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Bodnar GPS disciplined oscillator

Ken - NM9PKen - NM9P Member ✭✭
With so much discussion about GPSDO's, and the recent article in QST, I was wondering if the under $300 Bodnar GPS Disciplined Oscillator would be an acceptable substitute for the internal module for my 6500? I am interested especially in whether it's phase noise content would be within tolerance so as not to compromise the excellent response of the 6000 series.


  • AC9SAC9S Member ✭✭
    edited February 2017
    I spoke with the distributor at Dayton - pretty attractive price if it will work.

    Keith - AC9S
  • Steve (N9SKM)Steve (N9SKM) Member
    edited June 2016
    I purchased one on ebay that was cheap and according to my instruments accurate. it matches right up with my Rubidium standard on the scope and my old counter shows within a half a Hz of 10.0 (Pretty sure the counter is what is off.

    If you search BG7TBL on ebay you will find them, The thread below shows all the different versions.


    Some testing someone did

  • WaltWalt Member ✭✭
    edited July 2017
    I got one a few months ago - Without it, the 6500 calibration was about -517 or so.  With the 10 MHz input ref. it seems to always do a -3.

    Since I have no possible way to measure phase noise or receiver parameters - I have no idea how it relates to performance or if anything has changed.

    Maybe someone here with $$$$ of test equipment has conducted a trial and came to a judgement in which case I am all ears . .  in the meantime, I will keep it plugged in and the little antenna sits on the window sill.  Been running for months and the software that configures it tells me there have been no dropouts.

    Got mine from force12inc in colorado - got it in about 3 days.

  • k3Timk3Tim Member ✭✭
    edited May 23
    I inquired about the GPS / phase noise before and a Flex rep said the GPS 'bumps' the main oscillator to keep it on frequency. Hence the phase noise of the GPS device will not have an effect on the SDR except of course frequency accuracy. 
    Personally, I went with the internal GPS in case additional s/w functionality is added in the future (Time server / I-Q timestamping etc.)

  • George KF2TGeorge KF2T Member ✭✭✭
    edited February 17
    Like the Bodnar idea of dual, independent frequency outputs to lock my Flex AND transverter.  Both have TCXO's now, but the thought of being just that much more stable for weak-signal work has its appeal. Would love to hear some real user reports!

  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    As an option, the Flex GPSDO has a 10 MHz output that can be used to discipline other devices in the shack too.
  • Peter K1PGVPeter K1PGV Member ✭✭
    edited June 23
    And, just from a curiosity perspective, I'd like to see some actual specs on the Bodnar unit. I was pretty surprised to see a "review" (which amounted to little more than an editorial advertisement) I'm QST without a single specification... And especially no spec for phase noise... Except that a "lower phase noise" unit than the current "excellent" one was soon to be available. Peter K1PGV
  • WaltWalt Member ✭✭
    edited July 2017
    Google is your friend . .


    If you need more info, maybe send them an email with your questions


  • Peter K1PGVPeter K1PGV Member ✭✭
    edited June 23
    So, in response to Walt's suggestion I used Google, the spec'ed phase noise is:

    Measured phase noise of standard (TCXO) version is equal or better than

    -120 dBc/Hz at 100 Hz
    -133 dBc/Hz at 1 kHz
    -137 dBc/Hz at 10 kHz
    -140 dBc/Hz at 100 kHz
    -144 dBc/Hz at 1 MHz

    Not bad... but not great.

    That and the output power level are the only specifications given.

    There's a "custom low phase noise version" available on the Force-12 web site.  This seems to have about -5dBc better performance in close.

    I'd like to know more about the hold-over accuracy (the web page says a "continuous GPS" reception is required, and with a TXCO (as opposed to a single or double OXCO), that sounds likely to be true).

    But, for the price (about US$270... NOT including the cost of a suitable antenna US$15) this seems like quite an amazing little unit. This is true even when compared to the Jackson Labs LC-XO-Plus which is approximately twice the cost. 

    I *would* like to hear somebody from Flex comment on the importance (or lack thereof) of Phase Noise in providing an external 10MHz reference to the 6xxxx.


  • Jon_KF2EJon_KF2E Member ✭✭
    edited June 23
    Is this the unit being discussed?


    Sure is reasonably priced. Does anyone have one?

  • Steve (N9SKM)Steve (N9SKM) Member
    edited June 2016
    Scroll up to the first post reply in the thread that i made i posted a couple of links for you to do some reading. I dont have a calibrated counter that goes to less than tenths of a hz but mine runs right with my rubidnium standard if i put em both on the scope. People have tested and givin the differences in those units.
  • Peter K1PGVPeter K1PGV Member ✭✭
    edited December 2016
    If that replay was supposed to be to me (it's not clear).... We are discussing two different units. My curiosity and questions were with respect to the commercial Bodnar unit being sold by Force-12 here is the States, not the BG7TBL from eBay. Peter K1PGV
  • George KF2TGeorge KF2T Member ✭✭✭
    edited December 2016
    Jon, I've heard of some good results with the eBay unit. He makes a number of variants, it seems. Sine wave 10 MHz seems to be a great deal for the Flex. If you need a second, different frequency output, though, the Bodnar seems like the ticket. 

