[ARC5] AM modulating an "ARC-5" transmitter...

[DSP3]

Genrs,

Ken is correct about, especially, high-level modulation.  The actual 
power, peak, average, wherever is wholly dependent on the waveform.  The 
difference between the peak and average for two transmitters may well be 
quite different.  Its always best to "visually" characterize the 
envelope as well as use other measurement methods.  I recently got into 
a rather heated exchange with someone who refused to acknowledge the 
existence of low-level modulation modes.  He insisted that all AM 
resulted in a peak and average power greater than the un-modulated 
key-down carrier.  I could not convince him otherwise.  A scope in this 
fellows shack would have done wonders.

Jeep - K3HVG

On 10/10/2015 5:23 PM, Kenneth G. Gordon wrote:
> On 10 Oct 2015 at 13:10, Richard Knoppow wrote:
>
>> AM can be really confusing.
> Yes. I am almost constantly confused when dealing with AM...
>
>>   The PEAK power is four times carrier
>> but average is 1.5 times carrier.
> Well yes, but doesn't that really depend on the waveform of the modulating
> signal? I look on that 1.5 times carrier as the average of the average voice.
>
>> PEP works for AM but the FCC
>> definition does not make sense.
> No, it certainly doesn't. At least not to me.
>
>> In the old days the power of amateur
>> transmitters was regulated by _input_ power, I think because measuring
>> RF output can be difficult. It also applied to the carrier only.  So,
>> the output would depend on the efficiency of the transmitter. Likely
>> carrier output of a good plate modulated 1 kw transmitter with Class-C RF
>> output stage would be on the order of 700 watts carrier.  The FCC by
>> memory refers to the "average" PEP.
> Sounds like "the average of the average" to me...
>
>>   So average of a sine wave is about
>> 0.637 of peak. Now, does the FCC want the _average_ of a 1KW total at
>> 100% modulation or what?  If they specified peak power at the crest of a
>> 100% modulated wave as no greater than 1KW the carrier could not be more
>> than 250 Watts. If they are specifying the _average of the peak power_
>> then we have a maximum of 1.57 times this value or about 392 Watts
>> carrier or about 1.57KW for 100% modulation. Given our assumption of a
>> 70% efficiency of a Class-C plate modulated stage this would be on the
>> order of 600 watts input for the carrier.
> Yes....sigh...
>
>>       I am not at all sure this is correct but think the FCC could
>> certainly write the spec in a less confusing way...
> if they really cared to...
>
>>   They should also have
>> grandfathered all the 1KW input AM rigs which existed at the time the
>> new regulations were instituted.
> Although AM is NOT one of my favorite modes, I most heartily agree with
> you on this issue.
>
> However, I do think that the proper use of AM would be valuable when
> needed. If one uses the transmitter's VFO, turning off the receiver's BFO, to
> zero-beat an SSB station before transmitting, and if one keeps the
> transmissions very short, it will generally be some time before the SSB
> station will realize you are on AM. It always worked for me.
>
> Ken W7EKB
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