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[AMPS] Bias for SB-220

To: <amps@contesting.com>
Subject: [AMPS] Bias for SB-220
From: measures@vc.net (Rich Measures)
Date: Wed, 2 Jun 1999 14:33:08 -0700


>>Let's not forget the TS950SDX, which suffers from the same problem.
>>
>?  Only for those who believe that way mo' ALC is way mo' betta
>
>Not so. I'm not an idiot, Rich. 

?  Surely, however, there are plenty of CBers who run Kenwood amateur 
radio transceivers with the pedal to the metal.   //  Kenwood's  manuals 
are a also part of the problem.  

> I always set the carrier control according
>to Kenwood recommendations -- meter deflection within the ALC zone.

?  On my Kenwood , midway in the ALC zone makes abundant overshoot.  

>Actually, I normally set it as low as possible, just under the point where
>the output stops rising. But my 950 spikes 

?  How many peak volts on your 'scope?  With "normal" ALC indication,  my 
TS-440S overshoots to about 120v-p. into 50-ohms.  .  

>with meter deflection anywhere in
>the ALC zone, even when set to just start indicating at the bottom of the
>zone, as you have recommended. 

?  What if the ALC meter only occasionally flickers?  

>The rig was checked by a factory-authorized
>technician, who found the ALC to be correctly adjusted and working to specs.
>
>The only thing that reduces the frequency of the spikes is to increase the
>CW waveform rise time. Amazingly enough, the 950 has a menu setting to make
>this 2ms, 4ms, 6ms or 8ms. As the rise time is increased, the spike
>frequency is reduced, but never eliminated.
>
>In my opinion, it's a design problem: if you look at the transmit timing
>curves in the 950 service manual, you can see that after a 15ms delay, CW
>output is initiated by a sharply-rising square wave signal called CKY. A
>signal to turn on the ALC is initiated at exactly the same time, but rises
>and decays more gradually than CKY. In my opinion, this sometimes allows the
>output to spike to the max before the ALC has turned on. 

?    Without  spikes, the ALC can not turn on. 

>The timing is
>probably very close, one way or the other. 

?  agreed

>By increasing the CW waveform
>rise time, the ALC has more time to catch up. Just a theory.
>
>By the way, the spikes are easily observed on an 87A amp, which fault trips
>in response. All I have to do is send a steady stream of dits in QSK mode.
>Neither an FT-990 nor an FT-1000mp has ever driven that fault.

?  Interesting.  Kenwood has also designed some painfully problematic  
AGC circuits.  
>.......
-  cheers, Dick


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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