FM (frequency modulation) transmitters can yield a number of results, depending on their power and range. Extremely low-power transmitters can be used in very small locales, for purposes such as eavesdropping. At the high end, radio transmitters are sometimes used for propaganda and psychological warfare through broadcasting. Between these extremes are the low-power radio transmitters, capable of making every user a broadcaster, that have long been an issue of concern for the Federal Communication Commission (FCC).
Mini transmitters, which have a range of about 50 feet (15.2 m), are available commercially to serve purposes such as that of a baby monitor, but are easily adapted for eavesdropping as well. https://www.bestadvisor.com/fm-transmitters Although they are capable of operating anywhere on the FM dial, from 88 to 108 MHz, the recommended range for most of these is 88 to 95 MHz, where there is least likely to be interference. Low-power FM transmitters, with a range of 100 to 400 feet (30.5–122m), make it possible to transmit voices over a greater distance, and are applied commercially for purposes such as listening to compact discs (CDs) in a car that does not have a CD player.
Both mini and low-power FM transmitters have such limited power—less than 1 watt—that they pose no concern to communications regulators.
On the other hand, high-power or professional FM transmitters that are commercially available—some with as many as 35 watts of power—theoretically have the capacity to make anyone a radio broadcaster.
This could pose serious concerns with regard to interference and communication jamming, and by 1998, the availability of FM transmitters forced the FCC to at least consider the idea of legalizing low-power transmission. The concept has been under consideration for some time, but many would-be broadcasters are as likely to choose the Internet as a simpler, non-interfering environment in which to operate a radio site.
In the realm of very high-power radio stations, there are many such facilities overseas operated by the federal government for the purposes of winning over local populations. In February, 2002, a year before the administration of President George W. Bush launched Operation Iraqi Freedom, it provided assistance to the opposition Iraqi National Congress as it began transmitting from the Kurdish-dominated north of Iraq on the FM dial. The United States already broadcast on short-wave radio into Iraq, but FM is both more popular and harder to jam than short-wave or AM (ampere modulation).
In most communities, you will find two main sources of parts: Radio Shack, and tearing down junked electronics for parts. You will rarely get everything you need from these sources, although you might get lucky if you break down enough TV type stuff to find the small ceramic tuning capacitors you need and find a mica trimmer or two in some really old tube stuff. You will absolutely need a tuning capacitor from a small battery powered FM radio, they seem to be the most stable kind for making the tunable oscillator in the “premix” type exciter we’ve had good luck with at WSQT.
Hamfests are still a good source of all kinds of goodies, ranging from crystals to tuning capacitors to whole old radios that can be broken down for parts. Don’t let on your real use for these parts, and remember that the only thing that might be an issue for a seller at a ham fest is a complete, functioning ham transmitter or especially a linear amplifier. Look for trimmer capacitors, 27 MHZ CB crystals, 32 MHZ crystals, and VHF bipolar power transistors. Ham fests are also a good place to get all those computer goodies you might want as well.
In or near most larger cities you should be able to find at least one electronics supply house that sticks transistors, trimmer caps, and fixed ceramic capacitors and resistors in sizes no longer found at Radio Shack. Facebook
A related issue to availability of parts is the recent increase in “dirty” signals from pirate transmitters made with low-cost PLL chips meant for “Part 15” usage where spurious outputs can be permitted to equal the signal strength. Spurious outputs within a megahertz or two of the desired signals are nearly impossible to filter out at operating frequency. These little radio sets are tempting to use as exciters, as the digitally-tuned ones are right on frequency, but beware: Unless you get lucky, you will get nearby signals that interfere with neighboring signals and can never be filtered out. Hopefully by the time you can’t get parts to build your own exciter board, these become made in such a way as to produce clean enough signals to send to an amplifier.
