23cm PA using Ericson PTF10137 surface mount device
A
23cm amplifier was required that would produce a few watts from a 12v
supply. Fortunately, a number of Erikson surface mount PTF10137 devices
were made available at about this time, so it was thought worthwhile to
give them a try.
The data
sheet shows this to be a 1 GHz 12W part, operating from a supply of
28v, with a gain of 18 dB.
A pcb was drawn up from the data
sheet test board drawing, but shortening the lines by a factor of
960/1296, and initially fitting capacitors likewise scaled down -
crude, but quite effective in this case. Added to the board was a
simple 5v regulator to supply a bias pot to set the Idd for the device
(these are LDMOS devices, so require a positive bias to turn them on).
0.8mm Teconic RF-35 material was used
Since I cannot produce plated-thru holes, an alternative
method of applying the device the required. It's not obvious from the
photo, but actually, a hole was cut in the board so that the device
could be dropped through. The base of the device is 0.8mm below the
height at which the pre-formed gate and drain leads leave the package,
so it is convenient to solder a thin (1mm) copper plate to the bottom
side of the pcb, and solder the device slug (the source connection) to
this. It requires the pre-formed leads to be straightened, but they
seem quite malleable, and no problem arose doing this.
Ground interconnects are made using 0.8mm conical track pins
available through Farnell (114-3879).
Circuit diagram
Initial results
The input match was quite close to being correct with the initial value of line shunt capacitor fitted, and gain was already greater than 10 dB with a 12.5v supply. Initially, Idd was set to 150 mA. A trimmer C was then used to replace the output line shunt C, and with this a gain of 16 dB was obtained with a 1dB output compression power of 4W. A fixed value 2p2 chip C was then used in place of the trimmer, and gave similar results. Gain flatness and input return loss are shown below:
Increasing the supply rail to 15v resulted in a 6W 1 dB
compression power level.
The noise figure at 1296 MHz is 4.4 dB.