[AMPS] FT100D driving Alpha 87a

[Jim]

That is just what I said Tom....

Guess you did not understand my posting.

73
Jim W7RY

----- Original Message -----
From: "Tom Rauch" <w8ji@akorn.net>
To: "Einar Persson" <sm3mxr@swipnet.se>; <amps@contesting.com>; "Jim"
<w7ry@earthlink.net>
Sent: Wednesday, August 01, 2001 2:25 AM
Subject: Re: [AMPS] FT100D driving Alpha 87a


>
>
> > Using the band data output of the FT-1000, this data would be decoded
and
> > in turn would be used to address a string of potentiometers that would
be
> > used to individually set negative feedback levels back into the FT-1000.
> > This in turn would allow the setting of the power output on any band to
> > any power level simply by adjusting the pot for that band. Fairly easy
> > explanation.....And I DID NOT even need to use 4 letter words to do
it....
>
>
> Actually that system would depend on leading edge response time
> of the ALC.
>
> A better system would decode band data and set fixed negative
> bias for each band. That bias would get within ten dB or so of
> proper gain. Then the loop could simply sum-in the correct amount
> of additional ALC to hold level constant.
>
> Most ALC systems aren't as bad for splatter as people seem to
> think. The leading edge overshoot that exists on *some* radios is
> so short it doesn't create much average energy. It mostly is an
> aggravation for solid state PA's or firing an arc in tank circuits.
>
> There are actually several problems that cause problems. One is
> many new radios have very poor transmitter IMD performance. Look
> at the TS-2000 as an example. It is almost class C quality, yet
> reviews all ignore that fact.
>
> Another problem is many exciters have poorer IMD performance if
> power is substantially reduced. They have peak performance
> around half or more of full PEP output, and if operated so they
> spend most of their time at low power levels they have increased
> IMD.
>
> For people on adjacent frequencies it is a time duration and level
> problem of the IMD, not just the fact it might have a leading edge
> spike.
>
> I haven't found a rig yet that has a keyclick from ALC problems, so
> it appears to be a SSB problem. Keyclicks are designed in by
> manufacturers using excessively fast rise and fall times as well as
> the wrong filtering (producing the wrong shape of rise and fall, since
> shape controls harmonics of the keying waveform). A second
> problem on CW is some radios transmit while VCO's are still
> settling to new frequencies, causing a leading edge thump as the
> VCO system(s) sweeps to a new frequency.
>
> I'm not sure if VCO settling time is a SSB problem or not, I've never
> looked for it.... but I'd bet it happens because it sure happens on
> CW. Meanwhile the ALC circuit gets 100% of the blame.
>
>
> 73, Tom W8JI
> W8JI@contesting.com


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