[Boatanchors] SP-600 "S" meter anomaly?

[shoppa_boatanchors at trailing-edge.com]

> Whe I tune in a station the meter reads signal strength "normally".
> HOWEVER, the meter swings DOWNWARD with modulation, not upward
> as one would expect, and as other radios in the shack do.

> [This is on AM]

For AM without overmodulation or clipping the signal strenght with
modulation is the same as without modulation.

BUT... what bandwidth were you using?  If you center the carrier in
the filter, you get maximal S-meter reading.  Any modulation means
signals at frequencies away from the carrier, and if the filter is
narrower than the broadcast then the S-meter will go down with
modulation.

[other radios have S-meters that go up when AM is modulated]

This could be related to AGC action working on peak signal in
the IF, most old-timey AM-only radios don't do this (they base
AGC on the average) but radios intended for SSB will probably
base AGC action on the peaks.

Tim.