002: Precision power meter with built-in noise source (JH1BRY design)

Power range +13dBm max (HF-430MHz),  ENR 12.9dB at Id=1mA, 7.9dB at Id=4.5mA (144MHz)

This is a measurement tool what JH1BRY introduced to the JA CQ magazine in the 70's. It is very found useful to measure the output power of Lo oscillator and the QRP transmitter. Therefore, after I made it in 1977, I have used it frequently for years. Calibration procedure is as follows. If assembly finish, Input +13dBm signal from SG and make it matches to the full scale with Vr3. Next, the scale of the reading is recorded in the meter panel while lowering the SG output by every 1dB (down to -10dB), and then the calibration of the power meter is completed.

A practical range of the measurement is from -6dBm to +13dBm, and it is OK to use on 430MHz as the error is small. I also made the variable ATT in the photograph. And, the output measurement up to +33dBm is achieved by using it. It is the point to use B-E of a cheap transistor as a Zenner diode of 7.5V for the noise generation. If you set Vr2 to the full scale 10mA beforehand, Id can be varied by Vr1 within the range of 0.15-5mA. ENR is about 16dB on 144MHz in the vicinity of Id=0.15mA, and it is suitable to tune the receiver and LNA of HF to UHF band.
Power range +13dBm max (HF-430MHz),  ENR 12.9dB at Id=1mA, 7.9dB at Id=4.5mA (144MHz)




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