Josh wrote:
Hi Ed..
I downloaded the manual from BAMA.
Interesting.
It says you can use an AM receiver to adjust the deviation control to make
the signal no wider than an AM signal until the audio is perfect. (quote
form manual)
Can be used on AM?
Hooked up to a Central Electronics low drive amplifer might make a
respectable transmitter.
MmMmMmMmmmm...; )
Josh

Hi, Josh

No, the Sonar 680 puts out NBFM phone only
(actually, the rig is phase modulated not frequency modulated).
The 6AGC buffer operates in Class C, wiping out any resisdual a.m.
(much like a limiter stage in an FM receiver).

The manual talks of using a +narrow+ receiver, actually tuned
to one sideband, and adjusting the transmitter audio gain "deviation"
control so the signal sounds good on that band.
This is the definition of "narrow" FM, where almost all
the sideband energy is in the first set of sidebands.
For example, if your transmit audio is limited to 3 kc,
and your total FM transmitter's bandwidth is 6 kc, you are
transmitting NBFM. If you increase the deviation further,
additional sideband energy appears further away from the carrier,
and you are now transmitting FM, not NBFM.

An NBFM signal could still sound good to a listener
using a narrow a.m. receiver, like a 75A4 with 3.1 kc filter,
set up to receive a carrier and one sideband.
However, someone listening with a wider
a.m. receiver set up for double-sideband with carrier reception
would hear a muffled signal, unless he realized you were transmitting
NBFM. If so, he could shift his receiver tuning to one side
or the other for "slope detection" of your transmitter audio.

73,
Ed Knobloch