Once our interest in electronics is piqued, our inventory starts to grow — first in knowledge gained by books and select articles, followed by a small inventory of parts, and a few pieces of basic test equipment.
We usually start with a simple DMM and some sort of power source. As time goes by, we accumulate a fair amount of basic equipment. However, no test bench is complete until it has an RF signal source of some type.
What I will present here is a sweet little general-purpose RF signal generator that won't take up much bench space, will fill that missing gap, and can be built fairly cheaply.
Signal generators come in a wide variety of flavors. Starting at the very top end would be a generator that oscillates at only one frequency that is extremely accurate, such as might be used by NIST National Institute of Standards. These are primary frequency standards and time bases by which all other frequencies are referenced to. Today, these mods can be quite complex. Then, we drop down to mid-range generators that — although they still have excellent specifications — will be more application-specific limited frequency bands, etc.
One corporation I worked for involved using a very complex microwave generator which had excellent specs in a myriad of features and — although you could perform just about any frequency related test with it — it was also slow to get to each specific point of interest.
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These are basically intended for consumer product service and non-critical design work. Although they lack the features and quality of higher-end generators, they have several glaring advantages: ease of use, the speed to run the gamut of their entire output range, plus the biggest merit very low cost.
No array of pushbuttons or programming here. Just flip a switch, turn a knob, and rapidly get to where you want to go. Their intended market is directed at ham operators, hobbyists, or people that like to tinker with electronics which would be people just like us.
Having tried several commercial general-purpose generators over the years, I felt that better performance could be achieved which set the stage for designing one from scratch. As I will explain later in this article, there is a procedure for forming your own.
The heart of this unit is the RF deck. If you read my article in the December issue MHz Sweep Generatoryou will see a very similar design here.The RF signal generator is a must to have tool when playing with radio receivers.
It is used to tune a resonant circuits and adjust the gain of different RF stages. Very useful feature of the RF Signal generator is its modulation capability. If it can modulate the frequency amplitude or frequency makes it non replaceable tool for RF design works. Some time ago I have designed an AM modulatorwhich could be used for such purposes.
It works fine in some cases, but it has the disadvantage to be not able to work as standalone device. It requires additionally power supply module and two signal generators - for the RF carrier frequency and for the modulating signal. This makes it inconvenient to work with it outside the house.
I decided to create an RF signal generator working as fully functional stand alone device. Instead to base the architecture on the modern DDS chip, I decided to use the analog approach.
As a basis I have chose an existing RF signal generator published here. Similar design is described also here. The credits for this design go to their authors.
I repeated mainly the first design adding additional digital frequency counter instead the not very precisely radial scale analog calibration. I will not go deep inside the circuit explanation - you can visit the links above and read all you need there. I will show step by step instruction how to reproduce the design with minimum efforts and errors rate. Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson.
For the PCB I used the toner transfer method and the picture attached here. Because the circuit does not contain any chips the image can be mirrored or can be printed without mirroring. The scale is also not very important. After the finishing of the PCB I started the soldering. It has to oscillate at some sound frequency, but it did not. I played a little with it and found that shorting the R15 resistors brings the circuit in oscillations that is the green wire on the picture instead Ohm resistance.
If your circuit makes a sound with this resistor - you can leave it there.
After that I have soldered the RF generator part. To test it functionality I used two fixed capacitors pF and two chokes uH instead the dual variable capacitor and the inductors bank.
I saw that the RF generator works fine and produces AM modulated output signal. As described in the sources there is also some frequency modulation observed at the output signal. For the supply I used 15V transformer salvaged from some old device. It had only single secondary winding and I used a bridge rectifier module, instead the two diodes shown in the original circuit. As a frequency counter I intended to use this DIY kit.
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International Shipping Info. Send Email. Mon-Fri, 9am to 12pm and 1pm to 5pm U. Mountain Time:. Chat With Us. This product has shipping restrictions, so it might have limited shipping options or cannot be shipped to the following countries:. Added to your shopping cart. Function generators are useful in a ton of applications from RF to embedded logic.
