Michael Black wrote:



But from reading of material from that period, nobody seemed to be
plate modulating an SSB rig.

Michael VE2BVW


Thank you.

-Bill

Plate modulation is not a way of producing SSB. The SSB signal must be
amplified linearly, and generated at low level. FM, I believe, not only
can but benefits from being run through a Class C stage. The idea with
plate modulation was that the RF path was CW all the way to the finals,
and the audio directly modulated the final amp. The modulated signal
then had to be handled only in a linear fashion, but that was at the rx
end-the last stage in the tx being, obviously, the final.

The gizmo we are looking at seems to be a simple mod xfmr placed in
the plate supply to the 6146s in the tx. An audio amp such as a stereo
or guitar amp hooks to it and the mic goes to a preamp. In fact my
guess is back then a guitar amp was exactly what was most used.

Bret Ludwig wrote:

Plate modulation is not a way of producing SSB.

Ok, you are vindicated.

-BM

On 25 Aug 2005 21:37:42 -0700, "Bret Ludwig"
wrote:

Plate modulation is not a way of producing SSB. The SSB signal must be
amplified linearly, and generated at low level. FM, I believe, not only
can but benefits from being run through a Class C stage. The idea with
plate modulation was that the RF path was CW all the way to the finals,
and the audio directly modulated the final amp. The modulated signal
then had to be handled only in a linear fashion, but that was at the rx
end-the last stage in the tx being, obviously, the final.

The gizmo we are looking at seems to be a simple mod xfmr placed in
the plate supply to the 6146s in the tx. An audio amp such as a stereo
or guitar amp hooks to it and the mic goes to a preamp. In fact my
guess is back then a guitar amp was exactly what was most used.

Well, you can't use it to plate modulate a kwm2 or collins S line
either. The finals in those transmitters can not be run in class C.
There is not enough grid drive available in the CW mode to do it. Also
the plate tank components are not hefty enough for the added plate
voltage plate modulation supplies. Neither is their power supply heavy
enough for AM operation.

73
Gary K4FMX

"Bret Ludwig" ) writes:
Plate modulation is not a way of producing SSB. The SSB signal must be
amplified linearly, and generated at low level. FM, I believe, not only
can but benefits from being run through a Class C stage. The idea with
plate modulation was that the RF path was CW all the way to the finals,
and the audio directly modulated the final amp. The modulated signal
then had to be handled only in a linear fashion, but that was at the rx
end-the last stage in the tx being, obviously, the final.

Well actually, you could do phasing at high levels. And depending on
the high level balanced modulator, it just might be plate modulation.

You put two high level balanced modulators at the output of what
amounts to a CW transmitter. The balanced modulators knock out the carrier.
Then you use the phasing method to knock out the unwanted sideband.

No commercial rig did it this way. I'm not so sure any homebrew rig
did it. But it is within the realm of possibility. Certainly, there
were a fair number of articles for high level balanced modulators so
you could take an existing rig and output DSBsc. It was far easier
to add such a stage, or modify the output stage of an existing transmitter
to make it a balanced modulator, than to put in a low level balanced
modulator and then linearize the rest of the transmitter.

Michael VE2BVW

The gizmo we are looking at seems to be a simple mod xfmr placed in
the plate supply to the 6146s in the tx. An audio amp such as a stereo
or guitar amp hooks to it and the mic goes to a preamp. In fact my
guess is back then a guitar amp was exactly what was most used.

Hi,

CQ magazine, May '65 page 75, gave a simple method
of transmitting a.m. with a KWM-2.
They said if you unbalance the pot
in the KWM-2 "carrier balance" circuit
(on the right front side, on top of the chassis),
but leave the trimmer capacitor alone, you can get about
90mA of plate current due to the carrier, about 15W out
with the rig in SSB position.
Keep the mic level down so the plate current barely flickers on peaks,
and you will be transmitting a.m. with one sideband.
Return the pot to its original position for SSB use.
Chuck Scheuers said he tried it and that it works.

QST had a better method, reinserting carrier
after the mechanical filter, by adding it to the PTO output
using a variable pot for carrier level control
in place of the headphone jack on the front of the KWM-2.
See June '63 QST page 48. (A correction appeared,
that turret connection E40A should read E20A).
The relay connection information in the article applies to the older,
non-plug-in relays (Winged emblem KWM-2).
Relay K4 shorts out the carrier injection during receive.
With this method, you should run 120mA carrier plate current,
and will get about 25W carrier out.

73,
Ed Knobloch

Edward Knobloch wrote:
Hi,

CQ magazine, May '65 page 75, gave a simple method
of transmitting a.m. with a KWM-2.

And Swan 350's had the carrier balance (null) pot right on the front
panel, and they claimed that allowed you 125W dc input AM on all bands.

Unfortunately, the carrier is injected before the SSB filter, and since the
filter's rejection skirt is positioned well over the top of the carrier(better
SSB carrier rejection, you see), you lose most of your carrier power before
you even start.

There was a certain amount of interest in running early SSB rigs in AM
mode, but fortunately that faded rapidly.

-Chuck

The Globe DSB 100 did! Sparks