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BITX20A
Mechanical Construction


What follows is not a detailed 'how to' but an illustration of how I put the BITX20A into a box and (hopefully) made it look pretty. I have included UK sourcing details and cost of any bought items. (Click on any image for a larger version.) By the way, this really is "kitchen table" construction, I have no workshop, but do have a small pillar drill with vice which is what makes the drilling practical. The pillar for the drill is very cheap and comes with vice from Machine Mart. A vice with soft jaws and some good files are essential for the rectangular cutouts and a 16mm Q-max cutter makes short shrift of the SK259.



LCD Counter Assembly The Frequency Display:
I have use the Minicounter from Cumbria Designs which at 40 is as expensive as the Hendricks kit! The counter has a number of pre-programmed IF offsets or any required offset can be set on board or by remote switching.





LCD Display The kit is of very high quality and with the excellent instructions make an enjoyable project in itself. It would make a very useful stand-alone frequency counter.







Tuning cap drive Tuning Capacitor Drive:
This assembly is a Jackson 4511 6:1 ball reduction drive which will mount on the radio 'motherboard', the tuning cap will be glued to a block that is also attached to the motherboard. The latter is a piece of single-sided 160 x 220 mm copper clad board that slots into the enclosure and holds the transceiver PCB, auxillary boards relay, etc. The 6:1 drive can be purchased here for around 4.00. I would swear that the design of this drive and the materials it is made from have not changed in at least sixty years! The drive is set back as far as possible on the motherboard so that the pot that drives the fine tuning voltage can sit between the reduction drive shaft and the motherboard.

Marked out panels for drilling The Panels:
The panels are part of a Lincoln Binns extruded aluminium enclosure type E-Case which cost me about 25. The panel size is 169 x 53 mm which makes fitting everything onto the front panel (top one) quite a challenge!

I covered each panel with good quality masking tape and marked out using a sharp pencil, the most complex and tightest section is the cutout and mounting holes for the LCD readout. Checking and re-checking each mark makes this a somewhat tedious job. Another bit of fun will be producing the 2mm vertical slot to the right of the LCD cutout, this is for the LED SWR/Signal Strength bar graph.

Rear panel assembly Rear Panel Assembly:
The rear panel layout from left to right (viewed from front of radio) is aerial socket (PL259), ground terminal, power leads, on/off switch, audio out.





Front panel assembly The front panel layout is, from left to fight: LCD frequency readout, vertical bar graph, below the bar graph is the Tune push button. Then top row is audio gain and main tuning, below these are the TR/RX switch and fine tuning.


Front panel assembly from the rear The rear of the front panel showing the frequency counter assembly, the stripboard standing off the panel is the LED bargraph and driver for indicating relative SWR and signal strength. On the left can be seen the tuning capactitor with the 6:1 reduction drive between it and the panel, in reality the slow motion drive will sit some 25mm back from the rear of the panel giving clearance to the fine tuning pot below it.


Layout of the radio Mockup of the layout for my BITX20A. The white piece of paper represents a small board that will carry the SWR bridge and two relays, the two relays are in parallel in order to cheaply give 4 sets of changeover contacts. There will be a 50mm fan extracting air immediately over the PA heatsinks which will only switch on when power is applied to the PA. There will be two jack sockets on the rear panel for microphone and 'phones or 'speaker.


(click on any image to enlarge it.)


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