[Amps] Questions on Alpha 8410
jim.thom at telus.net
Wed Mar 1 12:16:57 EST 2017
Date: Wed, 01 Mar 2017 09:56:45 +0800
From: Alek Petkovic <vk6apk at bigpond.com>
To: AMPS <amps at 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.
## 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.
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