Well, I don't understand your math . . .
Yes, 100w is +50 dBm.
The TX noise is 77 dB below the carrier (for a SSB bandwidth).
We subtract 77 from 50 noise level = -27 dBm
This is the level of the wideband TX noise as it leave the TX.
S9 = ~ -72 dBm
-27 dBm is 45 dB above -72 dBm
Hence the TX noise level is S9+45 as it leaves the TX . . .
Now . . . the RX noise level is whatever the TX noise level is minus
the path losses.
Assume skywave path losses of 100 dB.
RX noise level is -100 - 27 = -127 dBm.
This would be approx the MDS of most RX and would usually be buried in
the band noise.
Now assume ground wave path losses of 60 dB.
RX noise level = -27 - 60 or -87 dBm.
If S9 is -72 dBm this is only 15 dB below that or about an S6 noise level.
The level of any RX signal is irrelevant (except for whatever AGC
action it may induce). It is what it is. This is wideband noise which
the RX will hear as wideband noise. The noise level will jump up each
time the Flex is keyed. Note that no modulation need be sent. All that
is necessary is to key the TX.
And, no, the station listening to the Flex TX does not hear the noise.
He hears the signal. The guy tuned to another signal, even one 300 kHz
away, is the one that gets blasted by the wideband TX noise.
And the paper linked-to was indeed about VHF/UHF contesting. But for
those ops the path loss is mountain-top to mountain-top and is much
less than skywave path losses. So any Flex model is really, really not
welcome by the VHF contesting crowd. That was the point of the paper.
And the same thing applies to most ground wave paths as well.
73 de dave
ab9ca/4
On 12/31/13 3:38 PM, Bruce Beford wrote:
For those, the noise from a Flex at 100w, at -77 dBc (which is -27
dBm), can be quite substantial. Recall that S9 is approx -72 dBm. A
Flex is transmitting wideband S9+45 noise.
OK, I'm not a Flex user. But, I don't agree with your math. I am not trying
to defend the transmitted phase noise performance of the Flex products,
but... Your math is flawed.
Assume 100w transmitter is delivering +50 dBm to an antenna. (100W is 50 dB
greater than 1 milliwatt) Also assume you are at a receiving station, and
hearing this station at S9+30 dB, on a receiver calibrated to 6dB/S unit,
S9=50uV at 50 Ohms, or -73dBm for S9. Your receiving the fundamental signal
at -43dBm (S9+30dB). With the transmitted phase noise 77dBbelow the carrier,
it would be received at -120dBm, or about S2.
Granted, it would be 10 dB stronger (abt S3.5), if you were receiving the
fundamental transmission at S9+40dB, etc. But... the Flex is not "
transmitting wideband S9+45 noise."
Let's not blow this out of proportion.
Bruce N1RX
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