I decided it was time to redo my 10GHz portable unit to increase power without increasing the size, so that it could continue to be mounted at masthead. It was decided to use the Qualcomm Omnitrak PA (ref 1) with the DB6NT original transverter design (ref 2), G4DDK004 oscillator and the G3WDG preamp (ref 3). There was insufficient space in the box for the Omnitrak psu board that came with the amp, especially as it’s TX /RX switching was already provided in the DB6NT module. I therefore needed to devise a small PCB, which could provide 10V at 1A max and –5V at around 50mA.

For the positive rail the LT1086 1.5A low volt drop regulator would be used again (ref 4). However the usual 7660 chip was not capable. Looking through some regulators data sheets (ref 5) I came across the LT1054 chip which had many advantages over its predecessors: -

1.It is capable of providing 100mA (7660 max is around 20mA)
2.It is rated for an input voltage of 15V maximum so can be run directly off 12V supply (7660 maximum is 10V
3.Most importantly it has an internal regulator that regulates the negative output voltage. (don’t need to worry about the 120 ohm internal resistance of 7660)

Accordingly the circuit shown in Fig 1 was devised. Failure of the negative supply reduces the positive supply to around 1.2V. The component listing is shown in Table 1. The PCB layout is shown in Fig 2 and the overlay in Fig 3. Note that the components are mounted on the track side of the board and that pin 7 of IC3 is chopped off and not soldered to the track below it. SMT resistors and capacitors can be used on the board. The PCB was mounted on the back of the amplifier casting (the back of which had been milled flat) taking to care to insulate the metal tab of IC2 from ground

The output voltages of the 3 modules built so far were measured as 9.82 and –4.89. Purists may be tempted to adjust the resistor values slightly to achieve exactly 10.0 and –5.0V. I tried it, but doing so made no difference at all to the Qualcom’s 1.1W output power, probably due to its on board bias regulators.

It has been noted on occasions that the 10V rail's appearance is delayed, especially if keying the PTT in quick succession. This was traced to the inverter not starting due to it still having a negative voltage on its output due to the Qualcom PA not providing an effective discharge path. This lack of negative voltage of course inhibits the positive supply, as designed. The fix was to provide a 4k7 resistor from the  -ve supply rail to ground to provide a discharge path

References
 

1. http://www.ntplx.net/~wz1v/w1ril.html
2. Dubus Technik III pp324-333
3. Dubus Technik IV pp276-339 (also Proceedings Microwave update 1991 and 1995)
4.  "Using the California Microwave 11-026700 transmitter assembly"  Microwave update proceedings 1995
5. http://www.linear.com/prodinfo/dslist.html
 

Fig 1 Circuit of PSU