High-Z Active RF/AF Probe with AGC. Making something good even better.
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- čas přidán 21. 06. 2022
- Only $5 for 10 PCBs and every new member get $5 bonus. + Express 24 hour / 48 hour service on www.pcbway.com/
After my first attempt at building an active high-impedance RF/AF probe, many of you asked about adding an AGC function, so I went looking for a solution. I think I found it.
The result was quite surprising. Not only is it extremely sensitive, but the use of a commercially available preamp module with AGC makes this a really simple solution to build. The PCB files that I have made available through the PCBWay Share page also makes it easy for anyone to order boards and build their own.
CORRECTION: I mention that the preamp unit is a MAX4066. Obviously this is incorrect. It's a MAX9814 unit.
SCHEMATIC: her's the link to the schematic, in the event that it is not clear from the video: drive.google.com/file/d/1YHeX...
The Gerber files are available on the PCBWay website in the share section, so feel free to order your own boards and try out this handy gadget. Here is the link:
www.pcbway.com/project/sharep...
You can now support the channel:
/ mcaldeira
paypal.me/macaldeira
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Very, very cool! The PCB looks great and the integration of the AGC turns it into a super probe. Hope this finds you doing well. All the best. Don
Thank’s Don. Great idea to begin with 😊
The preamp board will be incorporated into my next Qrp radio build, thanks for the presentation.
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Very nice! I will keep this in mind for my next tool project once I get the two I'm working on now off my workbench. As for your wand's wider than expected b/w, I'm not too surprised by that. When I updated my Rigol DS-1054z scope's firmware I was expecting the b/w to go from 50 to 100MHz but tests showed the scope will read signals up to 500MHz, albeit with some attenuation, as long as you use high quality probes. Cheap probes will cause the greatest drop in amplitude at high frequencies, a fact that Rigol no doubt understood all too well. It would appear then that some chip amps can go well beyond their ratings as long as your circuit can sustain a large drop in output level.
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Great tool. I made one using your design and it looks and works great! Many thanks
Pleasure
I have been working building the mr Carlson probe. It is a non contact probe. The very simple sulotion he has when it comes to gain control is interesting and I want to make som test of how it works. I supose that it is no HIFI but who cares if it works. Yours is a beautiful version and using a MAX amp is damn smart. Keep up the good work.
Thanks 😊
Outstanding! Thank you for the clear explanation.
pleasure
Very good ideas.
I suppose if you look at it from a very basic level the Maxim IC is made of the same material as higher bandwidth components. Just because they didn't spec it for higher frequencies doesn't always mean it can't achieve. Great idea to experiment with where you put the board, often the best inventions are discovered by accident. Another great video, thanks again.
pleasure
Looking at the datasheet for the MAX9814, it has flat gain out to beyond 20kHz, so even if it rolls off at 12dB/decade past that, you still have usable gain out past 2MHz, especially if you're starting at 60dB.
Great work Manuel. That’s a very useful tool. I really must get around to making a probe for my Velleman kit. Cheers Graham
Yes, they’re very useful.
Manuel, Maxim and Analog Devices, are the "BIG ENABLERS" at analog linear electronic world, every device designed by these firms meets the requirements, and exceed them to provide. So it is common that the gain /bandwidth ratio reaches those IF frecuencies. Years a go a common audio amplifier IC, TDA 2030, used to have a G/Bw several hundreds of Khz, so that could oscillate easily at those frecuencies & destroy it, so selecting(or changing...) some decoupling capacitors at the Aplication Note, was "risky business",... Look I've got more treble.. Yeah now you've got smoke😈. Other ways it looks great, very practical, it is great tool for the shop👍👍👋👋👋again you did it Manuel😀😀
Thanks 😊
I believe amplifying before the detector works better since you will have an larger signal that overcomes the 1n34 diode drop.
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Very clever solution ! Would be fun to incoparate a small bluetooth transmitter in the probe so you do not need a external amp and speaker?
