Reality of FRS frequency spectrum (interstitial/FRS only)

A lot of people don't fully grasp why it's not legal by FCC regulation to just use any radio on FRS (Family Radio Service) at full power and what does it really hurt if using a non-certified radio at power levels exceeding the current limitations of 500mWatts or even the newly proposed power levels of 2 watts E.R.P. (Effective Radiated Power).

There is a lot to this so bear with me and it will probably be vague, in time I am sure a lot of Hams on this section can help me to clarify and explain.

First definitions.

FRS channels 1 through 7 are referred to as the Interstitial Channels. By definition Interstitial: 1. pertaining to, situated in, or forming interstices, interlaced.
2. Anatomy: situated between the cells of a structure or part.

FRS Channels 7 through 14 are refered to as FRS only but as you'll see they too are by definition Interstitial and interlaced with licensed G.M.R.S. (General Mobile Radio Service) Repeater Inputs.

For starters lets start with the fact that the GMRS channels were the first ones allocated by the FCC and consisted of 8 channels of 25kHz (462.xxx) each with 8 Repeater Inputs (467.xxx).

When the FCC laid the spectrum usage for FRS they did not allocate any new frequencies to the spectrum, they only interlaced the FRS channels on top of the existing GMRS channels. So for example: GMRS channels 3 and 4 are 462.600 and 462.6250, respectively, with a bandwidth of 25kHz each, thus they meet at 462.6125. FRS channel 3 is 462.6125 with a bandwidth of 12.5 kHz. With it's center frequency exactly at the border of GMRS 3 and 4.

So when transmitting on FRS 3 half of the signal will be using GMRS 3 territory and half of GMRS 4 territory. Thus, the reason that the FCC limited the transmit power out of a non licensed FRS radio to 500mWatts so that the interference to licensed users wouldn't matter. It has been proposed that the power limit be increased to 2 watts E.R.P., but as of this writing has not been formalized yet. Licensed G.M.R.S. users are allowed to use these channels 1-7 at 5 watts so that they can communicate with FRS radios more effectively, Although it is possible to hear the signal from GMRS 3 or 4 on FRS 3, it is garbled and most the time indecipherable.

At the low power levels of FRS (non-licensed) interference is minimal across licensed G.M.R.S. channels. Thus, the reason why there are strict rules regarding no detachable antennas, no repeaters and power levels on FRS radios.

The misnomer of FRS only channels 8-14. (467,xxx) Refers to the fact that G.M.R.S. radios were not set up to communicate with FRS radios like the Interstitial Channels 1-7. However, just like the 462.xxx frequencies. No new bandwidth was given. The channels are interlaced with GMRS Repeater inputs. So the same thing. Half the signal from FRS 10 (467.6125) uses the allocated bandwidth of G.M.R.S. 3 repeater Input and the other half uses GMRS 4 repeater input allocation.

As mentioned if you adhere to the power limits and narrow bandwidth there is minimal intereference, because emissions of a wideband/narrowband signal does not fully use the entire 25kHz/12.5kHz.

So as also mentioned, coming up on an FRS channel with High power levels will interefere with licensed GMRS users. Also, no repeaters are allowed on FRS channels to further minimize interference with licensed GMRS users.

Anyways, this is as basic as I can get it. There is also a lot more to this. But I hope it at least explains that why the FCC is so stringent on low power, non-detachable antenna's (which alter the Effective Radiated Power out) and no repeaters for FRS radios.

Part of the new proposals is that the GMRS license duration be raised to 10 years versus the current 5 years. Still at $75 for 5 years, it is only $15 a year to be FCC compliant.

Let's block ads! (Why?)

Reality of FRS frequency spectrum (interstitial/FRS only)