Wavemeter D

Wavemeter Class "D"

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General Description

The British Army WW2 Class D Wavemeter is a portable heterodyne wavemeter. It replaced a previous instrument known as "Corrector Frequency".

It was designed for adjusting senders and receivers to particular frequencies, for checking frequency calibration of these sets and for determining the frequency of a received signal. In particular it was used with British WS I9 and WS 22 sets.

Technical Data

The accuracy of the wavemeter is +- 2kc over the frequency range.

The frequency band covered by the Class D Wavemeter is 1900 kcs to 8000 kcs in two ranges,1900 kcs-4000 kc and 4000 kc to 8000 kc. The instrument is also capable of supplying check frequencies spaced apart by I000 kcs up to 25 000 kcs. These check frequencies are used for verifying gross errors of calibration.

The wavemeter is powered hy an external 6 volt accumulator. This provides filament power for the valve and dial lamp and also supplies an internal vibrator to provide HT through a bridge connected metal rectifier system. The total current consumption is 1.1 amps at 6 volts dc.

The unit contains one valve, an ECH35, which is a triode - hexode. The triode is used as a crystal oscillator,1000 kcs for calibration marking or on 100 kcs when used on the 1900-8000 kc ranges for heterodyne wavemeter use. The Hexode is used as a free running oscillator to provide a signal to beat against the 100 kc crystal, hence producing a tuneable calibration marker.

The "Check" button function is used to discriminate between true and false beat notes. On the press of the button if the frequency of the note does not change, the beat note selected is false. A change in frequency indicates the correct beat note has been selected.

Headphones are used to measure the frequency of a local transmitter, by tuning for zero beat. To measure the frequency of a receiver, the Wavemeter is set to the desired frequency and the receiver is tuned to zero beat the signal.

While the Wavemeter is still a useful instrument, it does not provide sufficient accuracy for current use. It was a very reliable aid in the davs of am/cw during WW2.

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© Ian O'Toole, 2009. Page created: 28/04/03 Last updated: 4/12/2009