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Number7on YOtlr Feedback u rd
The G3IGU Transceiver
QRP on 80 meters.
by Keith Coates G31GU
T
he circuit for the G31GU direct conversion
receiver, based upon the ci rcuit by
J. Young in the February 1975 issue ofRadio
Commun ication, is straig htforwa rd. The RF
amplifier is tuned, though, and I found that an
RF gain control is essential for evening use.
The AF amplifier is a simple circu it.
Constr uction
The layout is not critical. The VFO, AF,
and PA are very well screened, with the componerus
mounted on a length o f tag strip. The
receiver and sidetone generator are buill onto
paxolin panels (see Figures I and 3), and
wired up at the rear. The whole tra nsce iver,
including the ATU. is buil t into one box so
only ae rial and earth connections arc required
. You may also place batteries inside
the case.
You may consider the PA stage odd , with
the 6800: and 100 resistors, but I tried several
other types of coupling which resulted in
accidents to the BFY51. This circuit has
neve r damaged a PA transistor. The actual
RF power output will depend upon the tra n­
sistor you use . Some BFY5 1s have given DC
power inputs of from 850 mW to 1.3 Watts.
The AF filter (L5, L6, and L7) is based on
the ci rcuit of J. Young (RaJ Com , October
1973) using 38 SWG on Mullard ferrite
rings. type FX 1593. In the prototype . I used
scrap ferrite rings, and l could wind only
abou t 200 turns onto them, but they worked
all right.
Wind the PA and ATV coils on ferrite rod
+i. in diameter and 2 1h · long. Wind 15 tums
of 20 SWG , tapping the ATV coil every two
rums for aerial impedance matching.
Different values of RlO will alter the drive
VA'
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TO
52B
A4
II
TO -.---:--0
T1 -
1 TRI
c,O
-
T
A'
C5
A2
1 \:?
I
C6
I
+
02'
All
A'O C20
A3I
+
CI7
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R 5 ~
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26 73 Amateur Radio • June, 1989
Figure J. Pans placementformereceiver board.