At 05:54 PM 5/29/2007 +0000, you wrote:
Try these:
This is the better, but the FET is very pricy.
<<>>
OK...
There are some issues I see with my VERY little experience (basically,
none) with building circuits but I will see if I can make a try.
Why is there a gas discharge tube in the dipole? And if you use
speakerwire for the connection between antenna and receiver, wont it
pick up noise inside the house?
Hi:
Let me help with your questions .... the short (1 meter) antenna is
connected to the FET in either a mono pole or dipole version of his
circuit. The gas discharge tube is a safety device that will discharge any
DC static build up to ground. It provides no function to enhance
reception. As I mentioned he shows 2 versions of his antenna/amplifier ...
the first is single ended (mono pole) and should really be mounted right on
the ground next to the ground rod. The second version is a dipole ...
which will allow the antenna/amplifier to be mounted away from ground.
The speaker wire or zip cord is a balanced feed line. His objective (he
goes to great lengths) is to completely isolate the antenna (1 meter in
length) from the amplifier and feed line. The amplifier is high gain, high
impedance input and low noise. He uses RF transformers to isolate the unit
from the feed line. In critical situations it is much easier to maintain
balance and isolation using balanced feed line instead of coax. Properly
terminated balanced line will not pick up RF ... eg noise. The reason is
that the noise signals are picked up at any point in the feed line in
exactly the same strength and phase. When the meet at the terminating
transformer winding they will be 180 deg out of phase and cancel each other
out .... eg no noise. This is not true in coax.
And finally, he speaks of just LW and AM, but my interest is in the
shortwave (60mtr tropical band is my main focus I want a new antenna for).
I do not know how well the unit will work on 60M tropical band. The
antenna and amplifier should be just fine .... the limiting factor will be
the transformers .... which are designed for LF/MW frequencies.
Jim, VE3CI
