[Elecraft] Incidental AM using FSK-D

[Myron WVØH]

Don et al,

I would try the Elecraft DL1 and the power turned down on the rig to about 10 Watts. The DL1 is the most accurate RF power measuring device under $30 and competes with RF power meters costing much more. Couple it to an accurate DVM and you have a very decent power measuring setup. Of course it's absorptive and not in line like a Bird but hey, it's a start.

If you put the scope probe across the 25 Ω tap where the diode is connected and left the DL1 output open, you could get an accurate "sample" of the RF envelope across 25 Ω.  

Myron WVØH
Printed on Recycled Data

> On Nov 10, 2014, at 7:38 PM, 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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