aerial tuning mod devised by club member George McLean for the ZC1 Mk2
is an easy one to do.....
were designed to work with short non resonant aerials such as whip's or
random wire antennas under battlefield conditions. Bypassing
the ZC1 aerial tuning and
using an external tuning capacitor across the link coupling permits
effective coupling to more efficient aerial types.
As described below the
modification permits a good match to a 50 Ohm load and a worthwhile
fivefold increase of RF out.
The "clip-on" modified antenna
of a short clip lead is connected to the wire coming up from the tuning
link beneath the antenna tuner with the other end being connected to the
wire going over to the 'transmit" side of the changeover relay on the
end of the aerial tuning coil (Red Link
on diag. below).
thin insulated wire is taken from this connection and "fed" out through
the left hand receiver "flick" tuning indicator hole in front of the
metal flag. An old broadcast type three or four gang, paralleled-up
tuning capacitor is connected to this wire, the frame of the tuning
capacitor is earthed to the set. (Blue Links
on diag. below.)
aerial by going from maximum capacity to minimum.
the other way around could tune the link to the second harmonic instead
of the fundamental frequency!)
plate meter should then be tuned for MAXIMUM not minimum reading.
aerial tuning mod increases the plate current from a normal un-modified
22ma to 35-40ma when the modified aerial tuning is "peaked".
The increased power out
high lights the low modulation % of the ZC1. This is best overcome
by installing the official
modifications to increase modulation published in Breakin Magazine
modification increases RF output from around 1W to 5W.
method could also be used with the Mk1 but the different location and
configuration of the sets aerial tuning unit makes it slightly more
difficult to make the necessary connections.