Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Click here to find out how to win free radios from Retevis!

Call channel for FM, on the legal channels?

Tweek

Tweek

Hushpuppy Jr in the Tarheel
Nov 10, 2013
58
32
28
Youngsville, NC
www.wb4iuy.net
Wasn't sure how to word this...is there a "call channel" folks use for FM operations, within the legal 40 channel range? I've not read anything about one, other than one that's out of band. I saw a few folks say they had use channel 1 in the past, maybe that's a good start. If those with FM can hang out on the same channel somewhere, we'd probably have more luck finding others on the same mode. If there isn't one, I guess I'll park a FM rig on channel 1 and see what happens.

Dave
 

Tweek said:
I've not read anything about one, other than one that's out of band
Click to expand...
Actually that’s correct because the frequency deviation of the modulated signal on FM can vary doubling the bandwidth or more of an AM channel spacing depending on the strength of the modulation. That's how FM works.

This would mean using on channel 1 or 40 on FM mode would have part of your signal transmitting off the CB band.

That's just going by the book.
 
maximum deviation limit is controlled by the transmitter.

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.
* * * * *

same as + or - 4 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.
* * * * *

https://www.worldwidedx.com/threads/fm-coming-to-cb-in-the-us.262202/#post-768248
 
Last edited:
  • Like
Reactions: Shadetree Mechanic and NZ8N
fourstringburn said:
Actually that’s correct because the frequency deviation of the modulated signal on FM can vary doubling the bandwidth or more of an AM channel spacing depending on the strength of the modulation. That's how FM works.

This would mean using on channel 1 or 40 on FM mode would have part of your signal transmitting off the CB band.

That's just going by the book.
Click to expand...
I should say my posts refers Amateur radios on FM bandwidths. The export radio's with FM maybe different.
 
FM bandwidth is 2x the highest mod freq (3khz or less in most cases) + 2x the deviation (typically 5khz). All of my repeaters on the ham bands are 16khz wide because of that. I wasn't as much concerned about occupied bandwidth as I was just trying to establish a "hangout" channel on CB for FM use. I'm not too worried about legalities, but operating down on .805 can call unwanted attention.
 
  • Like
Reactions: NZ8N
My guess is something above Ch28 AM high power and below Ch36 where the SSB users hang out, say Ch30, Ch31, Ch32, Ch33, Ch34. Edit the Wikipedia and it will become a de-facto standard.
https://en.wikipedia.org/wiki/CB_radio_in_the_United_States

Ch31 (27.315 MHz) is the FM calling frequency in Europe according to the Finnish CB club Foxtrot Lima, so you could go with that. The FCC basically adopted the CEPT FM rules to harmonize EU and US usage of the band, anyway.
http://fldx.org/site/11m-call-frequencies-and-operating.php

The days of waiting for S9 magazine to publish a suggested band plan based on usage and reader comments are long gone (August 1977 issue of S9 band plan below).
https://worldradiohistory.com/Archive-CB-Radio/S9-Magazine/S9-1977-08.pdfS9 Usage Tips.png
 
Last edited:
  • Like
Reactions: Rebel Outlaw, RoadRanger and Shadetree Mechanic
fourstringburn said:
I should say my posts refers Amateur radios on FM bandwidths. The export radio's with FM maybe different.
Click to expand...
Ham wide FM uses 5 kHz deviation above 29 MHz. Ham narrow FM (NFM) is about 2.5 kHz deviation. FCC Part 95 CB Service, following the European CEPT standard, will be 2.0 kHz deviation, which will fit just fine in the 10 kHz CB service channel spacing.
 
  • Like
Reactions: Shadetree Mechanic
ljh505 said:
... S9 magazine - August 1977
Click to expand...

Wow! That S9 edition is an example of CB radio at its finest. 131 pages of CB radio goodness from cover to cover.


R8n31R.jpg
 
  • Like
Reactions: edfiero, Rebel Outlaw and ljh505
cralt said:
I think channel 1 is good
Click to expand...
Makes no sense. Most people run shortened/base-loaded/compromise antennas in the mobile that can't tune Ch38 LSB and Ch1 equally well, you get high SWR on one of the two band edges. Pick a FM calling frequency closer to the existing two calling frequencies Ch19 AM and Ch38 LSB.

Or, if you don't want to think about the technical reasons, just do what the Europeans are doing as best practice --- start modulating with FM, and use Ch31 as the calling frequency. The FCC punted decades ago on FM, and finally just adopted the CEPT FM standard. No reason to re-invent the wheel here in the U.S. if the rest of the world has something already that works. There aren't any US radio manufacturers left anyway (Cobra and Midland were the last, they're just importing these days, right?), so it's not like there's a manufacturing market to protect by coming up with a US-only incompatible standard. Sometimes the FCC does that --- remember AMPS analog cellular followed by the U.S. digital TDMA standard, rather than adopting European GSM? --- but in this case, they didn't.
 
Last edited:
  • Like
Reactions: Rebel Outlaw and Shadetree Mechanic

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back