Me>>
>>You can't really tune a fiberglass stick, except with a matching network.
John>
> Ummmmm.... not exactly true. The "antenna" in a fiberglass unit isn't the
>rod, but rather the copper wire wrapped around it. Tuning an antenna for SWR
>means either lengthening it or shortening it to get the lowest resistance.
Okay - but some I've seen have the wire embedded in the plastic. They're
generally designed to be pretty broadband antennas, so they match pretty
well out of the box. They're also not very good as far as gain... it's
definitely a tradeoff.
You're not lowering the resistance, but matching the impedance of the
antenna to the characteristic impedance of the medium (air) the radio
wave is being injected into.
>On a fiberglass unit, pull the rubber cap off of the top & spread the coils
>apart a bit. If the SWR goes down, keep spreading them until you reach the
>lowest reading. If it goes up, push them back together & cut off 1/4 coil at
>a time until you reach the lowest reading. If no SWR meter is available, key
You really don't want to have to solder bits back on, so I agree with
John - snip bit by bit. You should also check the SWR at the extremes of the
CB band - Ch 1 and Ch 40, as well as Ch 18 - just in case you've made the
antenna more peaky.
>you have any excess coax, make sure it's coiled in at least a 3 foot
>diameter circle.
Excellent advice. Also check the coax for kinks, and damage to the outer
casing that lets the shield corrode. Replace the coax if you find any
serious damage [most CBs use 50-ohm coax, not 75-ohm like TV cable].
Not only can the damage cause your noise problem, but it could get hot
in use and start a fire -- not likely with five watts, but...
Jim
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