Thanx again for your great video's, always entertaining and usefull !
Best regards Eric
Thanks Eric
Eine sehr interessante gute Idee. Hab mir gleich zwei bestellt.
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What I would like to know is what happens if you short out (I mean remove completely) the original detection section. Then you can say if the detection takes place in your new microphone amp, and it could even give you more gain without the original detection. Detection is no more that getting rid of the negative flank of the carrier, so that the positive part fluctuates from the modulation, and that could easily be done by some diode or transistor inside in the front end of the added amp.
That’s a good idea.
If you purchase *LM386-4,* that version will deliver *1 Watt.* Most people ignore this and end up with a -1 or -2
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Interesting. Thank you.
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You should also examine your explenation of the connections to your probe to connect with the Vellmann unit as your basic source of this newer project. Some of us are left alone as you swerve off into a new world.
@bjarvis435
As the only one complaining, you must be the issue.
Fault Finding 101...
Operator error.
Saludos M. Caldira. Solo mencionar que el C16 que aparece en el PCB, no esta en el esquema del amplificador, se entiende va conectado a VCC y es de 100uF. Un seguidor
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Electronics old and new your utube video are cool
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Once again another fine project.. Thank You for your development work. I was about to order the PCB's from PCBWay but at $52.88 for 5 boards - in which I really only need 1 - plus the Canadian to US exchange rate , it comes to $75. WAY too Much!
Is this the normal pricing or why so high ?
I see you have offered to send gerbers to others, but first off, as a newbie, I would be unsure if I would make all the right choices for options. I guess I might need info outside of the gerbers? Also it sounds like you would get no rewards which I think you deserve. So I am at a bit of a loss but thanks for putting your project out there anyways. Doug
I believe the dual board option that I designed makes it far more expensive than it needs to be. You are welcome to download the Gerbers from the share page and use it as you wish. I don’t get a commission from them for every board sold, and that’s not my goal anyway. Good luck.
Hello.. love the concept and design.. What are the dimensions of the probe PCB..?
So cool! One thing I was wondering about with the placement of the AGC bolt on, is if the change in placement within your circuit impacts the workable bandwidth. In other words, is there a difference in the cut-off frequency or or range that you can hear the signal (albeit perhaps, at less amplification across the board)?
Not sure as I’ve not tried that. May have a look at that if time allows. Thanks.
I’m not sure. I was just thinking that in radios they place an RF amplifier right up front at the antenna and the automatic volume control downstream. I’m not sure how that compares to what you’re doing if at all.
Thank you so much for sharing this, I just want to know if you are selling a “complete kit” that is ready to assemble right away once I get it from the mail?
I’m afraid I don’t sell kits at all.
So, regarding the behaviour of the AGC module:
Either the MAX9814 just has a way higher bandwith than it is supposed to (unlikely; do you have another module you could measure?), or it is actually seeing AF at its input.
I may have this completely wrong, but could the JFET be working as a demodulator? Unless it is perfectly linear, there will be intermodulation between the carrier and the sidebands, so there could be some AF present at its output.
Could be the JFeT.
Really nice design. I can not find a 2N5457 anywhere reliable. Do you know if a substitute might work? If so any suggestions would be appreciated.
I think the 2n5458 will be fine. Maybe a mpf102 or even the J310?
B.T.W not a newbie - I am a qualified electrician, just want to play a bit, an I need to repair my Stagesound monitor speaker -this obviously with my training in semiconductors in the early days with diodes makes sense to fault find it. Any suggestions ?
I need a JFET (Hi Z) unity gain buffer probe for my oscilloscope, as my scope loads some circuits (RF preamps, oscillators, etc.) somewhat.
Do you have an idea for that?
Probably best to just get a 100:1 probe. The normal 10:1 gives you 10Meg of input resistance, so the 100:1 should do the trick.
