Take a look at the new

Galbraith

Noise Bridge:

What are noise bridges for?

Many people are intrigued by noise bridges, and want to know what to use them for. The truth is, it is a tool to be used when designing or testing radio equipment. Useful in the MF and HF spectrum, it can be used in a myriad of situations. Here are some:

1. Measuring aerial impedance and resonant frequency

2. Checking output impedance of transmitters.

3. Testing impedance transformation in matching networks.

4. Measuring characteristic impedance of coax.

5. Measuring resistance, capacitance and inductance at the required frequency.

6. Checking resonance of tuned circuits.

This instrument was used many times in developing the matching and tuned circuits of the ALIVO2 QRP 80m transceiver.

It can also useful to make regular measurements on your HF aerial to check for deterioration.

Easy to use?

The instrument has two BNC connectors on the back. Connect the unknown impedance to one and a receiver to the other. Tune the receiver to the frequency of interest, adjust the “R” and “C” knobs till the noise heard in the receiver drops to nothing, then read the impedance values off the front panel calibration.

Alternately, set the controls to the impedance you require, and hunt the receiver frequency until a null is found.

Is it the same as the old Galbraith noise bridge?

Only in princible. The Galbraith Noise Bridge, in its original form, became available in the late 1980’s and provided the user with a simple instrument to measure RF resistance. The new Noise Bridge, introduced last year in the NZART magazine BREAKIN, has the added facility of measuring reactive impedance, and a modulated noise source.

Is it available?

Branch 05 can supply to you the bare PCB $7 with instructions, and case $12, all inclusive of postage in NZ. The parts can be obtained from Dick Smith, or South Island component centre in Christchurch.

Send a cheque, payable to K.P.Barnsdale to

Projects group, 50 Cardrona Street, Christchurch, NZ

K.P.Barnsdale ZL3KB