6ft Prime Focus Ku Setup

[Pixl]

I have a 6ft microwave dish I mounted on a sat. polar mount, was going to use it as a 3rd C-band fixed dish. But my movable 8ft dish works so well I don't really need it for C-band. I had a DMX741 mounted on it worked fine for C, but nothing from Ku. I think the Ku section is defective as it has a -35 db noise floor on a spectrum analyzer. So I tried a Invacom SNF-031 bolted up to a prime focus scaler feed. Works ok, but not any better than my 1m Channel Master Ku dish. Anyone with a Ku only (not combo C/ku) have a 6ft. setup that you are happy with.

Jim

 

[Mr Tony]

yep.

see my signature. I use a prime focus KU Band LNB for it. SatelliteAV sells them for $10
Satellite AV - Free to Air Satellite Equipment Distributors - GEOSATpro, Glorystar 888-483-4673

I use it for those "hard to get" KU feeds and it helps alot
Here is a test I did a while ago on 97W
http://www.satelliteguys.us/free-air-fta-discussion/181927-bsc321sp-f-d-ratio.html#post1903812

 

[Mr Tony]

I used it a month or so ago for a college football game. It was 103W so it has the oddball skew. Skewed my 36" for 103W and had minimal signal (like 20 or so)
Used the setup above and a 60 quality signal

I'm going to try it this weekend for the North Dakota hockey games. The TP they use seems to be weak (66-67 on the CS5000 and threshold is 63)...gonna see what I can do with this setup

 

[Pixl]

Ice,

Thanks for the info and link. I wonder though, my 6ft dish calculates out to a f/d ratio of .375, the SL1P specs for a .5-.7 dish. Although your tests show improved performance would I see the full size of my dish at that f/d?

Here are some pictures of my project with the Invacom mounted to a Ku scaler feed.

Jim

 

[pendragon]

It's not possible to make measurements of your Ku feed, but at a coarse level I would say it looks like it is set for a higher f/D than your dish's 0.375. If true your effective dish diameter is smaller than actual.

I've tried several Ku combinations on my Fortec 1.8m prime-focus with fairly decent results. The performance was better than my 1.2m offset, but short of theory. I then put up a 1.8m Prodelin offset. While I'm still investigating some odd phenomena, it stomps both the Fortec and the 1.2m offset.

 

[Pixl]

It's not possible to make measurements of your Ku feed, but at a coarse level I would say it looks like it is set for a higher f/D than your dish's 0.375. If true your effective dish diameter is smaller than actual.

What measurment are refering to ?

You have a good eye! At the time the photo was shot the distance from the feed horn to the dish surface was 29" arrived at by moving the button hook in and out. I calculated the distance at 27" (D=72" d=12") today but have not re-set it yet. I think I need to find a feed horn that will match the f/d .375 . The one pictured came off a commercial dish years ago and it's specs are unknown.

 

[pendragon]

I was only referring to the f/D of the feed itself. My gut says the scalar rings are too far forward for 0.375, but without making accurate mechanical measurements and a certain amount of modeling, this is just an informed guess. I'd suggest considering the Invacom ADF-120 feed. It's easily adjustable over a wide range of f/D and has worked quite well for me.

 

[Pixl]

I was only referring to the f/D of the feed itself. My gut says the scalar rings are too far forward for 0.375, but without making accurate mechanical measurements and a certain amount of modeling, this is just an informed guess. I'd suggest considering the Invacom ADF-120 feed. It's easily adjustable over a wide range of f/D and has worked quite well for me.

Pendragon,

The feed that I have is one piece non adjustable. It was something one of the radio networks sent our station when they had us change over their C-band dish to Ku. This was for a 8ft dish, but they must not have been looking for optimal performance to send a feed designed for a smaller dish, but it worked good enough. It was quite a few years ago, the system long taken out of service and this was laying around as I tend to pack rat stuff like that, thought I'd try it. I did wear out Google looking for a Ku feed, all I found was more of the same .5 to .7 feeds out there. Your Invacom ADF-120 looks like the ticket, found it right away. I will give one a try let you know how it works out. Could you guess from my pictures what size dish my feed might have been made for, and would that be prime focus or offset?

Jim

 

[pendragon]

Actually the feed could work with any size dish or type (offset or prime-focus), as long as the feed f/D matched the dish f/D. I would guess the feed f/D is nominally about 0.42, but I could be way off. Offset dishes are rarely manufactured for this low a f/D, so I assume this feed was intended for a prime-focus reflector.

 

[Pixl]

While I'm waiting for the Invacom ADF-120 feed to come in I got to thinking about the scaler rings again. This Andrew dish I'm working with came from a cable co. tower, was a microwave dish used in the 12ghz service. The original waveguide feed had NO scalar at all, in fact I've never seen a scalar on any microwave dish. Why do we need them for satellite dishes when the microwave dishes using nearly the same frequency's have none?

 

[Pixl]

Here is the microwave dish feed, mostly just a bent length of rectangular waveguide.

The feed is just a plastic cover and housing, no scalar.

I took the cover off, bare waveguide inside slightly flared.
Other than it being single polarity, I don't know why this would be so different from a satellite dish feed.

 

[Mr Tony]

Tantalus
This past weekend I used my 6 footer for 2 different feeds and they make a difference

Friday the Sioux feed was at a 40-42 quality on the GeosatPro and 30"...the 6 footer it was at 65-67
Saturday something happened with the signal because on the 30" it was at 72 and the 6 footer it was 80
Saturday night for a late night college football game the 30" had the signal at 40 and breaking up....the 6 footer...nice and strong 70

 

[Pixl]

Tantalus
This past weekend I used my 6 footer for 2 different feeds and they make a difference

Friday the Sioux feed was at a 40-42 quality on the GeosatPro and 30"...the 6 footer it was at 65-67
Saturday something happened with the signal because on the 30" it was at 72 and the 6 footer it was 80
Saturday night for a late night college football game the 30" had the signal at 40 and breaking up....the 6 footer...nice and strong 70

Ice,

You make me impatient for the UPS guy to show up with my Ku feed. Glad your 6ft Ku is giving you good performance.
Now if I could just get Pendragon to show up in here and answer these feed questions.

Jim

 

[Mr Tony]

The only drawback of using a large dish with KU is it can be a bigger to find that satellite.... I ended up aiming at 125W first then move to 123W as I couldnt find it on my ghetto rigged 6 footer

 

[pendragon]

Terrestrial microwave links are generally not limited in terms of transmitter power compared to satellites. The distance they have to cover is also dramatically less. This puts a much lower premium on an efficient feed and beam pattern.

Scalars have several purposes, but in lay terms one of the primary reasons is help control the beam so the feed sees almost the full dish, but not beyond the edges. This reduces the amount of noise and minimizes interference, which are very important for satellite reception. There are other feed design methods that will also work, but this is a well understood an fairly inexpensive approach.

 

[Pixl]

Pendragon,

I hadn't thought about distance vs. power. The cable co. was shooting 30 miles with about 1 watt. Satellite tp's are what, about 5 watts, that has to travel 25,000 miles.


Ice,
Yea, I noticed how tight the aim was on it so far.
What is "ghetto rigged" ?

 

[pendragon]

C-band transponders are in the neighborhood of 20W. Ku transponders on DBS birds are generally a bit more than 100W in low-power mode and double that in high-power mode. Although the physics makes perfect sense, I still find it impressive that entire continents can be covered with such a small amount of carefully directed power.