Why people are not using FM on CB in States?

[144inBama]

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

A friend of mine got a new radio and we were talking back and forth for about 5 minutes at about a mile apart before I realized I was on FM and he was on AM. We had zero problems talking to each other.

 

[Shadetree Mechanic]

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

"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."

It states that am or ssb MUST be used and MAY also use FM.

At the same time?

This could get messy.

 

[144inBama]

I personally believe, with my admitted limited knowledge on AM/FM CB usage, that there will be almost zero benefit to using FM because of my previously mentioned experience. If half the people go to FM, 1/4 stays AM and the other 1/4 goes SSB on say CH 38, that channel will be totally unusable to everyone at DXing distances.

 

[freecell]

unlike am or ssb where signals close to or on the same frequency are sum added by the receiver, on fm when the same thing occurs then the strongest signal is passed while the weaker signal is attenuated / eliminated. this is what is referred to as "capture effect" in the discriminator section of an fm receiver. the stronger signal actually "captures" the full attention of the receiver to the exlusion of all other weaker incoming signals.

https://duckduckgo.com/?q=fm+receiver+discriminator+and+the+capture+effect&t=h_&ia=web

 

[freecell]

cbrs part 95 has only been officially amended now for a whole 17 days. give 'em time.

 

[144inBama]

unlike am or ssb where signals close to or on the same frequency are sum added by the receiver, on fm when the same thing occurs then the strongest signal is passed while the weaker signal is attenuated / eliminated. this is what is referred to as "capture effect" in the discriminator section of an fm receiver. the stronger signal actually "captures" the full attention of the receiver to the exlusion of all other weaker incoming signals.

https://duckduckgo.com/?q=fm+receiver+discriminator+and+the+capture+effect&t=h_&ia=web

So, if I'm running my 800 PEP on AM 10 miles away from a guy, and he is talking to someone 20 miles away on a stock FM radio (same channel as I) ....chances are he'll never hear the guy 20 miles away, correct?

 

[Captain Kilowatt]

"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."

It states that am or ssb MUST be used and MAY also use FM.

At the same time?

This could get messy.

What it means is that manufacturers cannot make an FM only CB radio. It MUST also include AM and/or SSB in addition to FM.

 

[cralt]

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

In my state we used to have a decent group on 2 meter simplex. Horizontal FM only.
I ran a 2m7 on a rotor. Other guys ran stacked 2m9's or stacked loops if they didn't want to mess with a rotor. The king of the frequency ran 3 stacked 2m9's with a beko LDMOS amp that did 1KW+. I can only imagine what his ERP was with all that gain. Every once and awhile we would get in to shoot outs to see who could "wam-bam" who. Ya most of these guys where old CBers

Biggest signal to your radio wins in FM. And there is no question who that is with the capture effect because the other guy is just gone.

 

[WECSOG]

We had a weekly net on 2M SSB about 20+ years ago. Some of us used to see how low we could go in power and still maintain communications. That was a lot of fun.

 

[Blackcat630]

We had a weekly net on 2M SSB about 20+ years ago. Some of us used to see how low we could go in power and still maintain communications. That was a lot of fun.

We enjoy doing the same. On occasion I still meet up with buddy on 2m ssb on Friday night. We will reduce power to as low as we can go.. me about 1/2 watt him about 1/8-1/4 watt. I run 13 elements at 60 ft and he runs 17 at 125. At 35 air miles we have no trouble at all holding a qso. The real fun come in when we start to turn away from each other. Off the back we can still pull it off. When we get to the sides or corner nulls that's when things get dicey. Some nights we can't null each other out, some nights we can. Granted, he's doing most of the work at his height but his tighter pattern can make it a little more difficult.

 

[ExitThirteen]

Seems to me that FM on 27mhz (at least in simplex) would be rather inefficient. And 100% cycle duty on any amplification devices used doesn't seem desirable either... I suspect there will be a huge influx of blown up amplifiers in the near future. I'll just stick to SSB and ~20W.


~Cheers~

 

[144inBama]

I suspect there will be a huge influx of blown up amplifiers in the near future.

Not really understanding this.... If I switch to FM, key up and modulate, my amp only does what my AM dead key is, which is 100 watts. So that's 700 below her normal swing. Now I could see it if people set their DK at an ungodly level so they could transmit at higher power, but hopefully they're not so uneducated that they can't understand the 25 watt per transistor max regardless of mode.

 

[Mustang 131]

Finally...all those over-driven class c amps will sound good. Well until they get cooked.

 

[ExitThirteen]

Not really understanding this.... If I switch to FM, key up and modulate, my amp only does what my AM dead key is, which is 100 watts. So that's 700 below her normal swing. Now I could see it if people set their DK at an ungodly level so they could transmit at higher power, but hopefully they're not so uneducated that they can't understand the 25 watt per transistor max regardless of mode.

You get it.

However, there will be plenty of clowns out there that DON'T understand this, and they are going to believe that "more is better"... and it will result in a lot of blown amps.

~Cheers~

 

[144inBama]

You get it.

However, there will be plenty of clowns out there that DON'T understand this, and they are going to believe that "more is better"... and it will result in a lot of blown amps.

~Cheers~

Well, I guess the old saying " A fool and his money are soon parted " will be running rampant then. Shoot, might be able to get a good deal on some decent amps that just need new transistors after the 2nd time they blow them.