Date: Wed, 01 Mar 2017 09:56:45 +0800
From: Alek Petkovic <vk6apk@bigpond.com>
To: AMPS <amps@contesting.com>
Subject: Re: [Amps] Questions on Alpha 8410
Correct. The overshoot, generates a DC voltage which holds the drive
down for the next bit of the rf envelope. The overshoot has already
passed out of the radio and through the amp.
However, if you have a permanent, constant voltage applied to the ALC
line of the transceiver, you can set it up so that you will not get
overshoot or overdrive.
Learned that from VE7RF.
73, Alek.
VK6APK
## I own 2 x FT-1000ds. They have very minimal overshoot, even when set to
low power output. The problem with any ALC is.... the time constant in the
XCVR has
to match the ALC time constant in the amplifier. ALC was all the vogue back
in the
old days, when the typ tube xcvr or tube TX had NO power output control when in
ssb
mode. The 120 watts po from a drake T4XC was a bit too much when driving the
mating
drake L4B linear amp. And no, the mic gain control is not a po control on ssb
mode. On CW,
any of those tube rigs had adjustable po.
## Even with no overshoots, you cant expect the ALC in any alpha amp to
throttle back
the 200 watts po of a FT-1000D. You put 200 w into the input of the amp, the
ALC then
sends back a dc voltage to the xcvrs alc buss input, and cross ur fingers that
the alc in the amp
in question will put out the correct negative dcv back to the xcvr. Even if
it does, its too late.
The way alc works is you initially overdrive the amp, alc is derived in the amp
and sent back to
the xcvr. Too late, you still have overdriven the amp everytime for a short
period of time.
## Its works when time constants are matched, and the alc control inside the
amp is front panel
adjustable. If its not front panel adjustable, you are dead in the water.
## If using a drake T4XC with a drake L7, a cap has to be changed in the L7,
so the time constants
are identical. Ditto if using a Drake TR7 with an older drake L4B. In that
case, a cap has to be changed
out in the L4B. In normal operation the front panel adjustable alc worked
good. You could dial the PO
of both the xcvr or tx and the po of the amp at the same time, over a huge
range.
## these days, with SS xcvrs and both tube and SS amps, alc is a waste of
effort hooking up.
On my pair of MK-Vs, there is 3 x max power output settings in the menu to
choose from.
Choices are 10w, 75w and 200w. These 3 x can be set to any po from 0-200
watts, since each has its own
calibration pot. So if you have an amp that requires 110w of drive, the 200w
option can be tweaked to 110w,
or the 75 watt option can be tweaked higher to 110 watts.
## On the FT-1000D, there is a drive control on the front panel. For CW mode,
the drive is adjusted so the
ALC meter just barely shows any deflection. You will still get your desired
PO. Its NOT necessary to have
globs of ALC showing. On the MK-V, the drive control is a hidden menu item,
also easily tweaked for min
alc deflection on cw mode. On SSB, the FT-1000D has no overshoots when its
internal RF clipper is used
correctly. 2 thirds alc deflection dialed up via mic gain control 1st. Then
rf clipper switched on. Clipping level
set to 2-10 db. Meter switched back to alc, and drive control now tweaked
for any amount of alc deflection you want.
In this case, on ssb mode, with rf clipper engaged, the drive control is
actually an RF clipper output control.
With rf clipper engaged you will get far less alc meter variations, its a lot
smoother.
## The mk-V generates ssb either via DSP method, or analog mech and xtal
filter method. MK-V in either mode,
does not use a traditional rf clipper for rf processing. Instead it uses rf
compression. You can get the same effect
with rf compression , by using a faster alc decay. Implemented correctly, it
works fairly good.
Jim VE7RF
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