On Dec 29, 9:29*pm, "Tio Pedro" wrote:
" DOH! In fact I do have access to one via a friend. Why didn't I think

of that in the first place? Too much wine and egg nog over Christmas I
guess. But also, thanks to v\everyone for all their comments - all
very useful and if the scope doesn't work for me I will try some of
the other ideas out. Cheers...

Larry VE7EA

don't forget the scope is going to give you a very high reading,
since the display is peak-to-peak. *You'll have to take the
reading from the waveform's *0 voltage cross-over
poiint to the peak of on one side of the full
waveform, and multiply by .707 to get the RMS value.

Pete

Another point about scopes and their probes: they commonly put quite
a bit of capacitance (several pF) at the point they're measuring. A
10:1 passive probe with a couple meters of cable will have several
tens of pF capacitance in the cable, and the capacitive part of the
divider at the probe body can't drop that by more than 10:1. I'm not
sure where the OP will be probing; it may be low enough frequency and
low enough impedance that it doesn't matter. But it's quite possible
for a decent diode-based RF probe to present lower capacitance than a
scope probe. Probing things without disturbing them can be very
tricky at times.

Cheers,
Tom

K7ITM wrote:
SNIP


Sensitivity for very low RF voltages is greatly enhanced by using a
high impedance meter. I would NOT put a 10k resistor to ground there
if I wanted sensitivity to low millivolt RF, since the diode average
current at low RF voltages is very low indeed. You can see that from
my reported results with the 1N4148 detector, with a 1 megohm meter
load versus with a 10 megohm meter load. With the high impedances
involved, the 100pF cap allows response down to well below what would
normally be considered RF frequencies. In the circuit described
above, the low-side 3dB corner frequency will be about that of the
100pF cap and the 10k resistor.

Cheers,
Tom

You might find this interesting:
http://www.cliftonlaboratories.com/d..._rf_probes.htm


Charlie.

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