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Old 20-Jan-2012, 3:36 PM   #11
RenoPaul
Junior Member
 
Join Date: Jan 2012
Posts: 12
Quote:
Originally Posted by GroundUrMast View Post
Antennas Direct is pretty good about providing technical information for their products: http://www.antennasdirect.com/clearstream2gain.html

Radio Shack is not as forthcoming with such technical information.
I've noticed that a few commercial manufacturers are lacking in this specification.

Please correct me if I'm incorrect in my next assumption/question.

My only experience in measuring VSWR was back in the late 70's during the CB radio craze. In order to adjust VSWR, you had to actually transmit on a specific frequency, and if my memory holds, the 40 channel CB range was from 26.965 - 27.405 MHz. Ideally, you would adjust the length of the antenna to give the lowest possible ratio over that band, by changing the length of the antenna mast to match the entire system of cable and antenna to the actual wavelength. Even at this small band, adjustment was quite tedious, and at best, was never equal across the entire band.

In my experience, I noticed that an antenna's VSWR would change, sometimes drastically, if moved from 1 location to another, indicating that surrounding objects and cable length had quite an effect in this measurement.

With my nature of always being a bit on the skeptical side, I experimented testing VSWR with a dummy load (terminating resistor), finding VSWR results all over the board, and rarely even close to 1:1 on factory made cables.

So, my first real question is, how would the normal person (with limited technical knowledge) legally be able to transmit, even a very low signal, to test a homemade antenna of any sort?

My second question is, 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?

And my third question is, has anyone ever tested a commercial antenna in more than 1 type of non-laboratory installation, and do the results ever match manufacturers' claims?
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