They're not usually super cheap though. Good news: we found a kit. But that's only one of the tricks this thing can do. Three different operating modes allow the FG to generate 7 different types of continuous waveform as well as servo test and control signals in micro-second resolution. The LCD screen and menu system make this an easy instrument to operate. Frequency, amplitude and offsets can all be set with the number pad and incrementally adjusted with the rotary encoder. The incremental step size can even be adjusted to make sweeps over a wide range easier to handle.
It can even be used as an adjustable DC voltage source by setting the amplitude to 0. Double check your solder joints and verify that you have a stable 15 volt output on the power supply.
This skill defines how difficult the soldering is on a particular product.Users browsing this forum: Lou deGonzague, Majestic [Bot] and 13 guests. Posted: Jun Mon 18, pm.
Yeah, it looks like it has already been recapped. So it should be ok to power up. Still, you might want to rig up a dim bulb tester to prevent damage to the transformer if the power supply caps happen to be shorted or if there is some other fault in the circuit.
It'll come in handy for bringing up any piece of gear. Still, you might want to rig up a dim bulb tester to prevent damage to the transformer Hmmmm. I am not sure what that is as I am new to the Hobby is this the thing I need to make in this vid? That is an interesting looking unit, the knobs are neither the chicken-head of the early issue nor the grey plastic skirt type that were used until it was discontinued.
Also the BNC connectors are unique. I wonder if it was a special run made for a training school. Did you get the manual? Posted: Jun Wed 20, pm. Very simple. The purpose is to limit the amount of current applied to the unit. The "bulb" is simply a resistor in the AC power line.
You use different Wattage bulbs to adjust the maximum amount of current. Thanks,I am gathering the stuff today to make it. I got a lot of old test equipment from estate sales to power up. Nice setup, but a fine point. The black wire of the pigtail socket should go to the wall plug, and it should go to the smaller of the two pins. Posted: Jun Thu 21, pm. OK I think I got it going to try to power up something on it, how long can I safely run something on it? Posted: Jun Fri 22, am.
If you use a resistor lamp in series with something, the general rule is that an undervoltage condition is not recommended. If the device you were testing had a voltage regulator, it would be maxed out trying to keep the voltage at the correct levels internally. For testing, however, the lamp is great, since it prevents burnouts in the case of a short.
Posted: Jun Wed 27, am. The one thing about your video, that would make your tester deadly is : You did not tell them that the hot wire going to lamp must be connected so that the button terminal on the light bulb goes back to the wall plug, and the shell goes back to the radio.
In your first tester you showed usyou used a pigtail lamp holder, that can be polarized, that way, by using the black wire, which goes to the button, connected back to the hot wire of the wall plug. In the second version you made, you used a pin-type festoon lamp holder and your connection polarity is unclear.
If you get this wrong, the following scenario could happen. In testing, the user tries to unscrew the bulb, to possibly use a different one for a bigger load.
If he touches the lamp base shell while unscrewing the lamp, one hand touches the hot wire of the power circuit, and he gets a shock if any other part of his body touches a grounded surface.
All fixed lamp sockets are mandated to to be wired shell-to-neutral exactly for this reasonand have been for more than a hundred years.The version I built was to fill in the gaps not covered by my old commercial unit and also provide an item of test equipment in its own right.
I soon discovered that my first ever lesson in Amateur Radio, all those years ago, held true. This law meant the case I had bought was too small and had to be enlarged as I am lazy and did not want to do any more major metal bashing, I achieved this as shown below by using longer metal bolts and a homemade case "extender". As with all my project designs this is of a modular construction and you can build as many of the extras as you wish, I may well do some external plug on units later.
Please note calibrated dials can be used instead of the meters with, I would recommend, an external frequency meter and scope used for setting up. The main board is the only one you have to build for the minimalist version as the regulator etc. The circuit is based on a modulated wideband colpitts oscillator. Unfortunately with such a simple approach the signal amplitude will vary with frequency particularly as to keep it simple and the price down I have not included any form of AGC.
