Gentlemen,
I too have seen this effect (spectrum analyzer) on several newer solid
state CPU controlled rigs. It is due to the "drive control" actually
controlling power leveling circuits that look at power sensing, rather than
an analog drive control feeding a fixed gain linear amp stage.
The answer is to use the radio at full power with a broad band attenuator
pad. Also with some rigs that only barely meet spurious standards, some
switchable bandpass filtering or tuning would be nice too. The two
functions could be incorporated into one box with rg-142 double shielded
cable interconnections.
As an aside; double shielded pigtails and jumper cables have helped
immensely to tame the squabbles between various radios and appliances in
the shack.
Jim, ac6tk
----------
: From: w8ji.tom <w8ji.tom@MCIONE.com>
: To: CQK8DO@aol.com; towertalk@contesting.com
: Subject: Re: [TowerTalk] Short-Snort
To: <towertalk@contesting.com>
: Date: Saturday, October 17, 1998 2:40 PM
:
:
: 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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