Why people are not using FM on CB in States?

If i want an effective mode i pick SSB.( C.W., or digital)
If i want to see a meter "swing" i use SSB.
If i want clear communication i pick FM.
AM equals Antique Mode.

Having said that, i DO still use AM mode on our green old army set nets, or 160 with some UK amateurs on their AM nets.

I figure if more people had FM as an option on their Radios, They would use it... Sure FM isn't a legal CB 11 Meter mode in the USA, but then again... everyone is running 4 W Carrier and 12 W SSB... right? sure they are...

Benefits of FM modulation/reception.

• Improved signal to noise ratio (about 25dB) w.r.t. to man made interference.
• Smaller geographical interference between neighboring stations.
• Less radiated power.
• Well defined service areas for given transmitter power.
• Less interference in neighbours equipment .

Disadvantage, needs a more complex demodulation circuit in the receiver compared to AM.

Resilient to noise: One of the main advantages of frequency modulation that has been utilised by the broadcasting industry is the reduction in noise. As most noise is amplitude based, this can be removed by running the signal through a limiter so that only frequency variations appear. This is provided that the signal level is sufficiently high to allow the signal to be limited.

Resilient to signal strength variations: In the same way that amplitude noise can be removed, so too can any signal variations. This means that one of the advantages of frequency modulation is that it does not suffer audio amplitude variations as the signal level varies, and it makes FM ideal for use in mobile applications where signal levels constantly vary. This is provided that the signal level is sufficiently high to allow the signal to be limited.

Does not require linear amplifiers in the transmitter: As only frequency changes are required to be carried, any amplifiers in the transmitter do not need to be linear. ( Class C amps.).

Enables greater efficiency than many other modes: The use of non-linear amplifiers, e.g. class C, etc means that transmitter efficiency levels will be higher - linear amplifiers are inherently inefficient.

All the transmitted power in FM is useful, while in AM most of the transmitted power is in carrier which contains no information.
The amplitude of FM is constant which makes it independent of the modulation depth, while in AM modulation depth directs the transmitted power.
Noise in FM is reduced to a large extent by employing amplitude limiters to remove the amplitude variations caused by noise. However these amplitude limiters cannot be used in AM as information is contained in the amplitude variations of the signal. Thus FM reception is immune to noise then AM reception.

The noise in FM can be further reduced by increasing the deviation, which is not in AM.
In FM if there are two or more signals received at the same frequency, the FM receiver will capture the stronger signal and eliminate the weaker signal. However in AM if there are two more signals received at the same frequency, then both will be demodulated which can lead to interference.

That will put most objections to bed about FM.

FM seems to work fine on my Anytone AT-6666. Last tried it a couple of months ago when I talked to a guy in Waterloo NY 635 miles North of me. I don't remember the power settings or if I was on a vertical or horizontal antenna.

vlad_k said:

I wonder why.

Click to expand...

Because the CB rules were written a long time ago, and they do not get updated very often.... I mean, they only recently removed the 155.3 mile limit for conversations over the air...

Nothing but static 10 through 12 meters, not even sure what FM is for, repeaters? just static here

FM sounds a lot clearer than AM.... less static and trash...

Bump for fun

Well its coming finally but I doubt it really takes off much. People on 11 meters are pretty set in their ways. The duty cycle is not too forgiving either.. especially on your run of the mill cb amps.

Back in the mid to late 90s I ran into a group of Florida boaters on 26.500 running fm. They all had Emperor TS 5010s and that's as low as a 5010 will go. I was running the same thing at the time. Talked to them a few times over one summer I was on break from school. Pretty cool to find them chatting away on FM.. way down on 26.500.

AM will never die. My Loose Cannon 858 Madison just whispers to me with no squelch on AM. Then a signal comes in loud enough to be almost startling. Then between signals, back to the whisper. Again, no squelch. Not needed at all. This is the way it was meant to be. This is AM.

The 10 meter exports totally missed the mark on AM. I don't know if there is a way to help them.




Ok, I like FM too. But it's just not the same.

For Tactical CB Communications ( Jamming and talking over someone) The FM Mode phoneme of "Capture" will entice many more is use FM and get bigger linears. As we have heard over the years on the 147.435 two meter repeater the "Capture" wars, when the strongest signal received is the only signal heard in the receiver.

When received signals are close to each other in signal strength at times a heterodyne can be heard.

Some of the waring dudes will drive up to the repeater site to take over the repeater to "Capture" all the other incoming stations.

While driving home from work once Iam listening to 435 I heard this:
I am running stacked 11 element Beam Antennas and a 1000 watts, and only a mile from the repeater and ZZzzzzz heterodyne the guy disappears into the jamming of other stations talking over him. What fun and entertainment to listen to all big straps out there in the San Fernando Valley. You can't buy entertainment like this.

Jay in the Great Mojave Desert

Did the FCC make it to where you can use FM on the 40 channel CBs ?

4. Section 95.967 is amended by revising paragraph (a) to read as follows:
§ 95.967 CBRS transmitter power limits.
* * * * *
(a) When transmitting amplitude modulated (AM) voice signals or frequency modulated (FM) voice signals, the mean carrier power must not exceed 4 Watts.
* * * * *

5. Section 95.971 is amended by revising paragraph (a) to read as follows:
§ 95.971 CBRS emission types.
* * * * *
(a) Permitted emission types. CBRS transmitter types must transmit AM voice emission type A3E or SSB voice emission types J3E, R3E or H3E, and may also transmit FM voice emission type F3E.
* * * * *

6. Section 95.973 is amended by revising paragraph (a) to read as follows:
§ 95.973 CBRS authorized bandwidth.
* * * * *
(a) AM and FM. The authorized bandwidth for emission types A3E and F3E is 8 kHz.
* * * * *

7. Section 95.975 is amended by adding a new paragraph (c) to read as follows:
§ 95.975 CBRS modulation limits.
* * * * *
(c) When emission type F3E is transmitted the peak frequency deviation shall not exceed ±2 kHz.
* * * * *

the appropriate sections of Part 95 with regard to CBRS and the FM option have been amended.

https://www.worldwidedx.com/threads/fm-coming-to-cb-in-the-us.262202/#post-768248

i can honestly say i never tried fm less than 1 time . haha. close trucking friend n i ran together a lot loading n unloading at same places. we used fm to get away from others. very few ever came to fm to join in