Hi Z probe for 50 ohm spectrum analyzer

[wd5jfr]

Has anyone found a good reasonably priced Asian probe.
Here's how to build one but I'd rather find a solution versus a DIY project.
https://www.edn.com/high-impedance-fet-probe-extends-rf-spectrum-analyzers-usable-range/
Thanks
Hank

[joeqsmith]

I made something like this.  There were a few places selling them at the time for $500 or so USD.   A few links that you may find of interest:

https://www.ebay.com/itm/High-Impedance-Buffer-Amplifier-1MOhm-FETAMP1-Similar-to-Tektronix-TCA-1MEG-/260750545356

https://www.eevblog.com/forum/projects/1meg-to-50ohm-trans-impedance-amplifier-for-general-instrumentation-use/25/

https://www.eevblog.com/forum/projects/high-z-wideband-buffer-amp-for-50-ohm-cro-inputs/

[Kean]

Maybe this is suitable for your application.  It is somewhere between DIY and a packaged solution.
"RF Active Probe 0.1-1500 MHz-1.5 GHz analyzer oscilloscope" from ebay seller 60dbmco in Ukraine
https://www.ebay.com/itm/332393676082

[joeqsmith]

Maybe this is suitable for your application.  It is somewhere between DIY and a packaged solution.
"RF Active Probe 0.1-1500 MHz-1.5 GHz analyzer oscilloscope" from ebay seller 60dbmco in Ukraine
https://www.ebay.com/itm/332393676082

Nice find.  Have you tried one to see how well it performs?

[Kean]

Maybe this is suitable for your application.  It is somewhere between DIY and a packaged solution.
"RF Active Probe 0.1-1500 MHz-1.5 GHz analyzer oscilloscope" from ebay seller 60dbmco in Ukraine
https://www.ebay.com/itm/332393676082

Nice find.  Have you tried one to see how well it performs?

Nope.  I've only had it sitting on the bench for 12 months... so maybe soon...
It is cheap enough to get one and try it out.  The delivery time is the biggest issue right now.

[Kean]

Apparently not that great - but still useful if you stay aware of its limitations
https://www.eevblog.com/forum/rf-microwave/response-of-cheap-rf-active-probe-from-ebay/

[Kean]

So I should be sleeping, but did a little more searching around this forum.  The topic has come up several times before, with Joe frequently appearing.

A couple of options from Mathews Engineering
https://www.mathews-engineering.com/store/p20/Active_FET_Probe%2C_1000_MHz.html
https://www.mathews-engineering.com/store/p1/High_Impedance_Buffer_Amplifier.html

Another DIY implementation of the earlier active probe https://www.instructables.com/id/DIY-1GHz-Active-Probe-for-Under-20/

If you want something that will work reasonably well out of the box and well specified that is "affordable", check Auburn Tech P-20A or P-20B.  Note that these are passive not active, so they may not be considered Hi-Z depending on your application.
http://www.auburntec.com/

This is another DIY passive RF probe design https://emcesd.com/1ghzprob.htm

Or go crazy here https://ggb.com/

[tautech]

Has anyone found a good reasonably priced Asian probe.
Here's how to build one but I'd rather find a solution versus a DIY project.
https://www.edn.com/high-impedance-fet-probe-extends-rf-spectrum-analyzers-usable-range/
Thanks
Hank

It might help if we knew what SA you were planning to use it with. 

[joeqsmith]

   12 months isn't too long to procrastinate.   I keep meaning to run that trash picked Fluke 77 but the lab is in need of some major cleaning.  I've been saying maybe next weekend for a few months. 

OK, I checked the link and you're right, it's not flat.  Some of that may be the probing and at $12ish, it may be worth a look.   

I was looking to get something DC coupled with close to 100MHz.  Once I get beyond this, I start using resistive probes.  Shown was my final attempt which with a 1dB of gain, still isn't all that flat. 

[Kean]

It might help if we knew what SA you were planning to use it with. 

I wouldn't think that would be as important as knowing more about the frequency range and type of circuits to be probed.

[wd5jfr]

I have a Siglent SSA 3021X hacked and and HP 8935 both 50 ohms.
Filter sweeps at HF (IF filters) and maybe later at 6 meters

[Kean]

What is your definition of "reasonably priced"?
I've not come really across anything between the ebay $10 device and the $200+ ones I listed above.

