GPSDO for HF

  • 1
  • Question
  • Updated 3 years ago
I use my 6700 for HF. Most of my activity is CW. I may play with some of the other digital modes a little. Is there any advantage to a GPSDO for this kind of operation?
Photo of Mark Erbaugh

Mark Erbaugh

  • 395 Posts
  • 34 Reply Likes

Posted 3 years ago

  • 1
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9152 Posts
  • 3478 Reply Likes
At this time, the value proposition of the GPSDO is improved short-term frequency accuracy and stability vs. the OCXO.  Since the GPSDO is constantly disciplining the XO, it "self corrects" for temperature variations and aging.  This is not to imply that the OCXO in the 6700 is a "slouch" by any means.  Eventually we have plans to use the accurate time-stamping of the sampled RF spectrum to do some interesting things, like geographic diversity reception. 
Photo of Steve - N5AC

Steve - N5AC, VP Engineering / CTO

  • 1031 Posts
  • 1002 Reply Likes
Mark, all crystal based oscillators (XO, TCXO, OCXO, etc) all have specifications for short and long term drift.  The short-term drift numbers are what you will see with temp variations, warming up, etc.  The long-term aging occurs in all crystals and causes them to gradually move off frequency.  For example, take a look at this data sheet:

http://www.mouser.com/ds/2/3/AOCJY6-35349.pdf

It's just a random OCXO I pulled off the web (we don't use it).  About midway down the page you will see specifications for freq. vs supply, temp and load.  These are all short-term stability.  Further down you will see aging numbers that shows the drift in a per day, month and year.  These are long-term drift numbers.  A GPS receiver has a very good long-term stability because the satellites are designed to keep exact time through various methods.  But the short-term drift of a GPS receiver is fairly bad.  Since a TCXO is really the opposite -- good short term but poor long-term, a GPSDO is "the best of both worlds."  We use the short term stability of the TCXO and the long term stability of the GPS system to get a very stable frequency reference.  

As Tim mentioned, the key value proposition is that you will always be on frequency and will never have to recalibrate or adjust your frequency as crystals age.
Photo of KD4HSO

KD4HSO

  • 52 Posts
  • 3 Reply Likes
Steve, so when locking to an external 10 MHz reference, what's the loop bandwidth used in that circuit?
Photo of Steve - N5AC

Steve - N5AC, VP Engineering / CTO

  • 1031 Posts
  • 1002 Reply Likes
10Hz