islandmanmitch
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I.D. This antenna?
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It's a 3 element Yagi - that's a common directional beam antenna - and I am not sure about the approximate frequency it is tuned for because I am not sure of the actual size of the elements based on the photograph.
I "think", given that the boom length you reported is about three feet long, that the elements are in the 6in range measured out from the boom (6in either side of the central boom so about a foot total for each element, though the three elements may not all be exactly the same length they will be close). If so then this is a UHF Yagi; finding the exact frequency would require some equipment like a network analyzer or an antenna analyzer or at least a VSWR meter and low power signal source. But, if I'm right about the element sizes then it is UHF so in the 400MHz to 500MHz range somewhere. It looks commercial so may be in the 450MHz to 470MHz land mobile range. Does the sticker on the boom say anything useful like a make or model number?
Measure the element lengths and let us know. From that we can determine the general band.
TIP - post another photograph with a 12 inch ruler taped to the central element perpendicular to the boom (center of the ruler at the boom just as with the element).
-Mike
I "think", given that the boom length you reported is about three feet long, that the elements are in the 6in range measured out from the boom (6in either side of the central boom so about a foot total for each element, though the three elements may not all be exactly the same length they will be close). If so then this is a UHF Yagi; finding the exact frequency would require some equipment like a network analyzer or an antenna analyzer or at least a VSWR meter and low power signal source. But, if I'm right about the element sizes then it is UHF so in the 400MHz to 500MHz range somewhere. It looks commercial so may be in the 450MHz to 470MHz land mobile range. Does the sticker on the boom say anything useful like a make or model number?
Measure the element lengths and let us know. From that we can determine the general band.
TIP - post another photograph with a 12 inch ruler taped to the central element perpendicular to the boom (center of the ruler at the boom just as with the element).
-Mike
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islandmanmitch
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Thanks Mike. It is shorter than I thought now I have a tape on it. Boom is 22". Element closest to mount is 13 5/8" over all. Middle one is 12 3/4" overall and the last one is 11 3/4" overall.
islandmanmitch
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Oh yeah whats left of the sticker says something about use caution around electric wires.
It may have been used for monitoring equipment. Lots of them monitor rain gages, flood sewers, water levels, electric power currents, and such. It sends back data to a monitoring station.
islandmanmitch
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The question that will answer your question is how long is the center element? That's all we need to know to determine the approximate resonant frequency. The do-thingy in the middle is a series gamma match, don't mess with it or you'll throw the SWR off.
Yeah, it's UHF. That means it's in the 400MHz to 500MHz range. The posts about it possibly being for telemetry monitoring are potentially valid.
In any case, as Warren said, the "do-thingy" is a gamma match. In the right hands and with the right measuring equipment it can be adjusted to alter match of the antenna. I would just leave it alone. If you are wondering, the antenna might work well on a scanner within the 450MHz to 460MHz band but it might be too short to work in the 440MHz Ham band at least for transmitting. Then again, we can't be absolutely sure about the center frequency so some local Ham with the right equipment and knowledge might be a good candidate for you to bring it to. Check for a local amateur radio club in your area and see if you can contact them. If you don't want it and cannot find a need for it for yourself then you could donate it to them or at least get some info about it and figure out a fair price for it and put it up on Ebay or some such.
-Mike
In any case, as Warren said, the "do-thingy" is a gamma match. In the right hands and with the right measuring equipment it can be adjusted to alter match of the antenna. I would just leave it alone. If you are wondering, the antenna might work well on a scanner within the 450MHz to 460MHz band but it might be too short to work in the 440MHz Ham band at least for transmitting. Then again, we can't be absolutely sure about the center frequency so some local Ham with the right equipment and knowledge might be a good candidate for you to bring it to. Check for a local amateur radio club in your area and see if you can contact them. If you don't want it and cannot find a need for it for yourself then you could donate it to them or at least get some info about it and figure out a fair price for it and put it up on Ebay or some such.
-Mike
Now where did that picture come from? I must be reading with my eyes closed! Now we're getting somewhere, a 12" element tells me it's operating range lies centered around 450MHz. If you want accuracy take an accurate measurement and use this calculator.
N3DNO's Antenna calculator
You'll have to jig around with it a little, these calculators determine element length from frequency so enter a few around 450 until the measurements match or at least closely approximate as much as possible.
This doesn't look like anything a ham can handle, we don't have equipment for that band and a UHF antenna analyzer for our purposes only goes up to 450MHz and accuracy is not guaranteed at the edges of it's range.
Now we get to the bottom line, it's an excellent receive antenna (and rugged as they come) which is what I expect you may use it for so no real need to get picky about it. It'll cover a good chunk of UHF but the farther removed from 450MHz the more it's directional characteristics are degraded, just so you should be aware of that little fact. Otherwise I say go for it, that antenna will be going strong when you are in your grave.
N3DNO's Antenna calculator
You'll have to jig around with it a little, these calculators determine element length from frequency so enter a few around 450 until the measurements match or at least closely approximate as much as possible.
This doesn't look like anything a ham can handle, we don't have equipment for that band and a UHF antenna analyzer for our purposes only goes up to 450MHz and accuracy is not guaranteed at the edges of it's range.
Now we get to the bottom line, it's an excellent receive antenna (and rugged as they come) which is what I expect you may use it for so no real need to get picky about it. It'll cover a good chunk of UHF but the farther removed from 450MHz the more it's directional characteristics are degraded, just so you should be aware of that little fact. Otherwise I say go for it, that antenna will be going strong when you are in your grave.
islandmanmitch
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Yes, I was hoping to use it as a receiving antenna and did not know what frequency I could use it in. I appreciate all the information from everyone.
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