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IC 7300 Frequency stability using a GPS reference - anyone done this?

Discussion in 'General Technical Questions and Answers' started by KN4LGM, Sep 14, 2020.

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  1. LU5ADW

    LU5ADW QRZ Member


    I Share the OP's interest in frequency precision, so I'm also looking for a mod for my IC-7300 with interest and for my Heathkit SB-104A that I build 40+ years with even greater interest.

    As to whether the 7300 needs the mod, well no, but the 104A certainly does (moves around by 100's of Hz).

    Actually if you think of it, except for emergencies, the comms abilities of our great hobby aren't really needed anymore any place you have IP connectivity (and thanks to Elon Musk's Starlink that will soon be "everywhere") because no ham rig comes even close to allowing you to videoconference with folks 1. in all different continents, 2. at the same time, 3. in the palm of your hand and 4. on batteries. Totally beyond Dick Tracy's Videophone or anything Inspector Gadget could have dreamed about. But who cares, we are who we are and our interests are our passions thus we need no justification for what we do.

    Many of us have strong scientific backgrounds and as such we find precision standards appealing, including a radio shack where all transceivers new and old are locked (GPSDO'd) to the U.S. Naval Observatory's Atomic Time via GPS because, well, it's cool to do so.

    And if you're into time, then you might find the Strontium-87 optical lattice quantum clock appealing: At an oscillation rate of 429,228,004,229,873.0 Hz (that's 429 THz; anyone care to build a Yagi for this frequency?) and with it's 18 significant figures it's the World's most precise measurement of anything made by humankind, ever. It's error rate is less than one second in all of time, as in the 13,750 million years since time started with the Big Bang. (Formally, the error rate is < 1 Sec in 15 billion years).

    Also with its 18 significant figures, you can use two Sr-87 clocks to measure the width of the slice of toast lying on your breakfast plate because the two faces of the toast are at different distances from the center of the Earth thus, like the Atomic clocks onboard GPS satellites, the must be adjusted to account for different rates of time according to Einstein's Special Relativity (time is affected by orbital speed which increases with distance from Earth) and General Relativity (time is affected by gravitational fields which decrease with distance from Earth). Thus the two clocks would measure time at different rates and working backwards there difference in distance from Earth's barycenter would have to be exactly the width of that slice of toast.

    Indeed, without compensation for Einstein's relativities, GPS distance measurements would have a CEP - Circular Error Probable of about 1 NM.

    Finally, the precision of the St-87 clock gives rise to a new field: Relativistic Geodesy, i.e. measuring altitude not barometrically but relativistically by the different rate of time passage between two Sr-87 clocks at different altitudes.

    If this all seems to esoteric, there's a collector of old atomic clocks that took 3 of his clocks and his 3 kids up to Mt. Rainier for a weekend to prove Einstein's relativity theories. When they returned home he compared the average time of the three clocks he took with him and found they had lost 22 nanoseconds against the average time of the clocks he left behind in his basement, exactly as predicted by Einstein so very long ago.

    Sr-87 Clock:
    Dad Takes 3 Kids and 3 Atomic CLocks Up Mt. Rainier:
    Just two GPSDO 10 MHz Reference Clocks:
    - ("10,000 000.000 0 MHz")
    - ("9.999 999 999 917 MHz", 83 microSec slow!)

    Perhaps if enough of us badger Leo Bodnar he might come up with boardlets for the 7300 and the 705.

    So, anyone have suggestions for a VFO that accepts a 10 MHz reference signal and that I can use to drive my 104A? :)

    Sorry for the long post; I hope you all find this stuff it interesting.

    Cheers to all!

    KN4LGM likes this.
  2. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Ensure to check this post to understand how are the frequencies derived in the IC-7300.
  3. KV6O

    KV6O Ham Member QRZ Page

  4. K8DO

    K8DO Ham Member QRZ Page

    I remember when the guys experimenting with 1.2 gigacycles (gasp) used to bury an oscillator in a metal can at to a depth of 4 or 5 feet in the dirt to get a constant temperature "Oven". And to measure power output they put a coil of coax in a water tank and measured the temperature rise of the water. The advance of technology has made things easier - but not as much fun,
  5. K8JD

    K8JD Ham Member QRZ Page

    I got my 7300 this May and from a cold start, measured the freq of WWV on 2.5, 5, 10, 15, 20 and 25 MHz at different times of day to get all freqs monitored. set to the one Hz readout and sat listening to ZERO beat , could hear no slow hetrodyne at all for 15-20 minutes for each freq. Tuned up and down one Hz and heard the "thump, thump,thump" Beat once a second ! This was in CW mode on a narrow filter.
    Did it again this month (November) and it seems like it's about one Hz off now.
    Compared to my TS440s, that never has been recalibrated (ref osc) and it's about 110 Hz off.

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