Simple test equipment to build
This time we plug in our soldering irons and put together some pieces of basic test equipment. Though inexpensive, the projects described will prove useful in the radio shack. Any one of them can be assembled in an afternoon. They are described in order of complexity, so that the reader can find a project suitable for their expertise.
Field Strength Meter
A field strength meter is perhaps the simplest piece of RF test equipment that can be built. Used for checking transmitters, antenna experimentation, and testing RF oscillators, field strength meters provide an indication of the presence of RF energy. They are not frequency sensitive and are useful where indication of a change in level is more important than the actual strength of the signal indicated.
Figure One below shows a schematic of an RF field strength meter. Like a crystal set, it requires no power source. However, unlike a crystal set, the meter has no tuned circuit. It responds to signals of any frequency.
The meter works by converting any RF signal present at the antenna to a DC voltage. This voltage drives a meter movement to give an indication of relative RF. The meter includes a control to reduce its sensitivity where required.
Because it uses few parts, a printed circuit board is not necessary; components can simply be soldered to one another. However, a box is desirable for operating convenience. The case and aerial from a discarded toy walkie-talkie was used in the prototype (see photograph), though any small plastic case will suffice. The meter movement need not be large; we are only detecting the presence of RF, and not making precise measurements.
A meter from an old radio or tape recorder should work fine. The diodes can be any germanium type; the actual part number is not important. Germanium diodes can be recognised by their 6mm-long clear glass case with two coloured bands towards the cathode end. None of the component values shown are critical; a 50 percent variation would have little effect on circuit operation.
To test the operation of the meter, a transmitter is required to provide a source of RF. Placing the field strength meter's extended antenna near a handheld VHF rig should produce an indication on the meter, assuming that the sensitivity control has been set to maximum. No indication means that the meter is not working. Common construction errors include connecting the diodes or the meter wrongly and using silicon diodes in place of the germanium diodes specified. In this case, the meter will still work, but with reduced sensitivity. The earth wire is optional; when working with low-powered oscillators, it is useful to clip it to ground (of the circuit under test) to ensure a better indication on the meter.
Those without a transmitter can use an RF signal generator or crystal oscillator (such as that described later) for testing purposes. In this case, place the meter's antenna directly on the output terminal to verify operation. However, only attempt this with transistorised circuitry; component ratings and safety considerations make the meter described here unsuitable for poking around valve equipment.
The field strength meter is a useful instrument in its own right, but it can be made more versatile. Modifications include adding an amplifier (for greater sensitivity), including a tuned circuit (so it only detects signals in a particular band), or converting it into an RF wattmeter and dummy load. Circuits for such instruments are found in the standard handbooks.
Below is the circuit of a simple crystal tester. It switches on a light emitting diode (LED) if the crystal is working.
The crystal under test is placed in an oscillator circuit. If it is working, an RF voltage will be present at the collector. This is rectified (converted to DC) and made to drive a transistor switch. Applying current to the base causes current to be drawn through the collector, thus lighting the LED.
If an indication of frequency is required, simply use a general coverage receiver to locate the crystal oscillator's output. Note however that when testing overtone crystals (mostly those above 20 MHz) the output will be on the crystal's fundamental frequency, and not the frequency marked on the crystal's case. Fundamental frequencies are approximately one-third, one-fifth or one-seventh the overtone frequency, depending on the cut of the crystal.
The circuit may be built on a small piece of matrix board and housed in a plastic box. Alternatively, a case made from scrap printed circuit board material may be used. Either a selection of crystal sockets or two leads with crocodile clips will make it easier to test many crystals quickly. The RF choke is ten turns of very thin insulated wire (such as from receiver IF transformers) passed through a cylindrical ferrite bead. Its value does not seem to be particularly critical, and a commercially-available choke could probably be substituted.
The circuit can be tested by connecting a crystal known to work, and checking for any indcation on the LED. A shortwave transistor radio tuned near the crystal's fundamental frequency can be used to verify the oscillator stage's operation. Note however that this circuit may be unreliable for crystals under 3 MHz, and some experimentation with oscillator component values may be required.
