Excellent explanation Tim! I think, from my perspective, that the Rb standard, that I have, will be sufficient....and should be good for an FMT. That coupled with my Wavetek 5120, will allow me to measure frequencies to about 1/10hz, which is about as good as I can do here due to Doppler issues. In actuality, I have been able to get good measurements to 1/100 hz by interpolation; but, my goal is just to get to 1/10hz.
---------------------------------------------------------------------------------------------------------------- Right now am fighting an issue that has cropped up when using the Flex in scope mode with a narrow bandwidth (10hz). Periodically I see some low frequency signals that interfere with my hetrodyne measurements. It does not occur all the time; but, it is frequent. I suspect that I have a ground loop or that I have some device in the shack that is causing interference. I will try to track this down tomorrow. Am going to eliminate all antenna sources and feed the Rb 10mz signal directly into the Flex via a simple padding arrangement to lower the input level. I would expect no problems. Then I will start introducing other devices into the equation one-by-one until I find the problem. The symptoms are when in AM mode, looking at WWV, with no BFO or synthesizer or Rb running, I see a strong, low frequency, beat signal in the scope. Its appears that the BFO is running; but, its not. George K2CM ________________________________________ From: Tim Ellison [[email protected]] Sent: Friday, June 10, 2011 10:25 PM To: George R Allen; [email protected] Subject: RE: [FlexEdge] Rubidium or GPS disciplined, External Standard for the F5K " Are there any advantages for me to consider a GPS disciplined standard?" Depends on what your objectives are. The short term frequency stability of a GPS alone is fair. A combination (system) of a GPS disciplining a low cost XO, that by its nature is not highly accurate or stable, has the advantage of short term frequency stability via the XO and long term stability via the GPS. It is a good cost effective system. A Rb clock source can provide a highly accurate and stable clock frequencies, but it has to establish a good thermal equilibrium before it is "rock solid". Also you have to periodically calibrate it due to very long term drift and aging. The ultimate solution is the combination of the two; where the Rb is phase locked to and disciplined by the GPS, provide the best results. If the GPS loses satellite lock, the Rb clock can maintain accurate and stable frequency. You can improve the very long term frequency accuracy of a Rb clock from 10^-9 to 10^-12 which is close to the accuracy and stability of a Cs clock. I have just a Rb source that is contained in a forced air ventilated cabinet and is fairly thermally stable, it runs all the time so there is no "warm up" period needed when I operate. I have a 10 MHz distribution amp on it so it is a common time base for stuff in the shack that needs or can use external clocking. This meets my needs fairly well. I would love to have a GPS disciplining the Rb clock, but I have not found a cost effective solution to mate with the LPRO-101. So the obvious question is do you *need* that level of accuracy and stability. Maybe if you are driving microwave transverters or are into FMT. Or you could be like me and try to squeeze the best performance you can out of your "toys". -Tim -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of George R Allen Sent: Friday, June 10, 2011 5:51 PM To: [email protected] Subject: [FlexEdge] Rubidium or GPS disciplined, External Standard for the F5K I read somewhere that the GPS disciplined standards are more accurate than the Rubidium standards. As a external standard for the F5K, does it really matter? The specs for my Rubidum Standard appear to be astounding to me. Are there any advantages for me to consider a GPS discliplined standard? Thanks George K2CM _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software. _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using beta versions of the software.
