On Mon, 06 Mar 2006 13:47:04 -0800, Roy Lewallen
wrote:

Ed wrote:

The bottom line for the Rx, all it cares about since it doesn't know
what kind of antenna is feeding it, is the signal strength at the
input.... so I'd say a calibrated microvolt reading reflecting that
strength is not very meaningless at all. Any changes in the antenna
system will of course change that, but the whole point of any antenna
work is to maximize the signal voltage to that rx input, so I'd think a
calibrated reading would be extremely useful over an S meter alone.

I'm afraid it might require more than simple calibration. The S-meter
typically just shows the AGC voltage. The AGC response is only
approximately logarithmic, and depends on the gain characteristics of
the various stages being controlled. Gain characteristics are commonly
very temperature sensitive, so any calibration scheme would have to take
that into account, as well as the common deviation from true logarithmic
response of the various stages. Calibration would also be different on
different bands, with and without preamplifier or attenuators, etc.

Of course, you could make a receiver with very nearly true logarithmic
response, by use of one of the excellent, wide dynamic range log amps
which are available these days. But however much you or I might like
one, the vast majority of amateurs couldn't care less about what their S
meter is really indicating, so they wouldn't pay the added cost for it.

On top of that, most amateurs would consider a 6dB-per-S-unit meter to
be "dead", and would rather have it wiggle more.

Roy Lewallen, W7EL


Back many years ago, and probably still today, many hams would turn
away from a receiver that had what they called a "scotch" S meter. To
them a receiver that read S 6 while another receiver only read S 4 on
the same signal "had to be much better". Manufacturers started making
receivers with more lively S meters.
Looking at some of the older receivers such as the Collins had much
more realistic S meters than most today.

The calibration points that Mike did on his receiver should be valid
for any band for his antenna comparisons. An actual signal strength
measurement is not required nor would it be valid between bands. All
that is really needed is the difference measurements between the two
antennas so his calibration between points on the meter scale will be
valid on any band.

A really nice instrument that would be good for signal strength
measurements is an old HP 3586C selective level meter. It covers from
around 100 hz to 32 Mhz and has a digital readout to 2 decimal places
in dbm signal strength. Hard to use with other than a steady signal
though.

73
Gary K4FMX