regarding VHF to UHF beam antennas

[KD5VHF]

I'll let the antenna "gurus" answer the tech part but wanted to comment on the swr thing. Remember that just because the swr reading is good dosent mean the antenna will work very well. A dummy load has GREAT swr readings and although you can talk on it you won't be talking far.<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/wink.gif ALT=""> Some VHF antennas can show a good swr reading on the UHF freq.s but the pattern is straight up. That might be fine to talk to a plane as they pass over but not much good for anything else. Not sure how the pattern will be the other way around but I'm guessing the results would be about the same. Heck, try it....it might just do what you need it to.


<hr />73, Mike </p>

 

[Icom 706 King Cobra]

Hello all..



I have not asked a question for a bit now..lol..



so here it goes..



I have a UHF 16 element beam..designed for 430-450 mhz..



now i realise that one can often use a single antenna engineered to operate on a said frequency within a given ham band...

yet often it is found that it will show a good SWR on another ham band..outside the original design parameters of said antenna..



so now back to my question...my 16 element beam is made for 430-450 mhz..

yet shows exellent SWR's as well across the 2 meter band..

i guess i should check it out on the 220 band as well..



ok i fully understand that if the given length of boom is within the abilities of other frequencys wave lengths..

this is why it is not difficult to design a dual band 2 meter & 70 cm bands..



my question is..

given the differences not in boom (the greater the boom the greater the amount of wave lenghts obtainible for a given frequency...so where a antenna used for say both 225 mhz as well as 450 mhz...at 450 there is a double long boom as compared to 225 mhz when looking at the wave length of those frequencys)..



ok so then..

how is the elements lengths effect this..

does the shorter wave length still favor the greater size in width of the elements as well...

or is this far less importent...



how are the lobs so effected by this...



just trying to minimise my antenna farm if i am so able to do so...while mantaining decent use across multible bands..



Later All



Bob

KC2MLZ


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[Jay in the Mojave]

Hello Icom 706 King Cobra:



The beam antennas as well as other antennas may have a frequency that does have a lower of even perfect match on other frequencies. As a exaple, your Interceptor 10K will show a very low SWR near 146 to 147 MHz, ballpark. This is the tuning hoop T1 acting as a horz folded ground plane. It works but its not the best. Better than sitting inside the house on a rubber duckie antenna tho.



But this lower SWR at something other than the design frequency just indicates a place where the antenna has a combination of charactics that allow for a lower SWR. But that does mean that it will be an effective antenna.



They make a beam antenna that has the elements for 2 meters and the 440 band. And this works pretty well I am told.



Using a 2 meter beam antenna for 440, may be worh a try. You will need to measure the SWR Vs Frequency, to see if there is a low SWR somewhere. Then do a signal check to its ability to get out.



I think one of the amatuer antenna manufactures makes a J Pole Antenna that will work on both 2 meters and 440.



Most all antennas will have a place where they have a lower SWR at something other than the design frequency. But again it may not be to effective of a antenna.



Hope this helps.



Jay in the Mojave



www.a1antennas.com


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