The Truth about Digital Modulation
Certain Hidden Fence companies advertise their products as offering DM, or "Digital Modulation".
They describe this as the most modern and up-to-date radio transmission technology for Hidden Fence systems. The "next generation" that is newer & better than even FM radio.
The educated customer needs to be informed that this is nothing more than marketing hype on the part of these organizations. Please, don't be misled…
Digital Modulation (DM) is a radio signal processing technology used to send and receive information over FM (Frequency Modulation), or AM (Amplitude Modulation) radio waves. It's commonly used today in almost any device that performs some type of communication. Everything from cell phones to Hidden Fences function by sending "digitally modulated" signals over an FM or AM radio band. Although DM is based on AM/FM radio technology, it is NOT a next generation replacement for it. Rather...
Digital Modulation is the "digital" form of 
AM/FM radio.
Everyone is familiar with the differences between AM and FM radio. It's widely known that FM signals are far more clear and secure than AM signals. This is why FM music plays over the radio with no static (at all...), and fire/police departments typically communicate over FM channels. Bottom line; digital FM is superior to digital AM.
When applied to a Hidden Fence, the problem with a digital AM system is that the radio signal switches "on" and "off" throughout its transmission...
Whenever the AM Hidden Fence signal is "off" it's open to interference with other AM radio signals coming from a number of common household electronic devices. The result of this interference is a digital AM Hidden Fence system that's prone to "misfire", randomly shocking your pet. This can lead to a confused and frightened animal.
Alternatively, the DogWatch® FM Hidden Fence uses a "continuous" radio signal that does NOT switch on and off throughout its transmission. Since the fence signal is always "on" the FM system doesn't respond to ANY ambient radio wave interference. Therefore...
ALL Hidden Fence companies use Digital Modulation throughout their entire product line(s).
Your car radio is a good illustration of this. Installed in each (late model) automobile is a "digital" AM/FM radio. Regardless if the channel you tune to is AM or FM a "digital" (DM) radio is processing the incoming signal, providing you with something to listen to.
Also, no matter who manufactured your car (Ford, BMW, Toyota, etc), the radio is using a form of Digital Modulation to interpret the AM or FM radio signals. What makes one car radio sound better than another often comes down to simply tuning it to an FM station rather than an AM station. Similarly…
What makes one Hidden Fence product better than another is simply the type of radio modulation it uses, FM -vs- AM.
Anyone interested in getting closer to the technical details of this subject can visit a number of different sites that provide more information.