Yes, Mark, you have identified the whole point of this discussion. Good on
you!
The notion that "the input should be 5 mV or -67 dB" is meaningless in
itself as I have tried to demonstrate with the formulas and numbers. What
the manual is "trying" to say is that the mic must be putting out around 5
mV in order to drive the rig properly AND that a mic rated at
"-67 dB" will probably do the job.
There is really nothing here to relate these two numbers since there is no
reference given for the -67 dB figure. The mic voltage output can be
measured on a scope while you talk into it. Its hokey "dB" rating is a
generalization used by mic manufacturers which is useful to a degree but is
not technically rigorous as stated. That is the basis of your problem.
There is a standard reference that most mic manufacturers use but unless it
is clearly stated that it *is* being used, you are left to guess what the dB
number really means. In this case, the 5 mV is the key spec.
Don't blame you for getting confused.
The waters got a little muddy when you question seemed to be how 5 mV
relates to -67 *dBm* ( subject line reads "5 mV = -67 dBm")which is
altogether a different matter. I tried to run the traps on that one and show
that the value of resistance that had to be involved in order for those two
values to be related.
Another list subscriber is still insisting privately that (a) I didn't read
your question - which I didn't see - and (b) that I seem to be full of
prunes on this topic. A few thousand hours in the classroom teaching this
and related topics has helped on the prune situation.
Hope you are feeling better about this and feel that you learned a little
something new. Plus developing the idea that you have to be careful reading
spec and manuals! <:}
Glad to have been of some help.
73/72, George
Amateur Radio W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
<mailto:w5yr@att.net>
----- Original Message -----
From: "Mark Erbaugh" <mark@microenh.com>
To: <tentec@contesting.com>
Sent: Saturday, July 26, 2003 6:01 AM
Subject: Re: [TenTec] 5 mV = -67 dBm
> George,
>
> Yes, I think you are right. If the mic input were rated 5 mV, it should
> be -46 dBv. But I did verify that the Pegasus manual says 5 mv or -67 dB.
I
> wonder what reference point TT is using?
>
> Mark
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