Julian, and all: As far as stability and accuracy, I believe the GPS are referenced to a better atomic standard than the Rb, but for ham needs probably not a significant difference (unless you do microwave, like >10-GHz).
I have the LPRO Rubidium (5xE-11), an OCXO (5xE-12), a couple Jupiter GPS which I have yet to set up. I chose to run my OCXO 24/7 as my station frequency standard because its phase noise is best (-150 dB/Hz at 1-KHz). The Rubidium is much better for long-term accuracy (the OCXO drifts over months time by a Hz or two). But if you are needing a low phase reference the OCXO is considerably better than the Rb (-119 dB/Hz at 1-KHz). Phase noise is important for good receiver sensitivity. If the Rx uses a PLL phase-locked to an external reference, then that is linked to the phase-noise of the reference. My 1296/28 transverter has a PLL so it is locked to my OCXO with error < 1 Hz. The PLL is rated at -80 dBc/Hz of phase noise so the -150 dB/Hz phase noise rating of the OCXO is overkill. My mw counter has an ext. ref. so I can use the Rb when making critical frequency measurements (in practise, I cannot see a difference using the Rb vs. the internal TCXO in the counter at 1296-MHz). I found that my OCXO had drifted down about 1 Hz in three months since installing the OCXO (it runs continuously on a battery). It implies 2-3 Hz annual drift. If I ran the Rb there would be no drift beyond +/- 5xE-11. But the Rb has a finite life and the ones for sale are used so unknown how much life is left. The OCXO was $39.99 on e-bay. On the other hand the K3EXREF is not a PLL so the reference does not need to have super low phase noise. It does need to be stable and accurate. As Wayne explained it to me they chose not to PLL the TCXO as then the phase-noise spec of the K3 would be subject to whatever a ham used for a reference. By using a method of periodic Frequency correction, the phase noise is only affected during the frequency adjustment that occurs about every 4 seconds. The rest of the time the K3 enjoys the excellent phase noise performance of the TCXO which all the synthesizers in the K3 are locked to. So discussion of best phase-noise reference sources is not really germane to the K3EXREF (Wayne and others correct me if I am misunderstanding this). A OCXO, Rb, or GPS-DO will all work well as external ref. for the K3. You want short term stability and long-term accuracy in the reference. For the record my OCXO keeps the K3 within about 1.5 Hz at 28-MHz: http://www.kl7uw.com/K3EXREF.htm When you monitor the TCXO (CONFIG: REF CAL) you will see the frequency shift over time. That is the action of the K3EXREF shifting the TCXO to match the external reference. I found that my TCXO-3 after a year's use was 36-Hz high at 28-MHz when measured on my counter (with ext. ref off). The ext. ref moved the TCXO to 49.380.074 after about an hour. But with the ext. ref. the K3 was on frequency from the moment of power on. With just the TXCO there is a warm up period when the K3 will drift (about 30-minutes). This is the time that the K3 internal temperature comes up to working level. The amount of drift is much less using a TCXO. And almost non-existent if using a ext. ref. like a OCXO. (sorry, probably way more than you wished to know) 73, Ed - KL7UW ------------------------------ Message: 20 Date: Tue, 5 Apr 2011 08:09:26 -0700 (PDT) From: "Julian, G4ILO" <[email protected]> Subject: Re: [Elecraft] K3EXREF and Trimble Thunderbolts To: [email protected] Message-ID: <[email protected]> Content-Type: text/plain; charset=us-ascii What are the advantages / disadvantages of this type of frequency standard over the Efratom LPRO-101 which is a rubidium standard? Julian, G4ILO 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-1.4kw, 432-100w, 1296-testing*, 3400-winter? DUBUS Magazine USA Rep [email protected] ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
