RadioBanter - View Single Post

March 12th 06, 03:50 PM posted to rec.radio.amateur.antenna

wrote:
When I connected a
10 foot RG-8X jumper, time delay was about 13.5 nS.

Let's take a look at the measurement results. That
13.5 nS delay through the coax would make that piece
of RG-8X 1/4WL self-resonant at ~18.5 MHz, higher than
the specified 16 MHz self-resonant frequency for the
coil. So the laws of physics would dictate that the
delay through the coil cannot be less than the delay
through that piece of coax.

By definition, the physical meaning of that piece of
coax being 1/4WL self-resonant at 18.5 MHz is that
it takes 1/2 of a cycle in time for the forward wave
to make a round trip to the end of the coax and back.
1/2WL of a cycle at 18.5 MHz is 27 nS. So the one-
way delay through the coax is 1/2 of 27 or 13.5 nS.

By definition, the physical meaning of that 10" coil
being 1/4WL self-resonant at 16 MHz is that it takes
1/2 of a cycle in time for the forward wave to make
a round trip to the end of the coil and back. 1/2
of a cycle at 16 MHz is 31 nS. So the one-way
delay through that coil is 1/2 of 31 or 16.5 nS.

The 1/4WL self-resonance point *IS* a measure of the
delay through the coil just as it is a measure of
the delay through a piece of transmission line.

If the coil is indeed 1/4WL self-resonant at 16
MHz, the one-way delay through the coil is *already
known* to be 16.5 nS and that is what should have
been measured. The fact that the *known value* of
the delay through the coil was not measured runs up
a red flag and is technical proof that something was
amiss with the reported results.
--
73, Cecil http://www.qsl.net/w5dxp