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[TenTec] AGC

To: <tentec@contesting.com>
Subject: [TenTec] AGC
From: bohnovic@worldnet.att.net (John/K4WJ)
Date: Mon, 01 Feb 1999 10:53:43 -0500

 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

"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
        * 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     
        * reliable hang release. A signal drop of 2 DB at s9+30 DB and less
         6 DB from s9+40 through s3 will start the hang timer. This
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 
        * QSK speed increase to over a 55 WPM dot rate
          (about 2x typical stock chassis) This was hand written on the
        * 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?


And at this point I'm tired of typing. I'm listening to Stevie Wonder sing at
the Super Bowl during half time. BTW, the Omni-C modification was $94.50 and it
was $139.50 for an Omni-B (or converted Omni-A). The Volume equalized headphone
jack was $10.00, the Externally accessible AGC controls was $15.00. A Weighted
tuning know (lead and epoxy filled) was $8.00 and the Product detector
threshold extension was $12.00.

Ron-Lee AGC was located in Laurel, MD. A reduced size letter from Jack
Burchfield, President of Ten-Tec, and dated March 31, 1982 was attached. Oh, I
just noticed it was also signed by Richard Frey, Chief Engineer.  :-)

Does this sound like your Omni C performance? Stan, W9WBL, has a Ron-Lee
modified Omni C. You two can compare your units. I think Stan told me that
there are only about 50 Ron-Lee modified radios in existence. (I may be wrong
about this number.) I sure wish I would have had my Omni C modified, but if I
remember correctly I was doing some heavy DXing at the time and the Omni C was
the only radio I had.

I hope this helps. Reading and typing this brochure sure brought back some

73..de John/K4WJ


At 09:40 PM 1/30/99 -0500, you wrote:
>Well if I had a copy of the Ron-Lee mod I could tell you in a flash. However
>unless this mod included a new circuit board, I seriously doubt it. As you
>know, the Omni C was advertised as having "hang agc". Even the manual tells
>about it and the schematic shows the components used to produce the "hang".
>However, this C simply doen't have them, nor are there any empty holes. It's
>as if it were a different rig altogether when it comes to agc. So I have a
>hangless Omni C and I like it that way.
>Here's one for you Omni C owners. Open your manual to page 3-6 and find the
>TX Mixer board. Gaze upon this then turn to page3-44. Notice anything
>different? Hmmm. Where's T1? It's on the schematic!
>N4LQ Steve
>>Is it possible that your Omni C has the Ron-Lee AGC mod?
>>73..de John/K4WJ
>>At 09:39 PM 1/29/99 -0500, you wrote:
>>>>(but I know it is since the notch affects AGC).
>>>Well you hit the nail on the head with that last comment. TenTec was able
>>>obtain good selectivity at a low cost by using audio filters and having
>>>agc taken off after the audio filter. My Omni-C is of course this way but
>>>for some strange reason it's agc is quite smooth and doesn't have that
>>>thump when a strong signal hits it. Interestingly, the schematic of the
>>>IF/AF board doesn't even come close to what's really there! They must have
>>>gone through several mods during production.
>>>With the Corsair series I belive they should have taken the agc from ahead
>>>of the af amp due to the excellent xtal filters available. Anyway, this
>>>didn't happen until the Paragon/Omni-V series.
>>>FAQ on WWW:               http://www.contesting.com/tentecfaq.htm
>>>Submissions:              tentec@contesting.com
>>>Administrative requests:  tentec-REQUEST@contesting.com
>>>Problems:                 owner-tentec@contesting.com
>>>Search:                   http://www.contesting.com/km9p/search.htm
>>        John/K4WJ in Pembroke Pines, FL
>>     QTH is 26 00 51 N
>>                80 16 16 W
>>     K8PXG from 18 Jun 59 to 11 Feb 97
>>     K8WJ  from 12 Feb 97 to 07 Apr 97
>>     ZF2HZ from 17 May 84 to 31 Dec 84
>>FAQ on WWW:               http://www.contesting.com/tentecfaq.htm
>>Submissions:              tentec@contesting.com
>>Administrative requests:  tentec-REQUEST@contesting.com
>>Problems:                 owner-tentec@contesting.com
>>Search:                   http://www.contesting.com/km9p/search.htm
>FAQ on WWW:               http://www.contesting.com/tentecfaq.htm
>Submissions:              tentec@contesting.com
>Administrative requests:  tentec-REQUEST@contesting.com
>Problems:                 owner-tentec@contesting.com
>Search:                   http://www.contesting.com/km9p/search.htm

        John/K4WJ in Pembroke Pines, FL 
     QTH is 26 00 51 N   
                80 16 16 W 
     K8PXG from 18 Jun 59 to 11 Feb 97 
     K8WJ  from 12 Feb 97 to 07 Apr 97 
     ZF2HZ from 17 May 84 to 31 Dec 84 

FAQ on WWW:               http://www.contesting.com/tentecfaq.htm
Submissions:              tentec@contesting.com
Administrative requests:  tentec-REQUEST@contesting.com
Problems:                 owner-tentec@contesting.com
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