FYI
I have used either 470 or 510 ohm carbon comp resistors way back when as
20dB probes for a sampling scope and Spectrum analyzer work. If I recall,
they were quite comparable to the scope's regular probes for pretty fast
digital signals.
I would, however, get nervous with the high values stated / needed here.
At first I was thinking I'd series-up 500 or 1K resistors if I had to do
this, but then strays start to become significant as has been well
discussed.

If you have the equipment, I like the frequency response / sweep idea. This
way you may even be able to adjust the compensating caps for best high freq
(10M) response. You could also use the calibrator on most good scopes to
start out....
73,

--
Steve N, K,9;d, c. i My email has no u's.

"Richard Clark" wrote in message
...
On Fri, 17 Sep 2004 10:35:25 -0400, "Tam/WB2TT"
wrote:
I think the curve ignores C, and is based on skin effect only. There is
no
explanation for the data.

Skin effect would tend to increase resistance which contradicts the
trend. As for explanation:

From "Electronic Components and Measurements," Wedlock and Roberge,
1969:
"At high frequencies the performance of a resistor will depart
from Ohm's law because of stray capacitance and lead inductance."
[pg. 77]
There is an identical curve to your reference shown in Figure 7.4,
same page:
"Change in resistance of a ½ Watt carbon-composition resistor as a
function of frequency. Frequency in MHz times resistance in
Megohms"
In Chapter 18 "RF Impedance Measurements":
"Such behavior is often termed stray capacitance or stray
inductance. Because these effects are usually undesirable and
serve to limit the high frequency performance of components, they
are also called parasitic effects." [pg. 276]

However, my expression of this being rolloff was too simplistic as the
curve does not follow the typical 10dB/Decade characteristic. Rather,
it shows a 6dB/Decade+. Some of this may be accounted for in lead
reactance, but at the Megohm scale this is inconsequential for
conventional leads.

73's
Richard Clark, KB7QHC