Recently I obtained a couple of remote head Codan 7727TB transceivers from the EMDRC at a pretty good price. The transceivers had no remote heads or outside covers unfortunately, but for the price they were good value. The plan was to add a digital VFO, make a new local control panel including LCD display and band switch for amateur bands including 80 / 40 /30 / 20 metres. So far this is the result, although I’d like to mount some grab handles at the edges and finish the control labels.
The attraction of these sort of transceivers is low idle current consumption which is only a few hundred milliamps compared to typical 100W amateur rigs that can draw nearly 2 amps on receive, making the former ideal for fixed portable operation.
This is what the front panel originally looked like –
The first job was to disconnect all the wires from the rear of the remote connector. White heatshrink tube was put over each wire and the pin number then written on it. It was a slow job but necessary so as not too lose track of the connections.
The front panel was then rotated 180 degrees and sanded back. The speaker hole, display cut-out and controls were drilled out. The larger cut-outs were made by drilling many holes within the slot boundary and then filing them square.
The speaker grille was 3D printed. The LCD is a common 1602 type. A 3D printed bezel was made for the display but it didn’t look too good, so for the moment, the display is tightly fitted to the cut-out.
The digital VFO is built on a board from VK3ZYZ and uses an Arduino Nano and Si5351a clock generator for the frequency generation. Shepparton Amateur Radio Club (SADARC) were selling these a while back. I just used a simple one intended for a land mobile transceiver crystal replacement. A good thing about the remote 7727 is that the band switching and PA low pass filter selection are done electronically via relays. This makes it easier to interface to the VFO board than the local control version that has a multipole selector switch.
At the moment it’s just running on 40m and 30m, the next step is to add some channel inductors for 80m and 20m. To sense the selected band, a stepped analogue voltage is obtained from the main board and applied to the Arduino analogue input. There is a convenient unused header on the PA filter board that takes a pin low depending on the selected band. A socket was connected to this header with an array of diodes and resistors on a piece of proto board soldered to it.
Sideband selection is automatically done based on tuned frequency.
The power connector was replaced with a common XT60 socket as I have them on a lot of 12V devices already. A 3D printed bulkhead mount was made for the socket as can be seen in the above photo at the top.
The microphone socket was replaced with a 5 pin DIN socket as I had a couple around. The microphone is an old Philips PRM80 mic. with the internal preamplifer bypassed as there is enough gain in the transceiver.
The top and bottom covers were folded from 1.2mm aluminium sheet. Unfortunately, my guillotine’s cut length was not quite long enough, so there is a slight gap between the sides of the top and bottom covers. The sheet was obtained from an aluminium supplies shop in Dandenong from the offcut bin near the front door for about $10. The front panel and sides were primed with etch primer and then painted.
3mm Rivnuts were fitted to the sides of the chassis to secure the new top and bottom covers.
It’s making about 100W on 40m / 30m and sensitivity isn’t too bad. Initially, the mute would not work and this turned out to be a trimpot with a slider that wasn’t contacting the track. It looked like someone else had tried to troubleshoot this as a few caps had been replaced and there was some recent solder work in the area. Just to make things more difficult, there is an error in the service manual on the mute voltage polarity on the comparator that enables / disables the mute.
Still more to do……