[Elecraft] Testing how loud it is!

[Francis Belliveau]

All,

This is more that a dissertation, there are technical questions at the end.

I had been ignoring the list for a couple of weeks while installing VHF in
my new car.  When I returned I noticed that
the "Low Audio" thread had been resurected 'in spades'.  I too have been in
these discussions before and always thought the issue was in the audio
chain, but never thought it had anything to do with serial number.  What we
need is a good engineering aproach to be applied by many with varied
backgrounds.  Creating an approach to be used by many that were trained
similarly is difficult enough, but throw in the variation of skills and
equipment and the difficulty is significantly amplified.

I praise Gary, Tom and the others for trying to crack this issue.

I find it interresting that Tom has a problem and Ron does not.  I expect
that this is a good indicator that the issue is at least partly 'luck of the
draw'.  I hope that Elecraft can create a solution that reduces the need for
luck.

Having read all the posts I have no doubt that subjectiveness plays a major
role.  I once suggested an approach that was technically useless as answered
by both Ron and Tom.  I will try another kernel of hope that I got from
these last discussions.

The issues to be untangled are:  Subjectiveness, Test equipment differences,
Audio Stage issue, Rx stage issue.
Since it looks like Tom believes his problem is Rx related and both he and
Gary are working toward diagnotics there.  Hopefully their aproach will
minimize the effects of the first two on my list.  I do not claim it to be
complete.

That leaves the Audio Stage for the rest of us to tackle.  This should be
easier because it should be easier to equalize the test equipment we have.
I look to Tom and Ron to validate my aproach/technique.

Signal Source:
        We all have what should be an equivalent audio source, the sidetone
generator.  Let's agree set it to 255 at 700Hz for the tests.

Test Fixtures:
        Since Ron indicates the reactiveness of speakers can cloud the
measurements, lets just use pure resistances.  Since 10 ohms is an easier
standard to find than 8 ohms I propose using 10 ohms inplace of the speaker
and 30 ohms in place of the headphones.

Test Equipment:
        After reading the list since the early days I am convinced that we
cannot trust AC voltage measurements at something other than 50-60 Hz.  I
suggest using an O-Scope and reading peak voltage.  This will also not
equalize us all but with a 10x probe we should be close enough.  My scope is
old and only good to 1 MHz but that should suffice.

Test Conditions
        Sidetone volume set to 255
        Sidetone frequency set to 700Hz
        Put the rig into test mode so that it does not generate any RF when
the key is down.

Tests
        1.  Connect nothing to the headphone jack.  Replace the speaker with
the 10 ohm load and measure the voltage across it both 'key up' and 'key
down'.  Also try to measure how much the voltage peaks vary with time to get
an idea of how much oscillation there may be.

        2.  Create a set of 'test phones' by wiring a 30 ohm load onto a
headphone jack.  Plug this in an take the same measurements accross this
resistor as indicated in the first test.

        3.  In order to equalize the test results we will need to measure
the amplitude of the signal source.  I do not have a schematic handy and am
preparing to leave on a trip so it will be at least a week before I can run
the tests.  I expect that Ron and/or Tom will be able to validate/improve my
suggestions above and determine a good measurement point for this test.

OOPs I forgot that we need to know if the 'scratchy audio fix' has been
applied or not.  I have not applied it since I do not feel the need.

The results of these tests should help separate those of us with Audio stage
issues from those with Rx issues as well as splitting the Audio group into
one of three areas to focus upon.  That should help sway the statistics to
identify some that should be easier to help than others.  If I read the
opinions in the mail correctly Tom (with an audio issue) will expect his
results to match Ron (who has plenty of audio).

Now I fess up.  I am a software engineer with mechanical training.  My
entire knowledge of electronics coes from this hobby so I am not that good
at troubleshooting when things get tough.  Like the rest of us I just do the
best that I can.  As a result I would wait to hear what Tom and/or Ron
identify is wrong with my approach before proceeding.

73,
Fran