[Elecraft] K3 DSP AGC Question

[Joe Subich, W4TV]

Lyle, 

> > 4) Is there a table that provides a dBm equivalent of each 
> > of the threshold values? Or alternatively  are the values 
> > on the Clifton Labs site correct?
> >
> >  (2	-117 dBm
> >  	3	-110.5 dBm
> >  	4	-105 dBm
> >  	5	-103.5 dBm
> >  	6	-102.5 dBm
> >  	7	-101 dBm
> >  	8	-99 dBm    )
> >   
> 
> There is no available table, and Jack's measurements were 
> accurate at the time they were made for the then-current 
> firmware release.

Assuming that the threshold values have not changed in a major 
way since Jack's measurements, would it be possible to extend 
the range of threshold values - say to AGC THR=016 at about 
-80dBm (assuming 2 dB per step)?  

Such a change would put the K3 more in line with the K2 as 
measured by Jack Smith ... as well as numbers reported by 
Sherwood for the FT-1000D, FT-1000MP and even the IC-7600. 

73, 

   ... Joe, W4TV 
 
 





> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Lyle Johnson
> Sent: Sunday, February 07, 2010 2:21 PM
> To: Guy Olinger K2AV
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 DSP AGC Question
> 
> 
> 
> > Some follow-on questions:
> >
> > 1) When you say "The DSP outputs a voltage to control the 
> IF gain of 
> > the radio." are you referring to VIFGAIN1 input to U3B on the RF 
> > board?
> >   
> 
> Yes.
> > 2) Assuming so, is there anything that influences the voltage on 
> > VIFGAIN1 other than on behalf of the RF gain pot, and is 
> the voltage 
> > appearing at VFGAIN1 on behalf of the RF gain pot "processed" away 
> > from a linear replication of the pot wiper voltage?
> >   
> Without staring at the DSP code to verify the veracity of my reply, I 
> recall that the RF Gain control is the only thing that 
> currently drives 
> the VIFGAIN1 voltage.  Subject to change, of course, since it 
> is a DSP 
> firmware function.  And yes, the value read from the pot is 
> processed by 
> the DSP on its way to becoming VIFGAIN1.  Again, the 
> algorithm applied 
> is subject to change.
> > 3) The hardware AGC appears to have fixed slope, attack and decay 
> > constants. What would be the DSP slope and decay config 
> constants to 
> > mimic the hardware AGC constants?
> >   
> Correct as to the first, and I think there may be that there are no 
> settings that exactly mimic the HAGC.  Their purposes are quite 
> different.  To the DSP, influences of the HAGC voltage on the 
> received 
> signal are treated no differently than changes in propagation.
> > 4) Is there a table that provides a dBm equivalent of each of the 
> > threshold values? Or alternatively  are the values on the 
> Clifton Labs 
> > site correct?
> >
> >  (	2	-117 dBm
> >  	3	-110.5 dBm
> >  	4	-105 dBm
> >  	5	-103.5 dBm
> >  	6	-102.5 dBm
> >  	7	-101 dBm
> >  	8	-99 dBm    )
> >   
> 
> There is no available table, and Jack's measurements were accurate at 
> the time they were made for the then-current firmware release.
> 
> 73,
> 
> Lyle KK7P
> 
> 
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