Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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My Hobby Website:
HP87512/VNA - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: HP87512/VNA
Unread postPosted: Thu Nov
11, 2004 4:32 pm
I have a question for those who have 'worked'
closely with the equations involved in the VNA, and particularly for
the calibration procedure.
At work we have a HP8751A VNA (5Hz-50MHz)
working with a
reflexion/Transmission Test Set HP87512. As I'm always
loking for 'the way it work', I opened it, thinking it was a directional
bridge made with 50ohms resistors (Wheastone bridge) with the design
adapted to work from 5Hz to 500MHz.
But it was a great surprise for
me to see that the 'bridge' from HP,made of resistors, have nothing
to do with a Wheastone bridge (from what I could understand !!). With
the schematic from HP, I can't manage to find a 'directivity' behavior
of the 'bridge' made of resistor. As the HP8751A work with a S parameter
HP87511A or B, I know that the 'bridge' is not a Voltage/Current method
of measuring the reflexion parameter. And if I look on the 'mathematics'
for the calibration of a VNA (TRL or SOL methods,...), there is always
a correction factor for the unperfect directivity of the directional
So is it possible to obtain the correcting factor even
with a nondirective bridge, or a SOL method is able to accept a nondirectional
bridge ???? It seems that the signal from the Output connector is 'split'
with diferent levels to the Reference Port and the A port...
in a real confusion ...!!!
If you have any idea about the way
the HP87512 work with the HP8751A, I would be pleased to read you on
the subject (or if you know a link with the description of the way it