Winter 2004 Issue

MICROWAVES

The 1152-MHz Synthesizer

 By Chuck Houghton,* WB6IGP

The Qualcomm synthesizer PLL chip (top left) and 10 MHz TCXO (bottom right).

This will be the first of many articles bringing to amateur radio operators items of microwave interest both in new developments and surplus material available for conversion to our sub-microwave and higher frequency bands. For over 40 years I have been involved in conversions, beginning with military-surplus ARC-5s and slowly shifting up in frequency to other items of interest, starting with a surplus APX-6, which was to be converted into a 1296-MHz transceiver.

I took the APX-6 out of town with me to work on while I was attending a company school on microwave and baseband IF processing for my employer, Pacific Telephone. Working on that APX-6 so many years ago brings back the memory of attempting the conversion in a motel room, where I had few tools and spare parts. The project seemed doomed from the start. I got the oscillator cavity functioning, however. Until I blew the power fuse, things were starting to work.

Many lessons learned from this experience can be traced back to that conversion, which occurred in a faraway town with few resources and no automobile available to go scrounge for parts. Using that memory of what I went through, understanding what individuals in small towns must pay in effort and scrounging ability to locate key component parts to bring a project to completion, I suppose I am still working on that APX-6 today.

In this arena, I would like to open with a very noble tool in a microwaver’s arsenal of test equipment—an oscillator, or much more, an accurate synthesizer that can be converted from commercial surplus. What I want to cover is a surplus converted synthesizer for 1152 MHz for use as an amateur-band-frequency harmonic marker generator.

This marker is very important in the frequency ranges of 1296 MHz to our upper microwave bands of operation, as 1152 MHz is related to each and every band of operation. The relationship for 1296 MHz is related by 1152 + 144 MHz equals 1296 MHz. Thus, with the 1152-MHz platform source oscillator and a mixer with a 2-meter source, you just got a key element to construct a 1296-MHz transceiver. Add a filter and an RF preamp, and you have a receiving converter.

What else can be accomplished using an oscillator with this noble number, 1152 MHz? If operation on the 2304 MHz band is contemplated, 2 ¥ 1152 MHz = 2304 MHz for an accurate frequency marker.
 

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