|[AMRadio] antenna tuners|
Mike Dorworth, K4XM
k4xm at arczip.com
Fri Apr 21 13:15:24 EDT 2006
I was beaten to the door on this. Actually there is a spot up about one
third wavelength that is 100 ohms,for a perfectly resonate radiator. So it
would be 2 to one and a dandy perfect resonate vertical with over a hundred
radials is about 35 ohms so the magical 1 to 1 is nothing magical. I would
beg everybody to read at least two chapters of Walt Maxwell's book "
Reflections". The right SWR for the wrong reason, and the Wrong SWR for the
right reason. The first I would call dummy load syndrome and the second as
above. This stuff is not opinion or politics it is pure science and can be
tested at YOUR house.. 73 Mike
----- Original Message -----
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
Sent: Thursday, April 20, 2006 10:12 PM
Subject: RE: [AMRadio] antenna tuners
> This is another tidbit to keep in mind for those that still may think that
> an antenna has to be resonant to give 1:1 swr.
> A dipole antenna rarely is 50 ohms at resonance. It is very dependent on
> height above ground as to what impedance it presents at the feed point. It
> can range anywhere from below 30 ohms to above 70 ohms.
> So if you cut your antenna so that you have 1:1 swr at the transmitter end
> of the coax, the antenna is probably not tuned to resonance! You have
> detuned the antenna to change its impedance that the coax sees.
> Only rarely does a resonant antenna turn out to be 50 ohms.
> Gary K4FMX
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