Locked Re: September 8th Program - Paul Guido - Service Monitors

Paul Guido

***If my math is wrong, please let me know.  I am very willing to be wrong. Unlike Bob Rodriguez that minored in Mathematics, I took my last math class when I was a minor.***

One of the things I have been pondering now that I have two working Service Monitors is "Which one is correct?".  If they are reading different, "Is either one correct?"  The person with two clocks, never knows the correct time.

To find out what is on frequency, I would like to reference a standard.  If I did this for a living, I could send the Service Monitor off to a lab and pay for the unit to be certified.  Owning a frequency standard, back in the day, could be very expensive and power hungry.  Back in the days of old (1970's and 1980's) lab measurement systems started being seen outside of national and government labs and most had a BNC jack for a 10 MHz input from a standard.  Some of the old equipment can be found on eBay today.   A frequency standard could have been sourced from a oven controlled crystal oscillator or a high end lab could have a Cesium based reference. 

Today you can buy a 10MHz reference that uses a GPS receiver for about $140 on eBay that is accurate to 10^12.  It is called a GPS Disciplined Oscillator (GPSDO) which is a 1 second error every 11,574,074 years.

Yes there is more phase error in a GPSDO then a Cesium clock but that is not an issue for the measurements I am making.  The GPSDO is 10^5 more accurate then the system I am testing.  

Connect a GPSDO to a Frequency Generator or a Frequency Counter for very accurate lab like results in your home.

How good does it need to be?  The service monitor has a 1 GHz signal generator that is in specification if it is +/- 100 Hz at 1,000,000,000 Hz (so we can drop two zeros).  That would make the error +/- 1 Hz at 10,000,000 Hz.  (10^7 or +/- 1 Hz at 10 MHz.) 

My hope is to show you how some of this works during the presentation.  Bring your Handy Talkies to the next meeting to check your radio's frequency error. 

Some other data below.

Paul Guido, N5IUT

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