(I forgot to include Flexedge in the reply.) On Sun, Mar 21, 2010 at 9:04 AM, Brian Lloyd <[email protected]> wrote: > On Sun, Mar 21, 2010 at 8:06 AM, Mack <[email protected]> wrote: >> I'd appreciate the thoughts of anyone who has tried to use the Flex 5000A as >> an exceptionally accurate frequency measuring standard. As many of you know >> the ARRL Frequency Measuring Test is upcoming on April 22nd. It will be a >> constant carrier. The test is described in this months QST on page 52. >> >> I would use a 10 MHz GPS Disciplined external frequency reference on the >> Flex. I could also use a Rubidium 10 MHz house standard as a reference. I >> suppose I would use 48 KHz bandwidth and a small number of buffers. Is this >> correct and are there other settings that would optimize resolution? I'd >> just like to show off how accurate the Flex is if this is feasible. >> >> I have other frequency measuring devices that can measure to 31 mili Hz but >> really want to use the Flex in this test. >> >> All thoughts and input are most welcome. > > You probably saw my post about using the Datum/Euratom LPRO-101 Rb > reference on the main Flex reflector. Jerry Flanders, W4UK, sent me a > very thoughtful post about F5K accuracy. He had been trying to come up > with a calibration curve for the F5K and was finding it to be less > smooth than for his Kenwood. He was therefore concerned that, perhaps > the F5K is not as good for the FMT as other radios. That caused the > light-bulb to go on in my head (only a 4W night-light so don't expect > too much :-). > > The DDS determines frequency by the ratio of a multiplier and a > divisor value. Basically you multiply the reference by a fraction. Now > the multiplier and divisor values are very large but they are > discrete. The result is, you can get very close to any frequency you > want but you are unlikely to land spot-on a frequency. Two things to > remember: > > 1. the steps are not an integer relation to 1Hz; > > 2. the step size is not uniform. > > The way to use the F5K as a high-accuracy reference receiver is to > know the exact multiplier and divisor values being used with the DDS > LO. This will allow you to calculate the exact LO frequency since it > will probably be several mHz (millihertz) different from the PSDR > display value. Once you know the exact LO injection frequency you can > calculate the proper offset to use. > > Now there are probably some fractional values that land spot-on a 1Hz > boundary. Knowing how to figure those out might be helpful. Still, > knowing the exact algorithm used to select multiplier and divisor > would be very useful. It is probably buried in the PSDR source. > Perhaps we can impose on someone at Flex to either provide the > algorithm used or a pointer to the particular module that does the > calculation. I bet that module can be modified to actually report the > error between frequency requested and actual LO frequency produced. > > -- > 73 de Brian, WB6RQN/J79BPL >
-- 73 de Brian, WB6RQN/J79BPL _______________________________________________ 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 alpha and beta versions of the software.
