[ARC5] Lopsided modulation

[Bob kb8tq]

Hi

Keep in mind that a few hundred Hz of FM deviation (not KHz) is quite adequate on 
40 or 80M to produce sidebands that are noticeably un-equal. There is a lot of energy
in a normal voice modulation signal below 1KHz (these radios aren’t noted for doing
well with music) …. the modulation index is not as low as you might think. 

Bob

> On Feb 28, 2018, at 10:58 AM, Dennis <dennis.monticelli at gmail.com> wrote:
> 
> Let’s drop the PA filtering explanation, guys.  It’s not even worth a back of the envelope calculation.  Not in the ballpark.
> 
> There is plenty of incidental FM going on in our MOPA’s.  Enough to support phased addition and subtraction of sidebands as the probable cause.  Here are some numbers taken a few years ago from my T-22.
> 
> 7.05MHz
> 50W plate input (500V at 100mA)
> 30W output
> Regulated supplies on osc, screen, and plate.
> Minor mods to PA tank. Otherwise stock.
> 
> 2.1KHz pull on key down with a selected high gm 1626.  2.5KHz pull with an average gm osc tube.
> 
> The resulting chirp is minimal because the change caused by osc loading occurs quickly.  There is only a mild thermal tail that one hears.
> 
> Now toss in plate modulation and about double those incidental frequency deviations.
> 
> Dennis AE6C
> 
> Sent from my iPhone
> 
> On Feb 28, 2018, at 7:09 AM, hwhall at compuserve.com <mailto:hwhall at compuserve.com> wrote:
> 
>> Perhaps the next time they are observing the lopsided sidebands, the transmitting station can wiggle the final tuning & then they can see if there is any correlation between the imbalance and the tuning. Nothing like experimentation.....
>> 
>> Wayne
>> WB4OGM
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