How To Repair Noisy Output On An Hp 8656a

Quote:

Originally Posted by cmjones01

What most the HP 8656/seven A/B generators? They seem to exist reasonably plentiful and the documentation available is practiced.
Chris

The 8656A was brought out every bit a new line of 'cheap' RF generators, fully synthesised and with a fractional-N 2nd PLL loop providing very fine frequency and phase control.

I suppose it fitted into the range replacing the old 8660A which was a thermal life-test machine if e'er in that location was i... later 8660 got a HUGE fan bolted on the dorsum.

8657 and B models came along with some useful improvement, and the addition of a doubler. These are reasonable sig gens if you lot want AM/FM and aren't trying to measure next channel rejection of good radios.

Below them in condition came the 8648 some years later which was an ultra cheap job aimed at oriental firms making radios and FM tuners as a quick source for a production line worker. Its schtick was a selection of 1-button presets. Single loop, poor phase dissonance, poor spurs.

THe intended replacement for the 8640 was the 8642. Fully synthesised, designed for low stage noise, designed to use about the same amount of rack space. So 8640 users could 'upgrade' and get synth accurateness and programmability. It'south quite a practiced sig gen, but hitting the time that everyone put their cellphone goggles on, and so didn't sell in loftier quantities. It is UNBELIEVABLY heavy. How they got the weight without lead or depleted uranium beats me. It'south a trivial heavier than the 8662 simply in a smaller instance, and so the credible weight is rather noticeable. it seems to have more and sharper corners when carrying one. Ours at work has a 'two person lift' sticker. Anyway, the 8642 parentage is the comms bespeak generator line.

The old 8660 was the synthesiser line primarily intended to make frequencies and be programmable as a lego brick in an ATE rack. The 8662 was a replacement for the 8660 and got born AM/FM without needing a plug-in. Forth with it came a big step in reliability a big reduction in racket, the 8660 was really early generation os synthesisers went. The 8662 begat the 8663 and the 8663 grew an extra-low phase noise option. This is what went into the stage racket measuring systems.

Adjacent channel and intermod tests were considered the hardest tests, but there was another less well known bugbear. If a broadband mixer gets a very broadband signal like say an FDM multiplex, and the LO has broadband noise from amplifiers etc, the resulting noise floor in fifty-fifty a narrowband IF can be most surprising. You begin to think the universe has information technology in for you! You're into the dissonance*racket mixing trouble. When I had to become through this the 8640 broadband noise from its amplifiers and jitter from those dividers was also much. Guy and Hugh plant that only the sometime generation valve sig gens like the 606/608 were low enough noise.

Horses for courses again..... (and I'm riding once again, after 12 weeks out of the saddle. Quite entertaining because the neddies are full of sass)

David

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Source: https://www.vintage-radio.net/forum/showthread.php?t=168100&page=2

Posted by: dusekoung1948.blogspot.com

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