On Mon, 06 Mar 2006 18:43:22 -0800, Roy Lewallen
wrote:

Gary Schafer wrote:
. . .
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.

I'm not sure I fully understand this. The difference from one S meter
division to another *is* likely to be different on different bands,
since it depends on the gain-vs-voltage characteristics of the
controlled stages which can vary with frequency. But I do agree that he
can make good comparative antenna measurements without good S meter
calibration, because he has a step attenuator. By simply setting the
attenuator so he gets the same S-meter reading on both antennas, S-meter
calibration is completely irrelevant -- the antenna gain difference is
the attenuator setting.

I find it useful, however, to be able to see the difference with
reasonable accuracy just by looking at my S meter. But that does require
calibration for the band in use.

. . .

Roy Lewallen, W7EL

Hi Roy,

I have been away for awhile so haven't had a chance to reply.

My point of the S meter being the same relative difference between S
units on all bands comes from the assumption that like most modern
radios, there is no AGC controlling anything in the front end of the
radio. All the gain control is done in the IF so it is impartial to
frequency.

So even if there is some difference in the gain of the first mixer, or
preamp if there is one, the gain controlled IF sees the same relative
signal level regardless of band.

I did a quick check on my old Kenwood TS430 using a Wavetek 3001
signal generator that has a step attenuator in it and got the
following results:

+60= -10dbm
+50= -20dbm
+40= -30dbm
+30= -40dbm
+20= -50dbm
+10= -60dbm
S9= -70dbm
S7= -80dbm
S4= -90dbm
S1.5= -100dbm

Test was done on 80, 20 and 10 meters with the readings the same on
all bands as close as I could determine the meter reading. I would
suspect that the signal generator leveling accuracy may be no better
than what error can be read on the S meter.

73
Gary K4FMX