-----Original Message-----
From: Jim Reid <[email protected]>
To: [email protected] <[email protected]>; [email protected]
<[email protected]>; [email protected] <[email protected]>
To: <[email protected]>
Date: Tuesday, August 25, 1998 1:39 PM
Subject: [TowerTalk] Rebutal to Steve Best's "Initial State" Mismatch
Arguments
{snip}
>
>And when does the first reflection arrive back at the tuner?
>On 100 feet of typical coax, say low loss RG213, which has
>a propagation velocity of 66% of the velocity in space, the time
>for an RF signal to travel out the line length, and then reflect
>back to the input end is 30 nanoseconds for the round trip.
>
>What does that number mean, in plain English??
>
>Consider an RF circuit to responding to such a short time pulse,that is
>for the voltage of the reflected wave to reach about 90%
>of it's eventual "initial value", the bandwidth of response
>required for the circuits to be "aware" of this initial voltage
>would have to be 2700 MHz !!! That is why even radar signals
>at microwave frequencies between 1 and 10 GHz are not even
>this brief; radar pulses below 10 GHz are in microseconds.
>
{yet another snip}
Jim, I was piddling around with my calculator and I got 308 ns rather than
30. Did I miscalculate, or is your number off by a factor of ten?
Would this mean the answer to the next question is 270 MHz, rather than
2700? Even so, I surely agree that your point about being irrelevant to HF
is still very valid.
Tnx & 73,
Bob KK4TD
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