The crystal checker also tests ceramic resonators. Other applications include use as a marker generator for homebrew HF receivers (use a 3.58 MHz crystal) and as a test oscillator for aligning equipment.
This project is more complex than the others described earlier. However, when finished, you will have an instrument capable of measuring all but the largest capacitors used in radio circuits. Unlike variable resistors, most variable capacitors are not marked with their values. As well, the markings of capacitors from salvaged equipment often rub off. By being able to measure these unmarked components, this project will prove useful to the constructor, vintage radio enthusiast or antenna experimenter.
The common 555 timer IC forms the heart of the circuit (Figure Three). Its function is to charge the unknown capacitor (Cx) to a fixed voltage. The capacitor is then discharged into the meter circuit. The meter measures the current being drawn through the 47 ohm resistor. The 555 repeats the process several times a second, so that the meter needle remains steady.
The deflection on the meter is directly proportional to the value of the unknown capacitor. This means that the scale is linear, like the voltage and current ranges on an analogue multimeter.
The meter has five ranges, from 100pF to 1uF, selected by a five position two pole switch. In addition, there is a x10 switch for measuring higher values and a divide-by-two facility to allow a better indication on the meter where the capacitor being measured is just above 100, 1000pF, 0.01, 0.1 or 1 uF.
Component values are critical. For best accuracy, it is desirable that the nine resistors wired to the Range switch have a 2% tolerance. If 0A47 diodes are not available, try OA91 or OA95 germanium diodes instead. Construct the meter in a plastic box; one that is about the size of your multimeter but deeper is ideal. The meter movement should as large as your budget allows; you will be using it to indicate exact values. A round 70mm-diameter movement salvaged from a piece of electronic equipment was used in the prototype. The meter you buy will have a scale of 0 to 50 microamps. This scale needs to be converted to read 0 to 100 (ie 20, 40, 60, 80, 100 instead of 10, 20, 30, 40, 50). Use of white correction fluid or small pieces of paper will help here.
The components can be mounted on a piece of matrix board or printed circuit board. Use a socket for the IC should replacement ever be needed. Keep wires short to minimise stray capacitance; stray capacitance reduces accuracy.
Calibrating the completed meter can be done in conjunction with a ready-built capacitance meter. Failing this, a selection of capacitors of known value, as measured on a laboratory meter, could be used. If neither of these options are available, simply buy several capacitors of the same value and use the one which is nearest the average as your standard reference. Use several standards to verify accuracy on all ranges.
To calibrate, disable both the x10 and divide-by-two functions (ie both switches open). Then connect one of your reference capacitors and switch to an appropriate range. Vary the setting of the 47k trimpot until the meter is reading the exact value of the capacitor. Then switch in the divide-by-two function. This should change the reading on the meter. Adjust the 10k trimpot so that the needle shows exactly twice the original reading. For example, if you used a 0.01 uF reference, and the meter read 10 on the 0.1 uF range, it should now read 20. Now switch out the divide-by-two function.
If you are not doing so already, change to a reference with a value equal to one of the ranges (eg 1000pF, 0.01uF, 0.1uF etc). Switch to the range equal to that value (ie the meter reads full-scale (100) when that capacitor is being measured. Switching in the x10 function should cause the meter indication to drop significantly. Adjust the 470 ohm trimpot so that the meter reads 10. Move down one range (eg from 0.01uF to 1000pF). The meter should read 100 again. If it does not, vary the 470 ohm trimpot until it does. That completes the calibration of the capacitance meter. Now try measuring other components to confirm that the measurements are reasonable.
With care, an accuracy of five percent or better should be possible on most ranges.
Most parts for all three projects should be obtainable. Instances where you might have some difficulty include: (a) Meter movement. These are becoming rarer and dearer. Hamfests and junk equipment sale are one source. If this fails you could use a digital meter in place of the analogue meter. Or use your multimeter on a low current setting instead. (b) OA47 diodes. Although not exactly the same germanium diodes as used in crystal sets may be suitable. (c) BC108 transistor. Can be any small signal transistor eg 2N3904 or 2N2222.
