[TowerTalk] Short-Snort

[Eric Gustafson]

>From: "Dick Green" <dick.green@valley.net>
>Date: Sun, 18 Oct 1998 01:39:29 -0400
>
>I must have zipped by and deleted the original post on this
>topic. Could someone forward me a copy? Thanks in advance.
>
>BTW, the Kenwood TS950SDX lets you adjust the rise time of the
>CW waveform from 2ms to 8ms. Wouldn't lengthening the rise time
>allow time for the ALC to ramp up? I think I'm seeing the
>effects of transients when driving my Alpha 87A amp from the
>'950, especially when sending fast CW from the computer (CT, for
>example) in full break-in mode. When the rise time is set at 2ms
>I see random spikes to infinity on the '950's LED SWR meter. As
>I increase the rise, the frequency of the spikes gradually
>diminishes and they disappear at 8ms. Anybody else ever see
>this?

Not being a frequent amplifier user, I can't say I've experienced
this problem.  But I _am_ a bit bewildered to hear that the amp
and transciever makers have apparently not been in communication
with one another.  And I must wonder why on earth anyone would
design an ALC circuit that had less than 10 times the bandwidth
required to follow the risetime of the envelope of the expected
input signal.

>
>I've never been able to figure out why the spikes show up as an
>increase in SWR. I've used a dual trace scope to check the
>timing on the T/R pulse from the '950 to the Alpha (I use a
>homebrew bipolar transistor interface) against the CW waveform,
>and it clearly shows the T/R signal rising well before the CW
>waveform begins (as I recall, it looked like the timing diagrams
>in the service manual.) 

>So, I don't think the Alpha isn't switching in time (unless
>those PIN diodes are really slow.)

Don't worry about the pin diode switching speeds.  Even if they
used the biggest slowest diodes available, the carrier lifetimes
are in the small number of MICRO seconds.  Now, the pin switch
driving electronics could easily be a cause of concern.  But
since this is so easy to get right and costs no more to do, I'd
doubt that this is a problem either.

Snip...

73, Eric  N7CL

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