Rf generator9/4/2023 ![]() In this design, various resistors (R13-R16) are switched in as the frequency bands are switched. It is easy to use and has built-in AGC (automatic gain control) that can be tailored to your particular needs. It can cover a large range of frequencies from MF, HF, and well into VHF portions of the RF spectrum. This chip is a member of the ECL (emitter coupled logic) family and is basically a high speed LC oscillator circuit. However, current versions are in SMD form and go by the name of MC100EL 1648, but are still available in the DIP version. (So popular, in fact, that it is still being produced today - almost 40 years later!) The IC is a MC1648 DIP. To begin with and referring to Figure 1, the RF deck is based on a marvelous chip developed by Motorola in the early ‘70s. I have used this style in seven or eight different designs over the years, which ran the gamut of simple one frequency oscillators to complex phase lock loop synthesizers, and it has always been a solid performer. I covered the theory of this section quite thoroughly in that article, so I won’t dwell on it too much now. If you read my article 180 MHz Sweep Generator, you'll see a very similar design here. As I will explain later in this article, there is a procedure for forming your own. This does not include a commercial housing, which at a minimum would cost $75 and up. The one I am presenting in this article will have superior performance in all specs and (assuming the builder has a moderate junk box of components) can be built for about $50. These generators were priced in the $180 to $250 range. 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. Their intended market is directed at ham operators, hobbyists, or people that like to tinker with electronics which would be people just like us. Just flip a switch, turn a knob, and rapidly get to where you want to go. No array of pushbuttons or programming here. ![]() 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. These are basically intended for consumer product service and non-critical design work. One other thing was that it reportedly came with a $38,000 price tag.Īt the very bottom of the heap is the general-purpose generator which may run from $200 upward. The user manual was a full 3” thick and it would probably take a year to become totally proficient at using this generator. ![]() 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. Once you pick your chosen frequency, they perform excellently, but they can cost anywhere from $1000s to $10,000s. Then, we drop down to mid-range generators that - although they still have excellent specifications - will be more application-specific (limited frequency bands, etc.) rather than “all purpose.” Many of these are slow in use due to programming and a myriad of pushbuttons. ![]() Next in line would be very high-end generators with super specs of accuracy and stability, along with any type of modulation that’s available. They have incredible accuracy and can cost upwards of $100,000. ![]() These are primary frequency standards and time bases by which all other frequencies are referenced to. 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). Signal generators come in a wide variety of flavors. Let me start with a brief overview of what’s out there. 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. However, no test bench is complete until it has an RF signal source of some type. As time goes by, we accumulate a fair amount of basic equipment. We usually start with a simple DMM and some sort of power source. 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. ![]()
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