California Microwave PE87P208 Oscillator  (Teardown) - Page 1
Forum section: electronics / rf-microwave

author: sean0118
author_rank: Frequent Contributor
timestamp: August 13, 2023, 09:21:13 am
content: I saved this from an ewaste skip, thought it looked interesting...I pulled it apart to try and find out why it failed. I only have a vague understanding of how it operates but I thought others here might like to see some tear down photos.There's similar oscillators on ebay etc, but they don't have an RF input like this one, I suspect it's so it can phase lock to a reference? Pretty sure is serial number 1 so might be a custom design.Text is difficult to read it says "52-100893-01(-) 8200 - 8750 MHz" & "PE87P208(-) SN:0001"I couldn't get a good photo but there's twoNEC 2SC1600s transistorsunder the cone at the end of the cavity. I'm guessing it's some sort of cavity resonator that's tuned by the slug moving in or out. There's what looks like two probes at the opposite end of the cavity to the transistors, I'm not sure what their function is?This is the back of the 2SC1600s, I think those are inductors in series with the leads, maybe diodes? Looks like they've started to melt:Those leads go back to this board, pretty clear something has gone horribly wrong:I suspect one of the 2SC1600 went short circuit which lead to the failure of the other components. I might attempt a fix one day, it looks pretty challenging though.

author: RoV
author_rank: Regular Contributor
timestamp: August 13, 2023, 04:29:28 pm
content: The first board is probably a sampler, driven by the external reference (I suppose something between 10-100 MHz). The two schottky diodes on the bottom left sample the signal from the probe and are pulse driven by an SRD (the red diode slightly at the right of the others). This architecture was common when high frequency digital dividers were not available.The cavity probably contains a Gunn diode and perhaps a varactor for fine tuning (unless tuning is done by varying the Gunn voltage). I suppose the 2nd board contains the Gunn power supply and the PLL, the last working from the sampler output.The screw is used for coarse tuning, then the PLL makes the oscillator lock to the closest harmonic of the input reference.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 14, 2023, 10:20:31 am
content: Quote from: RoV on August 13, 2023, 04:29:28 pmInteresting thanks, I've never looked into Gunn diodes or even heard of SRDs. I have some reading to do.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 14, 2023, 05:53:41 pm
content: Most of that is right except the sapphire rod cavity oscillatorproduces up to a Watt or so of energy and drives a varacter multiplier mounted in the filter block. No Gunn Diode involved.Most brands used nearly identical circuits and a triangle wave oscillator to initiate lock. The multiplication factor might be from 60 to 100 depending on the "Brick"Google "Ham Radio Microwave Brick" and you will have plenty of reading. It's possible to lock off frequency in multiples of the crystal oscillator steps.See attached..I own quite a few bricks.Steve

author: LaserSteve
author_rank: Super Contributor
timestamp: August 14, 2023, 05:56:38 pm
content: I see a damaged PSU board from a backward connected input.Most of these run off MINUS 19 volts.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 14, 2023, 06:29:46 pm
content: SPD patent attached..Steve

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2023, 01:38:02 pm
content: Quote from: LaserSteve on August 14, 2023, 05:56:38 pmAh good point, maybe that is what happened, this one is -20V. Thanks for all the info I will look into it.Also, just realised I missed a pic: