[Elecraft] Audio problem in WPX SSB

[Joe Subich, W4TV]

Andy, 

>   Here is what happens:  For phone contesting, I my software 
> CQPWIN, which plays wav files for DVK usage (as do other 
> programs).  I run the output in such a way that when the dvk 
> is playing, the mic is shut off, but the audio from the computer 
> goes into the mic connector of the radio.  As soon as it stops 
> playing, it disconnects the computer and reconnects the 
> microphone.  I run it from the computer into a W2IHY iBox for 
> isolation, and the output to the radio.  The Mic is a Heil 
> pro-set.

> >   With the K3, the messages play fine, but after one finishes, 
> if I use the mic, the radio starts out at lower power and takes 
> 2-4 seconds to build back up to high power.  This is the same 
> whether using the front or rear input and whether using high or 
> low gain. 

After working in this quite a bit over the weekend the problem 
is related to the K3 "microphone AGC."  It appears that levels 
from the microphone and DVK must be extremely well balanced - 
much more closely balanced than with any other radio or the 
stronger input will cause the microphone AGC to reduce the 
mic gain and the weaker input will be much weaker.  The 2-4 
second delay seems to be related to an extremely long ACG time 
constant (probably intended to prevent the ACG from acting like 
a clipper). 

The problem is made worse - at least in my case - because the 
ALC indicator provides only 5 very small, difficult to see, 
bars for adjustment and the "steps" are rather course (6 dB 
per division).  This means that the maximum "spread" between 
the two inputs can be almost 12 dB (!) even when the display 
only shows a slight flicker between the two adjacent bars 
(e.g., the mic is barely triggering the 5th bar and the DVK 
is hitting the sixth bar "hard").  

After some thought there are several ways (a combination of 
all is best) to help the situation: 

1) reduce the time constant (AGC "hang") to about .5 second 
   and "dump" any gain reduction when the PTT is released. 

2) Use more of the "ALC" display to get better resolution. 
   There are 12 "bars" in that part of the display but only 
   six are used (with the sixth indicating overdrive).  At 
   least expand the "good" range to seven (or eight) bars 
   to coincide with the right edge of the ALC bracket. 

3) Make the ALC display response logarithmic (like a VU 
   meter).  Instead of 5 x 6 dB or 30 dB total ... the same 
   total range could be displayed with the first bar = -20 dB, 
   the second = -10 dB, the third = -7 dB, the fourth = -5 dB, 
   the fifth = -3 dB, the sixth -1 dB, the seventh = "0 dB", 
   the eighth +1 dB, the ninth +3 dB and the 10th +6 dB.  
   Setting/matching levels would be MUCH easier.  It's no 
   accident that professional recording and broadcasting have 
   used similar scales for decades. 

4) Give the ALC meter a dual mode display - showing both short 
   duration "peak" and average (the current ALC) would help.  
   Alternatively, any "peak hold" dot above the ALC region 
   could show gain reduction by the mic AGC (and warn about 
   overdriving the input). 

5) Provide a "set-up mode" that disables mic AGC - this 
   will allow balancing sources (either FP/RP/Line or 
   multiple inputs on an external mixer) without chasing 
   the effects of the mic AGC.      

I understand there has been some work on the mic AGC in the 
firmware currently in test and that may help.  However, this 
area needs to be more "user friendly."  As it is, I can see 
significant issues when using the K3 in a multi-operator 
setting where the relative levels need to be reset completely 
for every operator change! 

73, 

   ... Joe, W4TV 
 



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Andy Faber
> Sent: Monday, April 07, 2008 12:08 AM
> To: nextk at elecraft.com; wayne burdick
> Cc: elecraft at mailman.qth.net
> Subject: [Elecraft] Audio problem in WPX SSB
> 
> 
> Wayne,
>   A peculiar audio situation arose using my K3 in Aruba in 
> WPX SSB.  It 
> works the same way at home, and isn't a problem I've ever had 
> with any of 
> many other radios that I've used in the same contest configuration.
> 
>   Here is what happens:  For phone contesting, I my software 
> CQPWIN, which 
> plays wav files for DVK usage (as do other programs).  I run 
> the output in 
> such a way that when the dvk is playing, the mic is shut off, 
> but the audio 
> from the computer goes into the mic connector of the radio.  
> As soon as it 
> stops playing, it disconnects the computer and reconnects the 
> microphone. 
> I run it from the computer into a W2IHY iBox for isolation, 
> and the output 
> to the radio.  The Mic is a Heil pro-set.
> 
>   With the K3, the messages play fine, but after one 
> finishes, if I use the 
> mic, the radio starts out at lower power and takes 2-4 
> seconds to build back 
> up to high power.  This is the same whether using the front 
> or rear input 
> and whether using high or low gain. Also, the W2IHY box has 
> to be turned up 
> to a level that normally would overdrive other radios.
> 
>   I tried not using the W2IHY box (ie, running the audio 
> straight from 
> either my laptop or my desktop to the radio) with the same 
> result.  It also 
> doesn't matter if the radio is using PTT or VOX, or whether 
> it just remains 
> in transmit.
> 
>   These seems like a some kind of odd impedance issue, but, 
> as I said, it's 
> one that has never shown up with Icom-Yaesu or Kenwood radios.
> 
>   Any ideas?  I'm using 1.78/1.58 firmware, and the radio was 
> just back to 
> you for Rene to do hardware mods (serial number 76).  In all 
> other respects, 
> I loved it in the contest.
> 
>   73, Andy, AE6Y 
> 
> 
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