1. Why is the PCB manufacturing so expensive?
2. Which program you used for the design?
3. Can you post an modified design with TWO of your probes side by side?. (It's only 50mm wide)
Manuel Absolutely beautiful job, When you do such brilliant work you should follow up by branding it on your tube like they do on Cuban cigars tubes. I can see it now your channel logo and model number "brilliant 01".
I’d have to roll on the label on my naked legs. 😊
@@electronicsoldandnew Brilliant come back, you need to take your guitar a three-legged stool down to the local bistro Strum a few notes and tell a few jokes.
I’d starve 😊
@@electronicsoldandnew, watch a concert video of Louisiana-based blues-rocker Tab Benoit; he's not only a great singer and guitarist, but he is funny as heck, and tells great stories. He's also a drummer, and so his comedic timing is perfect!
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Thank you so much for this. I was wondering if you could point me in the direction of a suitable switch which is compatible with the footprint on this PCB. Thanks!
I’m afraid I can’t find the reference to that switch and am away from Madeira at the moment. It is a sub-miniature and is right angles toggle.
@@electronicsoldandnew Thanks for the prompt reply! I'll see if I can find something that will do the job. All the best!
I am interested in the scope probe dissecting:
1. What was the model/bandwidth?
2. Do you have more pictures of that?
3. Is the coax cable the correct type with the very thin nichrome resistive wire?
it should not matter what model it was...since it ends up being just a simple probe with all of the original probe 'circuitry' removed, so ANY old scope probe will work
@@holgers5216 I am not interested in the probe tip, I am Interested in the special coax and asked about it.
The passives were removed from the probe tip and replaced with a straight through connection, but he said it was a x10 probe. However he is only using the probe for the tip and ground connection as stated. The cable from the board to the amp appears to be 2 conductor shielded microphone cable ( see 21:43).
@@materialsguy2002
I understood that the first time.
I am not interested in the probe tip, I am Interested in the UNUSED PART OF THE PROBE.
I am Interested in the special coax and asked about it.
This is absolutely fabulous!
Is there any reason why all the components in the probe can't be in the box and just have leads to test with?
As long as you can fit everything, the layout is up to you 😊
@@electronicsoldandnew Good morning sir! I was wondering If I get the boards from PCB do they also have the parts to populate the boards?
I'm trying to find where I have lost 90 % of the audio volume in my Stryker 955 export radio.
After plugging in unkowingly a slightly shorted to ground speaker for about 6 hrs, the audio was 1st cut in half after smell of burned electric on receive, monitor and volume. I had to run everything wide open to use it another week in the dump truck. One final day though the audio gradually became so low that I could no longer use the radio.
I’m afraid you’ll have to source the components locally. These boards were designed as stand-alone and not linked to be populated automatically. Anyway, for populating the boards, the minimum quantities would be quite high.
@@electronicsoldandnew Ok do you have a parts list available?
I might be quicker to build the guitar amp version it only has 5 or 6 components.
I’m afraid not. All component info is extractable from the video.
Thank you for your effort! Can you tell if it's safe to touch anything with this probe?
That’s a very broad question 😊 The input capacitor voltage rating will determine the max voltage that it will handle.
@@electronicsoldandnew What about AC
Same thing: capacitor voltage rating.
So I was motivated and ordered some boards on PCBway and managed to source all components, but that micro switch offers a challenge
I know. Look on mouser. I think that’s where I bought it.
@@electronicsoldandnew oh thank you, I'll have a look around next time I order from them.
@@electronicsoldandnew And the design works like a charm. I also build the amplifier board into an old speaker but ordered a 9v hinged battery holder for some kind of guitar thingy on aliexpress for easy changing the battery. Many thanks for sharing your design.
My pleasure. 😊
Is it possible to switch off the AGC, to "feel" the gain of a stage?
Not as it’s wired
Can I currently buy one of these probes r the component build up for one ? pcbway currently does not appear to have this item. ?
