Topband: S-meter Calibration

[Richard Karlquist]

> However, now I will drop the other shoe. Assuming that the RX
> input is a 50
> ohm resistor is a mild approximation in comparison with assuming that the
> 'generator' driving it has 50+j0 source impedance. Particularly
> true if that source
> is something as ill-defined as a beverage antenna, which is what
> most of us
> listen with on 160. The approximations abound and cascade, which is why
> absolute calibration is so futile. What we really want to measure
> is the value of E
> or H of the incident EM field, which is the only true measure of
> received power.
> 73
> Eric von Valtier K8LV


What I do when giving signal reports on 160 is to switch
the receiver to listen on the transmit antenna (a 90 foot
vertical) and get an S-meter reading on the FT-1000D.
I then use a lookup table to convert the S-meter reading
to the correct reading.  For example, S-2 indicated is actually
something like S-5.  The SWR on the transmit antenna is
quite low so it can be considered to be a 50 ohm signal generator.
I think this number really means something, since a vertical
antenna is some kind of a known quantity.  I also give
a "readability" report on the beverage (armchair, adequate,
or rough copy).  That, I would admit, is not very "scientific"
but is still useful information to the other station just
in terms of operating procedures.

Rick N6RK