Frequency limitations to modulate on FM ?

Thread Starter


Joined Nov 29, 2005
What to expect on an attempt to frequency modulate a 100 KHz VLF radio transmitter ?
Any special considerations ?; voice range only. What about demodulating at reception ?

Any simple integrated circuits that can be used as building blocks for emission and for reception that you may know of ? Tx less than 100mW.


Joined Apr 5, 2008

Read this from the wiki:

Frequency modulation can be classified as narrowband if the change in the carrier frequency is about the same as the signal frequency, or as wideband if the change in the carrier frequency is much higher (modulation index > 1) than the signal frequency. [6] For example, narrowband FM (NFM) is used for two way radio systems such as Family Radio Service, in which the carrier is allowed to deviate only 2.5 kHz above and below the center frequency with speech signals of no more than 3.5 kHz bandwidth. Wideband FM is used for FM broadcasting, in which music and speech are transmitted with up to 75 kHz deviation from the center frequency and carry audio with up to a 20 kHz bandwidth and subcarriers up to 92 kHz.

FM modulation on 100 kHz is not done, as it would take to much bandwidth.
Maybe NFM for speach only might work, as the bandwith is about 5 to 10 kHz.


Thread Starter


Joined Nov 29, 2005
Thank you, Bertus.
I failed reading the wiki article before posting, clearer now. Seems that analog-voice narrow band FM is worth investigating for the 100KHz carrier,

If you know of a chip similar to XR2206 but for FM, please advise.

( AM modulator using XR2206 )