Total posts : 45366
A thought about why you got 3dB less with A/C.
Looked carefully at the schematic of C.crane FM 2 on FCC site.
The DC power( 3-6volts )whether applied to the adaptor jack or the battery compartment terminals is the same thing with a switching diode to have auto. power switching to battery if power goes out. Makes no difference where power is applied….goes straight to a regulator that supplies 2.5 volts to the transmitter. You can put 4 AAs( 6v )in the battery compartment instead of 2 AAs…doesn’t matter, 2.5 volts is still what the regulator supplies the transmitter….so why the loss of output with the adaptor?…..by adding more antenna via the 6 ft cord from the A/C adaptor you added “too much” antenna combining with the 6ft audio cable and created a mismatch which resulted in a drop in field strength.
This is really a good transmitter that sounds as good as any of them…even Decades, and the transmitter chip(S14710 DSP) has compression/limiting that actually works.