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

pcb ptf10137

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


Board Track pattern


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:

gain plot

 rl plot

 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.