HP VNA S-Parameter test set interconnect cables - Page 1
Forum section: electronics / testgear

author: LapTop006
author_rank: Unknown
timestamp: August 01, 2019, 12:58:04 pm
content: I've just acquired a HP 87511A S-Parameter Test Set for my 4395A VNA, but it came without cables.The control interconnect is a 25-pin Dsub cable, but I can't see anything in the documentation that states pinout.To save me trying to buzz it out just to be safe, does anyone know if the interconnect cable is simply pinned straight through (1 to 1, 2 to 2 ... 25 to 25) or otherwise?I also assume that the RF patch cables for TRAB should be good, short, low-less and identical, although a cal should eliminate any minor differences anyway.

author: Bud
author_rank: Super Contributor
timestamp: August 01, 2019, 01:18:25 pm
content: I remember reading somewhere Joel Dunsmore saying the patch cables do not have to be identical.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 01, 2019, 03:11:04 pm
content: I bought a test set for my 4395 without cables, standard DB25 in the back (though I remember same gender on both ends so my stock of them wouldn't fit), and standard N in the front (I bought 6 or 8 inch semirigid coax N cables off ebay for it for a pretty cheap price, since the frequency tops out quite low on the 4395, I wasn't too concerned with any loss).

author: guarneri0
author_rank: Contributor
timestamp: September 17, 2019, 09:28:05 pm
content: Were you able to find out the pin configuration? I just acquired 85046b test-set, and trying to see if a straight-thru D-25 male-to-male cable will work and not damage anything.Thanks,

author: hendorog
author_rank: Super Contributor
timestamp: September 17, 2019, 10:54:05 pm
content: The HP 85046/47 DB25 cable is documented in the service manual somewhere. I've posted about it before, as I made an emulator for it.From memory it is only a few wires and they are straight through. But I've heard about people having problems with off the shelf cables which don't connect the pins you need.As Bud mentioned, the RF patch cables do not need to be identical, as a cal corrects for that.From what I have seen, HP went to some effort to make their VNA's work to some degree without any calibration at all. So do you lose that if the patch cables don't match, but its not a problem once you do a calibration.Edit: Page 67 in this doc has the connector pinout for 85046http://pages.hmc.edu/mspencer/rf_lab/3G_VNA_85046A_S-Parameter_Kit_Manual.pdf

author: TurboTom
author_rank: Super Contributor
timestamp: September 18, 2019, 12:11:02 am
content: Quote from: guarneri0 on September 17, 2019, 09:28:05 pmIn case you didn't know before: Since the 85046B is a 75 Ohm impedance test set, the two N test ports are of the according impedance variety. NEVER EVER plug a 50 Ohms N connector into one of these 75 Ohms port connectors! The center terminal of the 50 Ohms plugs is of considerably bigger diameter and pushin it into the tiny 75 ohms sockets will definitely damage them (I learned it the hard way since I didn't know or notice before). Get yourself two suitable impedance matching pads if you want to use your test set with 50 Ohms equipment.The four interconnect ports to the VNA are 50 ohms, so no need to worry here.And yes, I also made a SubD25 interconnection cable for my 8753C -- it's straight through.Cheers,Thomas

author: LapTop006
author_rank: Unknown
timestamp: September 23, 2019, 01:18:22 pm
content: Quote from: guarneri0 on September 17, 2019, 09:28:05 pmStraight through D25 worked for me.