Antenna ground planes December 31, 2007, 12:53:37 am Yahoo Message Number: 87698Well Firestick blew their credibility with me. One of its suggestions is not to use an SWR meter to tune the antenna, then later they say to use one to tune your antenna. They state that even a half inch shortening of you antenna lead can mess up your antenna. That isn't true. Your antenna lead is designed to have a characteristic impedance that matches your antenna. Cutting (terminating) that cable can be done at any length, and isn't affected by the number of wavelengths length of the cable. Depending on the frequency you want to use and the amount of power you wish to push through the antenna lead, determines what cable you need. The final tuning of the antenna's SWR is usually done by changing it's length. A tunable matching network is another way of changing the effective length. The standing wave ratio needs to be as low as possible. The impedance match of antenna to cable is what causes problems. An impedance mismatch causes some power which should be radiated by the antenna to reflect back into the transmitter. The reflected power causes standing high and low nodes in the cable and in the transmitter. At much higher powers the 'standing' waves can damage the cable or transmitter. I seem to remember, in the distant past, that a two antenna array such as the CB antennas mounted on a mirror on each side of a vehicle would extend the pattern on the sides, but reduce sensitivity and transmitted power to the front and back. Essentially making reception worse ahead of and behind you. The best overall arrangement, since you don't know what direction your next contact will be, is an omni-directional single whip antenna in the middle of a good non rusting ground plane. Steel is a lousy conductor. To answer another post, I used to use a portable CB (4 watt, 5' extendable antenna) but it sucked batteries dry quickly (AA). I use FRS or GMRS now. But the old CB wouldn't work if it was too close (30') to the RV because it didn't have 'line of sight' to the antenna on the roof. I notice that the Firestick site didn't get into center loaded antennas, base loaded, 1/4 or 1/2 wavelength antennas, or mention a 'Smith chart' for working with antenna characteristics. Ron and Bluebelle a '99TKBSee AOL's top rated recipes (http://food.aol.com/top-rated-recipes?NCID=aoltop00030000000004)[Non-text portions of this message have been removed]
Re: Antenna ground planes Reply #1 – December 31, 2007, 07:26:12 am Yahoo Message Number: 87700This is the situation where the length of the transmission line does become significant. If of proper length, the 2 antennas become a "phased array" and the pattern is fore and aft - extends the range up and down the road...Regards,ray (Amateur Radio W0PFO)--
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Topic: Antenna ground planes (Read 4 times)
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