Below is the reverse engineered schematic of the famous BOONTON RF MILLIVOLTMETER probe (also Ballantine labs). The unmarked diodes
*must* have a square law characteristic like germanium in order to work down to a mere 50uV, but yet the thing works up into the GHz region and has a mere 1.5pF input capacitance, indicating that they are NOT a 1N34A. +-------+-------+ | If | Vf | +-------+-------+ Measured at | 10uA 140mV | 20 degrees | 100uA 210mV | Celcuis | 1mA 320mV | +---------------+ 1/8W CF 1/4W CC 100 ohm 330 ohm 5% 10% +---| out - | | | diode --- | 1nF --- Out to | Cer | differential GND chopper type | Cer | amplifier 1.5nF | 1nF --- and shaper chip | diode --- | | +---|>|----/\\/\\/----+----/\\/\\/-----> out + 5% 10% 100 ohm 330 ohm 1/8W CC 1/4W CCHow would I find out what these unmarked diodes are? Most of the boonton meters from eBay are without probes, and I would like to help folks make their own probes by posting this info. Please see:
Thanks from Stepan