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HP3577A 5Hz-200Mhz VNA Teardown

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rx8pilot:

--- Quote from: Calvin on January 18, 2020, 12:34:24 pm ---
btw. found prices in the 1990 HP catalog - 3577A: 25,570$, 35677A: 4,100$ - which would be ~52,000$ and ~8,400$ respectively. What a whopper :popcorn:

--- End quote ---

Lol! I paid $200 for mine in non-functional condition. Spent about $15 on parts and about 5-6hrs, now it works perfect. Bargain!!!

miken:

--- Quote from: Calvin on January 18, 2020, 12:34:24 pm ---The ´Port1´ and ´Port2´ outputs of the two bridges are of N-type but it appears to me that rather they feature SMAs with an SMA-to-N adapter screwed on.
Is that true?
--- End quote ---

It's an actual N bulkhead connector, with threading to attach it to the front panel. The back end necks down to a smaller diameter and solders directly to the board.


--- Quote from: Calvin ---I assume one doesn´t need additional D-Blocks when a (original) 35677 is connected to the VNA? Are those only required for useage of the VNA alone?
As alternative DIY-Setup ... would those cheap chinese/ucrainian 0.1-3000MHz bridges be suitable (with their Ref-otputs terminated into 50R)?

--- End quote ---

The bridges have DC blocking capacitors. They are pretty simple inside, caps, resistors, balun. You could probably make your own without too much trouble.

There is a measurement of the cheap bridge here: https://www.eevblog.com/forum/testgear/test-results-for-the-e-bay-rf-bridge-in-an-enclosure/msg1627738/#msg1627738
Though I will say that I measured one once and got worse results at the low end, better at the high end. Not sure if my mistake or if quality varies.

Calvin:
Hi,

thank You so much.
Yeah, the 35677A circuitry appears simple ... power splitter, 12dB-attenuator, coax relay, two directional couplers, a couple of some semi-rigid cables, and switch logic, besides loads of nude virgin breath  -aka known as used air- in a way tooo large casing.  ;)
Do You happen to know if the coaxial relay connectors are SMAs?
I ordered a pair of 33311Bs and also a pair of the (orginal) Bridges from transverterstore.com (just to be sure that I don´t get some crappy chinese fake something).
It´d be nice if it could be wird solely with SMA cables.

regards
Calvin

miken:
Yes, I believe the switch is also SMA. I bought a broken 35677A myself. Turns out it had one broken semi-rigid, typical solder joint break. One bridge measured really bad, so I replaced all the caps with SMD, but it turns out it was just the adjustment screw in the bottom... My future project is to build a VNA inside the 35677A box, plenty of space as you say  ;D

precaud:
I finally replaced the fan in my 3577A. I found a couple of these in one of my parts boxes and put one in:

https://www.mouser.com/ProductDetail/ebm-papst/W2G107-AD03-13?qs=RViDcLGODe0xrlbxBmPSjg%3D%3D

Result: Noise level reduced by half or more, down to a bearable level. Very worthwhile. And no noticeable drop in airflow. In fact, it feels stronger to me.

The original fan is noisy even unmounted.

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