SatSig topic:

Need help finding replacement OMT/Feedhorn

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Apr 16^th, 2009 at 7:05pm

Hello everyone,

I just received a modem, LNB, and BUC from a VSAT company in the UK. We told them we already had an antenna but didn't anticipate that our feed assembly would not match with their BUC. I have been asked to do one of the following:

) finding an adapter from the current circular flange to the UBR120 flange.

2) new feed-horn from Prodelin that matches both the
antenna type (1132) and UBR120 flange requirements

The waveguide size must be WR75

Any ideas where I can go to get either of these? Please help!!

Apr 16^th, 2009 at 8:44pm

I hope someone can help you with the parts you need.

The picture on this page may help clarify your requirements VSAT feed assembly

The Prodelin 1132 dish has an f/d ratio =0.8 and needs the matching, large, feed horn diameter, which is slightly larger than the older feed horns for older f/d=0.6 dishes which have poor cross-pol performance.

The OMT assembly shown has the important transmit reject filter located in the LNB side arm to protect the LNB. There is a supplementary filter, in this example, in the transmit port to further suppress spurious power from the transmit BUC.

Please will anyone help with hardware parts ?

Best regards, Eric.

Apr 16^th, 2009 at 9:13pm

Thanks for the reply! Here are some of the things that I am looking at:

https://www.sepatriot.com/TX-FDOMTKUL.htm - this seems to fit the specifications for the BUC that was sent over to me

https://cgi.ebay.com/Prodelin-Horn-Antenna-WR75-Reject-Filter_W0QQitemZ350144303
245QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item350144303245&_trksid=p3286.m20
.l1116#ebayphotohosting

Am I on the right track??

Apr 16^th, 2009 at 10:55pm

The ebay feed horn is too small diameter. It looks like a Prodelin receive only horn for use with f/d=0.6 antenna reflector.

The ebay OMT/filter appears suitable, but you need to verify if the circular waveguide joint will match up with the Prodelin Feed horn as shown in my picture. Do you have such a correct Prodelin horn now ?

The Patriot part is intended for use with a Patriot dish, not Prodelin. I don't know if is suitable. If it is for a Patriot dish with the same F/D as your Prodelin, then it would be worth a try but your problem will then be getting the focus right. The phase centre of the feed (its focal point origin) is not normally documented for public use.

The feed horn and associated dish should be regarded as a strictly associated with one another and always bought simultanously. If you mix and match you will either get low gain or high sidelobe interference, or both. If you use too small diameter feed the beam will be extra narrow but gain overall will be low because much power gets wasted past the side of the dish. Sidelobe interference, ground noise and cross pol will be high. If the feed is too large then the beam will be broad and the gain will be low because only the middle of the dish gets illuminated. Sidelobes and antenna noise temp and cross-pol will be low however.

The correct feed for the dish will give the best results.

Best regards, Eric.

Apr 16^th, 2009 at 11:28pm

Yes, we do have the Prodelin horn from the original dish (we actually have everything from the original dish but the new BUC doesn't fit) - the real issue is the connection between the BUC and the OMT.

The other option is get a converter, right?

We may have to just go for the full dish and feed assembly - it just stinks to have to spend the extra money.

Thanks for your help!

Apr 17^th, 2009 at 12:14am

I don't understand.

The transmit BUC normally has a square flange and rectangular waveguide.

The transmit input port on the OMT is also a square flange and rectangular waveguide.

Have you got one of the new Andrew TRIAs which combine a BUC and LNB in the same device?. These units have a circular waveguide interface that goes to the feed horn via an adaptor flange. No OMT or filter is needed. It looks really neat. The Andrew TRIA should come with a separate accessory box containing a set of interface flanges to suit all feed types plus two dongles to set whatever LNB LO frequency you want and even co-polor or x-pol operation in some models.

Best regards, Eric.