[Central-Electronics] 200V on AM

[Jim Candela]

Joe,

   I concur with the others on this topic. I'm a 20a
owner, not a 100/200v owner. That said there is
similar AM characterictics on all 3 of these rigs. My
point here is that these CE rigs on AM behave just
like plate modulated until you exceed 100% modulation.
>From that point on they are VERY different. 

I have some pictures at the following link:

http://pages.prodigy.net/jcandela/CE20AQRO/

picture d, and e show 100% modulation for envelope and
trapezoid patterns. This is the same for plate
modulated or low level AM like CE.

pictures h, and i show the same rig being over
modulated. This overmodulation turns into DSB with
reduced carrier, and on an AM receiver it sounds
awful. With a SSB receiver it is fine, or with AM sync
detection it is fine. As a result you must control
your audio level very carefully, or your reports on AM
won't be very good if the receiver is using a diode
detector. If you simply turn your gain down, then the
average modulation percentage will be pretty low. 

The 32V transmitter will show the envelope stay at the
baseline during the time that the 100% negative
modulation is being exceeded. The 32V will splatter
too when this happens.

The first thing to do is get your speech polarity such
that your asymetrical voice has the big peak being
positive modulation, and not the reverse. With the
D-104 you simply swap the wires in back of the
element, and see what the difference looks like on the
scope. A DPDT switch on the back of the D-104 head can
be used to switch the speech polarity quickly.

Going a step further you can use a peak limiter /
compresser pretty effectively to combat this DSB
reduced carrier issue. 

Going a 3rd step, you can perform a modification to
your transmitter. I call this "progressive negative
cycle loading". This is shown at PNCL.jpg at the web
link above. 

On my 20a I use all the techniques together with
excellent results.

The whole document on my AM activities with the 20a
are in the file QRO20a3.doc at the same link.

I think that CE equipment on AM is competitive with
plate modulation watt per watt so long as the issue I
brought up is addressed. That said the 100V/200V will
be about an 'S' unit weaker than the 32V due to the
power difference of say 25 watts versus 100 watts
carrier output.

Regards,
Jim
WD5JKO

--- joe sloss <k7mks at comcast.net> wrote:

> I have the chance to use a Collins 32V-3 for AM or a
> 200V for vintage SSB plus AM.  Leaning toward the
> 200V.  Would appreciate comments from those who have
> used their 100/200V's on AM as to audio quality and
> any other tidbits you care to pass on.
> 
> Thanks, Joe k7mks
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