HERE CAN YOU FIND A SCHEMATIC AND DESCRIPTION OF A NOISE BRIDGE
COMPONENTS LIST:
R1
1 K
C1
6N8
R2
22 M
C2
6N8
R3
1 K
C3
6N8
R4
22 M
C4
6N8
R5
1 K
C5
100 PF
R6
22 M
C6
10 M / 15 Volt
R7
820 Ohm
C7
1 M
R8
100 Ohm
C8
10 NF
P1
TP161
Transistors
3 x KF173 or Similar in Metal Housing.
D1
KZ721, 36NQ52
ZX
Entry - PL or BNC Connector.
RX
Output Connector Detector.
THE NOISE BRIDGE DESCRIPTION:
If you have the opportunity to choose, choose some type that has a wiper contact carbon.
These potentiometers that have a wiper contact used only shaped plate rather not use even at the cost that it will be as a substitute or similar type TP280.
We also suggest the use of all plastic potentiometers. rotary capacitor TESLA WN70414 2 x 200 PF, 2 x 25PF use only one section 200 pf, or you can use a rotary capacitor from old radios.
Suitable are miniature air rotary capacitors of course with a suitable capacity.
For those who are interested to set your antenna, I can recommend the construction noise bridge as a basic measuring equipment intended for adjusting antennas.
What actually can use such a noise bridge ?
A noise bridge is nothing new, it was in ancient times often published, but in recent years, due to low prices of microprocessor components, experiencing a renaissance period.
Noise bridge is the principle used in many high cost devices for setting and adjusting the antenna technology.
It finds its application and the CB antenna technology.
We can use it easily measured: input impedance of the antenna, antenna series system the phasing lines for antenna systems two or more antennas find electrical length of the power lines cable at the operating frequency. Shortening factor used cable and comparing the calculated length and the length of the measured electrical noise bridge resonant frequency of the current configuration of the antenna measure the real and reactive components of impedance with capacitive and inductive character. Measurements are characterized by accuracy and speed. Custom Wiring simple noise bridge is based on the scheme, which is not difficult.
Used parts should be chosen as small as possible preferably in SMD.
Generated noise on any semiconductor Zener diode is amplified to a desired level three stage RF amplifier.
From its output is powered by its own bridge.
The most important part of the bridge transformer, which must be made very carefully in relation to the symmetry.
Most failures in the construction of the bridge is due to the 95% currently unbalance transformer.
This is also one of the main reasons why this bridge is not just the most popular designs.
Here I would like to remind our own experience with the construction. HF, VHF, UHF.
I made three cuts noise bridges, according to this scheme and it is always for different frequency bands HF, VHF, UHF the last two slightly modified.
All three bridges operate smoothly and colleagues, who built it, reviving i had no problems setting.
THIS WORK IS NECESSARY TO PAY A MORE DETAILES DESCRIPTION:
Transformer HF band must be made very carefully.
For windings are three conductors, which are slightly twisted with them and windings 10 turns on a ferrite toroid with a diameter of 10 mm.
The material is suitable for use N05, N1 or N2. Color is marked in yellow.
Vine threads so that the perimeter of the toroid accounted for about 3/4.
We recommend to fix the winding thread, do not recommend using the so-called.
The achievements of modern chemistry.
Their RF characteristics usually are not excellent and our failures may not be error at first glance, looking at unsuitable properties of the adhesive or sealant!
One wire forms a primary winding and two symmetrical secondary windings.
In the scheme are marked with a dot winding beginnings.
Ensure proper connection winding start and end, if not, as shown in the diagram a noise bridge work certainly nedonutíte.
The winding outlet is appropriate to reduce to the minimum length with respect to solder to the PCB and all the same length.
Selecting a Zener diode power head do not break, best serve those most busy.
Although it is unsuitable properties of semiconductors for other applications, but because of it we This useful device for adjusting the antenna farm successfully implemented. Personally,
I have not tried this type Zener diodes, but with specific requirements on my bridge.
I used a diode noise labeled Tesla 36NQ52, which produced for use in the CB band without worrying about function may also use the junction even with one faulty transition the remaining good, well then serve as a noise generator. Who would want to expand the use of the bridge up in UHF, I can recommend the use of on site zener diode semiconductor junction transistor BFR90A, the amplifier will then need to change the original transistors KF 173 for BFR96 or similar. It is suitable for the low level of noise generated in the amplifier to add one more step depending, inter alia, from the total gain.
It is understandable that it will be necessary to replace the toroid transformer is more suitable for the type.
After this adjustment, bridge works with a satisfactory level in the frequencies 900 MHz to 1300 MHz.
It is possible when you request to work with frequencies up to 800 MHz used monolithic RF amplifiers.
The need to adjust the noise bridge may arise if you need to measure the PMR band.