[wd5jfr]

Thanks for the Ebay link.  I got an Ukrainian RLB about a year ago and started to compare it to my Eagle RLB but got distracted.  I will wait a couple of days and if there's no serious negative comment on the Ukrainian one I'll get it. The price is right, $19.00  as is the DIY part.  By the time it gets here I might get distracted again (easy at 79) and it can join the it's country cousin on the shelf.  Looks like I can run it with a couple of lithiums in series.
Hank

[tautech]

I have a Siglent SSA 3021X hacked and and HP 8935 both 50 ohms.
Filter sweeps at HF (IF filters) and maybe later at 6 meters

OK, the SSA has a 50V max input with an inbuilt DC block.
For additional sensitivity you also have a preamp you can engage and if getting near the limits of what it can handle audible and visual warnings are given so to not damage the input circuitry.

Still, be careful with it. 

[Kean]

I will wait a couple of days and if there's no serious negative comment on the Ukrainian one I'll get it.

Read that other topic I linked in reply #5 which shows some measurements with it.

The active probe is AC coupled at input and output, but as tautech points out you always want to be careful with what you feed into your SA.

By the time it gets here I might get distracted again (easy at 79) and it can join the it's country cousin on the shelf.

Easy at any age.  I'm in my early 50's now, but I remember having the same issue since my 20's.

[wd5jfr]

I'll use the builtin tracking generator.
I have a quite a few lithium button cells  but that would be a awkward fit for a probe case.  I wonder if there cylindrical lithiums about the diameter of a pencil.  Perhaps some knows.

[wd5jfr]

I just looked at Insatman's post linked by Kean and I'm ready to buy but maybe something more appropriate will show up in the next couple of days.  Or who knows I may lose the urge!
Hank

[Kean]

I wonder if there cylindrical lithiums about the diameter of a pencil.  Perhaps some knows.

If you mean 3.7V lithium ion rechargeable, then the AAA size aka 10440 is reasonably common.
If you want a 3V lithium primary, then there are very small ones (3-5mm diameter) used for fishing lures like CR425 or CR435.

I just looked at Insatman's post linked by Kean and I'm ready to buy but maybe something more appropriate will show up in the next couple of days.  Or who knows I may lose the urge!
Hank

I think for your use case it should be quite suitable.  In that topic they were testing it to compare against the sellers claimed specifications and it certainly doesn't meet those.  Nor would I ever expect it to based on the PCB layout!

[wd5jfr]

Man am I ever behind times, never heard of lit lures or floats.  I grew up on the Red Deer river and spent much of my time fishing and hunting till girls became the game.  Wow it would have been interesting to see what kind of luck a lighted lure would bring.
But getting back to reality, the task at hand, I wonder if that probe might work with one CR435 with the VR bypassed. I guess I'll find out if I buy one.

[tautech]

Wow it would have been interesting to see what kind of luck a lighted lure would bring.

You never used lumo lures/flys ? 

[wd5jfr]

In the late 1940s and early 50s, we had Devil Bait red and white was best and I can't remember the name of the plug. There was a Ruby Eye.  That was it, too poor to have anything else.

[joeqsmith]

Just for completeness, shown sweeping the homemade buffer to 1GHz.   Not a real good test setup but gets us in the ballpark.   Peaks up to 1.5 dB and starts to drop like a rock above 200MHz.  -3dB is around 300MHz.   

Really, for the 50MHz high end mentioned and sweeping filters I would have just went with that little NanoVNA.  I've played a bit with them and even for narrow band work, they seem pretty decent depending on how low a noise floor you need.   Worse case, a costly repair is limited to the time it takes to get a new one shipped and $50.   

[tautech]

In the late 1940s and early 50s, we had Devil Bait red and white was best and I can't remember the name of the plug. There was a Ruby Eye.  That was it, too poor to have anything else.

Before I was even a twinkle in my fathers eye ! 

Since then there are some nice lumo products we can tie into lures which you can charge with a torch or better an old camera flash unit which works much better and the glow last much longer. A flash unit is a must for the serious night fisherman.

[wd5jfr]

I thought about a nano but then I have to set it up, learn, and waste a bunch of time.
With my Siglent SSA 3021X  good to 50VDC  and a probe running at 5vdc it should be plug and play with no pray and pay.
That's a busy screen, pretty nice, which model is it?
Hank

[Kosmic]

Not really HighZ but the Tektronix P6056 goes to 3.5Ghz. It's a passive 10x 500\$\Omega\$ probe. Output is 50\$\Omega\$ so you can use it with a spectrum analyzer. Got one for 20$ on ebay the other day.

http://w140.com/tekwiki/wiki/P6056