(dug out of the list archives)
>From the RON-LEE AGC brochure,
"In designing your Omni-B transceiver, Ten-Tec
provided an unusually effective
audio notch filter and placed it within an audio
derived AGC loop in order to
prevent AGC capture by the offending signals. It
provides a 30 DB deeper notch
than IF notch systems. Though the performance of the
Omni AGC represented the
state of the art in its day for audio derived systems,
an excessive delay in
AGC build-up existed along with other cost versus
performance compromises. As a
result, blasting, distortion, and limited ability to
follow rapid fades, and DX
pile-ups were present. In addition, the QSK was
compromised. Later, the Omni-C
was introduced; its hang AGC offered improvements.
Unfortunately, the hang
timer doesn't release or attack readily, and the slow
AGC attack and QSK
problems were not solved.
"Over three months have been spent engineering a
complete system of novel AGC
modifications that afford very rapid attack time and
enhanced hang AGC and QSK
behavior. This is done without degrading resistance to
noise capture. Ten-Tec
has evaluated the modified system and their review
comments can be seen in the
attached letter.
"Such performance was not easily attained. Indeed, the
addition of 5 op-amps, 4
transistors, 8 diodes, 30 resistors, 13 capacitors, a
DIP switch, 15 cross
connections to the Omni-C hang AGC board, and various
foil cuts and chassis
grounding and wiring changes were all necessary. A
complesx interplay of BFO
signal leakage, ground loops, gain distribution, loop
filter characteristics,
hang circuits anomalies, notch filter subtleties, and
attack dynamics had to be
identified and resolved in order to attain
improvements of such significance.
For example, the group delay of the audio SSB/CW
filter necessitated relocation
out of the AGC lop and BFO leakage required the
addition of a T/R gate and
buffering and decoupling on the IF board. BFO leakage
also required several
grounding changes. In addition to full wave detection,
augmentation by a
parallel rate sensitive amplifier was needed to
achieve high speed attack.
"All of the added circuitry is inside the equipment.
Inside, two PC boards were
added and four others are modified. No changes to the
front panel are made, nor
are any holes drilled in the chassis. However, if
external controls are
desired, they are available. If not, an on-board DIP
switch affords control of
key time constants. We have named the resulting system
of fixes the Ron-Lee Agc
System.
"Here are a few typical observations:
Before modification:
* 15 to 30 millisecond AGC attack time
(variable with signal level
and filter bandwidth)
* 15 DB blasting transient during AGC attack
or QSK recovery
* .2 to .6 second hang time (variable from
chassis to chassis) (.6 is
too slow for typical QSB)
* .7 second hang discharge time after hang
time-out (too slow for
typical QSB)
* inability of the hang timer to release at
high signal levels (18 DB
drop at s9+30 DB is required) (not optimum for fast
DX or contest
action)
* QSK Upper speed limit varies 20-40 WPM
chassis to chassis
* under damped S meter in some chassis
* excessive volume level with 8 ohm headphones
After modification:
* 3 millisecond attack time resulting in
almost total reduction of the
clicks and distortion seen previously during AGC
attack.
* Independently selectable hang and post hang
gain-recovery time
constants to optimize the system for band condition
and operating modes.
Hangtimes are .25 to .75 seconds, independently switch
selectable in
four steps each.
* reduced hang droop to minimize background
noise fill-in in brief
pauses
* reliable hang release. A signal drop of 2 DB
at s9+30 DB and less
than
6 DB from s9+40 through s3 will start the
hang timer. This
improves
the fade tracking for a given selection of hang time
and allows optimum
DX/contest tracking.
* 3 DB blasting transient during the AGC
attack (hardly audible)
* significantly smoother and quieter QSK
without loud clicks on strong
signals
* QSK speed increase to over a 55 WPM dot rate
(about 2x typical stock chassis) This was
hand written on the
brochure
* post detection audio noise filtering of 2.5
khz bandwidth to
match the
crystal filter. This reduces the hiss level
and high frequency
components of the hiss caused by post detection audio
stages.
* (optional) equalized headphone volume for 8
ohm phones
* improved S meter damping when needed
"Subjectively, the performance becomes smooth,
unobtrusive, and highly
responsive. In pile-ups, QSK, or local rag-chews, an
optimum response can be
had by selecting the appropriate combination of hang
time or recover rate and
the set becomes far less fatiguing to listen to. In
the standard Ron-Lee unit,
selection of speeds is made via an on-board DIP switch
that is accessed by
removing the top lid. External controls are available
as a low cost option.
Other options are also available and are described
below.
"Why trade in your present Omni equipment and then
spend $500 to $2,000 more
for a replacement that may have a different set of
deficiencies when you
already have a basically well engineered set? A set
that is modular and easy to
maintain with one of the best company service
attitudes we have seen. Why not
install the Ron-Lee AGC and eliminate the principal
cause of annoyance for much
less money?"
__________________________________________________
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