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DC coupled 2.7 GHz Active Probe Project - Now Available!

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joeqsmith:
Looks like you have done a nice job with it.   Any idea on the selling cost yet?   With the 50 ohm drive, I can see using it for applications outside of a scope probe.   You mentioned using it with your VNA.  There was a thread some time back about someone wanting to make a buffer to drive their 50 ohm inputs.  I had posted a commercial one and some of my own but they are capped at a bit over 100MHz.   

If you are looking for people to evaluate them, I may be able to help as well.

Thanks for posting and keep us updated.   

lasmux:
Hi Joe,
I've appreciated a lot of your forum posts on VNAs this past year I've been working on this project!

Currently I'm aiming for around £150 for the 1GHz version, and £180 for the 2GHz version on ebay. I've not gone through my BOM thoroughly yet though, so things may shift, potentially down. I can do it a bit cheaper for the forumites as 12% ebay fees wouldn't apply, I just need to figure out how to set up a store correctly on my website  |O.

And yeah, I think some kind of sensor preamp, or an input buffer for a VNA are very valid use cases.

joeqsmith:
Very reasonable.   Just looking at used prices for the LeCroy 2.5GHz single ended HFP2500, about $400 - $500 USD.   Even then, you don't know if they work or how they were treated.  It's a total crap shoot.   

For the most part, when looking at single ended low voltage signals, I tend to stay with resistive dividers.  Cheap and minimalish loading.    I have a few LeCroy 4ish GHz diff probes for my scope.   I thought about trying to build a DC -  >>GHz differential probe for logic signals but at the time, I wasn't able to source popcorn parts that would do it.   I haven't checked in several years and would guess there are much higher performance parts available today.   

Having that DC-100MHz buffer around has been helpful.  I've used it to drive my spectrum analyzers as well.  Nice thing I can use what ever 1X // 10X  probe with it.  Downside, 100MHz.   

Thanks.  Yes, I've had a lot of fun playing with these low cost VNAs.  I'm very impressed with what they have been able to achieve in such a small package.  Especially with that LiteVNA and Dislords firmware.   Hopefully your scope probes will be as successful.   

KungFuJosh:

--- Quote from: lasmux on July 26, 2023, 07:08:30 pm ---I just need to figure out how to set up a store correctly on my website 

--- End quote ---

You already have woocommerce installed, you just need to make sure it's setup correctly, and setup the products, payments, and shipping options. I can help in exchange for a couple 2G probes. 😉

lasmux:

--- Quote from: joeqsmith on July 26, 2023, 08:28:00 pm ---Very reasonable.   Just looking at used prices for the LeCroy 2.5GHz single ended HFP2500, about $400 - $500 USD.   Even then, you don't know if they work or how they were treated.  It's a total crap shoot.   
For the most part, when looking at single ended low voltage signals, I tend to stay with resistive dividers.  Cheap and minimalish loading.    I have a few LeCroy 4ish GHz diff probes for my scope.   I thought about trying to build a DC -  >>GHz differential probe for logic signals but at the time, I wasn't able to source popcorn parts that would do it.   I haven't checked in several years and would guess there are much higher performance parts available today.   
Having that DC-100MHz buffer around has been helpful.  I've used it to drive my spectrum analyzers as well.  Nice thing I can use what ever 1X // 10X  probe with it.  Downside, 100MHz.   
Thanks.  Yes, I've had a lot of fun playing with these low cost VNAs.  I'm very impressed with what they have been able to achieve in such a small package.  Especially with that LiteVNA and Dislords firmware.   Hopefully your scope probes will be as successful.   

--- End quote ---
I'm glad you think the pricing is reasonable. In general, probes are in a weird space in terms of pricing. They don't feel like they should be so expensive, but they are quite difficult to get right, and contain expensive and low volume custom components. That said, I feel commercial active probes are unreasonably expensive. High speed passive probes aren't much better.

Yeah, DIY Zo probes are definitely a reasonable (and dirt cheap) alternative. That said, their linearity can be a bit questionable, and I think if you measured the input impedance on one of them (I've not done this), I suspect it may be a bit variable. The inductance of the ground connection really screws up everything, which is why the expensive active probes often provide ground blade/leaf connections. In my probe I can counter the issue with a resistive ground connection. I don't think that would work in a Zo probe.

I'll send you a PM tomorrow regarding sending you a probe for you to have a play with. Thanks for offering to help out :)


--- Quote from: KungFuJosh on July 26, 2023, 10:08:12 pm ---
--- Quote from: lasmux on July 26, 2023, 07:08:30 pm ---I just need to figure out how to set up a store correctly on my website 

--- End quote ---
You already have woocommerce installed, you just need to make sure it's setup correctly, and setup the products, payments, and shipping options. I can help in exchange for a couple 2G probes. 😉

--- End quote ---
I really hated setting up that website lol. The woocommerce plugin is just rammed full of features that make figuring out how to do something simple, very difficult. I really just need to watch a few tutorials on youtube and I'm sure it'll all be easy.

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