Digital Display for Racal RA.17L

RA.17L with digital display on top of the enclosure 

One of the things the Racal is missing for today's operation is a digital display with precise output. One day I found an auction on eBay offering a digital display for RA.17 and RA.117 units. I bought this small device, a LCD-display with a logic board. It used a BNC-connector to fit to the Northamerican versions of the Racal receivers and needs 12 VDC power supply. 

Interesting enough I was not able to get a connector for the English version's plug. This plug looks like a downsized antenna plug, I assume it's WW2 equipment which is not longer in use since decades. After sitting a while on this problem I detected that a F-connector will fit on the outside screw of the plug, and an additional 2 mm plug was able to hold the middle-pin. Right, a F-connector, a polyamid washer and a 2 mm plug together with Uhu Endfest glue did result in something like a fitting connector. I soldered the complete construction to a BNC plug. This adaptor connects to test point PL11 in the Racal receiver.

A small steel enclosure and a 12VDC 100 mA power supply completed the construction:

The display is showing the kilocycles in 999.99 format. When switched on it shows 100.24 kc until the receiver is warmed up and tuned.



Due to the capacity of the coax cable - you should keep it as short as possible - the output of the Racal's analog display will be shifted (or better said: the tuning is shifting). I measured a deviation of about 2500 cycles. This is small enough to be corrected by moving the cursor of the analog display sidewards until both displays are indicating the same frequency.