Date: Thu, 15 Dec 2016 10:33:55 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] MOSFET amp filtering - was: auto-tune
http://k9yc.com/P3_Spectrum_Measurements.pdf
73, Jim K9YC
## Excellent presentation. This is half the problem with amateur radio gear.
Here it is, almost 2017,
and most equipment makers have still not figured it out.... yet. The problem
is, there is no standards.
And all of this gear produced over the last 30 years still got rave reviews in
QST, etc.
## IF this was commercial – military gear, it would be built to a given spec,
or to the end users specs.
For amateur use, its not like they have to spend a ton of extra money... to
build a xcvr that doesnt put out
key clix.
## The k3 is a superb radio for cw. But its -29 db pep IMD3 on tx, is
nothing to brag about. The dishtronix at
-30 db pep IMD3 is no better. For the $10K price tag, it should be a helluva
lot better. If you look at any
marine ssb gear, the IMD is almost 2 magnitudes better...and without resorting
to Class A blast furnace
techniques, nor pre-distortion concepts. Huge difference between Icom marine
ssb gear...and icom ham gear,
like apples + oranges. Look at the design of the driver + final pa section
of some of this commercial SS gear.
They have increased the NFB, reduced the gain, and operated the SS section at
a reasonable power level, not
flat out. Z matching is optimized for that lower power level. Then the eff is
much higher. Typ ham gear barely makes
50 % eff...which drops like a rock, when xcvr operated at reduced power levels.
## Some of the SS kw+ amps get around the lower eff... when run at
reduced power, by auto lowering the VDC.
Solves the eff problem, but imd climbs back up.
## To be fair though, also notice commercial gear does not have mic gain
controls at all, nor speech processing.
If its a higher powered 1 kw + setup, its designed as a complete end to end
turn key system.
## some of the lousy TX imd on some amateur gear is astounding. Worse case
is typ on 12m + 6m.... but its all
over the map. Why is DX engineering still selling BN-86 baluns...go figure.
## One fellow in VE3 land bought a yaesu MK-V....complete with key clix.
Radio inspector read him the riot act,
and the dealer he bought it from. Had to be returned to the dealer asap, and
key clix mod done.
Jim VE7RF
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