First, you are quibbling about less than 0.5 dB *even at 10%*
difference in claimed power output. Second, my measurements were
taken with a watt meter capable of .01 W (10 mW) precision and the
worst case difference was less than 2% (0.08 dB) - not the 10%
claimed.
Dynamic (scope) measurements may show a slightly greater dynamic
difference - if you can read them with the precision necessary to
detect a 3% ripple on a 140V RF envelope - due to wave shaping for
bandwidth control. Even then, such minor (0.08 dB) differences in
mark/space power are insignificant with the majority due to ripple
in the IF filter. Both the 2.7 and 2.8 KHz filters show > 1dB
ripple in the passband - see:
http://www.elecraft.com/K3/K3_filter_plots.htm
73,
... Joe, W4TV
On 2014-11-10 9:52 PM, Hank Garretson wrote:
Keep in mind that this is one case where instrument precisipn is more
important than instrument accuracy.
73,
Hank, W6SX
On Monday, November 10, 2014, Don Wilhelm <[email protected]> wrote:
Not so easy even with a decent scope.
50 watts will produce 141.42 volts p-p, and 55 watts will produce 148.32
vp-p.
That is a difference on 7.1 vp-p for a 10% difference in power.
That small difference is difficult to discern on a scope at that vertical
amplitude.
Yes, a small difference in amplitude can be discerned, but to quantify it
to less than a 5% difference is difficult to measure with a 'scope.
73,
Don W3FPR
On 11/10/2014 9:23 PM, Hank Garretson wrote:
Easy. Put a decent scope on the RF envelope.
73,
Hank, W6SX
On Monday, November 10, 2014, Joe Subich, W4TV <[email protected]> wrote:
My K3 increases power by 10% when in Space as opposed to Mark.
Two things here ... 10% is abut 0.4 dB. How did you measure the power
difference and did you do so with an instrument with enough resolution
to accurately measure that difference at the power level you were using?
For example a Bird Wattmeter can't possibly measure with that level of
accuracy nor is one likely to be able to read an analog meter that
closely.
I have measured my K3 on RTTY with a wattmeter traceable to NIST and
specified for 3% accuracy and have done so at four specific power
levels (25, 55, 80 and 105 Watts) to eliminate any ALC non-linearity
or PA compression from consideration. The specific Mark/Space power
levels were measured by placing the rig into transmit in FSK_D mode
with the FSK input closed (Mark), measuring the power output for a
given power setting, then opening the FSK input and noting the PO
(and change).
In all cases, the difference between MARK and SPACE was less than 2%
(less than the meter's specified accuracy) and at two power levels (55
and 80 W) the measured difference was less than 0.2W (<0.2 dB at 55W).
These measurements were made with standard "High tones" (2125/2295 Hz)
and the K3 was equipped with the optional 2.8 KHz, 8 pole IF filter.
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