A transmit mixer-amplifier for a 1268MHz uplink
G0ORY-005a (or the stretched PCB)

This unit follows the universal design of the 13cm transmit mixer amplifier. Again the same budget techniques are employed to keep to the aims defined by the original 13cm article, and that text should be read in conjunction with the following notes...

The filter is made by the same methods (details to follow soon) and is capable of good performance at 1268 or 1296 MHz. The mixer is another mini-circuits model - a JMS-2LH. This was again removed and reused from surplus equipment. The two stage MMIC amplifier this time uses some MSA-1105's (MAV-11SM's). These are biased to 60mA current each, and this time the supply voltage is courtesy of a 7808 regulator. Everything else stays the same as the 13cm unit.

Here is the swept trace from the bandpass filter (in fact the trace shows the response through the entire assembly). The detector is a negative type, so the 'peak' is in the downwards direction. In the centre of the peak is 1268MHz. Half way up on either side of the peak is at around plus or minus 10MHz. I guess this is the 3dB point for the filter, but that will be confirmed by using a power meter and manually stepping the sweep instead.

The PCB layout is the same as the 13cm mixer-amp, but has been stretched to accommodate the new filter. The enclosure has only gained in length slightly - hence the 'stretched pcb'

As this layout is 'universal'. It should be possible to scale the filter for 902MHz (US) and modify the artwork.

A.M 04/03

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