[Elecraft] Incidental AM using FSK-D

[Joe Subich, W4TV]

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 <w3fpr at embarqmail.com> 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 <lists at subich.com> 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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