USING A NOISE BRIDGE

 

The RX Noise Bridge is one of the finer instruments to tune any antenna.

 

It simply attaches to the connector of the antenna and your feedline attaches to the Noise bridge. Thereby the instrument is at the antenna where you are working. It also considers the length and type of coax you are using.

 

If the antenna is mounted on a tall pole, simply tilt the pole over and support the antenna end at a convenient height. If it is a telescoping pole, again tilt it over and extend it to the height it will be standing up. Secure the coax to the pole temporarily. Check the tuning with the Noise Bridge. Then re-tract the pole, stand it up and then extend it to where you intended on having it.

 

Ah! You say the Noise bridge requires hearing the receiver and it is down in my basement.

 

This is not a big problem. Using a cordless phone you can attach the base with an adapter to the phone jack on your radio. You can go to the lower 40, climb a tower or sweat it out in the attic and hear the receiver.

 

Now it is just a matter of following the simple instructions that come with the Noise Bridge.

 

The bridge makes a noise that you will hear in your receiver. It has two controls, X and R.

 

1.Adjust the two controls until the noise is completely nulled out.

 

2. Take note of the X control. If it is on the X_L side, the antenna resonant point is lower than the frequency the receiver is set at. If it is on the X_C side the resonant point is higher than the frequency set on your receiver.

 

3. Adjust either the antenna or the receiver so the X=0.

 

4. With the noise nulled out, take note of the R control. It will tell you how close your radiation resistance is to 50 ohms. NOTE: This value can only be determined directly at resonance, X=0.

 

5. A 50 ohm match at resonance will give you a 1:1 SWR. If R reads 25 ohms at resonance, then your minimum SWR will be 2:1. Now you can adjust what is needed to match the antenna.

 

Currently MFJ sells a good Noise Bridge at a reasonable cost.