Solid State Shortwave Receivers For Beginners - The Listeners Guide

Normally the telescopic aerial should be fully extended, and a
fairly long type should be used (say about 1.2 Metres long). When
conditions are good and many strong signals are being received, it may
be beneficial to contract the aerial slightly, so as to give improved
selectivity. Naturally, this will result in some reduction of received
signal strengths.
Loudspeaker Version (Fig.25)
It is perhaps an advantage for a portable receiver to be completely
self contained, so that there are no trailing wires from headphones. Thus,
although most people prefer headphones for normal S.W. listening, an
internal loudspeaker is probably more convenient in the case of a portable
S.W. set.
The circuit diagram of the loudspeaker version of the ‘Portable
Reflex. Receiver’ is shown in Fig.25. This is the same the original circuit
except for the addition of a high gain common emitter output stage.
This uses Tr2 and has R4 as its collector load. R3 is the base bias
resistor.
This set will provide good volume from any reasonably efficient
speaker having an impedance of 25 ohms or more. It can also be used
with any type of headphone if a suitable socket is provided.
It is operated in the same way as the basic version of the receiver:
F.E.T. Portable Set (Fig.26)
The circuit of Fig.26 is for a sensitive portable receiver that
incorporates only two active devices, a f.e.t. and an integrated circuit.
The f.e.t. is used as a regenerative detector and the I.C. is an LM380N
audio power amplifier.
As in the previous design, the aerial is directly connected to the
tuned circuit in order to give optimum signal transfer. The aerial coupling
winding on T1 is simply ignored. No connections should be made
to pins 8 and 9 of the coil, even if these appear to be convenient anchor
points for components. The tuned circuit couples straight into the gate
of Tr1, and R4 is the source bias resistor. The latter has C3 as its R.F.
bypass capacitor, and C4 as its A.F. bypass capacitor. R2 is the drain
load for Tr1.
Regeneration is applied to the circuit in the usual way. R3 is
connected in series with the audio output from the detector in order to
ensure that a low level of R.F. loading is placed on Tr1 drain by the
audio stages, and in particular the R.F. filter capacitor, C6. If this were
not done there would be a very adverse effect on the regeneration
circuit.
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