Items were chosen for likely usefulness and a satisfaction rating of 4/5 or better.
Hawker, P Amateur Radio Techniques, Seventh Edition, RSGB, 1980
A Guide to Test Equipment
This article appeared in Amateur Radio April 1997 with minor updates since.
[Scott] wrote in to us with his simple, but well done RF signal strength meter. As he points out in his post, sometimes an Arduino is overkill, so a Picaxe 08M was used instead. Apparently this was a refresh of a high school project that he did. Certainly many of us would have liked to go to that high school!
An interesting part of this project is how he used a laser cutter to produce his PCB traces. This was done by applying black paint to the copper on his board and cutting everywhere he didn’t want copper traces. The results were quite good, and should work well when this project is finalized in an enclosure
Check out the video after the break to see this circuit in action. He explains the build in it, but if you just want to see the signal strength lights come on, fast forward to around 2:25.
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Introduction: RF Meter for Multimeter
Hello scientists, makers and people with free time. Let's turn our ordinary digital multimeter into an RF field strength meter (FSM). The FSM we are going to make is a very simple one that we will use to detect the relative RF power being transmitted from an antenna and plot its field. Since I am a licensed amateur radio operator this is designed to be used with HAM radios in mind. It may be possible to do the same for a 802.11 WiFi transmitter but because of the low power of WiFi you may need to amplify the signal before the meter.
Step 1: Part 1: the Meter
- 2 1N60 Diodes
- 1 0.05uF Ceramic Capacitor
- 1 470pF Ceramic Capacitor
- 1 0.01uF Ceramic Capacitor
- 1 50K Potentiometer
- 2 banana plug
- 1 1'-2' Antenna or stiff wire
- 2 1' people of wire 1 Digital MultiMeter
The capacitors can be of close values but the diodes need to be germanium diodes (1N60 in this case) as these have a low voltage drop of about 300mV instead of the usual silicone diode drop of about 700mV.
The potentiometer will allow us to better adjust the sensitivity of the meter as you will see later.
How it works:
RF is an AC wave, as the RF is collected by the antenna it passes through the first capacitor. Capacitors allow the RF (because its AC) to pass through and will block any DC voltage that may exist on the antenna. Next the RF comes into contact with the diodes, these are arranged in a half wave rectifier configuration meaning that all the positive RF voltage will remain and all the negative RF voltage will go to ground. Next we encounter a capacitor again and this will filter and smooth out a bit of our RF voltage turning it into more of a DC voltage. We now get to our pot and this acts as a voltage divider and allows us to control how much voltage gets to our multimeter. Immediately after our pot we encounter one final capacitor that will again filter, smooth out the voltage that is about to head to our multimeter.
Being that this is not a calibrated test equipment the voltage doesn't actually mean that at say 3 feet you are putting 7V on the air but it's more of a relative representation of the RF field you are generating in that area. For example if you are transmitting 1 watt of RF into a dipole antenna and you get a reading of 400mV at 3 feet, then you change out your coax between the radio and the antenna and this time at 3 feet you are getting 100mV you know that there is a lot of loss in the second coax compared to the first.
Step 2: Using the Meter to Plot an Antenna's RF Pattern
For this you will need the following:
- A radio capable of running at least 1 watt. A handheld radio like the Baofeng does really good for this.
- A polar graph (You can generate one here or print the attached PDF)
- Your new FSM
- The antenna you wish to plot
Collecting the numbers:
For this I used my tape measure yagi and my Baofeng radio set at low power. What radio you do use be sure to use it at its lowest power because you will be very close to the antenna and you want to limit the RF that you will be absorbing into your body.
First if the antenna is a omni directional antenna stand far enough away from the antenna that you get about a volt (adjust the sensitivity if you need to). If the antenna is directional/beam antenna you again want to move back till you are reading about 1V on transmit at main lobe. Most multimeters have a MAX function on them. This allows you to take a reading and it will display and hold on the peak voltage that it received.
