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Old 20-Jan-2012, 7:22 PM   #12
ghz24
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Join Date: May 2011
Location: Central Illinois U.S.
Posts: 72
Quote:
how is it possible to get a low VSWR on a VHF HI to UHF (174 to 806 MHz) across the entire range, on a receiving antenna?
Log periodic dipole arrays (LPDA) have dipoles of different lengths. And only 2-4 are used by any frequency. That is as the frequency increases the active region of the antenna shifts toward the shorter dipoles.
Some large commercial TV LPDAs are sensitive to 54 MHz through 900 MHz or more with relatively good swr.
Keep in mind also swr is not as crucial to a receive only systems compared to transmitters (less than 2.7 just costs a little gain) partly because any reflected signal caused by the bad swr is reflected toward the antenna to be transmitted not back at the electronics.
Quote:
and do the results ever match manufacturers' claims?
All my "tests" would be on models (so grain of salt time) but I think the mfg. claims (reputable companies) are accurate to the extent it's given.
The Antennas Direct like though revelation of swr graphs of the whole band are rare. Usually you get an average which can hide excessive swr on some frequencies with good swr at most.

Quote:
to test a homemade antenna of any sort?
Easiest and cheapest way is model it. No physical build necessary.
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