Manfred,
you do have a point BUT
My transceiver is a rather old and much modified FT102, using three 6146B tubes
in the PA with negative feedback to the driver. The 3rd order IMD is -44dB
relative to PEP: the 5th order is actually -42dB relative to PEP, the 7th order
is -54db relative to PEP and the 9th order is well below -66dB relative to PEP.
(Numbers from the ARRL product review)
The phase noise is VERY good because of using VCOs covering a narrow
band.................
So an amplifier to go with this DOES need to be good!
At the October RSGB Convention, I'm doing a presentation on "Clean signals or
Spreading the sewage": this has entailed looking at product reviews from 1972
and trying to boil down the info. What really does come out is the massive
increase in high order IMD products once the move to solid state PAs occurred.
Especially in the later days of tube PAs, IMPs higher than 7th order could be
ignored because they were so low as to not really be detectable; once we got SS
PAs, 9th and even 11th order (and even higher) were no longer negligible.
Before I retired, I was often criticised at annual reviews for having a
'negative attitude to change'. When I asked why a degradation that accompanied
change was a good thing, there were problems. The most honest appraisal came
from a manager who wrote "Peter does not suffer fools gladly, especially when
they are in management".......
But in 32 years, I outlasted all my 19 managers, including one who lasted for
an inordinate amount of time after a conviction for gross indecency in a public
lavatory with two other men, followed 18 months later by a DWI in a company car
- usually an instant firing occurrence!
73
Peter G3RZP
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