Jim Jarvis wrote:
> 1) What's s9? I've got references indicating 50uV or 100uV.
> The front end of a decent receiver is spec'd at .1uV
> sensitivity, making 100uV a reasonable 'full scale' signal.
> 100uV plus 60dB is....gee...100V! A very large signal,
> indeed.
Correction: 100 uV plus 60 dB is 100 mV, still a strong signal but a long way
from 100V. Decibels (for voltages) are defined as
dB = 20*log(V2/V1)
>
> Going the other way...9 wiffy-units*6dB is 54dB to get to
> S0. A mere 30dB down from 100uV brings you to .1uV, or
> the receiver noise floor. Where'd the other 20dB go?
> Or could it be the wiffy-unit problem, again?
Correction: 30 dB down from 100 uV is about 3 uV. See above.
>
> 2) Who among us has a receiver which is calibrated in dBm?
> Who among us trusts the logarithmic calibration of their
> wiffy-unit meter, really? And over how many decades of
> its range? (regardless of indicated units.)
The S-meter is still quite useful for measuring signal level differences if you
have an external step attenuator. You add step attenuation to equalize two
different signal levels on your S-meter and read the difference as the amount
of attenuation you added in. I built a very simple step attenuator many years
ago from a simple Handbook circuit. It has resolution down to 3 dB, which is
good enough for most measurements. You can easily build in lower resolution,
if needed.
>
> 5) Interesting if the new Tentec claims -140dBc/Hz noise output.
> Add 10dB for an amp..still impressive, and well below the level of
> atmospheric noise, if it proves true.
The Orion spec is indeed very impressive. (My IC-781, which I'm replacing with
a new Orion, has phase noise that measures at about -105 dBc/Hz for close-in
spacings). However, to compare phase noise to atmospheric noise, you have to
reference a specific input signal power level. If the input signal is strong
enough, then phase noise may be audible.
73, John W1FV
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