With the multimeter on MAX voltage and radio and FSM in hand, start transmitting for about 1-2 seconds. Now read and mark down the voltage. Now move around the antenna about 45 degrees from where you started and again transmit for 1-2 seconds and get the voltage from that point. When you move around keep the same distance between the FSM and the feed point of the antenna. Also hold the FSM so that its antenna's broadside is facing the antenna. This because the tips of an antenna don't receive RF and it's only the length of the antenna that does. Repeat this every 45 degrees until you have made it 1/2 way around the antenna.
Step 3: Plotting the Numbers
Now that we have our list of numbers we can use our polar graph and plot the antenna pattern. Attached to this step you will find a printable polar graph paper that you can use. I used http://incompetech.com/graphpaper/polar/ to generate the PDF so if you wish to change the size or details of the paper.
Starting at the front of the antenna I got the following numbers (in Volts):@90° 1.09 @45° 0.411 @0° 0.113 @315° 0 @270° 0
Because the opposite of 315° is 225°, 0° -> 180°, and 45° -> 135°. And because the antenna is left and right symmetrical we can fill out the remaining numbers like so:@225° 0 @180° .113 @135° .411
Now you can technically use these numbers as is and make the chart but the numbers are quite small so lets multiply them all by 10.@90° 10.9 @45° 4.11 @0° 1.13 @315° 0 @270° 0 @225° 0 @180° 1.13 @135° 4.11
Now that's more like it. Numbers big enough to see on paper so let's start plotting. So on the graph paper if you use the attached one you will see going outward from the center 12 rings. The center will be 0 and going outward 1...12. On the outside you will 0° on the right and going round counter clockwise. On my yagi 0° and 180° is the tips of my driven element, 90° is the front of the yagi and 270° is the rear of it (See image). If say you are measuring a dipole then again 0° and 180° will be the tips and 90°,270° will be the broadside.
Now that we are oriented and have our numbers let's finally get to plotting. Starting at 90° for my antenna I am going to put a mark at 10.9 or basically 11 and then continue until I have all my points on the graph. Now that we have all our points plotted we can connect the dots. Since the lines on a polar graph are circular the lines connecting the points will be arcs and not straight lines.
Because we have a sample size of 8 points it's going to give us an acceptable idea of our antenna pattern. More points will give a better accuracy obviously but as you can see this is quite good as it it.
Step 4: Bonus: Testing Coax Quality With Your FSM
Bad for me but good for the reader, I believe that my coax going from my main radio to my main antenna has some water damage. This weekend I started getting reports when talking to friends on 446.5 Mhz that I was not as clear as I once was and I was having issues with receive. When I disconnected the coax from the antenna I seen moisture. Long story short I ordered new coax and it arrived today. So what great timing and practical use of my FSM than to validate my concerns of a bad coax.
Like we did when we were plotting an antenna pattern we set the multimeter to MAX reading and transmit on 1 watt for about 1-2 seconds. First I did this with the suspected bad cable and I got a reading of 22mV. Is that a lot of loss? Well I didn't know until I changed out my coax to the new improved (dry) coax. From the same place at the first reading and using again 1 watt for 1-2 seconds I got my reading of 105mV. Wow no wonder they could not hear me I was hardly putting out any RF before compared to now. I had a quick chat with my friend over the new coax and antenna and when it was mostly static before, now it's basically like talking to him in the same room.
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DIY RF METER: LED IS 100% POWERED BY RF RADIATION USING DETECTOR DIODES
Simple DIY Cell Phone Radiation Detector
This easy to build microwave radiation detector circuit consist of a high brightness LED and nine germanium or 1SS86 detector diodes. They need to be connected correctly. All these components are ready to assemble, simply solder the germanium diodes and LED into a simple microwave radiation testing circuit as shown in the diagram.
On a new LED the long lead is the positive (anode) while the short lead is the negative (cathode). The germanium diode has a line (band) around the end which is the cathode. When correctly wired the LED and the germanium diodes are connected so they both allow current to pass in the same direction, i.e. in the circuit diagram the arrows point in the same direction. In practice this means the LED and germanium diode are joined at the cathode of one and the anode of the other.
