How high in the RF range?
You can pick up a nice surplus Tektronix active FET probe. High-impedance in, plugs into a BNC jack, drives 50 Ohms.
You'll need to get the separate external power supply for it, though - it uses small, latchable LEMO connectors for the power,
that are built into some TEK 'scopes, but probably not your analyzer.
-3dB bandwidth of 500 MHz, and I think also one that's 1 or 1.2 GHz.
I know a site where you can download the manuals for free, if wanted a look at the technical specs, schematic and servicing info
before you decide. New, they were pretty $$$ back in the day...Jim Williams actually wrote a whole app note about 'gotchas' to look for
with 'scope probes (AN-47?) and it included a 'how-to' for making your own. He requested that his bosses get him one for a project at work,
but they wouldn't approve the $500.
If you get one second-hand, though, make sure they give a money-back guarantee and state explicitly that it's a working unit :
- to keep the input impedance high, and input C low (0.2 pF), that tip goes straight to the base of a FET, and it is very prone being blown
by ESD, or exceeding the input voltage spec.
Far as the power supply goes, you can buy a couple of those LEMO connectors, and build your own.
That was your design article, wasn't it? - "Build a Wide-Bandwidth Power Supply" -
You can pick up a nice surplus Tektronix active FET probe. High-impedance in, plugs into a BNC jack, drives 50 Ohms.
You'll need to get the separate external power supply for it, though - it uses small, latchable LEMO connectors for the power,
that are built into some TEK 'scopes, but probably not your analyzer.
-3dB bandwidth of 500 MHz, and I think also one that's 1 or 1.2 GHz.
I know a site where you can download the manuals for free, if wanted a look at the technical specs, schematic and servicing info
before you decide. New, they were pretty $$$ back in the day...Jim Williams actually wrote a whole app note about 'gotchas' to look for
with 'scope probes (AN-47?) and it included a 'how-to' for making your own. He requested that his bosses get him one for a project at work,
but they wouldn't approve the $500.
If you get one second-hand, though, make sure they give a money-back guarantee and state explicitly that it's a working unit :
- to keep the input impedance high, and input C low (0.2 pF), that tip goes straight to the base of a FET, and it is very prone being blown
by ESD, or exceeding the input voltage spec.
Far as the power supply goes, you can buy a couple of those LEMO connectors, and build your own.
That was your design article, wasn't it? - "Build a Wide-Bandwidth Power Supply" -
Last edited:
http://cds.linear.com/docs/en/application-note/an47fa.pdf all known back then!
DIY 1GHz* Active Probe for Under 20$**: 5 Steps (with Pictures) there are still some new designs coming out.
DIY 1GHz* Active Probe for Under 20$**: 5 Steps (with Pictures) there are still some new designs coming out.
Virtually all of Jim's lab was used we had access to the military surplus dump in Taunton MA and blank MIT purchase orders. 😀 Then there was Eli's in Somerville.
Oh man, that would have been amazing!!!
Having access to Bell's used stuff would also be amazing. So many schools and hobbyists / small businesses could really use that stuff.
-Chris
It was to die for, circa 1970 literally hangars full of stuff. It's where all the folk lore started about folks reassembling Nike missiles, etc. IIRC someone found a pure platinum ingot inside some tool box.
Really doesn't matter if it's true, still paints a wildly entertaining picture. 🙂
Yes pretty much anything from Jim is a treasure trove for designers. You can't avoid learning something from every read.
Jan
OTOH, one of Scott's AD4817's and the ADI eval board with a +/-5V Silentswitcher will fix it too. Much cheaper ;-)
Jan
well Jim used an EL2004 which is an older version of similar?
Edit: that's a lot of performance for a £5 (in singles) 8-leg!
Edit: that's a lot of performance for a £5 (in singles) 8-leg!
Last edited:
I was thinking distortion in a spectrum analyzer context.
As the spectrum analyzer is basically a narrow band pass filter tracking the oscillator, or vice versa, the distortion (or, in specan parlance, spectral purity) is not of prime importance.
Right?
Jan
As the spectrum analyzer is basically a narrow band pass filter tracking the oscillator, or vice versa, the distortion (or, in specan parlance, spectral purity) is not of prime importance.
Right?
Jan
Well, after the filter, all energy is counted for that bin. So some spectral purity is required and will count towards the noise floor.
-Chris
-Chris
Yes but the narrow band filter (down to 1Hz in the R&S) will block the harmonics, right?
Jan
Jan
If it is a multiple conversion swept LO analyzer the 1Hz would be on the IF and the harmonics from the mixer still show up since they are all converted down to the IF frequency. A 20Hz to 100MHz SA does not have an oscillator that goes down to 20Hz.
Last edited:
The only SA (signal analyser) with a 1 Hz filter I know of is the HP 3580A. It's not very speedy, being analogue and all. I wish that the "adaptive sweep" had carried over to later models. It probably did but is buried in a sub-menu somewhere.
-Chris
-Chris
I think I was mixing up a vector network analyzer sweeping a bode diagram and a spectrum analyzer that looks for spectral lines in a signal. Duhh.
Jan
Jan
There is commonality between a VNA and a Spectrum Analyzer. They both have tuned receivers (real or synthetic). However not many VNA's are set up for spectrum analysis. Some SA's have tracking generators but no phase info.
This preamp has 'AD4817' written all over it. Some of the data sheet values, and the option for 500Gohm input Z are identical to the AD4817:
High-Z Spectrum Analyzer Amplifier, 1MOhm, 4pF, FETAMP1 | eBay
For that money, I can build one myself 🙂
And I can build in some gain.
Jan
High-Z Spectrum Analyzer Amplifier, 1MOhm, 4pF, FETAMP1 | eBay
For that money, I can build one myself 🙂
And I can build in some gain.
Jan
Last edited:
- Status
- Not open for further replies.