[CQ-Contest] How close is too close?

Tom W8JI w8ji at w8ji.com
Mon Feb 20 08:56:20 PST 2012

> Numerous times this weekend I am being asked to QSY when "firing up" about
> 350 to 500hz away from a BIG GUN Multi.  One of them was 10 over to me on
> 40M and I had zero problem hearing the noise floor where I was sitting and
> was actually running at 100 rate.  Yet this clearly bothered the other op.
> What's with this?

Probably the MP.

> Why would the FT1000MP Low Power guy be bothering the full power guy with
> much newer and clearly better gear?  Is it that they are expecting 700 -
> 1000hz of quiet breathing room in one of the biggest CW contests of the 
> year
> on an open band?  I certainly hope not.

There is an unmodified 1000MP south of me, and I can't operate within 2 kHz 
of him even when he is barefoot.

Some people are fine 300 Hz or 400 Hz away. Some people, even though 
barefoot and not particularly strong, are problems. Two of the worse rigs 
ever for transmitter clicks were the FT1000MP and MP MKV. The Inrad mod just 
barely makes the 1000MP passable, and not for close stuff.

Measure the rise and fall times. The lowest possible bandwidth is the 
reciprocal of rise or fall times, assuming a sine shaped rise and fall. 
That's as good as we can do, not as bad as it could be for that rise or 
fall. 2.5mS, with a good shape, puts the two lowest order sidebands 200 Hz 
away on each side.

The K3 is not without flaw either. It would be nicer if it could be made 
softer, and have ability to have TX delay without is chopping up the 
characters. The lack of being able to add TX delay was giving me fits with 
rising edge clicks from external switching times, until I added an external 
sequencer. It took major hardware and wiring changes to work around the lack 
of being able to just slightly increase TX delay.

I think 1 kHz is a good target spacing, unless the rigs are better. Then 500 
Hz is probably a minimum for most rigs. It should not be that way, but that 
is how it is. The lower the RX noise floor, the worse the transmitter 
problem becomes. I imagine a MP sounds OK with S7 or louder background 

73 Tom 

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