    Got to say, though, the 6500 is pretty darn stable on its own. My XV144 with TCXO and some after-market styrofoam work seems to be quite good, too. +/- just a few Hz on 2m, once I got it netted to a known good source.
  • Joe BeldenJoe Belden Member
    edited May 2017
    Ok I'm brand new to the Flex, (just took delivery yesterday.)  I have one of these Bodnar units, and would like to use it to calibrate the radio.(6500)  I plugged a feed over to the 10MHz in and clicked on calibrate, and it's still -550 or so.   I'm sure I'm doing something wrong, any suggestions would be appreciated.  The Bodnar is sync'ed and is spot on, I checked with my O-scope.
  • edited June 2016
    Joe, the Flex will only use the external reference if it's plugged in and active when the radio is started up. If you unplug it while the radio's running, it'll revert to the internal reference and you'll have to restart the radio to use the external ref again.
  • edited June 2016
    ...and you don't need to calibrate if you're using the external reference.
  • edited February 2017

    The higher-priced version of the Bodnar is still > 30 dB worse at a 100 Hz offset than a Trimble Thunderbolt with a Piezo-branded OCXO when powered from a low-noise, lab-grade supply.  For example, typical Trimble PN at 100 Hz is -160 dBc.  The upper-grade Bodnar unit is about -125 dBc. 

    Compared to what's available on the new and used markets, the Bodnar's performance is probably better characterized as good, but not excellent.  For Flex users it may not be an issue, but if the device is driving other test gear, that 30 dB difference may mean a lot. 

    The Trimbles were once plentiful on eBay for USD $99.  Scarcity has driven that up but with persistence, a watchful eye can still spot one for a reasonable price.   

    I ended up installing a Trimble unit and Lambda linear supply into a customized enclosure: 


    Paul, W9AC 

  • Kevin N9JKPKevin N9JKP Member ✭✭
    edited December 2016
    Any update for additional functionality for the GPSDO?
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    Not at this time.
  • SteveMSteveM Member
    edited November 2016

    KE5FX thinks the Trimble-branded OCXO's are the ones that perform to the specs you list, viz a viz, the Piezo. Also, note that those specs can only be reached if the Trimble OCXO is removed from the PCB.

    It's hard to tell precisely, but the Piezo looks like it lands somewhere around -142dBc at 100Hz. I do wonder what it would have been if he had tested the Piezo after removing it from the PCB, which is how he tested the HP and Trimble.

    Check the following link, especially near the bottom, under "October 24, 2011: Further notes on the Thunderbolt OCXO":


  • edited November 2016
    My error in reporting.  Yes, I meant the Trimble-branded OCXO and not Piezo.  I derived my data above from the Trimble-branded OCXO. 

    Even the Piezo model has a (roughly) 20 dB phase noise advantage at a 100 Hz offset over the precision Bodnar unit.  A decade later and the Thunderbolt performance is still extraordinary when powered from a low-noise supply.

    Look for Thunderbolt Rev. E units with a 2004 date code (or later) for the best chance of getting one with the Trimble OCXO. 

    Paul, W9AC
  • Mark ErbaughMark Erbaugh Member
    edited November 2016
    When is the 10MHz output active? Does the 6500 have to be powered on?
  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    It has to have power applied to it.
  • Joe BalesJoe Bales Member ✭✭
    edited May 2017
    Joe. Did you ever get your Bodnar unit to calibrate close to 0 as one would expect and actually work. I'm having the same issue with mine. I have removed the power cord leaving it off for a while to assure power is off. I know the Bodbar works, as I confirmed with a friends Icome 7800 and K3
  • Lee - N2LEELee - N2LEE Member
    edited August 2019
    I am still unclear about how a Trimble or the internal GPSDO effects phase noise. Does this improve the radios phase noise or just frequency accuracy ?
  • Larry DavisLarry Davis Member
    edited December 2017
    i run it on 2 432 222 lock radio and tranverter right on

  • SteveMSteveM Member
    edited August 2019

    Sorry. I'm digging up old threads to finish them off.

    See https://community.flexradio.com/flexradio/topics/external-10-mhz-reference-phase-noise-requirements

    For anything above a 20Hz bandwidth (i.e., negligible), Flex transceivers retain their own phase noise characteristics when using an external reference. Essentially, the external reference is only used for long term frequency accuracy.
  • Tom W3FRGTom W3FRG Member
    edited August 2019
    For those interested, I just received the Bodnar GPSDO Phase Noise Plot from SDRKits.
    Here is a copy for your review.

    Tom W3FRG


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