Following on from my experiment with my 23cm transverter whereby I augmented coax relay isolation by adding a PIN diode in front of the pre-amp . . . . I did the same for my 13cm transverter. And yes, that is a new MK2 DB6NT transverter pictured left! I recently treated myself and invested in the kit version of the latest 13cm box. The rather convoluted semi-rigid cable runs are historic and not having enough spare, I opted to leave them as they are. This time the PIN diode is shunt configured and is an HP-33123A. I made up a DB6NT-style sequencer with an additional output to drive the diode and stuck it on the mounting plate for the diode. When the PTT is pressed, the transverter goes onto transmit. The 12V (nom) TX output from the transverter asserts the sequencer which actuates the CX-520 coax relay and at the same time biases the PIN diode hard on. Finally the sequencer enables the Spectrian PA by applying 12V (nom).
Below are two views of the PIN diode assembly.
In my haste to mount the diode, the complete assembly ended up higher than the box itself, so I had to punch a hole through into the PA compartment for the top SMA connector to poke through . . . A wee bit embarrassing, but acceptable. The performance of the MK2 DB6NT 13cm transverter is superb and probably doesn’t need an external pre-amp for troposcatter work. . . .
. . . . whilst the TX output easily drives the Spectrian board up to a final Drain current of 15A. The fan control PEC is set for the fans (2) to come on at 37 degrees C and go off again around 33 degrees C . . . . much more acceptable! The meter and front panel controls allow me to monitor the Driver and Final bias currents and an additional red LED comes on to let me know that the temperature has exceeded 35 degrees . . . As if it was possible to ignore the fans!
13cm/60W left - 23cm/30W right
Finally, big amplifiers need big power supplies. Gone are the days when solid state equipment all ran off 12V. Here on the left is a view under one of the desks in the shack. These brutes started life in the 1970s as 24V MoD battery chargers. Only the cases remain though. The one on the left is the 26V/20A PSU for the 13cm PA. The one on the right is the 48V/20A PSU for my home-brew 300W HF PA. Both PSUs employ soft-start to protect the house mains wiring, hi! hi!