The photo shows the transceiver with the ‘bonnet’ open.
Usually the display would be forward-facing, fitted to the front of the Raduino
board. Because I wanted the display facing upwards I had to connect the display
via a ribbon cable. I used a 20cm ribbon cable supplied with so-called Dupont
connectors, male on one end, female on the other. Note that the connections
between the Raduino and the main PCB should not be extended as the Raduino
board contains the frequency synthesizer and hence has high frequency signals
on it.
The audio amplifier on the V4 UBITX PCB does not have
sufficient output to drive a low impedance speaker. I tried it with the 4 Ohm
speaker from the donor record player and the output was feeble. I have not
tried it with a high impedance speaker. I therefore made use of the amplifier
that came out of the record player. The UBITX headphone/speaker output is fed
to the 3.5mm headphone jack and the switched contact on the jack connects to
the input of the record player amplifier. Therefore the input to the record
player amplifier is disconnected when the headphones are plugged in. If you
wire the headphone jack in accordance with the instructions on the HF Signals
website it must only be used with stereo jack plugs! A mono plug will short
circuit the output and may damage the amplifier. The amplifier board can be
seen in the photo below. I fixed it down using double-sided sticky pads.
The original record player (hence the amplifier) was
designed for a 9V supply. However, looking at the circuit, I see no issue with
powering it from 12V instead. The amplifier uses a TDA2822 chip. Funnily enough,
the original UBITX board used this chip, but it was replaced with a discrete
transistor circuit in version 4. I only used one channel of the stereo
amplifier as I was only using one of the speakers. I removed the other speaker
to create a ventilation grille at the front of the case.
Wiring of the microphone and Morse keys will be covered in a
future post.
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