Category: Rf current meter

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Rf current meter

05.05.2021 Rf current meter

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They accurately measure actual RF currents flowing in antenna elements, radials, ground wires, and on the outside of coax feed-lines. Use them to study and optimize your antennas for peak performance! They're also great for tracking down RFI-causing currents on household wiring and cables. Their sense coil simply snaps over wires and cables for fast measurements.

Results appear directly on their easy-to-read meter. You may select from five ranges to measure actual RF-current from 30 mA to 3 A full-scale. A sixth range has a variable sensitivity control for quick, fast checks. At maximum sensitivity, RF currents of 1 mA or less will yield a usable meter deflection. This function is especially useful for tracking RFI pickup on household wiring and cables. Do you wonder where that RFI is coming from? Would you like to map your antenna's efficiency?

Was this review helpful?It takes a special meter to measure current accurately in the presence of strong electric fields, and to not disturb low-capacitance high impedance systems. The meter described below is suitable for measuring RF current accurately in high voltage applications, such as short antennas.

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It is also accurate in normal applications. Another current meter project link not suitable for mobile antenna measurements, however! The meter is constructed with a uA all plastic case meter. The meter scale is plastic. The movement and all metallic areas are small.

The lack of large metallic components minimizes stray capacitance added to the circuit under test by the proximity of the current meter. Low capacitance ensures the meter has the least possible effect on the circuit being tested. This meter has a 1. Just behind the meter is a calibration pot and all the circuitry. The toroid and circuitry is hot-melt glued to the meter with only the screwdriver calibration pot exposed.

I did not add a Faraday shield because the shield would increase the capacitance. Since this entire meter floats above ground there is no need for a shield. Balance is not critical when the load is physically very small and floats from ground because common mode impedance is very high. The meter has a low threshold Schottky diode detector, a series resistor for calibration, and standard.

T1 is a current transformer. I used a powdered iron T core. When the single turn primary a whip or mast has 1 ampere, the secondary will have. R1 flattens the response and limits the voltage. It turned out that ohms gave the flattest response from 1. With ohms we have.

MFJ 854 RF Current Meters MFJ-854

The peak dc voltage is 1. The low current and high voltage improves detector linearity. Dissipation in R1 is.

There is a single 16 Teflon wire running between the center pins. Note the numbers "2" and "B3" on the meters. My elements and meters have calibration charts that correct for linearity errors in tracking and readings.

FS accuracy is not required in comparison measurements, since the meter references against itself. Linearity within a few percent is important.This R. It is often useful to be able take measurements of RF current in the antenna system and the primary need that I had was to confirm the balanced RF current in each leg of the ladder line used on my multiband dipole.

A balanced antenna system requires that each half of the dipole including each side of the transmission line be a near mirror image and should also avoid nearby trees and structures in particular metallic structures. When the system is balanced the transmission line will have equal, but opposite current flowing in each line.

This will cancel out any radiation or reception on the transmission line. My test to confirm a balanced antenna system was to simple measure the RF current in each leg of the transmission line as it leaves the Z-match tuner. Accurate determination of the current while desired is not entirely necessary providing the measurement is consistent for each transmission line leg.

Tune for max brightness: LED RF current indicator for end-fed antennas

Top view showing current selection switch Internal view of the RF current meter. Front view of the R.

Clamp-on RF Current Meter

Internal view of the RF current meter. Page last revised 10 October This site has been designed to cater for x resolution. Site is best viewed with Internet Explorer 5.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Amateur Radio Stack Exchange is a question and answer site for amateur radio enthusiasts.

rf current meter

It only takes a minute to sign up. Is it possible to measure RF voltages with a multimeter? 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? 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.

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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.

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If you also have an RF signal generator of known power check eBaythen you can also calibrate your test equipment to give quantitative measurements. Sign up to join this community. The best answers are voted up and rise to the top.Also in Japanese. Introduction 2. Circuit Description 3. Construction 4. If some of the RF current from a transmitter flows into mains wiring, this can increase the chance of breakthrough problems in nearby TV, video or audio equipment etc.

A clamp-on RF ammeter allows this current to be measured, so that steps can be taken to minimize it.

rf current meter

For RFI investigations, you can also clip this meter on to coaxial cables, rotator cables and other wiring in your shack, to find out where the RF currents are flowing, and how big they are. You can also use this tool for measuring currents in wires and radials. This is a large split ferrite bead with a 13mm diameter hole and a hinged plastic carrier which can be clipped around a cable.

Although intended to be clipped on and left, with care it can be opened and closed repeatedly. It is intended for suppression of computer interference but can also be used as a wide-band current transformer. This type of split bead offers better coupling than a ring core and is usable from below kHz to over 50MHz. What's needed for reasonable coupling is a split bead where the length of the hole is about 2. There are many sources for these cores.

