The poor man's Adret - Marconi surplus lock box
PROVISIONAL - NO PHOTOS YET
Some of the PLL (PLO) 'Bricks' require a 100MHz (88-108) reference signal to lock up. Ultimately a custom cut crystal is the aim to park them on the frequency of interest, but for tests, a variable frequency signal is required.
Some very lucky amateurs have been able to acquire the Adret locked reference units to help them tweak and walk these bricks up or down into the amateur band. Other's haven't been so lucky. Recently a surplus firm in the UK advertised a pair of boards, with 15 TO5 crystals in the 81-109MHz range spaced at 2MHz intervals, removed from Marconi equipment.
Each board contains a 93L01DC BCD - Ten line select chip. Bussing the select lines together and adding one 1K pullup resistor makes it easy to add a hexadecimal thumbwheel switch and switch the entire bank. The two boards also 'common up' on the RF output, as part of the original design, so a single BNC socket passes all the crystal oscillator ouputs. Both boards run from a single rail 5V supply. Each oscillator has an etched inductor (no tune, no microphony), and the oscillator transistor is a 2N918.
I found an old diecast box, and mounted the boards together, and added a small 5V supply consisting of an old 100mA 9-0-9 transformer, and a 7805, and a hexadecimal select switch from the junkbox.
Power output from each individual oscillator is healthy, and exceeds 0dBm (though no detailed measurements other than indication have been taken as yet). If the output is less than 10dBm (typical level for bricks), perhaps a small buffer (MMIC) is required here. If an 8-10.9MHz output is required, a /10 prescaler could be added, or a driver and diode multiplier to generate combs of harmonics at an area of interest (maybe combine all three options in one box?)
These look like just the thing to help with experiments on the PLL Bricks.
A.M G0ORY 19/08/02 PROVISIONAL
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