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

"Edward Knobloch" wrote in message
news:gXmcd.662$UX3.379@trndny03...
Joe wrote:
Hi..
I cam across a Sonar VFX-680 exciter.
It appears to have a VFO in the 75 meter band.
A 6L6..maybe 5 watts out?
It's not in bad condition.
Will need a recap etc.
I am looking for info on it and specs.

Hi, Joe

There's an ad for the Sonar VFX 680 in Apr 1947 QST, page 88.
It looks like an interesting find.
Here's the ad copy:

Everything in one complete unit, containing
Narrow Band FM on all bands* - an exclusive Sonar circuit.
CW on all bands - free from all chirps and key clicks.
Two band operation with one set of plug-in coils for top efficiency.
"VFX" rubberizes any cut xtal.
VFO or xtal - just plug in the xtal and you are set - no switching.
CW monitor ideally suited for the bug operator.
Phone monitor - no auxillary equipment required.
RF output power 4 to 6 watts on all bands except 6 meters.

* NBFM at present permitted on 11 meters and above 29 Megs.

73,
Ed Knobloch

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

"Joe" ) writes:
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

It can be used on AM if you've got an external modulator.

It dates from a brief period when quite narrow FM was touted as a new
and advantageous mode for HF. No big modulator needed, and if it's narrow
deviation, doesn't fill up the band. Use "slope detection" to receive
it on an AM receiver; you mistuned the receiver a tad so the signal is
on the slope of the receiver's IF selectivity. Thus as the signal is
modulated, the frequency variation causes the signal in the receiver to
vary in amplitude as it moves along the IF slope. This can then be
demodulated in the AM detector.

Whether or not narrow deviation FM was a good replacement for regular
AM, SSB came along at about the same time and won out.

Michael VE2BVW

"Edward Knobloch" wrote in message
news:gXmcd.662$UX3.379@trndny03...
Joe wrote:
Hi..
I cam across a Sonar VFX-680 exciter.
It appears to have a VFO in the 75 meter band.
A 6L6..maybe 5 watts out?
It's not in bad condition.
Will need a recap etc.
I am looking for info on it and specs.

Hi, Joe

There's an ad for the Sonar VFX 680 in Apr 1947 QST, page 88.
It looks like an interesting find.
Here's the ad copy:

Everything in one complete unit, containing
Narrow Band FM on all bands* - an exclusive Sonar circuit.
CW on all bands - free from all chirps and key clicks.
Two band operation with one set of plug-in coils for top efficiency.
"VFX" rubberizes any cut xtal.
VFO or xtal - just plug in the xtal and you are set - no switching.
CW monitor ideally suited for the bug operator.
Phone monitor - no auxillary equipment required.
RF output power 4 to 6 watts on all bands except 6 meters.

* NBFM at present permitted on 11 meters and above 29 Megs.

73,
Ed Knobloch

In article ,
(Michael Black) writes:

Whether or not narrow deviation FM was a good replacement for regular
AM, SSB came along at about the same time and won out.

National was pushing NBFM in that era, and the HRO-60 had a chassis socket for
a plug-in NBFM detector, and the front panel mode switch had a labeled position
for it.

Not suprisingly, the HRO-60 that I had for a hwile, the previous owner had
homebrewed an SSB product detector module into that socket! And even
Dymo-labeled the knob skirt over the "NBFM" with "SSB" just so he wouldn't
forget!

The Drake R8 family includes NBFM detection. I actually heard some on 10m not
too long ago. NBFM is simple to generate and lets you use Class C finals, as
others have ppointed out. But the S/N ration of FM goes up with increased BW,
so narrow BW must not perofrm well. And it's less handy than SSB for "netting"
a group of hams who try to all talk at once.
73, Mike K. AA1UK

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