Orthomode Feed and Big dish : WOW !

[Labgate]

Hello everyone

I installed my orthomode feed this week-end.

In case you wonder, an orthomode feed is a feedhord with 4 lnbs (2 cbands and 2 ku bands.)

So I replace my "old" regular feed with my orthomode feed. It's been very easy to setup.

You have to have 4 cables. One for each lnbs. You then use multiswitches to connect the input from each lnb to the 922 and the dvb receiver.

Since you have a multiswitch you don't have to worry about changing polarity on the 922 to use your dvb receiver. Just be sure to be on the right sat and it works.

Right now I have connected my trusty pansat 3500s on it but I maybe getting on of those 4:2:2 receivers to get feeds.

Now I will be able to enjoy my big dish. My 922 receiver for big dish programming and 1 or 2 dvb receivers to get dvb.

I recommend this to anyone. From what I see it is stronger too than a C and KU Band lnbf. Here are some pictures.

Best regards

Labgate

 

[Shawn95GT]

Very nice!

 

[BKP]

Great dish farm...

 

[Stefan]

I've been using an orthomode feed on my 8.5' birdview for quite a while and yes combined with a multiswitch it makes for a more convient setup especially if your mostly interested in FTA. However, there are a couple of downsides to take into consideration.

First and foremost is that if your connecting your LNBs directly to the inputs of your multiswitch, without power inserters between them, the vertical polarity LNBs will be powered by only 13v. This is actually out of spec for these type of LNBs. These kind of LNBs (the kind you generally use on a BUD with a polar servo) are generally rated for 15 to 24v. Therefore if you power them at only 13v this is out of spec and they may not perform as expected. In fact, some of them will not work at all at these voltage levels. I've found this to be particularly true with some Norsat PLL LNBs (both C and Ku band). So, this is something to watch out for. If you happen to notice that you always get reduced performance on vertical signals this could be the problem. Having said that, some do seem to work okay at only 13v (even some Norsats) despite the fact it's out of spec. Anyway, just be warned that this could be an issue especially if you ever upgrade to some of the more top of the line LNBs.

The second thing is it can actually be advantagous performance wise to have a polar servo because there are a few satellites where the skew might be off just a bit and the ability to fine tune it with a polar servo can help. Also tweaking skew with a polar servo can sometimes help problems with cross pol and interference from adjacent satellites.

One other thing to keep in mind with using a multiswitch in a configuration like this is if your using 22khz to switch between C and Ku, some older receivers, analog and Digicipher II, may not be able to generate 22khz tone switching signals. Therefore if you want them to be able to access whichever band uses the 22Khz tone (let's say for example Ku) youd need to either have a device that could inject the 22khz tone onto the cable feeding those receivers or youd have to slave them off your DVB reciever.

 

[Labgate]

Thank you Stefan

It is important information to know.

I understand that I'm lucky because :

I have two power inserters, one on each multswitches.

I have a 922 receiver so I don't use 22khz to switch between C and Ku sats. On my 922 there are separate inputs for C and KU.

I use a diseqc switch for the dvb receiver.

I have four very good lnbs (Norsat) also to help reduce the minor adjustment I don't have anymore (skew).

So yes this is a great feed but you has to make sure to do it right and with the right tools.

Best regards

Labgate

 

[vfrjim]

Labgate, I tried to go to your website but it prompts for a userid/pw.

I was wondering where you purchased the orthomode feedhorn?

Thanks,

Jim

 

[Labgate]

Hello

I bought the orthomode feed last november (yes november) on ebay.

For my web site, I don't receive any popup. You are typing the correct name.

hxxp://www.labgate.info

Labgate

 

[vfrjim]

Now it is working.

The orthomode intriques me since I have a 922 and multiple DVB receivers.

 

[Labgate]

Great.

I will update the site very soon with the orthomode feed pictures.

Labgate

 

[HDTVFanAtic]

Out of curiosity, what 13 birds are T90 looking at and what area of the Country are you in?

