Garry & Yelena wrote:
>
> Another guy asked if anyone has done anything with the 4CX1600B. Marv
> did--see Communications Quarterly. No, I am not going to send out
> copies.
>
> I have a 4CX1600B and am accumulating parts and info--almost there.
> Power supply is built and currently running a Swan MkII converted to 160
> meters.
Be careful in the design. Marv's stuff looks good but beware that the
pPA should be set up to use maximum drive available from the exciter. In
other words, DON'T build a PA that drives with 50 watts and use it with
your 950 SDX or FT-1000, or even a ICOM 706.
The reason is virtually all PA's overshoot. Many of them also produce
POORER IMD perfrormance when operated far below rated design output
power.
My IC-751A measured -28 dB third order (below one tone) at 100 watts,
and around -22 dB when at 10 watts. The rig would actually produce a
cleaner signal at full power.
Another problem is overshoot. The ALC is often too slow to correct
leading edges. My 950SDX overshoots to 250 watts or more at the leading
edge of waveforms, and continues to do so even if operated at 50 watts.
My IC-706 does the same thing, overshooting to ~150 watts even when set
for five watts output.
A 30X desired level spike can cause all types of distortion, arcing and
damage to a PA.
Second, watch the screen design. Svetlana's articles make too light an
issue of screen regulation and current protection. Use a well regulated
screen supply that protects the screen from excess dissipation.
73 Tom
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Sponsored by: Akorn Access, Inc. & N4VJ / K4AAA
|