4 decodes of WD2XSH/17  all -29

 2017-03-06 01:26  WD2XSH/17  0.475648  -29  0  FN42pb  0.1  PA0O  JO33hg  5630  49 
 2017-03-05 23:04  PA0O  0.475602  -30  0  JO33hg  0.2  SV8RV  KM07ks  2042  142 
 2017-03-05 22:58  PA0O  0.475602  -25  0  JO33hg  0.2  SV8RV/1  KM07ks  2042  142 
 2017-03-05 22:10  PA0O  0.475601  -27  0  JO33hg  0.2  EA7HPM  IM67xj  2017  214




QTX  and IRF540Z  ( my last one  i smoked 9)
 this version has about 2500 pF  G-S 
It can run at 5A 22V   with the highest output sofar
but at 100W input level everything heaths up coils and IRF
the antenna current meter  relative  60-70%  
must be close to  100W  rf 

the standard IRF540 measured 2700pF
this one is second best   about  antenna  50%
it is very critical in tuning  the IRF540 starts in self oscillating mode  then the output and current
sudden drops to very low

I can get 100W level with the QTX but on the edge  and only with the Z version of the 
IRF540   still have to fine tune with a piece of ferrit to have max out and good pulseform
it is not  plug and play this QTX  it needs fine tuning and some C values differ a lot with the original
i had to use  C2 C3  15 + 15 nF   and the loading C is 10nF + 6n8 
plus a fine tuning of L3 with a ferrit rod is needed.
Until now every day i saw a different output and or tuning..
The type of IRF makes a lot of difference
This season only one time my QTX was decoded by WD2XSH/17


I know I should have build a heavier PA  that is less critical ?
Awaiting mosfet drivers TC4422 type that can drive the IRFP4227 a heavier type FET


I tried the IRF510  this version has the lowest G-S capacitance of the 3  about 400pF measured
So this  IRF510 should be the most usable RF amplifier 
  But no output with this setup  and worse in standby receive the IRF510 still draws elevated bias current  0.040   The other IRF's do not have this leak current.
  this generates 4-5 S units noise in receive

                                          QTX  IRF540Z   22V 4.5A 
                                         h=50V/dev  Drain pulse 125V  output 370V tt  # 132V eff 


 

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