[ARC5] Harmonic question

[Dennis Monticelli]

Richard,

Makes sense to me.  Bill F. essentially said the same thing.

Applying the non-linearity pre vs post modulation produces a very different
effect.  A final stage that has plate modulation applied is akin to plate
modulating a series of harmonically related carriers.  Each such carrier
would be modulated normally.  If the modulation is applied prior to the PA
then the non-linearity of the PA would act upon the carrier and its
modulation components equally creating horrible distortion.  Speech
components from say 500 to 1500Hz would get doubled, tripled, etc along
with carrier harmonic generation.

Dennis AE6C

On Sun, Apr 16, 2017 at 12:23 PM, Richard Knoppow <1oldlens1 at ix.netcom.com>
wrote:

>     I was aware of this circuit but had not seen this paper. Thanks for
> posting the link.
>     As far as modulation of harmonics is concerned. I think it depends on
> where the modulation is applied. I mean if the carrier is modulated at a
> low level and amplified by an amplifier which produces harmonics it seems
> to me the modulation sidebands will be multiplied in the same way as the
> carrier. If the modulation takes place in the final amplifier the harmonics
> will be modulated as though they were secondary carriers and modulation
> will be the same as the carrier. I am not quite sure of the theory and not
> quite sure where to look it up.
>    If we consider broadcast transmitters the use of plain linear
> amplifiers ended around the late 1930s. After than most transmitters were
> either plate modulated or Doherty type. The Doherty is, in fact, a linear
> amplifier.  So, what happens to the modulation of the harmonic output of
> these two types or of a plain linear as used for SSB?
>    The effect on SSB should be the same as for AM, i.e., if a harmonic is
> generated by the linear it should multiply all components of the signal.
> That would result in doubling the bandwidth of the second harmonic or
> tripling it for the third harmonic.
>     Does this make sense?
>
> On 4/16/2017 11:37 AM, Sheldon Daitch wrote:
>
>> Neil,
>>
>>
>> Sure, as all transmitters develop some level of harmonic emissions.
>>
>> Most modern commercial transmitters have near negligible harmonic
>> emissions, but near negligible doesn't mean they don't exist.
>>
>> As to audio quality, here is what I just found on a quick and dirty test
>> for the second harmonic of 690 kHz, WOKV (the old WAPE).
>>
>> Why this one?
>>
>> Their day-time transmitter site is about 1228 smoots or 6860 feet from
>> my house and the second harmonic very  easy to receive.   Audio quality,
>> not so great, although it was perfectly understandable, with maybe 10%
>> distortion.  What was interesting was the amount of "buzz" associated
>> with the second harmonic, no doubt a product of the digital type
>> transmitter.  I also noted nothing heard 10 kHz on either side of the
>> second harmonic, the resolution of a digital tuned automotive receiver.
>>
>> On the specifics of the third harmonic, RCA utilized the third harmonic
>> energy of a tube amplifier to increase the plate efficiency in the 5kW
>> BTA-5T.
>>
>> One technical document on this transmitter is at:
>>
>> http://www.nrcdxas.org/articles/bta5t/
>>
>>
>> 73
>>
>>
>> Sheldon
>>
>> WA4MZZ
>>
>>
>>
>>
>> ------------------------------------------------------------------------
>> *From:* ARC5 <arc5-bounces at mailman.qth.net> on behalf of AKLDGUY .
>> <neilb0627 at gmail.com>
>> *Sent:* Sunday, April 16, 2017 4:52 AM
>> *To:* ARC-5 List; milsurplus
>> *Subject:* [ARC5] Harmonic question
>>
>> Suppose I have a properly adjusted AM transmitter and am operating it.
>>
>> What would a nearby listener hear at say, the third or fifth harmonic,
>> assuming a good strength carrier at that frequency is present at his
>> receiver?
>>
>> Is the bandwidth of the sidebands 3x or 5x, so all that's heard is
>> incomprehensible splatter?
>>
>> This is not a trick question. The textbooks don't address this at all.
>>
>> 73 de Neil ZL1ANM
>>
>>
>>
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>>
> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
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