Experiments with thermocouple milliammeters at very high radio frequencies

A description is given of the calibration of commercial thermocouple milliammeters at frequencies of 100 Mc/s and 700 Mc/s. Errors dependent on current amplitude were found, and were shown to be due to the magnetic properties of the material used for the heater wires. The occurrence is confirmed of frequency-dependent errors, due to the method of constructing the ordinary instruments. Specially made instruments, though superior in respect of these errors, are likely to be of limited usefulness on account of the disturbance which is caused by the inclusion of any such device in a circuit carrying current at very high frequencies.