How it works and how to use it
When a radio wave passes across a metal object the EM fields cause the charged electrons in the metal to oscillate and this causes small AC currents at the same frequency to be induced into the metal.
When placing a call or texting, the radio waves emitted from the phone pass across the RF detector diode loop and this induces a voltage into the diode loop– if it is close enough — current will light the LED and warn you of potentially dangerous microwave radiation.
A Smartphone automatically tests the network and adjusts its transmission power to maximize battery life and minimize network interference. As a result the brightness of the LED meter will depend on the data being sent (the average signal), the local signal strength and how close the diode loop is to the cell phone.
The detector diode is made up of a tiny wire which only makes a point-of-contact onto a piece of semiconducting germanium so it’s ‘self’ capacitance is very low and keeps current in the diode loop flowing in one direction.
The germanium diode will rectify the AC signal from the diode loop forming a series of DC pulses that will be nicely smoothed by the LED’s capacitance. Without the diodes however the raw AC signal from the conductive loop will tend to be averaged to zero by the LED’s capacitance.
RF Safe Case vs Pong Case vs Microwave Oven
SKU: 636684233801Categories: Cell Phone Radiation Safety, D-I-YTags: 1SS86 detector diode, Cell Phone Radiation Meter, germanium diode, LED RF MeterSours: https://www.rfsafe.com/product/diy-rf-meter-led-powered-rf-detector-diodes/
Rf meter diy
RF Field Strength Meter
Most transmitter has several variable capacitors which are used to match impedance for transistors and antennas. I know people hate trimmers and so did I. The reason is that it is difficult to trim a system if you can't measure the performances. To trim a transmitter you need to measure the output power. Most transmitter are tuned with a dummy load of 50 ohm to substitute an antenna of 50 ohm. Not everyone has a power meter, and how can you know that the antenna you connect is purely 50 ohm. If not, the hole trimming is waste of time! What you would like to do is to measure the radiated power out from the antenna you actually are going to use. If you can measure the radiated energy field you can easy tune the system for max output field strength (max power). So, how can we measure the radiated energy field? The block diagram at right show you one easy way to measure the RF filed strength. To the left you find a dipole antenna. The antenna should be cut to match the receiving frequency ...
The length of antenna is not a critical at all.
Length = 0.95*300/(4*freq) <= (freq = Mhz)
The RF signal is then rectified in a diode and the DC voltage is then amplified in an OP-amplifier. To display the voltage I use a panel meter. The amplifier gain can be set with a potentiometer and I have also added a bias voltage to set the zero level of panel meter.
This unit will not show you the exact power like a power meter, but it will show you the relative power transmitted out from your transmitter and antenna. The panel meter is connected to the PCB with 5 meter long wire.
In this way I can put the field-meter 5m away from where I am and still be able to watch the panel meter.
I will tell you how I use my filed meter.
I place the RF field meter 5 meter away from my transmitter.
I then put all variable capacitor to middle.
I switch on the transmitter and go to my RF filed meter. I then set the gain (with potentiometer) so I get half of max reading on the panel meter. I then switch off the transmitter and set the offset (with other potentiometer) so I get zero reading on the panel meter.
I repeat this tuning process unit it looks good.
Now I can start tuning the transmitter and watch the panel meter.
All I need to do is to tune for max reading on the panel meter. Then I know the RF field is at max strength.
I also advice you too receive the signal you are transmitting to check that it sound good.
I also check the current to the transmitter so it don't get to high.
Usually the current go down when good tuning has been done and you got max power.
Another good thing to monitor is the temperature of the transistors.
Don't let them go to hot.
I find my RF field meter to be a very simple and powerful too.
This RF filed meter works from 30mW to several watt.
Hardware and schematic
Click to open in new window Please look at the schematic to follow my function description.
At the bottom left corner you will see a voltage divider. This divider is to produce a virtual ground of 4.5VDC. Above you will find the dipole antenna.
