[Amps] MOSFET amp filtering - was: auto-tune

[Jim Thomson]

Date: Thu, 15 Dec 2016 10:33:55 -0800
From: Jim Brown <jim at audiosystemsgroup.com>
To: amps at 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