RadioBanter - View Single Post

June 18th 06, 10:09 PM posted to rec.radio.amateur.antenna

wrote:
Anyone understanding the basic system at all would understand if the
little charges made noise from transferring charge, that noise would be
at a radio frequency. Anyone looking at what you drew and understaning
what you drew would also understand in order to short the noise energy
at the radio frequency the path would also be required to short the
good signal.

Absolutely false! Good grief, Tom, don't you even understand
impedance transformation? The impedance changes along a
transmission line with reflections. The impedance at the receiver
is NOT the same impedance as exists at the antenna feedpoint.
Since my noise problems were with a G5RV used to receive on 40m,
let's take that as an example.

G5RV dipole---30 ft. 300 ohm matching section--x--coax to RCVR

Let's assume a 50 ohm impedance at point 'x' looking toward
the receiver. What is the impedance at the dipole feedpoint?
Are you capable of that calculation? The 300 ohm matching
section is known to be 1/2WL on 20m so it is 1/4WL on 40m. The
impedance seen at the dipole feedpoint looking back toward the
receiver is therefore ~1800 ohms. A 500 ohm RF choke across the
feedpoint will considerably decrease the RF noise at the receiver.

So, Tom, which way would the RF noise rather flow? Through a
500 ohm RF choke at the feedpoint or down the transmission
line that is exhibiting an impedance of 1800 ohms. I thought
you were kidding but you really are trying to refute Ohm's law.
--
73, Cecil http://www.qsl.net/w5dxp