[TenTec] Ron Lee AGC (repost with better formatting)

[N1EU]

>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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