A Four Band Transmitter - Eddystone Short Wave Manual

EDDYSTONE SHORT WAVE MANUAL
21
A FOUR BAND TRANSMITTER
FOR THE AMATEUR FREQUENCIES .
Here we have a low to medium power
Transmitting Set built to achieve at reasonable
cost, efficient telegraphy and telephony work-
ing on the most used amateur bands.
The
installation is designed around the new screened
grid H.F. Pentode Transmitting Valve, which
has improved features in that it is low priced,
economical to use, easily excited as a driven
amplifier and does not have to be neutralised.
It needs only one watt R.F. excitation.
Using suppressor grid.. modulation it can be
100% modulated with only 1 to 2 watts audio
input. This feature alone has a special appeal
by the saving in cost of the usual high power
modulator valve and its
associated supply
unit. To avoid the cost of individual meters
in each valve stage a single current measuring
meter is fitted with plug.connection, and can
be connected to a jack in each circuit.
The crystal controlled circuit is arranged
to allow quick change -over from C.W. to
Telephony on the
14, 7,
3.5 and 1.7 m/c
Front view of completed Transmitter showing panel
lay out and rack construction.
amateur frequencies.
The change from one
band to another being speedy and simple.
To provide sufficient output to fully load the
modulator an external single stage speech
amplifier is recommended ; a circuit diagram
for this is provided.
The general circuit embodies three valves ;
pentode Crystal Oscillator, frequency Dolibler
(Pentode with control and screen grids tied
together to function as triode) and the final
amplifier.
The three -tray welded steel rack
provides a solid foundation and the completed
transmitter forms a neat and presentable
instrument.
The power supply unit is built
separately and a suitable circuit is shown.
This can, of course, be varied to suit the power
it is desired to use. Blue prints are available
showing the top and underneath view of each
tray, clearly illustrating assembly. The point
to point wiring there shown makes the wiring
quite straightforward. In addition there is the
theoretical circuit diagram given herein. With
the valves specified an input of 10-50 watts
can be obtained according to licence and
power unit available.
TUNING AND OPERATING
PROCEDURE.
Select crystal and coils for wave desired
by reference to the table shown.
WAVE.. CRYSTAL. CRYSTAL
COIL.
DOUBLER
COIL.
FINAL
COIL .
4.NA/ I.
".'
160 160 160
NONE
160
OUT
80
160
160
80
.80 IN
40
40
40
NONE
40
OUT
20
40
40
20
20
IN
Example (1).
Wave desired, 160 metres.
160 metre crystal and 160 metre
coil in plate circuit of V.1.
160 metre coil in plate of V.3.
No doubler coil, as stage is switched
out.
Example (2).
Wave desired, 20 metres.
40 metre crystal and 40 metre coil
in plate circuit of V.I.
20 metre coil in plate of V.2
(stage
switched in) SW1 at rear.
20 metre coil in plate of V.3.