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Telamon · September 30th 06, 06:54 PM posted to rec.radio.shortwave

In article . com,
wrote:

wrote:

I use the ALA 100. The smaller loops may not be as good on MW. It is a
good idea to insure the amplifer is actually doing something. The fuse
could be blown, the wall wart bad, etc. Unplug the power connector and
make sure the signal strength drops. You will get reception from the
loop even if the amp is off since some RF will leak.

Some of the Wellbrook amps were positive ground. The unit is fused and
I would guess there is a reverse biased protection diode. If the wrong
wall wart was used, it would pop the fuse. In my portable set up, I
have red shrink wrap on the connector that goes to the Wellbrook, just
to make it clear the ground is backwards.

As far as the 1530 goes, it may not have a good resale value since they
released the "plus" version, which has response in the FM BCB.

This ALA 1530 requires a reversed, is shell positve and inner negative,
wall wart. But the center conductor of the coax was positive. I left
the
original power injector/diplexer intact and built my own. I verified
the
problem with the stock wall wart/diplexer before trying my own.

With out power I get virtually no signals. A few very strong MW and SW
at way less then S1. So the amp is working. The original owner says
it always behaved like this. OK, but clearly not the do all end all
of antennas.

What you are calling a "power injector/diplexer" would probably be best
described as a bias-T. This is a three port device:

Sample schematic:
http://www.smelectronics.us/biast.htm

1. DC voltage. (DC input) This is connected to the power supply.
2. AC voltage. (RF output) This is connected to the radio.
3. DC + AC voltage. (RF input, DC output) This is connected to the
antenna/amplifier.

Port 3 to 2 is connected with a capacitor of very low reactance (zero)
to the signal you want to pass through these two ports.

Port 1 to 3 are connect with an inductor, which passes DC voltage from
port 1 to 3 but blocks RF (high Z) going from 3 to 1 so the RF only sees
a path from 3 to 2.

Port 3 and 2 are coax cable and port one could be two terminals. One
terminal is common grounded with the coax shield grounds. Using a ground
independent power supply to the terminals on port 1 allow you to have
either a positive or negative power supply to the remote amplifier.

--
Telamon
Ventura, California