[time-nuts] 5MHz x 10MHz

Bob Camp lists at rtty.us
Fri Aug 2 14:15:37 EDT 2013


Hi

If you go back far enough, you will find 1 MHz and 100 KHz used as reference standards. They certainly were common place in gear through the 1960's.

Pre-WWII,  open 100 Kc quartz bars were often the "standard" of choice. Anything much higher than that was increasingly less stable.

Post WWII,  well behaved 1  Mc  fundamentals came along in glass sealed enclosures. Sealing them up helped a lot with aging. By the late 40's and early 50's low frequency overtone designs (1 to 5 MHz) were worked out. 

5 MHz third overtones (and 5th's) became popular with the Bell Labs / Western Electric / AT&T crowd by the mid 1950's. They made and bought enough of them to turn them into a standard by the early 1960's. As cold weld packages took over from glass, the older 2.5 and 1 MHz 3rd's / 5th's became impractical. 

10 MHz is a creation mainly of HP. They were more after the microwave end of the business than some of the others. The higher starting frequency gave them better phase noise and fewer spur issues. 

Depending on where you are in the world, 10 MHz may or may not have caught on. The Russians stuck with 5 MHz long after HP had converted the US over to 10. 

Intrinsically quartz just keeps getting better as you go down in frequency. There is nothing magic about any one frequency. Lower is always better in terms of Q, provided you can scale up all the dimensions. A 1 MHz OCXO that is 10X the outer dimensions of an 10 MHz OCXO obviously would have some limitations that had noting to do with quartz. As an example, the blank in a 5MHz precision crystal is probably 0.5" diameter. To make an equivalent 1 MHz crystal, the blank would need to be 2.5" in diameter. At 100 KHz you would have a plate 25" in diameter. Good luck finding the raw quartz for those blanks ….

Bob
  
On Aug 2, 2013, at 12:31 PM, Euclides Chuma <euclides at w2c.com.br> wrote:

> Hi,
> 
> Why any equipments use 5 MHz and others use 10 MHz reference standard?
> 
> Thanks
> 
> Euclides Chuma
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



More information about the time-nuts mailing list