I got a good answer in mail:
"J" == Jerry writes:

http://www.rdrop.com/users/billmc/phone_antenna is built around
a ".01uF capacitor", but what kind? Are big .01uF capacitors better
than small ones etc.?

J It isn't the size but the voltage rating that matters. The point of the
J capacitor is to protect the RF stage of your radio from the ringer signal of
J the phone, which will be anywhere from 40 to 70 volts. Considering that
J your radio may be sensitive to signals in the microvolt range, it isn't
J surprising that 70 volts could be a radio killer. I'd use a cap of 200 volt
J or more rating. There are a lot of different kinds of caps. A ceramic disk
J would be appropriate and dirt cheap.

Sure wish there would be that warning on that regular posting to
rec.radio.info . Yes I emailed McFadden.

Is .01uF critical or is there actually a range that is acceptable?

J The point is to have it big enough to pass all the RF signals your
J interested in, but not signals lower in frequency than you want. 0.01uf is
J a standard value, but double or half that would be OK.

Also the "RF connector" isn't clear. What are examples of this "radio
frequency connector"? Perhaps just coax to alligator clip?

J Just connect one end of the capacitor to the phone line and the other to
J your radio. If your radio has a telescoping antenna, just clip it to that.

Is the 50 ohm coax critical? How about a plain wire from the capacitor
to the radio's telescoping antenna? Should the telescoping antenna
still be extended, or retracted?

J You're making this too complicated. Just connect the capacitor to the
J antenna. Any wire will do. Considering that the phone wire may be miles
J long, whether or not you extend the telescoping antenna is probably
J irrelevant.

How do we know if our phone line antenna is working properly? Should
time signals on 5000, 10000 khz etc. jump out in perfect clarity?

J HF signals are rarely perfectly clear, no matter what the antenna. You
J ought to hear more than you do with the telescoping antenna alone.

Certainly there must be a slight advantage between one of red and
green vs. the other... or might we not even bother comparing, as they
are certain to be the same?

J If you have 4-wire phone, one of them will be ground, and that one certainly
J will NOT work. The others are probably equal as antennas. Just try them
J all.

By the way, I found a .01uF capacitor that the capacitor numbers web pages
don't seem to decode: 103K PE50. I can't figure out what the PE50 or
PE5Q means.

J Probably means 50 volts. Not enough. The first time the phone rings will
J damange this capacitor. A 1000-volt 0.01uF cap is only a quarter or so a
J Radio Shack.

Far from stores, I wonder if the necessary high voltage capacitor
could be found in my pile of broken radios. I suppose I would look
for meaty cylindrical types rather than pill shaped types. OK, will look.

Best way to do this is to use telephone quad (station)\
wire between the telco demarc and the rj-11telephone
block. Phone pair will be the White, White/Blue
or Red/Green pairs. You can then use any of the unused
wires in the cable as the antenna lead. Radio signals
will be common mode on the cables, and will capacitively
couple to the adjacent pairs. No need for a direct
capacitive coupling to the hot phone pair.

Pete

"Dan Jacobson" wrote in message
...
http://www.rdrop.com/users/billmc/phone_antenna is built around
a ".01uF capacitor", but what kind? Are big .01uF capacitors better
than small ones etc.?

If you have your computer modem connected to the phone system, you may pick up
monitor noise.

One time I eliminated monitor noise in the my dining area just by disconnecting
the modem line from the phone block in the dining area. I didn't even have to
pull back the modem cable. (My computer is in another room.)

Bill, K5BY