My only concern with the transceiver was the lack of any protection on the power input. DC at 12v is fed via a DC barrel connector to the unit, via only a series diode. This means, apart from the Vcc being 0.6v lower than the incoming supply due to the drop across the diode, that the only protection is against reverse polarity. I doubt however, that the diode would really hold up in that situation for very long!
The unit is relatively simple, and so I was more worried about a fault in the transceiver knackering an expensive power supply! Or, and probably of greater real concern, of causing a huge current draw and melting the power cable, a definite fire risk. As someone who has but one level of OCD, which is an obsession with fire extinguishers, this is what needed sorting.
The solution was, obviously, to fit a fuse holder! This needed a surprising amount of thought, as not only must it be in keeping with the layout of the rest of the rear panel, but I also had to consider the depth of the devices penetration into the housing. Too deep, or in the wrong place, and I run the risk of damage to the transceiver components. The photo shows the new fuse holder fitted in place. This holder had a little locating stud, so as well as drilling a 12mm hole, I had to file a little extra cutout for the locating stud. A small piece of heat shrink tubing covers the end terminal as further assurance against any contact with the board components.
As the PSK-20 has no power switch, I decided to add one at the same time. The connection to the fuse holder for the incoming power comes from the reverse polarity protection diode. The cathode leg of this was cut and the wire removed, the holder and switch then being wired in series.
The two other issues with the transceiver design were the lack of any indications of when the unit is powered, and when it is transmitting. To solve this, a pair of 5mm LEDs have been fitted onto the front panel
Keeping things simple, ive gone for red and green. The green LED will be the power indicator, and will be lit whenever the rig is switched on. The red LED will indicate Tx, and is a bit more complex! The drive for this will come from the addition of an RF power sniffer circuit, which will sense the RF power at the output of the LPF, just prior to the antenna connector. Its a simple diode detector circuit. The addition of this will also act as a rudimentary VSWR indicator, although im likely still to make use of a proper VSWR bridge in line with the antenna.