The dipole antenna will pick up some radiated energy and the diode will rectify the RF signal to a DC voltage at VRF. This voltage is still quit low and needs to be amplified before it can control the panel meter.
The signal then enter the OP which amplifies the voltage to suitable level set by the "Gain" potentiometers". The second OP acts as a voltage follower and set the offset (zero) for the panel meter.
The panel meter is connected to the board via two wires (5meter long).
To prevent any RF signal to be induced in this long wire I have added 2 ferrite block which will act as high impedance units.
You can use any ferrite block or large inductor (10uH).
This little unit has helped me so much to tuner my transmitter.
Easy to build and to use.
RF Signal Meter Circuit
In this article we discuss the circuit details of a couple of very interesting and sensitive RF signal meters, which can be used for measuring the RF strength of the transmitted waves from the RF source without making any physical contacts with the source.
Simple RF Signal Meter using IC 741
A RF signal meter of this form is very helpful for identifying the radiation qualities of directional beam transceiver aerials. This makes it possible for the person to dimension the antenna correctly to have the best transmitting radiation pattern. An additional aerial must be placed close by from the primary transmitting antenna.
The signal received by the second antenna is subsequently provided to a resonance circuit created by L1, L2 and the varicap C2. This allows the meter to be precisely tuned to the specific transmitting frequency which needs to be measured. With the inductance values shown for the coil in the schematic the 'band width' of the meter can be anywhere between 6 and 60 MHz.
The RF signal after this is applied to the diode D1, consisting of a rectifier/demodulation stage. Lastly the signal is directed to the non-inverting input pin#3 of opamp IC1. The gain of this opamp which decides the sensitivity of the 1 mA meter is fine-tuned by the preset P1.
The working performance of this RF signal meter circuit was tested to be incredibly sensitive, and tremendously selective. A set of headphones could be attached to the output of the opamp enabling the original RF transmission to be examined. The general resistance of the recommended headphone must not be below 2k2 or else that may call for an additional amplification Stage in the design.
Discussing How to to Build a RF Signal Meter
A neat little RF signal meter circuit has been discussed in the following post, which can be used to trace even the minutest RF signals in the ether through an illuminated LED bar graph display. Courtesy: Steven Chiverton.
Hello swagatam busy getting next subject ready for you but here's a circuit from my collection you may like to play around with signals, like it may be useful as another rf ghost detector .
The below given circuit is one of many i collected off the net this one isn't my design bu as years go by many circuits eventually disappear off the net and are then no longer there to build but the idea is if you find something and experiment enough you can improve the old one and or upgrade it.
Using a Gravity Wave Detector Concept
The gravity wave detectors if you still like the details may become handy in the paranormal field as they are on the hodowanec gravity wave detector site but no printed circuits for them and just part of a circuit so ive built them added the amplifier myself and made the printed circuit myself and upgraded them myself and tested them myself and have notes going back a few years
and ive also come up with some of my own using old no longer circuit data say a mic preamplifier you see them on the net but not this one if your not lucky enough to find this exact one anymore i experimented with it and integrated it into my version gravity wave detector that uses a ceramic mic as what you may like to call a ceramic mic ,
its the reader like an areal so the modified mic preamp i used to feed signals to the audio amp ic another one has the 741 as used in the original gravity wave detector and its surrounding few parts but i whacked the modified mic preamp after it in another similar gravity wave detector and so signal gets amplified by the 741 and then fed into the modified mic preamp to amplify it more then to the 386 audio amp is so the amount of changes and upgrades and improvements and modifications using bits of circuits etc is awesome and there's no limit to what you can get ,
so i make printed circuits from old schematics that don't have printed circuit board designs for them and i test and experiment and upgrade and add new ideas to them.
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Of the meeting, talked mainly with old friends, avoiding thoughts of her husband and sex. The evening was going well, and she almost calmed down when Edik asked her for help. His wife, who was almost one and a half times larger than him, pretty pumped up and Marina helped to take her to. The room. When Edik and Marina returned to the restaurant, he said that his wife usually does not drink so much, but flared up because of the meeting.