[VHFcontesting] Testing IC-7300 for TX power overshoot

John Ackermann. N8UR jra at febo.com
Thu Oct 4 21:03:47 EDT 2018

Hi Marshall --

The 'scope in my test was set to trigger as soon as RF was detected, so it should catch what you described.   The digital scope has a memory that captures a single-sweep snapshot showing both before and after the trigger point, so it should catch any key-down spike.  I did a couple of tests with as fast as  500 nanosecond sweep, where you could see the individual cycles at 14.2 MHz, and saw no signs of a spike.

I suspect the 7300 (and probably 7610) behave differently in this regard than the older Icom rigs.  I'd love to test any of the other rigs if I could get my hands on them.


On Oct 4, 2018, 8:33 PM, at 8:33 PM, Marshall-K5QE <k5qe at k5qe.com> wrote:
>Hello John and other VHF Contesters.....I may be completely lost here, 
>but I thought that the "ICOM spike" occurred when PTT was pushed just
>the first of a transmission......The overshoot was in the first few 
>milliseconds of TX, not at key-up.  The causes are poor design and have
>been around for years.  There have been several different "work 
>arounds", but that is what they are.  They are not fixes.
>I use the transverter port on my Pro2s and Pro3s to run my 
>transverters.  Those ports are supposed to be -20dbm.....1/100th of a 
>milliwatt.  You cant hurt anything with that, so even if there is a 
>spike, it is so low that no harm is done.
>I am also not an instrumentation guy, so it would be nice to see how 
>this spike is measured.  You would have to have a very fast scope to
>the spike, but certainly there are such instruments running around.
>If I am completely lost on this, here is the chance for the real
>to beat me up......HI.
>73 Marshall K5QE
>On 10/4/2018 12:19 PM, John Ackermann N8UR wrote:
>> This may be old news, but I wanted to see if my IC-7300 had the
>> power spike that's been reported on other Icom rigs when the power 
>> output is turned down.  The short answer is that I don't see any sign
>> of overshoot, so this rig should be safe to use with amplifiers or 
>> transverters that want the wick turned down.  (Of course, you can 
>> still blow things up by forgetting to turn the power down...)
>> Details and pretty screenshots at https://blog.febo.com/?p=321
>> 73,
>> John

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