The use of a class "A" power amplifier 2N or similar means the oscillator should be able to drive a 7dBm mixer directly SBL-1 etc on most ranges, a very useful feature. The modulation is achieved by the use of a phase shift oscillator controlling the supply voltage to the oscillator, crude but effective, this produces amplitude and slight frequency modulation, very useful.
Before anybody asks I opted for an analogue approach rather than DDS dirty digital synthesis as it is easier for the average person to build at home and does not involve the use of a pic etc.
I cannot guarantee to see your questions if posted elsewhere.Skip to main content Rf Signal Generator. Currently unavailable. Burton Indiana. I have a amateur radio license and like building electronic projects requiring a signal generator.
For the price this not a bad unit I could not make one that looked this good for the same price. I will say after looking at the schematic in the manual, I questioned it cost verses what I got to the point that I took the unit apart to see what was in side.
It was neat and clean inside and the coils are what justified the cost. The coils looked expensive and would have been hard to design. I would recommend this at the hobbyist level. See All Buying Options. In Stock. But it works! Puts out a nice signal and not extremely difficult to figure out. Excellent tool to have when you don't need to haul out the expensive gear. Metal case, great battery life, and a small package. I bought one along with the Spec An unit and I am very pleased.
Add to cart. Only 4 left in stock - order soon. In stock.DIY RF Signal Generator
I've been using high-end test and measurement equipment for over thirty years. Just going on first impressions, I'm just amazed by what you can get for your money now. This is a great little piece of equipment with all kinds of neat features, comparable to gear I've used that costs orders of magnitude more money.
RF Explorer - M. This review is based upon limited use. I have the 25Mhz version and the only difference between it and the lesser units is it can put out a sine at 25 Mhz. The usable range of triangle, sawtooth, and square wave output remains the same so you can save a few bucks by buying one of the lesser units. The unit seems to work as advertised.
To get a high quality arbitrary function generator with similar functionality would cost time the cost. There are some trade off you make when going for the budget version. Pros: - As far as I can tell, it does what it is supposed to do and shipped equipped as it was supposed to be.
Much of its function can be determined without documentation. I've had it for almost a year. Its a great function generator, probably the best bang for your buck out there. The overall GUI is very intuitive and easy to understand.
One thing that is good about the function generator is the waveform that it displays as it can really help you know how the signal will look like with certain configurations such as modulation schemes.It started when I read an article in the June issue of Nuts and Volts magazine. Seemed like a great idea — rather than spend a hundred fifty bucks on an RF signal generator for aligning my radios, I could just build one and learn something in the process. If I recall correctly, buying a subscription gets you electronic access to back issues.
The first change I made was to use a common cathode varactor diode instead of a common anode varactor diode. The capacitance of the diode varies from Okay, so using a common cathode diode allows us to bias our VCO with a positive voltage. That eliminates one of the needs for the dual-rail supply. The other need was for buffering the amplitude modulation AM signal. I knew my AM signal could go from — 0. Not so! It suffices to use a voltage divider to pull the AC signal up into the range that a single-supply op-amp can handle.
Let me illustrate with a schematic snippet:. The modification I made is the addition of R7, R8, and C8. C8 AC couples the signal again, and the voltage divider R7 and R8 will pull the signal to approximately 6V.
The signal is then AC coupled again by C5. So what does this AC coupling do? We still have an AC signal that is 1 volt peak-to-peak, but instead of it going from That eliminates any need for the a dual-rail op-amp. We can power our TLC from a single 12V supply. Otherwise the TLC became too unstable. I tried numerous op-amps in this circuit. LMN seemed pretty noisy. TLC was the winner as it was less noisy than the LMN while offering a single-supply design that can go almost all the down to ground.
I have some TLC on order, which are supposed to be even better. Now that we can get by with a single-source op-amp, I was able to modify the power supply design considerably:.
I did manage to drive it all from one single 24VAC center-tapped transformer.