Ian White, G3SEK wrote:
>
> Peter Chadwick wrote:
> >
> >Is this phenomena peculiar only to Icom rigs, or do Yaesu and Kenwood do it
> >also?
> >
> >Funny, these rigs - slow attack on ALC, too fast a rise on the rising edge of
> >the keying waveform...........somebody has reversed priorities!
>
> They seem to have solved it on the IC-746. That's as far as I can see,
> on a non-storage scope but with the brightness turned way up to make
> even a very short spike visible.
>
> It's certainly very visible on the FT-990. As W8JI and others have
> noted, the design mistake was to use the ALC to vary the RF power. It
> could have been done much more effectively by manually controlling the
> gain in the TX IF stages (one day, I'll work out how to re-wire the RF
> PWR pot on the '990 to make it do just that).
>
> As K6NDV has also noted, a competent amplifier control circuit like the
> ACOM will detect this spike and may signal an "overdrive" fault. To
> avoid the same problem, I've reluctantly had to advise users of the
> Triode Board and Tetrode Boards to slow down the response of the grid
> current detector circuit slightly... reluctantly, because the source of
> the problem is in the transceiver, not the amp.
Your comments are leaning me towards the 746. I'm glad this came up
because I was just getting ready to order a 706mk2g, and hadn't heard
about the large spike problem. Now, I will use it mobile mainly, but I
still want to have a halfway decent rig in the house as it will sit in
there 90% of the time. I only put it in the car when I travel somewhere.
I have a friend who had this problem with an icom and and alpha amp but
I had forgotten about it. I plan to eventually use the rig with a solid
state amp. A kw spike when running cw or fone does not turn me on too
much. I can handle a small spike , full power? Not too crazy about that.
I think most all rigs will spike a little. I searched the net looking
for other comments on this problem and pretty much mirrored what I read
here. BTW, good news for FT-100 owners...Supposably they are pretty
clean for spikes by what I read. So I guess I could go that route, but
I'm starting to like the features on the 746 better. The reviews have
all been glowing pretty much, so I may just cough up the extra 400$
bucks or so. I just need to make sure it's a 12v rig, which I think it
is. Should make a good mobile rig. MK
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