Re: Water Fall display distribution of users #Waterfall #question


Chuck Moore <wd4hxg@...>
 

Bill

I appreciate the feedback and guidance. I suspect based on the premise the
harmonic problem is due to overdriving the rigs modulator that there is hope
I am not one of the lids agitating Mike.   :-)  I generally keep the output down
to 30 to 60 watts. The rig is rated for 200 watts out and microphone gain is
reduced to avoid running higher power. Also I will go back to the IF Bandwidth
and throttle it back to a nominal 2.4 KHz with Split turned on. Hopefully that
will keep me off the radar and in good graces of other ops.

I have a couple of friends about 125 miles distant and will ask them to critque
the signal using their water fall display.

Regards

Chuck WD4HXG

On Oct 6, 2021, at 9:01 PM, Bill Somerville <g4wjs@...> wrote:


On 07/10/2021 01:43, Chuck Moore via groups.io wrote:
 A couple of us have been on the war path the last few years to clean up all the operators generating harmonics.  None of them were using split mode as that mode avoids even the 2nd harmonic which could be at a minimum of 3KHz (i.e. 1.5Khz*2=3KHz).  We're down to seeing about 1 or 2 ops generating harmonics per week now.

It is likely I am one of the PITAs. I had not been using split, as up until now it was not clear to
me what it really did. I did however follow the advice to not drive the audio to the point that
the ALC was driven active as displayed on the rigs meter and I keep the audio set to less than
55%.

Chuck,

this is a misunderstanding of the issue and such advice can easily lead to a very poor transmitted signal. Audio harmonics are generated when the audio input to the rig is too high causing clipping at the modulator input. ALC is not a measure of that issue, it is too late in the system. To understand this consider an audio tone of 3000 Hz being input to the rig, you will not get an ALC indication however high you set the audio input level, this is because the audio tone plus all the generated harmonics from gross over-driving of the rig's audio input will be attenuated by the SSB Tx filter before even reaching the PA  where ALC is measured. Then if you set your Tx offset to 500 Hz then the over-driven input will now mean you will transmit a tone at 500 Hz and harmonics at 1000 Hz, 1500 Hz, 2000 Hz, and 2500 Hz.

The lesson to be learned here is that ALC *may* be used as an indication of audio over-drive, but *only* if the setup is done with a tone around 1500 Hz. Further to that do not *ever* attempt to compensate for low output when using audio offsets near the edges of the rig's SSB Tx filter, particularly the lower bounds!

This pinned post contains recipe for setting the correct Tx audio levels: https://wsjtx.groups.io/g/main/message/13890

73
Bill
G4WJS.








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