[ARC5] Lopsided modulation

Tom Lee tomlee at ee.stanford.edu
Sun Feb 25 02:58:58 EST 2018 

Of course! I did not mean to imply that no other steps were involved. 
But it's an economical technique nonetheless.

--Cheers
Tom

-- 
Prof. Thomas H. Lee
Allen Bldg., CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3383 (public fax; no confidential information, please)

On 2/24/2018 11:42 PM, Fuqua, Bill L wrote:
>
> Yep, except you are left with the carrier.
>
> Bill
>
>
>
> ------------------------------------------------------------------------
> *From:* arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> on 
> behalf of Tom Lee <tomlee at ee.stanford.edu>
> *Sent:* Sunday, February 25, 2018 2:28 AM
> *To:* arc5 at mailman.qth.net
> *Subject:* Re: [ARC5] Lopsided modulation
> Combining AM and FM is in fact one way to produce SSB. Flip the 
> polarity of one to select the other sideband.
>
> --Cheers
> Tom
> -- 
> Prof. Thomas H. Lee
> Allen Bldg., CIS-205
> 420 Via Palou Mall
> Stanford University
> Stanford, CA 94305-4070
> http://www-smirc.stanford.edu
> 650-725-3383 (public fax; no confidential information, please)
> SMIrC Lab - Home <http://www-smirc.stanford.edu/>
> www-smirc.stanford.edu
> Stanford Microwave Integrated Circuits Laboratory Website ... Mission. 
> The field of radio frequency (RF) circuit design is currently enjoying 
> a renaissance, driven by ...
>
> On 2/24/2018 11:21 PM, Fuqua, Bill L wrote:
>>
>>    You can use spectrum lab to experiment with simultaneous AM-FM 
>> moduation. Low modulation levels you can completely cancel out one 
>> sideband and double the amplitude of the other. It is sort of fun 
>> thing to play with.
>>
>>   73
>>
>> Bill wa4lav
>>
>>
>>
>> ------------------------------------------------------------------------
>> *From:* arc5-bounces at mailman.qth.net 
>> <mailto:arc5-bounces at mailman.qth.net> <arc5-bounces at mailman.qth.net> 
>> <mailto:arc5-bounces at mailman.qth.net> on behalf of Fuqua, Bill L 
>> <wlfuqu00 at uky.edu> <mailto:wlfuqu00 at uky.edu>
>> *Sent:* Sunday, February 25, 2018 2:15 AM
>> *To:* AKLDGUY .; ARC-5 List
>> *Subject:* Re: [ARC5] Lopsided modulation
>>
>> 	
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>>
>> FM does not manifest itself on a carrier but as sidebands. Provided 
>> that bandwith limitations don't exist, the only way a plate amplitude 
>> modulated signal can produce unequal sidebands is by simultaneous 
>> Frequency Modulation.
>>
>> 73
>>
>> Bill wa4lav
>>
>>
>>
>> ------------------------------------------------------------------------
>> *From:* AKLDGUY . <neilb0627 at gmail.com> <mailto:neilb0627 at gmail.com>
>> *Sent:* Sunday, February 25, 2018 12:29 AM
>> *To:* Fuqua, Bill L; ARC-5 List
>> *Subject:* Re: Lopsided modulation
>> Interesting analysis, thank you.
>>
>> Two things:
>> 1. The Command transmitters do have neutralization
>> 2. I appreciate that FM would not be discernable in a monitoring 
>> receiver equipped with BFO, but I'm pretty sure that it would show in 
>> the SDR's waterfall display, which is, in effect, a spectrum 
>> analyzer. No such FM of the carrier appears in either my signal or my 
>> friend's on the waterfall.
>>
>> Neil ZL1ANM
>>
>>
>> On Sunday, February 25, 2018, Fuqua, Bill L <wlfuqu00 at uky.edu 
>> <mailto:wlfuqu00 at uky.edu>> wrote:
>>
>>     Narrow Band Frequency modulation produces sidebands just like
>>     Amplitude Modulation.
>>
>>     A 20% AM signal and a FM signal with .2 Modulation index produce
>>     sidebands of equal amplitude.
>>
>>     The only difference is that the AM sidebands are in phase with
>>     each other and the FM sidebands are out of phase with each other.
>>
>>     Being out of phase the FM modulation does not have a modulated
>>     envelope.
>>
>>     When you have both simultaneous FM and AM modulation one set of
>>     sidebands subtract and the other adds. You don’t lose any
>>     sideband energy and would only notice it if you either used a
>>     spectrum analyzer or a very narrow band receiver and tuned the
>>     sidebands individually.
>>
>>     Since the final amplifiers of the ARC transmitters are directly
>>     coupled to the oscillator and that the finals are not neutralized
>>     the final acts as a reactactance tube modulator.The effective
>>     input additional capacitance of the tetrode (Miller Capacitance)
>>     is equal to the internal feedback capacitance times (the gain of
>>     the output tube +1)Cm=Cgp(Voltage Gain+1).At positive peaks
>>     modulation the effective gain of the tube is greatest and at the
>>     negative peaks the gain (at 100% modulation) is zero.This varying
>>     capacitance is directly across the tank circuit of the oscillator
>>     thus frequency modulating the signal.
>>
>>     I think even if the final amplifier were neutralized the audio
>>     rate changing of the load on the oscillator could cause it to FM.
>>     I suspect that during modulation the grid current of the final
>>     fluctuates.
>>
>>     You will not hear this FM using a BFO because it is at a audio rate.
>>
>>
>>
>>
>>     ------------------------------------------------------------------------
>>     *From:* arc5-bounces at mailman.qth.net
>>     <mailto:arc5-bounces at mailman.qth.net>
>>     <arc5-bounces at mailman.qth.net
>>     <mailto:arc5-bounces at mailman.qth.net>> on behalf of Richard
>>     Knoppow <1oldlens1 at ix.netcom.com <mailto:1oldlens1 at ix.netcom.com>>
>>     *Sent:* Saturday, February 24, 2018 8:02 PM
>>     *To:* AKLDGUY .; ARC-5 List
>>     *Subject:* Re: [ARC5] Lopsided modulation
>>          It depends on whether its FM-or PM- ing the oscillator. If
>>     it is its causing the asymmetrical sidebands. You should hear it
>>     on the oscillator signal. Try receiving it as a PM or NBFM
>>     signal, that is, slope detect it.
>>          Its not your antenna.
>>
>>     On 2/24/2018 4:09 PM, AKLDGUY . wrote:
>>     > You may be onto something with the B+ kicking downward on
>>     > modulation. I notice that the dynamotor voltage does kick down
>>     > significantly. This drop may be causing the plate voltage to
>>     > bottom out, or even go negative!, on modulation peaks.
>>     >
>>     > The MD7 modulator schematic doesn't show significant capacitance
>>     > decoupling the bottom of the mod tranny feed to the 1625 final
>>     > stage - about 1.2 uF IIRC, and I followed that when building my
>>     > own modulator. I suspect it may not be sufficient decoupling.
>>     >
>>     > But even if the final plate voltage is bottoming out or going
>>     > negative, where is the literature that says this causes lopsided
>>     > modulation?
>>     >
>>     > Neil ZL1ANM
>>
>>
>>     -- 
>>     Richard Knoppow
>>     1oldlens1 at ix.netcom.com <mailto:1oldlens1 at ix.netcom.com>
>>     WB6KBL
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