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Old 4th Dec 2022, 6:04 pm   #335
regenfreak
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Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: 6-gang FM stereo tuner heads

Quote:
Originally Posted by G0HZU_JMR View Post
I think the 5Hz to 50kHz spectrum analyser that David was referring to earlier might be the HP3580A. This audio spectrum analyser dates back to 1973.

The notes in the link below suggest it has a 1Hz RBW.

https://www.hpmemoryproject.org/wb_p..._b_page_04.htm

If you scroll down the link a bit further, you can see some stuff about the HP8568A. Back in 1978, this 1500MHz spectrum analyser really represented a huge step forward in terms of RF performance and features and it could be fully controlled via GPIB in an ATE system. I think a lot of the 8568 analysers were purchased for use in ATE racks. The high purchase price was presumably worth it, because it was able to speed up production testing and improve the quality/repeatability of the testing.
Thanks, I have found the schematic. The HP3580A has 5 pole crystals switching on and off RBW down to 1Hz. The RBW does not change with temperature. The crystals were individually matched for the temp coefficient and the inflection points with slope = 0 of their temperature curves.

Quote:
The two tubular 70MHz BPFs below were purchased from Telonic in the USA and these were designed to be very rugged and stable with very low VSWR at 70MHz. One is about 12MHz wide and the other is 3MHz wide. The filters were then sent to the National Physics Laboratory where the noise bandwidth of the filters was measured very accurately. For example, the narrow filter is stamped 66.12dBHz.
At work we have a 50-year-old, big wind tunnel from the National Physics Laboratory NPL.The fan motor is still going strong but the transducers of the 6-axis force balance are out of calibrations and no one at work knows how to recalibrate them.

Quote:
I have my own precision noisecom noise source to use with them.
The calibrated noise source costs an arm and a leg. Even the cheaper alternative with calibrated ENR values costs a few hundred pounds. Without the noise source with known ENR, it is very hard to measure accurately an amplifier with low NF and low gain.
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Last edited by regenfreak; 4th Dec 2022 at 6:29 pm.
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