[Elecraft] KX1 Spring Tune Up Update

[Don Wilhelm]

Jack,

You need to put an 'exponential' symbol between those parentheses and 
the "2" in those formulas - the voltage must be squared where the 
formulas you included indicate multiplying by 2.

For your power output level, it *may* be a bit low.  Check the output 
with a 13.8 volt supply voltage - if it does not come up close to the 4 
watt level on 30 meters (highest output band), you may want to add the 
"Power Mod" - it is just 2 resistors to change.
For those with KX1s already producing 4 watts or more on 30 meters, I do 
not recommend adding the power mod - see my prior responses on that 
subject.

73,
Don W3FPR

Jack Regan wrote:
> This update represents a more accurate determination of the power output AND
> an adjustment of the KX1 so it would reflect these new, accurate power
> measurements.
>
>  
>
> The DL1 was used to determine the power output. Some initial confusion
> occured becasue the DL1's formula for calculating power is not correct!
>
>  
>
> Many thanks to Don Wilhelm for helping sort this out!  He has been
> responding with detailed, accurate and elegant suggestions re: what is going
> on.
>
> The DL1 manual formula is...
>
>
>
> P(watts)=((V(volts)x1.414)+0.15))2/50
>
>  
>
> Three things are going on here. The TP1 is connected to the 25 ohm output of
> the resistor chain, the diode correction is not part of the rms correction
> and the value of the diode is not as accurate as it could be.
>
>  
>
> Don's formula is...
>
>
>
> P(watts)=((V(volts)+diode drop))2/25
>
>  
>
> In his note to me re: this he "left the derivation to the student" and this
> is the formula I came up with.
>
>  
>
> P(watts)=((V(volts)+diode drop))x 1.414))2/50
>
>  
>
> When my formula produced a result different than Don's (by a very small
> positive amount) I jumped to the conclusion that Don's formula was quick and
> easy ballpark technique! Wrong!
>
>  
>
> The difference in our figures was that Don used the square root of two
> whereas I used the "standard" approximation 1.414!!!!!
>
>  
>
> I will follow Don's lead and leave the derivation to the student! If you
> email me I will send you a copy of Don's math!!! Very simple and elegant!
>
>  
>
> To continue...
>
>  
>
> I measured my diode drop and found it to be .330mv so the formula for my DL1
> is
>
> P(watts)=((V(volts)+0.33))2/25 or
>
> P(watts)=((V(volts)+0.33))x (sq. root of 2))2/50
>
>  
>
> Taking accurate measurements and finding (as previously posted) that the KX1
> was showing too high an output I took Don's advice and redid the C9 and the
> Forward Power adjustments on the KX1.
>
>  
>
> After adjusting the KX1 to show the same readings as the DL1 I now have the
> following baseline figures on the KX1 with 12VDC(DISP:BAT).
>
>  
>
>  
>
> FREQ     TP1 VDC  TP1 WATTS   KX1 WATTS   KX1 SWR
>
>  3.550   7.84     2.60        2.6         1.0
>
>  7.040   7.34     2.30        2.3         1.0
>
> 10.120   8.45     3.25        3.24-3.26   1.0
>
> 14.050   7.03     2.19        2.20        1.0
>
>  
>
> With the new baseline the agenda has changed.
>
>  
>
> 1.   If in fact these outputs are significantly low then correct them thru
>      adjustments, not modifications. They are higher than the 9 VDC specs
> but are they
>      far enough below the 12VDC specs to bother with. I'll do some reading
> and research
>      and then decide.  Any input or suggestions would be appreciated.
>
>  
>
> 2.    Explore the possibility of increasing the power output to a full 5
> watts.
>       Don has pointed out the fact that more than just the oscillator, final
> rf
>       transistor and toroids are involved in putting out more than 4 watts.
> Perhaps an
>       out board power amp using the KX1 as a VFO would be the way to go!
> QST has had several
>       articles on power amp construction lately!
>
>  
>
> 3.    Understand why the Scope and the DL1 are not showing the same results.
>
>  
>
> 4.    Get the scope to match the DL1.
>
>  
>
> Again, just for the record, the KX1 is working on all bands.
>
>  
>
> Jack AE6GC
>
>  
>
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