Hi Adrian Glad to hear you're back on track and that all is now well I can understand that very thin coax being quite deceptive, it's certainly amongst the thinnest I've ever come across. I've got a couple of double oven10811s bought from one of the usual Chinese Ebay sellers a few years ago as potential spares for my Z3801As and both have one of the coax connectors chopped off, can't remember now whether it's the 10MHz output or the EFC input. Either way, should they ever be needed in anger I'm keeping my fingers crossed that the leads can be swapped over, cos fitting another connector sure don't look to be a very user friendly option:-) Regards Nigel GM8PZR In a message dated 14/10/2012 00:27:23 GMT Daylight Time, [email protected] writes:
A very good point! I checked the output amplitude with a spectrum analyzer, a power meter and a scope, the latter with a 50 ohm load to the input. I re-checked the power supply connections and can confirm they are the same as before. I used three different power supplies for the oscillators and two for the heaters, still no difference. But... To make it short, your comments helped to get me back on track. Both beauties escaped unnecessary dismantling and are now working as they should. Actually, the problem was caused by a long-term misunderstanding. I was always wondering why 'HP used simple stranded wire' and not coaxial cable on the 10 MHz output and EFC. As long as I connected them on the bench, I replaced the 'missing' ground connection with a short wired croc clamp between coax and ground. Today I realized that the thin blue wire IS actually coax cable, so I should have connected the coax shield to the BNC ground on my newly built 2x 10811 enclosure. With the new wiring, the output ground had just become much more inductive, up to a point where the nominal source impedance of 50 ohms had increased to over 120 ohms, causing the amplitude loss of some 3 dB and capturing noise. Btw. the Sprague 6800 uF / 40 V from my R&S NGA power supply has indeed died, but independently of the osc. problem. Adrian [email protected] schrieb: > Perhaps a silly question, but as I get the impression that both seem to > have failed simultaneously with the same fault I'm just wondering if you're > sure it isn't what you're checking them with that's developed a problem? > > Regards > > Nigel > GM8PZR > > > In a message dated 13/10/2012 13:52:46 GMT Daylight Time, [email protected] > writes: > > Hi All, > > both of my double oven 10811A's have been running flawlessly until now > when I noticed that the output power has dropped by about 3 dB (measures > only 4...4.5 dBm at 50 Ohm load), and the noise floor has gone up by > about 20 dB, while the frequency is still spot on. > > I used them for various mesurements, so I can unfortunately not remember > what might have caused the failure. Only the 12V linear lab power supply > that fed the heaters had developed a completely dead filter cap, so the > feeding voltage was a 100 Hz sawtooth rather than DC. The heaters appear > to be still working though. I'm only using the internal heater. They > draw some 700 mA at power up and drop to around 150 mA each when warm. > So the oscillators are unlikely to be cooked inside. Something must have > happened to the 10 MHz output, possibly an ESD issue? > > Before I start taking them apart, can anyone tell what has happened or > what to look for first? > > Regards, > Adrian > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
