Homebrewing a probe for Boonton 92 series RF Voltmeter. Posted: Feb Sat 22, am. I now realize it is different than my 93 series. So, I want to build a probe for the 92EA.
I found a previous thread that refers to a couple of people that have a schematic and parts list. I hope they see this or someone knows them and lets them know I'm looking. The thread is from I got caught by the spam filter, add the usual Htxx and ww thing before the link below.
The fact that it is passive and we can get surface mount parts, it seems like this would be a fairly easy project. I know there is some mechanical fabrication involved. If anyone has a picture, I'd like to see it, I have seen pictures, but none have any leads, so I don't quite understand the build.
Thanks, Mikek. The problem is finding the diodes. Boonton sold matched pairs their part number for about twenty bucks going back 25 years or so I picked up a spare set just to be safe. He had a nice website page that has been offline for several years. I'd suggest going over to QRZ.
It would be good to have it back in circulation again. Just remember the original probes were serialized and calibrated to the instruments they were sold with. For common every day use in a home shop, the loss of accuracy is probably minute enough to be of no concern. The probe cable is designed to be electrically quiet--I'm not sure what could be substituted for the cable, but I imagine used cables are cheap on eBay.
I'd like to know the RMS value of the voltage on my antenna. I have a scope which goes up to V peak-to-peak on the screen I'm not sure about its maximum ratingsbut I'm reluctant to try, because I'm not sure if the measurements of my multimeter are correct, and I wouldn't like to damage my scope. So: is it likely that a simple, common multimeter can measure RF voltages?
Red Wave Radio
I've seen this circuit which suggests that it's not possible and you have to put something in between the RF and the multimeter:. However, they're rectifying the RF voltage, so they in fact measure with the DC input.
My multimeter has an AC input - it's unclear to me if a circuit as this one is still needed in that case. For an ideal meter, sure, it's possible. However, most multimeters are not designed to work at RF.
There are all sorts of problems: what effect does the input capacitance have on the measurement? What's the characteristic impedance of the leads? Most multimeters don't take these things into account because the only AC voltage they are designed to measure is 60 or 50Hz.
The rectifying circuit in your question is a good solution. Note that you don't really need to use coaxial cable: since the output is DC, it hardly matters what kind of cable you use. The "cable" might just be the leads of your multimeter. You can also stick a sensitive analog meter something on the order of microamps directly on a circuit like this and get a decent RF detector. With an ideal rectifier, what you will measure with the meter set to DC is the peak-to-peak voltage of the RF input.
Of course, no matter what diode you use, it will be anything but ideal at RF. There is at least the forward voltage drop of the diode to take into account which can be reduced by using a Schottky or germanium diode. Real diodes also have capacitance, and all the components are going to have some inductances, and these reactances are going to filter the input signal in a way which may or may not be significant for your frequency of interest.
However, if all you care about is a qualitative measurement of the input, a simple diode rectifier is quite sufficient.
It's also worth mentioning because it's not always obvious, but if you have a receiver, that can make a valuable piece of test equipment. If you also have an RF signal generator of known power check eBaythen you can also calibrate your test equipment to give quantitative measurements.Arsenal milled ak
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Measuring RF voltages with a multimeter Ask Question. Asked 5 years, 2 months ago. Active 5 years, 2 months ago.
Viewed 9k times. I've seen this circuit which suggests that it's not possible and you have to put something in between the RF and the multimeter: However, they're rectifying the RF voltage, so they in fact measure with the DC input. Keelan Keelan 3 3 silver badges 15 15 bronze badges. Also, most of the time the RF voltage measurement is made on a "sampled" signal via a coupler.QRZ Forums. Hi, I am looking for suggestions on a decent RF Voltmeter that won't break the bank, but will give me a reasonably accurate reading in the HF frequencies and perhaps higher for IF.
I am trying to kill two birds with one stone here. Frequency is no problem with a counter. So I would like to be able to use the meter in conjunction with the attenutaors to get accurate output levels for aligning radios. ANy thoughts on a goof RF mili voltmeter? It would need to come with the probe, since I want it calibrated. K0OKSMar 12, It has been very reliable. I would advise you don't bother with the millivolt meter for a couple of reasons.
First, virtually ALL the meters you see on the bay are without a probe, and the probes are usually VERY expensive, so you're already into the low end digital generator territory, price wise. Secondly, they at best measure down to 1 millivolt, a long way up the ladder from the 1 or 2 micro-Volt levels of most receivers. These ancient warriors are very stable, and have accurate attenuators. For a couple hundred more you can find a few synthesizer generators lile a BoontonHP or I'd recommend the old venerablebut too often they have nylon gear problems.
