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Author Topic: Can any size dish antenna be used on the ham microwave bands?  (Read 5291 times)
N8FNR
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Posts: 138




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« on: January 29, 2012, 10:43:11 AM »

I have radar dish that I bought years ago at a hamfest and used it as a parabolic mic. However I would like to sell it as I no longer have a use for it. It seems to be made of some type of fiberglass and very light in weight. The seller told me that I was taken out of a military aircraft.

So my question is can a dish like this be used on most of the ham microwave bands or is a special size required for each band?

To see a photo got to http://www.flickr.com/photos/10025089@N05/ . The ruler in the photo is 12 inches across. The dish is 24 inches across and it is about 9 inches from the bottom of the dish to the feed point.

Thanks
Zack
N8FNR
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K2OWK
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Posts: 1054




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« Reply #1 on: January 29, 2012, 04:32:01 PM »

Hello N8FNR, A microwave dish can be used for some of the microwave ham bands. The size of the dish usually sets the gain depending on the frequency. The feedhorn on the dish would have to be focused for the frequency by moving it closer or farther from the center of the dish. To answer your question, yes the small dish can be used for some of the higher frequency microwave ham bands. I have seen many Dish Network and Directv dishes used for this purpose, but need to be refocused for efficient operation

Hope this helps.

73s

K2OWK
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K9MHZ
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Posts: 397




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« Reply #2 on: March 06, 2012, 05:42:28 AM »

Zack,

Definitely what K2OWK wrote.  The dish itself is nothing more than a big ear.  Frequencies to be used are the function of the type of pickup/feed at the focus of the parabola.  

There are some practical considerations though, just like anything in life.  If the wavelength gets too long (lower frequencies), then the gain associated with a given dish dimension decreases to the point of being impractical.  Too, as you lower frequency and increase wavelengths, the feed system will change from something that resembles ductwork to a more recognizable driven element like what's done on a yagi antenna.   Then, you're not illuminating the whole dish, but merely using a figure-8 pattern in the plane of the feed, so the rest of the dish is wasted.  That's why you'll often see parabolic grid antennas, not dishes, for 2.4 gig wifi, 900 MHz, etc.

Your dish would be interesting to someone who experiments with freqs at least in the wifi range, and that's very boutique activity today.

Good luck,

Brad, K9MHZ

« Last Edit: March 06, 2012, 05:44:13 AM by K9MHZ » Logged
N0YK
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Posts: 41


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« Reply #3 on: April 03, 2012, 12:27:25 PM »

I've always heard the rule of thumb to get good gain from a dish was at least 6 times the wavelength of the frequency you want to use it on.



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