I don’t sell kits at all. The link for the PCBs from pcbway is in the video description. It’s active. I checked.
Another fine project ! What's next ! Who's that person you mentioned?
Mentioned when?
Chris, at AllTheGearNoIdea czcams.com/video/j6X4rxOwom4/video.html
RestoreOldRadios czcams.com/video/OGrkIC-Mov0/video.html
Manuel, does an outstanding job of bringing it all together here
thanks
You mentioned someones site, but I couldn't make out what you said.
Is there a pcb manufacturer in the U who can sell pcb’s for a range of projects?
Where we can download part list and schematic ? Thanks
It’s in the description
I suspect that the 1mHz signal is passing capacitively through the amp and being detected by the diodes.
could be.
Have you tried this probe on a radio with a 10.7 MHz IF?
Not yet
Maybe AGC preamp works like AM detector
Probably
Can we hear noisy capacitors with this probe ?
Yes, I can. On max gain noisy components become quite obvious
Ok, I hope that in one of your future videos you will take a few seconds to show us how it can be use to detect noisy components.
I was looking for the schematics?
Email me and I’ll send it to you
@@electronicsoldandnew I’ll contact you on Patreon Mahalo
What is the value of electrolytic capacitor C15 ?
Where in the video?
4:29 when you show the PCB. C15 is on the amplifier PCB at the left corner just under the input BAT.
@andreb.3206 : I see it now. It’s 47uF just as supply smoothing.
I supose you could feed one probe into de other.. will it explode? :)
No, it’ll look like a python with a swollen belly for a few days then absorb it completely. Will probably give me double the input impedance 😊
About the RF in the MAX is not strange. A normal amp for audio easy works at 10 to 100 times the max used frequens I bet your gai is not that high at 1MHz as with 20 kHz. It is how I see it.
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I went to PCBWay and wanted to order the boards and PCBWay wanted $52.88 for the 5 board order. Is this what it is supposed to be? I am new to PCBWay and I must be doing something wrong.
I didn’t stick to a simple design and made it two boards in one, so it becomes more expensive. You can simply download the gerber files and see if you can get a cheaper solution.
@@electronicsoldandnew Thank you for the tip. I also found out later that there is a chance that I could have them shipped another way by choosing which shipping method to use. It seems that PCBWay likes to default to a more expensive shipping method. I'm new to having PCBs made and shipped to me and am learning as I go. Thanks again.
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How can I get the BOM?
Only by the schematics shown in the video.
@@electronicsoldandnew Would you or anyone here have a list of components needed for this project?
52 dollars no way
Sorry I meant UK!
What is the use of the dummy resistor switch in this schematic and WHY is it even there - it really confuses your lecture ?
As explained at about the 7 minute mark, I added this to an existing speaker with dummy load incorporated in it. I believe it’s quite clear.
excellent project.
But boards & shipment to Europe make it some 82 USD. Which is what you spend even if you want to build a single one.
Add the components and bits & pieces for the case and you end up with the Rolls Royce of the probes. Utterly nonsense.
So the way to go is build everything with a usual prototype board.
This is a very interesting device. I followed your link above for the "$5 for 10 PCBs", found your design (the PCB) described as "Description W224132ASC32_Gerber_PCB_AF RF Active Probe with AGC
However, maybe it is no longer available for order or I am doing something wrong, at least not for "$5 for 10 PCBs".
1) Cannot download Gerber files. Just get an Error, with no explanation of what the Error is. I did create an account.
2) If I click on order, it does come up with your design but the cost is $52.88. Like everything, the price has went up, in this case very much and this is for just 5 PCBs. Note, this is the least expensive opinion they offer, apparently. If I go through the "PCB Instant Quote" option and use the length and width of your PCB, it does show $5 for 10 PCBs.
Wondering if you know anything about this, or could help here?
Thank you.
I don’t know about the order details, but email me and I’ll send you the gerber files.