[MRCA] Providing 5 MHz

[Ray Fantini]

Use to be if you were accurate within one or two kHz everything was good, but lately been doing more and more stuff for others and now people want accuracy within Hz. Doing WJ receivers or just about any modern SSB radio this becomes more and more relevant. Have test equipment, signal generators and the like and would often just calibrate them by zero beating them with WWV and that's gets you fairly close but got tired of dealing with some people who when a question about accuracy comes up would be adamant how I must be wrong because their new Yahoowood Fangfang that they just purchased has to be correct because its new and everyone else in the Ham club has one and agrees that it's the best technology out there after you master the menus.
With that in mind I purchased a GPS disciplined 10 MHz oscillator a couple years back and feed that into a distribution amplifier to all the test equipment that has 10 MHz inputs. That gives an accuracy of around a couple Hertz to all that gear. The problem is that a lot of my older HP test equipment and almost everything that I have built by Harris wants a 5 MHz reference including my HP-8640 that's the go to generator for working with HF radios. Things like the modern synthesized Motorola Service monitor work there but the phase noise sucks when you are dealing with SSB radios.
Because of all this I decided the thing to do was put together something with a minimum of parts to divide 10 MHz down to 5 MHz
Growing up in the seventies and learning TTL I figured the 7474 was the answer, a dual D Flip Flop. Attached is a schematic of what I built up that has four parts. Part one is the input transistor to drive the clock input of the flip flop. Part two is the divide by two function, and part four is an emitter follower to drive a low impedance output. Part three is the tricky one, the intent is to try to convert the square wave output of the divider to a sine wave thru a RC circuit. If I were smart would have used a coil in place of the one hundred Ohm resistor to build a resonate 5 MHz network but not that smart.
Anyway, put this together and now the 8640 tracks along with the Motorola junk and Agilent analyzer. Next step is another distribution analyzer and syncing up the Harris R-2368 and 1310 exciter.

Ray F/KA3EKH

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