A 1N4007 or any other silicon power diode is a poor choice as a
detector, for several reasons. The first is the large shunt capacitance.
The second is the long reverse recovery time, which makes silicon power
diodes look like a resistor rather than a rectifier at HF. High voltage
diodes like the 1N4006 and 1N4007 contain an intrinsic layer to increase
the voltage breakdown. This dramatically increases the reverse recovery
time to the point that they can be used as PIN diodes at HF.

Schottky diodes don't have the reverse recovery problem, but power
diodes still have a lot of capacitance (and reverse leakage current).

Only a signal diode should be used as an HF detector. If you can't find
one with a sufficient reverse voltage rating, you'll have to use a
divider of some sort.

Roy Lewallen, W7EL

Richard Clark wrote:
On 17 Sep 2004 20:36:21 GMT, (JGBOYLES) wrote:


What say you?


Hi Gary,

For a diode, the 1N4007 is rated at 1000V. However, you have to
design with Peak voltage in mind, and then add 50% safety factor for
good design. Further, feeding a capacitive filter requires you DOUBLE
the PIV rating. All in all, this suggests your design choice should
tend toward the divider before the detector. Then the question
becomes, do you want a peak reading meter, or an averaging meter? A
peak reading detector (AKA Clamp) will lightly load the divider
whereas the averaging will load it more (and ruin any fixed divider
ratio - which returns us to the variable component to be designed in).

73's
Richard Clark, KB7QHC