[AMRadio] F/S Volumax

Bob Peters rwpeters at swbell.net
Fri Nov 30 21:37:14 EST 2007

Very well put Geoff  Thanks

-----Original Message-----
amradio-bounces at mailman.qth.ne
[mailto:amradio-bounces at mailma
n.qth.net] On Behalf Of
Sent: Friday, November 30,
2007 7:17 PM
To: Discussion of AM Radio in
the Amateur Service
Subject: Re: [AMRadio] F/S

Bob Peters wrote:
> It is the VOLUMAX 4300 And I
have the manual with it.
> Anyway offers???

Here's what I found on the
Volumax 4300...

in 1970, CBS Laboratories
produced a revolutionary
product.  The Volumax 
4300.  The first analog signal
processor for maximum
loudness.  It 
contains two circuits.  A
special compressor, and a peak
limiter.  This 
device is connected after the
main slow acting compressor.
The special 
compressor is a FAST acting
compressor.  Unlike the main
this one has a medium-fast
attack time, around 8.5 msec,
and a 
relatively fast release time,
around 260 msec.  Percussive
sounds faster 
than 8 msec do not trigger the
compressor and go straight
through with 
their original volume level.
The syllabic sounds are
compressed and the 
gain is re-adjusted very
quickly due to the 260 msec.
This only works 
well if the average signal
input is relatively constant -
the job of the 
main slow acting compressor.
The two compressors work
together in 
preventing gain pumping, and
allow percussive sounds to
sound loud 
because they don't reduce the
gain of the second compressor
(ie. their 
attack time is not altered),
yet the syllabic variations
are highly 
compressed and are brought up
to maximum gain quickly,
making the signal 
sound very loud, with a
further increase of 6 dB or 4x
power compared to 
not using it.


Thus the second circuit in the
Volumax 4300 is an
unsymmetrical clipping 
circuit which takes care of
the negative peaks, fixing
them at the -100% 
modulation level.  The 6dB
improvement from this device
alone is all 
totally useable since at no
time will the transmitter be
in the negative direction,
neither will it be
undermodulated, as the 
average signal will always be
close to the clipping level.
Every top 40 
radio station wanted one of
these.  One does not really
hear any 
distortion because the energy
in the clipped peaks is very
low - and 
what is left can fully
modulate the transmitter
toward -100%  almost 

On the other side of the coin,
there are these comments...

>/ >I have at one site a
Volumax 4300.  It's a single
channel 1U AM processor.
>/ I believe that model had
the clipper diodes BEFORE the
/>/ transformer. Self induced
tilt and overshoot!
Yeah, its peak control wasn't
that great.  But it did work
ok for limiting a 

Mind you, these reports are
from 'professional

Amateur signals aren't nearly
as 'broad' as broadcast
stations.  Typically, an
Amateur AM signal is 6kc wide.
stations have a 10kc channel

Isn't there something in the
Rules and regs about emission

Hmmm...  seems the only thing
I can find, is:

(1) No angle-modulated
emission may have a modulation
index greater than 
1 at the highest modulation

(2) No non-phone emission
shall exceed the bandwidth of
a communications 
quality phone emission of the
same modulation type. The
total bandwidth 
of an independent sideband
emission (having B as the
first symbol), or a 
multiplexed image and phone
emission, shall not exceed
that of a 
communications quality A3E

however, Part 97 doesn't not
define what the width of a
'quality A3E 
emission' is.

I -did- find, however, what
appears to be a reply to a

10.* Regarding Petitioner's
request that amateur stations
emission type A3E not be
authorized to occupy more than
5.6 KHz 
bandwidth on amateur
frequencies below 28.8 MHz,
_we agree with 
commenters who note
Petitioners have not
demonstrated there to be a 
particular problem with
stations that transmit AM
emissions. Moreover, 
the Commission has previously
declined to restrict bandwidth
for AM 
because to do so would be
inconsistent with the basic
purpose of amateur 
service and our desire to
offer amateur operators the
opportunity to 
experiment with various types.

It appears that currently, an
AM transmitter can have a
width of <6kc.

I feel, as Amatuers, we should
probably limit ourselves to
around the 6kc area, just to
be 'neighborly' to our
neighbors, as to reduce the
amount of bickering and
bitching on the 
band, which would lead to a
much more enjoyable
environment to all hams, 
regardless of what mode we are


Driving your AM Rig without a
is like driving your car at
night, without headlights.

73 = Best Regards,

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