Products > Test Equipment
HP3577A 5Hz-200Mhz VNA Teardown
bson:
An excellent workhorse - I use mine quite regularly, mainly for anti-imaging filters. The nice thing about the 4-port model (I hardly ever use the S param set) is it can be used with my LeCroy active probes and the ADPPS power supply. This way I can probe at the output of each filter stage separately, and if something odd is going on quickly track down what is invariably some mistake on my behalf. (The same power supply also allows using the probes with counters and other instruments, just brilliant.)
Doing something about that jet turbine fan would be a huge improvement!
precaud:
--- Quote from: Berni on July 29, 2018, 11:56:43 am ---I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy
--- End quote ---
Is it just the switches, or is the display quality becoming worse too? At some point we should probably start a separate thread about repairing those modules and extending their useful life. The NewScope5 is very cool but, as you say, pricey.
I thought it would be worthwhile to mention a few things for those readers not familiar with the 3577A. Measurement-wise, it set a new standard of accuracy and performance for VNA's in its freq range. The main thing a VNA needs to be able to do is measure inter-channel magnitude and phase differences over a) a wide freq range, b) offering a wide range of suitable filter bandwidths, and c) over as wide a dynamic range as possible. These areas are where the early VNA's had limitations.
Take dynamic range. Up until then, VNAs had amplitude accuracy of +-0.5dB and phase accuracy of +-1.5º over a 60dB dynamic range (below full-scale), and only at mid-band IF's and frequencies. Max freq range was in the 10-30MHz range, and smallest IFBW was 3Hz (and not very stable). HP 3570A and Anritsu MS420 are examples of this.
The 3577A comes along and betters everything by an order of magnitude, with worst-case amplitude accuracy of +-0.08dB and phase accuracy of +-0.5º over the same 60dB dynamic range, extending it to amplitude accuracy of +-0.25dB and phase accuracy of +-1.5º over an 80dB dynamic range. And doing it at ALL IF's and frequency ranges. And offering a stable 1Hz IF and 5Hz - 200MHz useful bandwidth in the process. Remarkable.
It was an incredible work of engineering, both analog and DSP. And HP sold a ton of 'em.
The fact is, the newer VNA's don't perform any better over this same freq range. 25 years later, and it is still as good as it gets accuracy-wise.
My main beefs with the 3577A are:
: The noisey fan is almost unbearable.
: The display is too small and crowded, with poor contrast. Causes eye strain for me.
: Scattered user interface. Control grouping reflects the underlying firmware organization, not the best ease of use.
: Like most instruments from that era, its big and heavy. But it was best possible at the time.
: No built-in power splitter. A silly omission.
: No AC coupling option on the inputs. Another silly omission.
: Output and all inputs are bonded to chassis ground, requiring isolated/diff probes and/or use of output xfmr for ground-isolated low-level measurements.
: 1 Hour warmup time for stated accuracy. The instrument will spend 1/10 of its life warming up for use :)
But considering that you will have to pay royal sums to find something that improves on these things, the 3577A is an incredible bargain.
EDIT: and worth mentioning... the 3577A has no firmware bugs I am aware of... I've never encountered one.
sixtimesseven:
--- Quote from: bson on July 29, 2018, 01:16:56 pm ---An excellent workhorse - I use mine quite regularly, mainly for anti-imaging filters. The nice thing about the 4-port model (I hardly ever use the S param set) is it can be used with my LeCroy active probes and the ADPPS power supply. This way I can probe at the output of each filter stage separately, and if something odd is going on quickly track down what is invariably some mistake on my behalf. (The same power supply also allows using the probes with counters and other instruments, just brilliant.)
Doing something about that jet turbine fan would be a huge improvement!
--- End quote ---
May I ask which active probes you use exactly?
Thanks
rx8pilot:
--- Quote from: precaud on July 29, 2018, 04:09:13 am ---Well I won't put DC on the inputs of mine... all three of my fixer-uppers have input stages issues, and DC is often the culprit... besides, DC shortens the useful life of relay contacts...
--- End quote ---
Did you build some AC coupled adaptors? Like you, I would prefer not to test my luck! Addressing this now could save any 3577A owner a lot of trouble.
--- Quote from: precaud on July 29, 2018, 02:51:03 pm ---: No built-in power splitter. A silly omission.
--- End quote ---
Is it worth buying a commercial splitter for under 200Mhz or is it easy enough to DIY? Searching around for some info - they only seem difficult when the BW goes much beyond 500Mhz.
Berni:
I have built a 3 way restive slitter before out of SMA connectors meeting in a triangle and some 0402 resistors joining them in the center and it seamed to measure just fine on the 3GHz network analyzer at work. It did get a bit wobbly past 2GHz but otherwise seamed pretty flat with a reasonably low SWR. Tho i did not measure how accurately it splits power and phase.
So for 200MHz i think a DIY one could work pretty well.
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