-----Original Message-----
From: Jack Regan [mailto:ae...@sbcglobal.net]
Sent: Monday, March 23, 2009 5:06 PM
To: 'Jack Regan'
Subject: RE: [Elecraft] KX1 Spring Tune Up Update
Don has pointed out that the formulas I posted did not appear as superscript
2, indicating a squaring function so I have changed the post to ^2 when
squaring is required.
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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