Geoff, GM4ESD, wrote: Quite right, but there is a way to overcome this problem which is to apply an offset DC bias to the diode(s) which cancels the diode's natural 'bias'. The diode(s) will then conduct with low applied 'signal' voltage. Requires a
stable and 'quiet' DC source e.g. a battery, and stable resistors in the DC 'level adjust' circuit, plus care when setting up. Perhaps it is not worth doing this unless there is a REAL need for a probe that can measure low RF levels. ------------------- Some years ago Wes Hayward, W7ZOI, published a nice design for such a low-level detector in "Solid State Design for the Radio Amateur". It uses a simple op-amp and a second diode to set up the proper bias for the detector diode so that ordinary small-signal silicon diodes (e.g. 1N914) could be used to measure very small RF voltages. I used the circuit myself for a number of years. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
