NARC DF100 Aerial Switcher

IC1

NE555N

Timer IC

R3

470R

R4

470R

R6

470R

R5

470R

C6

1nF

1N916

1N916

C1

10nF

C2

10nF

1

5

6

2

7

84

3

R1

1K

R2

100

K

Dipole 1

Dipole 2

C3

1nF

C4

1nF

C5

1nF

To

Receiver

DF

OFF

Monitor

Monitor

DF

OFF

9 Volt

‘PP3’ type

Battery

G3HUL Test Beacon

R4

470R

C3

68pF

R2

10K

R3

4K7

C4

10nF

R1

560R

C1

100pF

L1

(10t)

L2

(6t)

C2

100pF

TR1

BSX20

Xtal 1

12MHz

9 Volt

‘PP3’ type

Battery

This is the circuit diagram for a simple Test beacon suitable for testing the DF100. Please note

that Construction details and Technical support are not included!

For more information see Doug Mallett G3HUL.

4

Basic circuit description:

Power is provided by a PP3 9 volt battery switched via a 2 pole 3 position toggle switch wired

so that in either top or bottom positions power is connected. IC1 is a 555 Timer IC wired in

astable configuration as a square wave oscillator with frequency and mark space ratio

defined by R1/R2/C1/C2. The output from pin 3 is fed, via the switch in ‘DF position’ to a

network of 2 diode switches which are connected to the 2 Dipoles. The diode networks are

alternately switched (reverse biased) by the square wave output of the 555 so that the signals

from two matched dipoles are alternately passed to the output to receiver

The ‘Mon’ switch position simply connects a positive voltage from the battery to switch one of

the dipoles only on all of the time in order that one of the dipoles can act as a normal aerial in

order to monitor normal audio transmissions.