ku-Band involved.
As to the last link to ADL, both feeds are "circular only". In a way that sounds attractive due to the fact that the majority of satellites broadcasting to our part of the world do use circular polarization, (and it sure would be fantastic for someone who has a fixed dish for reception of one specific satellite only) but for the general hobbyist there's a good handful of satellites (I think 8 or 9) that do operate linear and to completely sacrifice those is a bit much to do. In a way it would be interesting to test one of these just to find out what you're missing but then again, all the work involved and the fact that it would be taken down afterwards is rather discouraging. Installing one more dish isn't only costly but also problematic because living in the inner city the only place where I can set up dishes is on our multistorey building's flat roof, and the way present dishes are placed there isn't any possibility to install a second C-band dish without it blocking at least in part the reception of the other.

 

[Ponny]

Hallo,

AV-COMM Polarwandler aus Australien bringt circularen Satelliten bis ca. 2,5 dB mehr zu gewinnen. Wer ° LNB in der AV-COMM um 45 ist der Empfang von linearen und circularen Satelliten möglich. Das kann mit der Servosteuerung des Titan ASC 1 erzielt werden, und ein Servomotor ist. Siehe Abbildung 1 und 2 Bild 3 bis 5 der AV-COMM auf dem Netz KTI 3, 65m.

Ponny

 

[paulvr]

Danke recht herzlich Ponny,
Allerdings hat uns die Firma AV-COMM kürzlich gemeldet das man die Variante die sowohl für zirkullär als auch lineair eingesetzt werden kann aus Kostengründe nicht mehr herstellt. Also ist es jetzt nur noch ein Gerät daß man einsetzen kann wenn man auf lineair ganz und gar verzichtet oder mit doppelten Feeds arbeiten will.

For english speakers: recently the AV-COMM company told me that they no longer made a polaritychanger that can be used simultaneously for circular and for linear polarization. That still makes it an interesting object for circular only but my aim was to get both kind of polarities using one single feedhorn in one single 3 metre dish.

 

[Ponny]

Hallo,

der AV-COMM ist immer für circularen und lineare Rezeption. Eine leere, die dann auf die verwendete C-Band LNB eingestellt wird geliefert. Um dies zu tun muss herausgestellt werden, so dass das C-Band LNB eingeführt werden kann. Je nachdem, wie die Antennen an den beiden Rippen einen linearen oder circularer Empfang möglich ist. Die Konstruktion auf die Bilder mit Servomotor ist ein Selbst-Konstruktion. Wir hatten einmal in unserem Shop angeboten dies.

http://www.avcomm.com.au/c-band-waveguide-polariser-blank-detail

Ponny

 

[paulvr]

Lieber Ponny,

Ich glaube es dir sofort, habe deshalb keine Ahnung wieso ich vom Techniker des AV-COMM die obengenannten Informationen bekam. Ich werde mich nochmals erkundigen was mit deren Aussage genau gemeint wurde. Das von denen mitgeschickte Bild enspricht deine Bilder, bloß stand es Kopf-unten auf einem Tisch im Raum. Vielleicht wär's besser wir kommunizierten zum Thema privat in Emails weil sicherlich keine Verwirrung stiften will. Du lebtst ja vom Verkauf wie ich vom Schreiben lebe und es wäre Unfug wenn ich Aussagen hinschreibe die vielleicht irrtümlicherweise von jemanden gemacht worden sind, auch wenn's ein Techniker des Produzenten betrifft. Auch weiß ich nicht in wieweit man auf diesem Board Diskussionen auf deutsch toleriert.