I was asked about "my first rule of engagement" posted earlier.
Considering the output of the computer and the interface has a definable and
measurable noise floor and the mike input has a signal level value required
to attain the desired output, one only has to look at the two levels and do
a bit of math.
As example, the noise floor of the computer, soundcard and interface is
some -60 dBv. This number encompasses all types of noise, electronic noise,
humm, RF on the cables. The level required at the mike input is
nominally -40 dBv to attain desired output level. Thus the signal to noise
ratio in this configuration is some 20 dB. Now taking the output of the
computer, interface and cables to the higher level input, the AUX or Line
input where the needed level is say -20 dBv to attain the desired output
signal and we have then the noise floor at -60 dBv to signal level at -20
dBv for a signal to noise ratio of 40 dB. A 20 dB improvement of ones S/N
ratio on the air is significant.
Now should the radio not have a high level or line input and the only choice
is to feed the data signal into the mike input, I suggest a suitable amount
of attenuation located at the radio should be employed. In this case a Pi
type resistive pad or attenuator providing some 20 to 40 dB loss it
preferable. In this case, extreme attention to grounding, type of cables
and such must be investigated. The point being the noise floor of the
computer and interface remains the same however the level required is raised
thus the S/N ratio is improved.
It just makes good sense to evaluate the levels required of the systems and
operate the systems at optimum values for optimum performance. Just because
the connector plugs in, is no indication it works correctly as it should.
73
Bob, K4TAX
----- Original Message -----
From: "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Wednesday, May 14, 2014 3:53 PM
Subject: Re: [TenTec] Eagle problem?
My first rule of engagement......."if it is a mike connect it to the mike
input. If it is not a mike then don't connect it to the mike input."
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