After 50 years in the business, I'm either confused or
amazed by the BDR and dynamic range discussions.
Maybe I've missed something?
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.
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?
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.)
3) Our discussions are not meaningful, if they don't provide
quantitative guidance to manufacturers on dynamic range.
Lacking that input, things will never get better.
4) Correlation of lab-data with field observations is further
exacerbated by competitive level adrenalin. Reality, though,
is...with an s3 noise level, and an s9 signal close by,
you'd only have....6dB/wiffy-unit times 6, or 36dB dynamic
range on the input. Even with 20dB louder interference, that's
only 56dB. A receiver with 60-70 dB close-in dynamic range would
have some dynamic reserve. I'd suspect most good receivers land
in that vicinity, within 2KHz.
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.
6) The present problem is legacy radios, overdriven amps, and impression-
driven, rather than data-driven analyses. The only reason we're having
the discussion about MP's is that most folks have moved on from the
930/940 vintage radios.
I had a guy with a 930 five miles from me in VT. Loved to park 200Hz
above the dx window in contests. He was perhaps 10 over s9, indicated,
...but his phase noise was s7-s9 over the entire window, on my 781.
Things are a LOT better than they used to be.
7) The 850 with good filters looks like a real sweet-spot.
n2ea
jimjarvis@ieee.org
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