[Elecraft] Testing how loud it is!

[George, W5YR]

Interesting, Tom, and thanks . . .

As a new K2 operator, my impression of the AF Gain control is that it
functions unlike the audio gain control of any receiver that I have ever
used before - and that is a fairly large number!   <:}

At times, it seems to progressively increase the signal or noise level
proportionally with knob setting. At other times, it seems to have far less
effect, again in terms of audio signal level increase versus knob position.
I suspect that the actual transfer function of the audio system is somewhat
dependent upon signal level, which while contrary to the usual objective in
linear system design and implementation, may not be all that bad in the K2
application. My K2 has not had the gain pot mod.

I agree that much more needs to be investigated. My K2 - #489 - produces
abundant audio at the 9 o'clock position on strong signals so I am unaware
of an overall lack of AF gain. But, it behaves substantially differently
with weak signals, acting more like an "RF" gain control.

BTW, procedurally I am finding that a noise generator is a preferred
"signal" source for such tests.

I will follow your results, Tom, and will attempt a similar study the next
time I have the lid off.

73/72, George    
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!


Tom Hammond N�SS wrote:
> 
> Good morning folks:
> 
> Sorry for the delay in replying, but I was out of town this weekend and
> just returned home Sunday evening.
> 
> >You are correct about the variations in side-tone level for the same
> >setting, I figured the last measurement would filter that out.  I guess we
> >could find the right test point and have Ron and Tom give us a measurement
> >at a setting of 128 or maybe even 200 and then we could all try to match it.
> >A more complete test would be to measure things at high, low, and medium
> >level inputs but I wanted to keep the test simple.  I guess we need to
> >decide if the problem is not enough overall gain or maybe non-linear gain
> >such that only the loud or weak signals are not amplified enough.
> 
> Here's what I'm planning on trying... today, if time permits... and I think
> this may fly... at least for the AF section.
> 
> I think that merely setting ST L to an arbitrary NUMERICAL setting may
> still not allow us to have confidence in our measurements. BUT, for those
> of us who have o'scopes which we believe to be relatively accurately
> calibrated, we should be able to set the output of the Quad, 8-Bit DAC
> (U8), to a certain measurable peak-to-peak level and THEN proceed with
> performing our output level tests for the rest of the AF chain.
> 
> I think it would probably be appropriate the begin by setting the P-P
> output of the DAC by measuring the sidetone level at the drain of Q5
> (2N7000). I've not done this yet, but I'll try to provide a usable level a
> bit later today. I DO think we should attempt to first use a P-P voltage
> somewhere in the lower to mid range of the volume level control. Probably
> somewhere below a DAC count of 100, and probably closer to 50.
> 
> I recently bought a new (for me) o'scope, so now I'll finally actually have
> a REASON to put it to some good use. I will be using the X10 probe, just to
> help to ensure that I'm not 'loading' any possibly high-impedance part of
> the AF circuit during my testing.
> 
> >The question I am looking to answer is what percentage of us have an Rx
> >problem and how many have a simpler audio problem?  This would be a starting
> >point so that those with an audio problem do not waste time looking in the
> >wrong place.  I figured that finding a way for us all to inject a matching
> >signal into the antenna to trace down an Rx problem will take a while.  This
> >seems like a place to focus efforts while the experts work out an approach
> >for the more complex possibility.
> 
> Once we can/cannot vindicate the AF chain itself, THEN we can focus on the
> RF chain.
> 
> Results later today.
> 
> 73,
> 
> Tom  N0SS
> 
> PS
> 
> Just as Fran has 'fessed' up, I shall as well (as I've done before). I have
> NO formal electronics training. Whatever small amount of 'knowledge' I have
> has come from several (44) years of hands-on experience, and having done it
> WRONG enough times to at least have a feeling for possibly doing it
> right(er) the next time... so I may still be going off on the wrong
> tangent, but at least it'll be MY tangent...<G>