Finally got off my duff and put all of my test equipment on the same 10MHz timebase. Years ago (at least 10) one of my friends gave me a little Video Distribution Amplifier, and I toyed with this idea, but never had enough test equipment to make it worthwhile. Then I bought an HP Z3801A GPS Receiver, which was used at cellphone sites to keep things synchronized.
And again, the little VDA sat unused. Well, I got it out the other night to see if it even worked, and it did, but two of the output connectors had low signals on them. I cleaned the connectors and nothing changed, so I'm guessing that's why my friend gave it to me. Fortunately, since I have three instruments to lock together, I was able to use the "Loop Through" port to pass the reference signal through to one instrument, and had two good ports for my other two instruments.
Not much to see....a black box on a black (dusty!) file cabinet with black cables running to and fro...
Since all the instruments have an internal timebase, the question becomes which one to pick as a Master Timebase? The RF generator has the optional HP "High Stability" timebase, so I picked that one. I connected it to my counter, and it read between 10,000,000Hz and 9,999,999Hz, so they agreed to one part in ten million, which is pretty good. I used the Loop Through connector to drive the 8904A Multifunction Waveform Synthesizer, and the other two outputs to drive the Spectrum Analyzer and the counter.
The internal timebase in the 8904A read 9,999,685, which meets specs, but it's several hundred Hertz low. The timebase in the spectrum analyzer measured 10,000,450Hz, which also meets specs, but is a bit high. Still, 450 parts out of TEN MILLION amounts to fly specks, but it gives me the warm and fuzzies to have all the equipment locked to the best timebase in the house.
RF generator set to 10MHz and 0.0 dBm output.
Spectrum Analyzer displaying the RF generator output.
Pretty close, and to get them to "exactly" agree would require sending ALL the equipment in use to a reputable Calibration Lab, and paying a whole bunch of $$$.
I consider this to be acceptable accuracy for a home shop, and I'm aware of the ambiguities in my system. The signal generator was calibrated before it shipped, as was the waveform synthesizer. Basically the differences I'm seeing is the difference between "Meets Specs", and "Dead Nuts On".
One more little thing scratched off the list....
Very cool. I use my signal generator to create a marker so I can see what frequency my spectrum analyzer is on. So, yeah, I'm assuming it's "right" in the sense that it's the closest to right I've got. I've compared it to WWV on a radio and it's far, far closer than the spectrum analyzer.
ReplyDeleteYou can really chase your tail deciding "Who's On First"!
DeleteWe're 8.5 miles from the WWV transmitters, so I don't have to worry about propagation delay, but I haven't tried to Zero Beat anything with them...
I read somewhere long ago that the line about "so strong you can hear them on your fillings" actually has a basis in reality. Something about the old amalgam fillings getting some corrosion and causing a crude diode?
DeleteIt would be something to get WWV on your fillings. The problem is I can see it becoming torturous.
Yeah, I've heard that story, too.
DeleteLOTS of google hits:
https://duckduckgo.com/?t=ffab&q=hear+radio+on+fillings&ia=web
Looks like you have a commercial-grade metrology lab right there at home! Congratulations!
ReplyDeleteOh, Lordy no! I'm not anywhere near that level of accuracy, but it should be Plenty Good Enough for my little shop.
Deletedrjim, I am envious. I missed buying an HP3801A when there were a bunch on the market because I didn't have the money at the time. I even had to sell my TS-140 at the time to get some cash for our needs (had some older radios that I could use).
ReplyDeleteHaving been in a metrology/calibration/repair lab for a while, I have to say you have a nice set up there for what you want to do.
The HP 3801 needs to be looked at. The last time I tried to use it none of the lights came one, and the power supply tested OK. All I've used it for was as a clock on Field Day so my laptop had accurate time.
ReplyDeleteI think I'll dig it out today and take a look at it. Not sure how to run a cable into the workshop. I have ONE RG-6 running outside that used to be used for the cable TV jack, and that's tied up with my FM broadcast antenna.
Maybe it's time to buy a hammer drill and some concrete bits! Be nice to have another cable coming in from the Real World!
Definitely 'close enough for government work'! :-)
ReplyDeleteAs said by the Man Who Knows!!
DeleteI've probably got one of the better setups here in town.