[Elecraft] Incidental AM using FSK-D

Tue Nov 11 04:06:17 EST 2014

I want to retract the conclusion.  Don't do this kind of mental exercise 
at 2AM.

There is a big difference in the "bit rate" between QSB and RTTY.

1)Those engaged in Frequency Measurement Tests typically observe carrier 
frequency shifts <1 Hz over several minutes due to propagation effects. 
  Most of this is due to Doppler effect of moving reflecting layers. 
Amplitude variations are due to multipath signal phase difference. 
Anyhow the effective "bit rate" is low.

2)FSK with 45 baud amplitude modulation, one would expect a series of 
sidebands.  They would occur outside the usually occupied spectrum for a 
series of RY's (essentially a square wave)-- maybe +/- 200 Hz and up. 
It probably makes a significant difference in sideband amplitudes and 
placements, whether the FSK transition is phase continuous or not.  The 
text content being sent affects amplitudes of the additional sidebands.

Maybe these conclusions made at 3:45 AM are more accurate.

Again it would be neat to compare the calculated bandwidths for the two 
point QAM scheme (F1,amplitude 1), (F2, amplitude 2) to the ideal FSK 
(F1, amplitude 1), F2 (amplitude 1) modulation schemes.

73 de Brian/K3KO

On 11/11/2014 08:03, Brian wrote:
> Phil,
>
> That's the right question.  There is no doubt that turning a pure FSK
> modulated signal into an FSK + AM modulated (QAM) signal increases
> bandwidth.  The question is how much and how far down are the additional
> side bands.  I'm sure there are guys here who can either calculate or
> measure the effect.  It would be interesting to know the answer.
>
> As a practical matter, mother nature does this to almost all FSK signals
> via propagation effects.  Often received mark and space amplitudes
> different by a LOT more than the amounts we're talking about here.  It
> is interesting to watch this.  Given this mother nature bandwidth
> smearing, it is doubtful that the real world impact of K3 QAM vs pure
> FSK is significant.
>
> 73 de Brian/K3KO
> On 11/11/2014 06:56, Phil Wheeler wrote:
>> As a practical matter "My K3 increases power by 10% when in Space as
>> opposed to Mark": is this really something to be concerned about?
>>
>> Phil W7OX
>>
>> On 11/10/14 10:51 PM, Brian wrote:
>>> And what if this was done this with the standard 2.7 KHz filter?
>>> Filter passband ripple has the the stock answer to what people are
>>> observing.
>>>
>>> Also what about dynamic vs static differences. Is it possible in the
>>> dynamic situation the differences would be greater?
>>>
>>> It does sound like there is some confusion precision with accuracy.  A
>>> measuring device might offer high precision and resolution but lower
>>> absolute accuracy.  People often make accurate difference measurements
>>> with with a device which less accurate than the delta one observes.
>>> If the difference are small, they can be quite accurate.
>>>
>>> 73 de Brian/K3KO
>>>
>>>
>>> On 11/11/2014 02:13, Joe Subich, W4TV 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.
>>>>
>>>> 73,
>>>>
>>>>     ... Joe, W4TV
>>>>
>>>>
>>>> On 2014-11-10 8:42 PM, Bill Lewis wrote:
>>>>> I am looking for information on how to eliminate incidental AM when
>>>>> using
>>>>> FSK-D.
>>>>>
>>>>> My K3 increases power by 10% when in Space as opposed to Mark.
>>>>>
>>>>> Thanks much, Bill, W8NN
>>
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