Hi Bob -

Thanks for your input!

I can understand the basic idea of a VHF/UHF offset for the "S-scale,"
based on the much lower ambient noise levels in that frequency range.
Twenty dB seems like a pretty large offset, though--but who am I to tell
the VK-VHF crowd how to do their "S-scale?" ;-)

Roger on your themal noise estimate. It's been a few years, but I recall
using -114 dBm/MHz as the thermal noise level back in my radar design
days. That would track with your figure. But S1 for you is 0 dB SNR
with a 0 dB NF? Wow, you VKs must have good ears!

73, Ed, W6LOL

"Bob Bob" wrote in message
...
So I cant resist

We had a similar discussion on the VK-VHF NG (a closed NG). The general
consensus for VHF/UHF SSB use as summarized by Gordon VK2ZAB was;
--------------
The scale is:
S9 = -93 dbm = 5 uV into 50 ohms.
S8 = -99 dbm = 2.5 uV
S7 = -105 dbm = 1.25 uV
S6 = -111 dbm = 0.625 uV
S5 = -117 dbm = 0.313 uV
S4 = -123 dbm = 0.156 uV
S3 = -129 dbm = 0.078 uV
S2 = -135 dbm = 0.039 uV
S1 = -141 dbm = 0.02 uV - Note that this fortuitously corresponds to the
level, on Earth, of the power due to thermal noise in a bandwidth of
2000 Hz.
And if you like:
S0 = -147 dbm = 0.01 uV
S-1 = -153 dbm = 0.005 uv
S-2 = -159 dbm
S-3 = -165 dbm
S-4 = -171 dbm
S-4.5 = - 174 dbm Note that this fortuitously corresponds to the level,
on Earth, of the noise power due to thermal noise in a bandwidth of 1Hz.
Those that wish to do so may exercise their arithmetic skills by
determining what S point and /or dbm level corresponds to the noise
power at say one [1] degree above absolute zero - which may exist
somewhere in space.
-------------

Note that there was a lot more discussion about the use/misuse of S
meter reports. I thought the scale the more useful though.

Cheers Bob VK2YQA



Old Ed wrote:
Hello All -

This reads like a tongue-in-cheek bit of good-natured trolling... but I
have
added a few comments, just in case some newbie takes it all too
seriously.

"Reg Edwards" wrote in message
...

..... etc

"Ed Price" wrote in message
news:Unbqd.4490$KO5.3803@fed1read02...

"Frank" wrote in message
news:wN4qd.217617$9b.158132@edtnps84...
I think S meters should be calibrated in dB uV/m, or at least dBm input.

Frank


You cannot do that. Even on a good meter (like a spectrum analyzer or an
EMI receiver), the meter is calibrated only for input power at its front
panel connector. You still have to add a frequency dependent correction
factor for cable loss and antenna efficiency. Very expensive measurement
systems operate under computer control, with a calibrated analyzer and the
computer adding the appropriate factors for cable loss and antenna factor.
(This allows for flexibility; a different coax or antenna can be
substituted at any time, so long as the computer has a table of factors
for the new device.)

As for how you mark the S-meter scale, I agree that we use an archaic
system with S-units. It would be more rational to use a simple dB scale
referenced to something like 1 picowatt (which would then become 0 dBpW).
OTOH, the purpose of an S-meter is not to provide absolute measurements.
It is used as a tuning indicator and for relative signal strength
comparisons. And the archaic marking system works fine for that need.

Ed
wb6wsn


Yes, I agree with your comments, and am familiar with EMC and ATR
measurement techniques. Mentioning dBuV/m was a bit tongue in cheek, but
just the same if you could add the antenna factor etc. it would be nice to
give accurate reports of field strength. Still dBm (or dBpW) is certainly
no big deal. Even if not laboratory accurate, it still means so much more
that the S signal strength scale.

Frank