I found this A for fifty bucks at a ham fest three years ago. Admittedly, these deals aren't common but they are out there. It requires you look under every rock every day, but didigence pays off. Last edited: Mar 12, KE0ZUMar 12, Lemme check, I might have the meter, but not the probe you want. Message me about it.
AA7QQMar 12, In a lot of old schematics I have seen, For aligning the Receive on a radio they would merely connect a VOM to the speaker terminals on a Radio, then apply a RF source to the antenna input There is so much tolerance as far as parts go, and I wouldnt think that you would need a high amount of accuracy as much as you would want to be able to see the peak reading After all, you are doing an alignment, not trying to design a new circuit where a O-scope would come in handy I like my Boonton 92EA.
It did come with the probes. Its useful for making sure the HP sig gen is accurate.#173 RF Troubleshooting Tips part 1
Many of the mechanical attenuators get sticky. Also good for measuring CM currents on coax with a simple homemade probe.Probe for measuring in the Radio Frequency range built inside an earphone jack, designed to have minimum capacitance and complete shielding.
Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. I used a small sliver of circuit board to hold C1. The turned pin socket was fitted to one end, the capacitor C1 soldered to it and then the resistor and diode leads formed to shape and soldered to the capacitor. It is shown next to the stereo earphone jack in order to see whether it will fit.
Adjust sizes, get a smaller capacitor etc until it does. The socket, capacitor and supporting board will go inside the barrel of the jack. A bit of filing, twisting and pulling will result in the jack coming to pieces. It is composed of a large number of precision formed metal and plastic pieces.
We need just the outer shell and the cover - It is best that the cover of the jack is metal, otherwise the shielding will not be perfect. The body of the probe is made from an old ball point pen. A piece of brass tube was found to serve as a join between the shell of the stereo jack and the ball pen body. The rubber grip from another pen was then slid over the metal to insulate it from accidental contact with circuit parts.Charles kinsey
A molded mono earphone lead was used to get the signal out from the probe. I used teflon tape to insulate the turned pin socket and capacitor, which had to go inside the barrel of the jack. A dab of petroleum jelly kept its bore from filling up as superglue was applied to hold it in position.
A HAM friend of mine measured about 5pf of capacitance for this probe, which is pretty good. In use, a sharp probe is inserted into the turned pin socket. The ground lead is wire wrapped around the barrel of the jack. This is necessary if accurate measurements are to be made in a noisy environment.
I hope this will be of use to the HAMs among us. Reply 8 years ago on Introduction. What kinds of things do you take apart? I find so many signal diodes 1N's typically in trashed electronics I don't bother desoldering them anymore. Besides, they're cheap enough that using a new one in a project is less troublesome than using a damaged scrap bin diode.
Me too :3 I prefer early 90's or late 80's era devices, before everything went surface mount. If you take recent products apart, you'll be quite disappointed at the component yield. You've probably seen few discrete signal diodes because manufacturers cram everything they can into ICs to reduce component counts.
On the other hand, an early 90's handheld four-in-a-row style game I recently took apart lack of backwards current protection fried a LED has 34 discrete transistors in it! Try going through free piles after garage sales or the free section on your local craigslist boards. Whenever I take apart new things I put the boards in the toaster oven or i destroy them. I thought the first picture was a person trying to pull their bike away from a huge cylindrical crusher.
Reply 13 years ago.
Reply 11 years ago on Introduction. It isn't, because the socket at the tip, the series capacitor and the ends of the resistor and diode are held securely inside the tip of the audio jack. You may use hot melt glue to hold them in position. I wrapped it in teflon tape available at plumbing stores and secured it in position using superglue.Any help would be appreciated! I was just looking for relative measurements in any case.
If the homebrew probe could provide functionality, it would suffice. Sent via Deja. Pete Gianakopoulos Chicago, Il. This tracked out many of the non-linearities in the detector diode and allowed the circuit to work from less than 70 mV up to 3 volts.
From the chart, it looked as if it'd measure down to less than 10 mV and for a relative measurement it ought to be fine. Unfortunately, I do not have a scanner, but the circuit is fairly straightforward with easy to get components.
I'd guess using surface mount parts in the detector rf section, you ought to be able to push the upper frequency limit up towards the microwave region. Hi Steve. I used one of these at work, some 36 years ago. I don't think that I'm wrong in saying that the probe was a diode rectifier miniature thermionic tubefollowed by a chopper circuit chops up the resultant low-level DC voltage into AC.
The resultant AC waveform was fed to a high-gain AC amplifer does not suffer from DC driftand fed to a synchronous detector driven by the same 1kHz chopping signal. This gave out a relatively high-level DC voltage, which drove the meter. I 'aquired' the unit but, by then, the probe was faulty you can only drop them so often!
