[BC] Re: Cutting Vs Matching Antenna Vs no code
Richard Fry
rfry
Sun Jul 24 06:43:49 CDT 2005
Larry Bloomfield:
>As for Antennas, we all know that an antenna is resonate at one
>frequency only. If you intend to change from that frequency, you MUST
>change the electrical length so the transmitter thinks it is the correct
>length - shorter or longer as the frequency you're putting to it is
>higher or lower.
_________________
This can be true-ish for a simple wire dipole or whip, but even then they
have an acceptably low VSWR over a small range of frequencies with no
physical change to the antenna, or needing a "matcher." And even a simple
dipole can have a fairly wide VSWR bandwidth if the radiator outer diameters
are suitably large.
Other radiator designs can have a very wide VSWR bandwidth. Recall that FM
broadcast Master antennas can have a measured VSWR of 1.1:1 or less across
the whole FM band (20% bandwidth), using radiators with fixed mechanical
dimensions. Some UHF TV transmit antennas cover the whole UHF TV band with
low VSWR.
RF
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