Larry
What is the insertion loss of the DA-121? That is what we really want to know,
isn't it?
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
On Sunday, October 27, 2024 at 08:40:26 AM CDT, Larry Haney
<larry41...@gmail.com> wrote:
Jim, I agree with this posting of yours except for the 1st and last
statements.
1. First you said: 'What has been overlooked is that there is an impedance
transformation from 50 to 125 ohms.' We are all very aware of this fact.
2. Lastly you said: 'To convert the SG voltage output into the voltage
actually seen by the R-390, multiply the SG reading by 0.1235 or divide the SG
reading by 8.097, either way works.' That is not right at all. You just went
through a nice step by step explanation about how to determine the power loss,
then you use that power loss ratio (0.1235) to determine the voltage seen by
the 390. Wrong, wrong, wrong. The last 3 steps in your procedure are: 1. dB =
10 Log ^ (.00247watts / 0.02 watts), 2. dB = 10 Log ^ 0.1235, 3. dB = -9.083.
No real disagreement there. The input watts to the da-121 = 0.02 watts, the
output watts from the da-121 = .00247 watts, that's a 12.35% loss of power in
watts, not voltage. You can not use the 0.1235 power loss relationship to
directly calculate the voltage loss relationship of the da-121 as you are doing
in your last statement.
One way to correctly calculate the voltage coming out of the da-121 (Vout),
would be to use the formula:
Vout = Sqr rt (Pout (watts) x impedance (ohms))
Where Pout is the power coming out of the da-121 (in this case, 0.00247 watts)
and impedance is the da-121 load impedance provided by the 390, 125 ohms.
Vout = Sqr rt (.00247 x 125) = 0.5556 Volts
.00247 x 125 = 0.30875 Sqr rt 0.30875 = 0.5556 Vout = 0.5556 volts
Vout is what's going into the 390 (in this scenario).
Regards, Larry
--------------------------------------------------------------------------------------------------------------------------------------------------
On Wed, Oct 23, 2024 at 9:35 AM Jim Whartenby <old_ra...@aol.com> wrote:
What has been overlooked is that there is an impedance transformation from 50
to 125 ohms. Any calculation that ignores this transformation is in error.
The only solution that accounts for different impedances is by looking at the
respective powers at both input and output.
1 volt into the DA-121 gives 0.556 volts out. Looking at the power-in verses
power-out using the respective impedances:
Power = voltage squared / resistance
Pin = 1 volt ^2 / 50 ohms = 0.02 watts
Pout = 0.556 volt ^2 / 125 ohms = .00247 watts
dB = 10 Log ^ (Pout / Pin)
dB = 10 Log ^ (.00247watts / 0.02 watts)
dB = 10 Log ^ 0.1235
dB = -9.083
To convert the SG voltage output into the voltage actually seen by the R-390,
multiply the SG reading by 0.1235 or divide the SG reading by 8.097, either way
works.
Regards, Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
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