[TenTec] Eagle problem?

[Bob McGraw - K4TAX]

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 at Blomand.net>
To: "Discussion of Ten-Tec Equipment" <tentec at 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."
>