On 2020-10-09 12:38 PM, Jim Brown wrote:
> W4TV, a retired broadcast engineer,
> traced the cause down to their method of doing ALC.
I can't claim credit for that ... the information was originally
identified by W8JI in Yaesu rigs as far back as the FT1000D and
FT1000MP (and other Yaesu transceivers of that era).
Not only do Yaesu derive their ALC based on overdrive of the final
amplifiers, they have excess gain in both their TX IF and ALC loop
which only makes matters worse (as anyone who is familiar with the
design of servo control circuits will understand). One can make a
noticeable improvement in TX IMD in Yaesu transceivers by reducing
the TX IF gain (if one knows how to access the factory alignment
menu) on each band to the minimum necessary to reach full output.
Reducing the IF gain also reduces "overshoot" and helps with the
key clicks but - alas - it does nothing about the phase noise
issues.
73,
... Joe, W4TV
On 2020-10-09 12:38 PM, Jim Brown wrote:
On 10/8/2020 10:43 PM, JR wrote:
K9YC published a paper purporting to document and quantify transmitter
noise figures - which belies the claim and ultimately validates what
the ARRL Lab told me - namely neither rig is a problem.
ARRL Lab engineers are not active in contesting, hence are unlikely to
see these problems. My "paper" you referenced is a re-plotting of ARRL
Lab data for all rigs on the same scale, and at scales large enough to
clearly see differences. It is THEIR DATA, not mine.
Not a problem? Yaesu rigs used to be pretty clean on SSB; current
vintage Yaesu rigs are VERY dirty on SSB, occupying three times the
bandwidth of a clean SSB signal. W4TV, a retired broadcast engineer,
traced the cause down to their method of doing ALC. I became aware of
this when trying to work next to one of these dirty stations on the
band; the P3SVGA display clearly showed the IMD-caused splatter on both
sides of the station's intended signal. The splatter extended more than
2 kHz below his USB suppressed carrier frequency, and almost than 5 kHz
above it. A clean SSB signal (not ESSB) signal is about 2.7 kHz wide.
After this first experience, I observed a lot of signals like this, and
asked some of them what rig they were using. It was nearly always a
Yaesu. Those that were not were splattering because they were
overdriving their amp.
This is NOT parochialism, it's solid engineering, which is my expertise.
What's yours?
73, Jim K9YC
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