That's right on ALL counts Dennis.
> In a message dated 10/16/98 1:37:20 AM Eastern Daylight Time,
n7rt@doitnow.com
> writes:
>
> << BTW: I have never owned an HF ICOM radio and never will............ >>
I assume N7RT has never owned a Ten-tec, Yaesu, or Kenwood either. Because
they have ALL had this and other problems.
That's why it is an especially poor idea to use 40 or 50 watt drive
amplifiers with modern 100 watt plus rigs.
> Hmmm, that is emotion, not intellect, and really has no place in this
> discussion...
> The IC-706 is not the only rig with this problem (not by a long shot)...
I
> seem to remember reading that it is due to the time constant of the
internal
> alc which does not ramp up quickly enough to control the amplitude of the
> first few milliseconds of the first dit upon the initial switch over from
> receive to transmit, but does maintain control thereafter...
That is the problem Denny. Most power meters (and even your eye when
watching a scope) are too slow to show the problem, but a good peak storage
meter or storage scope shows the problem right away.
It is a engineering problem with how ALC systems are implemented, not an
"ICOM flaw".
> I was simply
> floating the idea for discussion of having an external keying relay put a
> short-snort of voltage into the external alc connector upon initial
keyup... I
> am wondering if this port has a short enough time constant to obviate the
You'll lose the first half second or more of transmission. Here's how you
correct the problem...
You need an external box that supplies negative voltage to drive the
external ALC input. The box has to have an adjustable control and a
disconnect device like a transistor or reed relay.
You adjust that external box so the rig, with full drive on CW or normal
audio levels on SSB, is set just a tiny bit below the desired output level.
Then, when the rig is keyed, you use the external amplifier control line
to disconnect this voltage source.
The drawback is this external box needs adjusted after every band or mode
change.
The manufacturers could correct this with a simple internal ALC logic
change. Rest assured, they aren't likely to do anything about it. If they
don't worry about transmit IMD performance, they won't worry about a
transient that slowly eats away the grids of your 3CX800's and 8877's or
blows the gates of FET's in linears.
73 Tom
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