Modulation level indicator 678

Housed in a ripple black diecast case similar to the better-known 669 S meter, the Eddystone 678 modulation meter is a passive field strength meter using a pair of germanium diodes and a 200 microamp fsd meter. A small pickup aerial screws into a socket on top of the case, and one of six coils plugs into the rear. The six coils supplied cover the 10, 15, 20, 40, 80 and 160 metre amateur bands.

To measure amplitude modulation depth, the RF pickup is adjusted until the meter reading coincides with a special mark on the scale. On switching over, modulation percentage can be read off the calibrated scale directly. A jack is also provided at the rear for plugging in monitor headphones.

Here you find 253 models, 123 with images and 46 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from Eddystone (Brand), Stratton and Co., Ltd., Eddystone Radio Ltd.; Birmingham