small experimental CW 500mW transceiver using just 5 transistors
The Tenner uses the OXO circuit
for the transmitter and an SBL1 (or similar) double balanced mixer based direct conversion receiver. TX-RX offset is around 600-800Hz when the key is pressed,
so no special RIT circuit is included. The receiver is a decent
one with a respectable performance for something this simple. If
the SBL1 or similar is not available it could be substituted for
a single balanced mixer using a toroid and 2 matched diodes.
I have now roughed out the schematic although I
cannot guarantee all values are precise and will check these over
when I have a little more time.
On the circuit shown there is a switch to select two VXO ranges,
but only one is fitted.
Click on the schematic to enlarge it.
Note that the crystal uses a 28.06MHz
fundamental crystal - NOT 3rd overtone. These are a little harder
to find but this gives more pulling range. Even greater pulling
range can be achieved with a small inductor in series with the crystal
but watch out as chirp may become excessive and the difference between
TX and RX frequency less well defined. This is a basis
for experiments - don't take the values as optimised. Have a go
yourself and adjust the circuit to improve it further.
Specification
TX
Power 500mW
RX
sensitivity -110dBm
VXO range
25kHz
(2 x 25kHz with second crystal)
TX/RX switching Full break-in
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