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Increase RF Output from the ZC1 Mk-2  

Using A Simple "Clip On" Aerial Tuning Modification


This aerial tuning mod devised by club member George McLean for the ZC1 Mk2 is an easy one to do.....

ZC1's 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 tuning.

One end 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).

Next a 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.)

Tune the aerial by going from maximum capacity to minimum.

(Going the other way around could tune the link to the second harmonic instead of the fundamental frequency!) 

The plate meter should then be tuned for MAXIMUM not minimum reading.


  1. The aerial tuning mod increases the plate current from a normal un-modified 22ma to 35-40ma when the modified aerial tuning is "peaked".

  2. The increased power out high lights the low modulation % of the ZC1.  This is best overcome by installing the official AREC modifications to increase modulation published in Breakin Magazine in 1959.


This simple modification increases RF output from around 1W to 5W.

This 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.


top                                                                                         September 2010