One of the better articles on using/making a PA appeared in VHF
Communications 4/1985 by DJ4GC "Two-metre Power Amplifier using Valve 4
CX 1000 A" and "Power Amplifiers - How they are operated" with spectrum
displays.
The author discusses in detail the point that reducing mic. gain is no
way to drive a PA, one needs to have an adjustable RF control. Reducing
mic gain can have the effect of increasing intermods and splatter, the
object is to capture the exciter's ALC action in its linear range (at a
medium to high mic gain setting), so that the ALC action is continually
"on", not pulsing on and off only at voice peaks (the dreaded 1 ms pulse
on various modern rigs). Also, too much RF level from the exciter
increases the linear's IMD, and don't blame the poor LO or IMD of the
exciter for this! Get a copy of the article, its well worth it.
As they say, "if you are holding a hammer, everything looks like a nail"
(hams read: "if you have a 2 kW linear, everything looks like an
antenna, or smoke it").
> Why pay good money for a tube and not utilize it's emissive capability?
> However, one should not use more power than is necessary to
> communicate. Power adjustment can be easily achieved by adjusting the
> microphone gain control. My guess is that fewer than 0.001% of CBers and
> fewer than 2% of hams would even consider deliberately turning down
> microphone gain.
For too optimistic, Rich....
Ian ZS6BTE
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|