RAT5 Manual version 1.2.0
RAT5 Information Manual version 1.2.0 © GW4GTE 2010
Page 21 of 29
A carrier-triggered mute circuit could be devised such that a strong RF field from any
transmitter would externally generate a suitable mute signal to apply to PL3/6.
5.5 Squelch out
When used as an output the Squelch / Mute
line at PL3/6 provides a switched level
indicating squelch operation; zero volts for
squelch open, supply volts minus one volt for
squelch closed.
This could be used for instance to drive a
squelch LED via a suitable driver. See Figure
5.3 opposite.
Fig 5.3 LED driver circuit
5.6 Power Sources
The power requirement is non-critical as long as the maximum supply voltage of the ICs is not
exceeded (18V max). The usual shack supply of 13.8V DC is ideal.
The low current consumption of RAT5 also lends itself to battery operation. A supply of 9V to
15V is suitable. Maplin carry a stock of 10-slot AA battery holders which would be ideal for
NiCad or NiMH battery use. 10 x 1.25V = 12.5V. If the unit is to be battery powered and only
occasional use is planned (e.g. portable trips) then Maplin’s Hybrid battery range is worth a
look. They self-discharge much more slowly than other rechargeable types.
5.7 Choice of enclosure and boxing the unit
In the UK, Maplin carry a stock of various reasonably priced aluminium boxes as well as more
expensive but very nice looking ones.
Control knobs are not supplied in the kit – narrow controls are required due to the PCB size
limiting their dimensions. If the control placement is considered too close one suggestion is to
remove the squelch pot from the PCB and mount it on the front panel on the other side of the
volume knob. Mounting the PCB upside down in a box would then make a line-up of Squelch /
Volume / Tuning (left to right). The author uses a smaller central knob for the squelch control.
Installing RAT5 into an enclosure
The PCB is small and light enough to be supported by the potentiometers when they are
screwed onto a front panel. It is recommended however that the rear of the PCB is also
supported using the holes provided especially if not all three controls remain on the PCB.
Control knob spacing is 24mm.
There are four 3mm mounting holes drilled in the corners of the PCB, spaced 45mm x 71mm.
These can be drilled out further as required. The holes are all connected to the ground plane.
