Deep dish vs shallow dish?

[R390A]

Whats the primary difference between a deep dish like this 10 footer and a shallow dish like the one shown? Other than size does one perform better than the other? I understand the focal points will be different between the two.

 

[tvropro]

Whats the primary difference between a deep dish like this 10 footer and a shallow dish like the one shown? Other than size does one perform better than the other? I understand the focal points will be different between the two.

A deep dish rejects TI better, usually it has less gain than a shallow dish. A deep dish is about a .27 ~ .32 F/D a shallow dish is .38 ~ .42 F/D ratio.

Also a deep dish has a narrower beamwidth than a shallow dish which will work better with 2 degree spacing.

 

[Likvid]

Deep dishes are difficult as they need a special feed and the only one i know about that makes a feed for dishes deeper than 0.30 F/D is Seavey Engineering.

However their feeds are a bit hard to get, they are handmade to order and you pay a premium.

 

[R390A]

This is the feed horn that was on the deep dish. It does not look like the standard setup. Off center next to the C-band element is the KU element. It appears that the KU side has a fixed polarity. I was planning on mounting a standard scalar ring and feed, but according to Likvid that may not work.
I may have to modify the existing scalar ring by removing the center section and sliding in a new feedhorn such as a BSC621.

I am thinking about setting up the deep dish next to the existing 10ft Unimesh dish and performing several A/B tests. The loser goes back to the barn.

 

[tvropro]

This is the feed horn that was on the deep dish. It does not look like the standard setup. Off center next to the C-band element is the KU element. It appears that the KU side has a fixed polarity. I was planning on mounting a standard scalar ring and feed, but according to Likvid that may not work.
I may have to modify the existing scalar ring by removing the center section and sliding in a new feedhorn such as a BSC621.

I am thinking about setting up the deep dish next to the existing 10ft Unimesh dish and performing several A/B tests. The loser goes back to the barn.

The feed you have there is a National ADL feed. If you pull out the foam you will see the c band probe, the small one shown is the ku probe (the ku is not fixed). This feed is designed to work with a .35 to .40 F/D. What you need with a chaparral feed is a gold ring, this will let you use it on dishes to .27 F/D like a Winegard Pinnacle.

 

[R390A]

I removed the center section of foam. Interesting, the KU pickup is right up front and the C-band is further back. Both elements are connected together and turn for polarity.

 

[tvropro]

I removed the center section of foam. Interesting, the KU pickup is right up front and the C-band is further back. Both elements are connected together and turn for polarity.

I've used the ADL feeds for customers for years. I still run one on my own dish. Some people like the Chaparral feeds better some like the ADL's. Patriot took over ADL a few years back and still makes these feeds.

Look Here:

http://www.sepatriot.com/feeds-ADL_RP1cku.htm

 

[Gilgamesh]

I used to build parabolic antennas back in the day (early 80s) most factory built and home built had a F/D ratio of .32 - .36, for deep dishes, you could purchase a feed horn ring that slipped on the end. or just get a feed with adjustable scaller rings.

Advantages of shallow are, that long focal length allows more space between feedhorns and less loss for those parasitic feeds for not being at the cherry spot. also when building, the antennas were cheaper to build flatter and came out a bit larger.

Deep dishes were often used in areas where there was a lot of TI due to Ma Bell microwave towers using same frequency band. I even saw someone put a 10 footer in an empty pool. not much of an issue now days as telcos are using higher frequencies.

As for the look beamwidth, this is more related to diameter, higher gain means more directional, this goes for all atennas.

 

[Likvid]

The old deep Winegard Pinnacle dishes had extreme high sidelobes so they were diffifcult to align as the sidelobes were pretty strong compared to mainlobe.

Deep dishes are good for isolating surrounding noise like from terrestrial interference and ground noise coming from the warm earth, problem is designing good feeds which many could not do correctly, that's why most feeds don't go down below 0.30