what frequences does a dish work on

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Don_Burke

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burts said:
does a dish work on all frequences or just the hi frequences ??

from burt
Dishes work on the frequencies they are designed for.

Generally, I have found dishes in use from about 900 MHz on up.

A particular dish will have a maximum frequency due to the accuracy of the surface.
 

af5rn

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That's kind of like asking, "What roads does a car work on?" Can you be a little more specific?

What kind of dish are you talking about? A dish is just an antenna, and like all antennas, each is designed for a different frequency range.
 
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prcguy

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A parabolic dish should be at least a few wavelengths in diameter, otherwise less complicated antennas like Yagi's or corner reflectors will have as much gain. If you were asking about Dish Network (I dislike them) there dishes receive the 12.2 to 12.7GHz band and convert that down to 950 to 1450MHz to shove down the RG6 cable to your receiver. Directv uses he same frequencies and also 18.3 to 18.7GHz and 18.7 to 20.2GHz.
prcguy
 

burts

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more detail

i think it was on uhf satcom in the antenna gallery that i saw a dish being used for the 255mhz with what looked like a whip mounted in the middle of the dish ,
so my question was really does any old dish refect any old frequencey into a point of focus to produce a directional gain.or am i being stupid
 

zz0468

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burts said:
i think it was on uhf satcom in the antenna gallery that i saw a dish being used for the 255mhz with what looked like a whip mounted in the middle of the dish ,
so my question was really does any old dish refect any old frequencey into a point of focus to produce a directional gain.or am i being stupid
The reflector is quite broadbanded with a couple of caveats... As PRC stated, the high frequency is limited by the accuracy of the survace of the dish. The low frequency is limited by the size. The larger the dish, and the higher the frequency, the higher the gain. A 6 foot dish mught have 30 db of gain at 2 GHz, 40 db of gain at 10 GHz, and 10 db of gain at 800 MHz. The feed antenna is usually MUCH more narrow banded than the reflector. A 6 foot grid dish could have the same 10 db at 800, 30 db at 2 GHz, and be completely useless at 10 GHz. That's where the surface accuracy part comes in.

The long answer to your question is complicated. The short answer is no, any old dish won't work on any old frequency.
 

burts

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thanks again

many thanks for replys ,these antenna things are not always as simple as they look

from burt
 

prcguy

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A dipole or 1/4 wave whip cut to about 260MHz will work for UHF satcom if stuck in front of an old 8ft C-band dish, but you can use a much smaller antenna if done properly. UHF satcom is circular polarized and using a linear polarized dipole or whip as the feed will loose about 3dB over using a circular polarized feed. A simple crossed dipole with a correctly made phasing harness (to make it circular pol) over a simple reflector will work just fine and only takes up about 2ft X 1ft of space.
prcguy
burts said:
i think it was on uhf satcom in the antenna gallery that i saw a dish being used for the 255mhz with what looked like a whip mounted in the middle of the dish ,
so my question was really does any old dish refect any old frequencey into a point of focus to produce a directional gain.or am i being stupid
 
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