 |
 |
VK5ZVS |
|
| Projects 'n' Stuff |
|
|
| Home | Back |
|
| |
| RF noise bridge for HF. |
| This rf noise bridge will provide about 40dB of noise over the 160m to 6m amateur bands.
The unit uses 3 x BC547 transistors for amplification of noise produced by a 6.8 volt zener diode. Drawing a current of around 17mA,
makes the unit suitable for portable battery operation. The device has provision for providing a null on the receiver output,
using both adjustable resistive and reactive components.
|
|
|
| |
|
|
| |
|
| Here is an inside view. A bit of veroboard,
a handwound transformer and some commonly available electronic components.
The zener was biased for maximum noise. The capacitor is a miniature broadcast
variety. The potentiometer is a 500 ohm carbon linear. The transformer was wound
with 7 turns (quad) 0.125mm ECC wire. Two windings wired in series are used as
the primary supply to the bridge circuit. I used parallel wiring for the bridge
components, to reduce the effect of hand capacitance (as opposed to series wiring)
to the antenna and receiver sockets.
|
|
|
| |
|
|
| |
|
| Here's the schematic. I've also included an alternative detail
for C7 so one can determine if the antenna's reactance is more capacitive or inductive. The is also provision
for an audio modulation input (J5) for, say, a tone input.
|
|
|
| |
|
|
| |
|
|
|
