Topband: Choosing between a Receiver Noise Bridge and an AntennaBridge

[Bob Tellefsen]

Hello George
I've used the noise bridge method, and a couple of different antenna
analyzers.
Here's what I've found so far.

NOISE BRIDGE.  You need a known 50 ohm load to calibrate it.  One assumes
such a load
somewhere in your shack.  A good 51 ohm resistor will do the job.
On 160m, the noise bridge effectiveness depends on the amount of atmospheric
noise
you receive via the vertical, and the magnitude of the noise form the noise
gen.
If it isn't high enough, the ambient noise can actually mask it,
particularly
when you get down into the null.

ANTENNA ANALYZER.  I have used the Autek RF-1 and VA-1, and the AEA HF-CIA
analyzers.
If your load under measurement is outside of about the 2:1 circle on a Smith
Chart, they
are all over the map on their results.  Three different units will give you
three
different results, and you will never know which is correct.  Due to the
general nature of the beasts, I assume the MFJ units would have the same
general limitation.

An additional complication is AM BC energy coming in through the antenna.
I've finally
resorted to an ancient General Radio 916-A passive rf impedance bridge.  I
use my K2 at about 100mw for a signal source and a Sony 2010 SWBC receiver
as the tunable detector.  With this setup, my results are far more
repeatable than with anything else I've tried.

SUGGESTION.  Use whatever instrument you can borrow or buy to get you in the
neighborhood of correct matching unit settings, then use your swr bridge at
the feedpoint to fine tune the settings.  You could run a wire back to the
shack to key your TX remotely while adjusting with the swr meter.

Good luck and 73
Bob N6WG

-----Original Message-----
From: topband-bounces at contesting.com
[mailto:topband-bounces at contesting.com]On Behalf Of George Stewart
(VK5ALS)
Sent: Monday, January 12, 2004 6:33 PM
To: Topband at contesting.com
Subject: Topband: Choosing between a Receiver Noise Bridge and an
AntennaBridge


Hi Topbanders,

I am considering purchasing either the MFJ Receiver Noise Bridge OR the
MFJ Antenna Bridge (models 102B and 104B respectively).

Could someone please let me know of the pros and cons of these units and
e-mail me direct with your replies?

My initial use will be to aid setting up a short vertical for 160 metres
with top loading guy wires and tuned used a simple inductance at the
base - nothing very demanding really.

73 George/VK5ALS

E-mail: ggstew at bigpond.net.au



_______________________________________________
Topband mailing list
Topband at contesting.com
http://lists.contesting.com/mailman/listinfo/topband