Martin,
There are 2 ways to look at this. If you look at it from a "is this the
official lab-standard proper way" standpoint, it comes up a loser. I'm not
suggesting it is.
And If you look at it from a "is it a step in the right direction" and "can
it be done by average joe ham for a few bucks" and get somewhat interesting
results - the answer is yes.
If guys want to keep peppering me with the details of proper IMD
measurement, we can do that - but it's a sidebar to my key point. I get it.
This is not a proper Grandberg setup. So for all those guys who are reading
this or are sending me little off line mail about "IMD measurements 101,"
give me a break. You are missing the point.
Better the guy use a ruler to measure things than none at all. If one
headlight burns out in my car, I don't turn them both off because "if it's
not perfect, then it's not worth doing." There is no point to debate that a
ruler is not as good as a caliper and my mailbox is filled with guys making
that comment. Even if the ruler is a gross approximation, the simple effort
of looking at it raises awareness in an area of the hobby that as far as I
can tell, gets damn near zero attention. Well unless someone mentions
certain down-under amp suppliers, anyway.
Is better to have some newbie cranking away on his amp or his rig without
any thought at all to the stuff going out his pipe - than it is to have him
use less than perfect test setups? Not here, at least here in the fly over
country of KS.
But then again, I've got a lot of inbox nonsense suggesting I don't know
what I'm talking about. Maybe that is the case...
73/jeff/ac0c
--------------------------------------------------
From: "Martin Flynn" <maflynn@theflynn.org>
Sent: Sunday, May 23, 2010 3:06 PM
To: "Jeff Blaine AC0C" <keepwalking188@yahoo.com>
Cc: <amps@contesting.com>
Subject: Re: [Amps] How to read the 3-500Z spec sheet?
> Jeff,
> Is using a sound card good enough? One of my elmers <sk> had a dedicated
> two channel audio generator for testing.
>
> Motorola published a white paper by Helge Granberg on IMD measurements:
> http://w4neq.com/pdf/ssb_im.pdf
>
> Martin
>
>
> Jeff Blaine AC0C wrote:
>> Of course, a real IMD test requires a 2 -tone source and you can download
>> those applications on the web free of charge. A good quick and dirty
>> solution is to switch your digi mode application over to PSK. In fact,
>> if it were up to me, it would be a legal requirement for all PSK ops to
>> have station monitors of this type when running PSK. Lot of
>> misinformation and nonsense in that community among the rookie ops.
>
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