"Andrew VK3BFA" wrote in message
om...

This ALC detector circuit is common to all
bands, so its unlikely to be faulty. All test results were on a 50R
dummy load, so antenna variations have been eliminated.

Thanking you,

Andrew Blight VK3BFA

May be the sensitivity of the ALC detector is different at various
frequencies in the 3.5 to 30 MHz range. This circuit usually uses a
toroidal core transformer. May be they made a batch using the wrong core
type. May be the transformer has nulls in sensitivity around this
frequency. Or If your problem is at 3.5 MHz, may be is not designed
optimally and could do with a few more turns. Not too many more or it may
lose sensitivity at the 30 MHz end. Try to figure a way to check the ALC
detector sensitivity over the frequency range.