I think that I binned it 'threw it in the trash can', in American - much against my religion! Undoubtedly, I still have the large meter somewhere, and I think that I still have the manual green plastic cover.Cig z 2 3 0 2 b 0 6 1 9 oggetto: appalto di progettazione esecutiva
Rather than trying to fix the probe, it might be better to use modern technology, and construct completely new unit. I've spent a career designing electronic test equipment. In precision equipment, the devil is in the details. Physical circuit layout is often at least as important as the components. And the components are often selected or specially specified. I've been involved with the design of a number of products that you could have the schematic of, and in some cases a detailed layout, and still not be able to produce an instrument with anything like the performance of the real thing.
Sensitivity is often one of the easiest things to achieve. This isn't meant to discourage you from building your own probe, or learning from the way Boonton does it.
And you're likely to find a homebrew one to be very useful for lots of applications. But don't think that you'll necessarily have a probe with overall performance anything like the Boonton. Peter, I would certainly appreciate it if you would email me a copy of the schematic.
Spam Report. Red Wave Radio. Board index Radio construction. You will never be able to build one that will meet the spec's of the mainframe. You will always doubt measurements done with a homebrew probe!!!! I still have the diagram, and if anybody is interested, I can send it out to you. The most expensive parts of the probe are the Hewlett Packard zero bias schottky diodes.An RF probe is a device which allows electronic test equipment to measure radio frequency RF signal in an electronic circuit.
In Reed Gleason and Eric Strid invented the first high frequency wafer probe while working at Tektronix. They later went on to found Cascade Microtech in RF energy may be challenging to measure for one or more reasons, depending on the nature of the circuit to be measured and the measuring equipment at hand. The first kind of difficulty arises when the RF energy to be measured is at a frequency too high for available test equipment, such as a low-bandwidth oscilloscopeto process directly.
Such device will work as a RF rectifier and give a pulsed DC voltage. The second kind of difficulty arises when RF energy has to be measured in a circuit which is sensitive to small changes in its electrical environment. For example, with some oscillator circuits, the presence of an ordinary wire within a few centimeters of the active components may change the amplitude or frequency of oscillations, or even prevent the circuit from oscillating at all. In that case, the signal has to be acquired by a measurement probe which extracts very little energy from the circuit.
This can be achieved by employing very thin conductors, or tiny coils kept at some minimum separation from the active elements of the circuit. In a situation, where circuit loading rather than high frequency is the real problem, a variety of small-geometry, high impedance probes can be used, sometimes including an amplifier to boost the tiny amount of energy extracted from the circuit to a level that allows it to be measured by available high-frequency test equipment.
Coaxial structures with spring-loaded inner and outer conductors can serve as an RF probe for modern communication electronics. Such probes are for instance being used in mass-production, in-line testing of communication electronics such as mobile phone industry.
In such systems, like many other RF circuits, there is a higher requirement of matching probe impedance with that of the DUT. Efficient matching avoids reflection which in turn leads to efficient power transfer.
The second challenge to keep the power transfer efficient, is to keep the insertion loss as low as possible. Optimizing these parameters generally gets more challenging as the frequency increases.
From Wikipedia, the free encyclopedia. History [ edit ] In Reed Gleason and Eric Strid invented the first high frequency wafer probe while working at Tektronix.
It is a very useful test tool in a radio laboratory and usually has a capacitor direct current DC decoupling input that isolates any DC from the resulting measured voltage.
The RF probe may be used to test oscillators, receivers, and transmitters. A class A amplifier or a linear amplifier with a no-signal or quiet DC level at roughly half the DC supply voltage will generate an output that is a DC level with superimposed AC signal measured using an RF probe to isolate the effect of the DC component. For instance, a linear amplifier with a volt V power supply may have a quiet DC output level of about 6 volts direct current VDC.Obd2 scanner misfire data
RF oscillators are circuits that generate RF locally on the receivers where they are referred to as RF local oscillators. In the transmitters, these oscillators are referred to as RF carrier generators. The RF detector can be a simple capacitor input circuit that has a clamping high-frequency diode that acts to short out the negative cycle while allowing the positive portion of the RF cycle to reach the DC measurement circuit.
This results in a DC voltage with an average level that is approximately equal to the peak level of the RF signal. The amplitude modulation AM RF carrier has an average peak level that is proportional to the message. There is a very small passive circuit that uses a wire antenna connected to a simple RF diode as an AM detector, which includes a resistor and a capacitor to shape the result as low-power audio.
With an earphone, the result is a simple receiver with no active parts, and this passive receiver works only when there is a strong AM carrier in the area. Electronic test equipment use different types of RF probes. The oscilloscope displays a periodic waveform on a two-dimensional screen with amplitude on the vertical and timescale on the horizontal axis. There is the high- impedance RF probe used for oscilloscopes that assures the test equipment does not alter the measured signal.
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Oscilloscopes require specialized RF probes that prevent interference by the device itself. View slideshow of images above.
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