Almost any generic 'flea market' split ferrite bead should be OK, if the centre aperture is large enough to take both the secondary winding and the cable you want to test. In the circuit in Fig 2 abovea turn secondary is wound on one half of the core and terminated by a ohm load formed by R1 and R2 in parallel. Note that more turns on the secondary would give less secondary current.

For primary currents up to 1A the power rating of the ohm secondary load should be 1W.

rf current meter

Clipping the current transformer onto a cable adds a small series impedance which in theory is 0. This gives a DC output about 2. On the mA range, the forward voltage drop of the diodes is significant, so that the minimum current which can be measured is 30mA and an extra scale should be marked on the meter as in Fig 3 below.The RF Ammeter series encompasses both single and dual scale models to provide RF current measurement over the range from 5 Amperes full scale to Amperes full scale.

These current ranges follow the FCC rules for linear scale meters. The standard interconnecting coaxial cable length is six feet. Longer coaxial cable lengths and double shielded coaxial cable are optionally available for any TCA system for high RF field conditions and for RF radiation exposure reduction.

Every RF Ammeter is calibrated and sealed at the Delta laboratory.

rf current meter

The flat frequency response and compensated temperature characteristics of the ammeter assure accurate current measurement. The calibration of the RF Ammeter is warranted for a period of one year under normal use conditions. Excluding damage due to lightning, Delta will recheck the calibration and make repairs, if necessary, without charge during this period. These services are available at a nominal charge at any time thereafter.

The system consists of a current transformer, a six foot coaxial cable, and a meter enclosure housing the meter movement, rectifier circuitry, and external output connector. The external output can be used in conjunction with a series 10K Ohm variable resistor connected to a second meter to provide for remote metering. The external output may also be used to drive automatic logging, remote control, or ATS equipment.

A two-position toggle switch mounted on the front of the meter box turns the circuit on and off, and when switched off, protects the rectifier circuit against lightning damage. A spring-loaded, momentary contact toggle switch is optionally available to prevent leaving the ammeter in the on position. The transformer provides a 3. The transformer provides a 6.

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The ammeter uses a toroidal current transformer to obtain a sample voltage proportional to the RF current flowing in a conductor. This voltage sample is connected by a 50 ohm coaxial cable to a temperature compensated rectifier circuit. This circuit converts the RF voltage to a DC voltage which is applied to a linear scale meter, calibrated in RF Amperes, for display of current magnitude.

The ammeter provides a DC output voltage to drive a remote indication instrument which may be calibrated against the primary meter and used for remote indication. The ammeter also includes relays to enable remote control of the meter operation. These transformer voltage ratings are the RMS equivalent of the peak modulation voltage.

The rectifier circuit provides a 50 ohm load resistor for proper termination. This circuit converts the RF voltage sample to a DC voltage for meter display. The rectifier filter circuit is designed to follow the modulation envelope accurately. The meter ballistics average the audio content and thus, the meter indicates the RF carrier current.

The meter provides a stable reading independent of modulation, but may deflect slightly under high modulation conditions due to carrier shift.There are two things that I wanted to do which would be made easy with a current meter Both are related to the unusual nature of the antenna here at AC0C.

With the high cost of ferrites, placing them with the aid of a current meter is very helpful in that you can compare the before no ferrite and after with ferrites attached - and know that you have addressed the current problem on a given bit of line.

This is typically at the center of a dipole element. However, the center may or may not be the actual high-current point for the element depending on the frequency. My EZNEC models can indicate where the current peaks are - and by looking along these lines manually - comparing them with readings taken from the driven element, I can make current checks even in non-standard location of the array.

Due to the voltage-doubler nature of the circuit, it's capable of exceptional sensitivity. The meter was calibrated for full-scale 1A on the higher scale, but I have left the lower scale set on a very high sensitivity setting which I find very handy for the common mode checking.

Once parts were in hand, construction was very easy and took perhaps an hour. I had a uA meter in the junk box along with the other parts needed and orienting them on the back-side of the meter was really the most time consuming aspect. The switch is held in position with hot-glue. And a bit of hot glue is applied to the meter terminations as a safety precaution - just in case I were to brush the meter up against something carrying high levels of current.

Selection of the toroid used was based on what would physically fit around the RG sized cable and could be easily opened and closed. The rubber band shown in the picture makes for a very convenient closing mechanism - and in a lot of applications, I simply hold the toroid closed with my finger pressure which makes moving the meter along a wire - and moving from cable to cable - very quick and easy.

Checking common mode surface current on coax and control cables up in the attic antennas. Otherwise, it seemed to me, that ferrite placement was more of a guess than a science. The meter described below accomplishes these two tasks very nicely.

Wraps around the toroid were made with wire-wrap type wire, 30 Gage. Home Page. Prior Antennas.


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