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[TowerTalk] [Fwd: Antennas and their ratings(ssb:rtty:cw)]

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Subject: [TowerTalk] [Fwd: Antennas and their ratings(ssb:rtty:cw)]
From: (Richard T. Mainhart)
Date: Sat, 05 Apr 1997 18:24:14 EST
On Sat, 05 Apr 1997 19:27:31 +0100 "Johan Van de Velde,ON4ANT" wrote
(Header and apology deleted)

>Can anyone give me an idea about the correlation between SSB PEP 
>CW and RTTY??
Sure ... the duty cycle.

SSB (without horribly overdriven, overprocessed audio) has an approximate
30% duty cycle when taken over several minutes. 

CW has a somewhat higher duty cycle ... for the serious cw op you may
well see 60-70%.

RTTY has 100% duty cycle ... for if it isn't a mark, it IS a space, and
vice versa.

Why are we concerned about duty cycles?  Heat. That's right, heat. Some
of the antenna components will exhibit heating when exposed to RF
current. This heat, over several minutes will build up. If the antenna
component we're talking about is an RC network (like a trap) with a
plastic polymer insulator, the heat will, given enough time, cause the
plastic to melt and flow.

By limiting the total input power (based on statistically based, but
pretty much meaningless assumptions) the manufacturer's are trying to
keep you from destroying their product. 

You can see why some of the SSB ratings are 3 times as great as the RTTY
or continuous power ratings ... "typical" SSB is 1/3 the average power of
a RTTY signal. Note I said "typical" SSB ... processed, compressed audio
will have a much higher ratio, thus more RF, thus more heating.

Hope this helps,




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