 

[vfrjim]

What manufactuer's orthomode feedhorn did you use? And it works fine with the 922? Does it use a Polorator Servo Motor? I am very interested in updating my feedhorn.

 

[Stefan]

What manufactuer's orthomode feedhorn did you use? And it works fine with the 922? Does it use a Polorator Servo Motor? I am very interested in updating my feedhorn.

No, an orthomode feedhorn does not use a servo motor at all for polarity. It has 2 separate probes for each band aligned to recieve each polarity and then each polarity is sent to a separate LNB. That means for an orthomode feedhorn you'll need 4 LNBs, 2 for C and 2 for Ku and each of the 2 LNBs for each band gets a different polarity. An orthomode feedhorn is also sometimes called a "bullseye" feedhorn. Anyway seeing as how you need 4 LNBs in total using an orthomode feedhorn can be quite expensive especially if you buy high end LNBs and that's not even taking into account the feedhorn itself and the switches (and perhaps power inserters for the vertical LNBs) you might need. Here's a link to an orthomode feedhorn.

http://www.daveswebshop.com/pmcku.shtml

In the pics there you can see how all 4 lnbs attach and it'll give you some idea of how it works.

 

[Labgate]

Hello

I'm in Canada.

A picture is worth a thousand words

hxxp://www.labgate.info/Tests/Toroidal%20Dish%20t90/lnbs%20identiifed%20t90.JPG

Out of curiosity, what 13 birds are T90 looking at and what area of the Country are you in?

Labgate

 

[Labgate]

I agree this could be expensive.

I have been lucky. I found it on ebay last november and paid 250 $ for everything.

Then I bought two active multiswitches for 30 $ each.

So it was not that bad for all the benefits I have. There were even two other c band norsat lnbs in the box.

Labgate

No, an orthomode feedhorn does not use a servo motor at all for polarity. It has 2 separate probes for each band aligned to recieve each polarity and then each polarity is sent to a separate LNB. That means for an orthomode feedhorn you'll need 4 LNBs, 2 for C and 2 for Ku and each of the 2 LNBs for each band gets a different polarity. An orthomode feedhorn is also sometimes called a "bullseye" feedhorn. Anyway seeing as how you need 4 LNBs in total using an orthomode feedhorn can be quite expensive especially if you buy high end LNBs and that's not even taking into account the feedhorn itself and the switches (and perhaps power inserters for the vertical LNBs) you might need. Here's a link to an orthomode feedhorn.

http://www.daveswebshop.com/pmcku.shtml

In the pics there you can see how all 4 lnbs attach and it'll give you some idea of how it works.

 

[vfrjim]

So, the active multiswitches allow the 922 to work and also allows a DVB receiver to use the LNBs?

I already have 2 Cband lnbs, so I would only have to purchase a 2nd KU lnb, so limited investment other then the feedhorn

 

[Labgate]

exactly

Here is my setup

Again an image is worth a thousand words.

Labgate

So, the active multiswitches allow the 922 to work and also allows a DVB receiver to use the LNBs?

I already have 2 Cband lnbs, so I would only have to purchase a 2nd KU lnb, so limited investment other then the feedhorn

 

[HDTVFanAtic]

Hello

I'm in Canada.

A picture is worth a thousand words

hxxp://www.labgate.info/Tests/Toroidal%20Dish%20t90/lnbs%20identiifed%20t90.JPG



Labgate

Thanks.

2 Questions -

1) Do you have any problems with the Linear feeds further out on both ends of the railing?

2) What did you use to make the extension for 61.5 and its mounting? I could use one of those!

 

[Labgate]

Hello HDTV

No I don't have a problem with linear feeds there.

As far as what I used it is a round aluminium piece that I screwed there.

The screw is small enough so the lnb holders can pass.

I'm even sure that if I would put another one at the other end I would get 119.

Labgate