Has anyone tried talking to the newer FFC authorized FM radios with an older FM mode capable radio like the 5555 or older Pluto type radios. The max modulation deviation on the newer radios is significantly lower. Technically the older radios will receive the newer radios even if the volume heard is lower. On RX though the newer radios may have trouble with the wider deviation from the older units.
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FM mode with newer FM radios and older FM mode capable radios
- Thread starter gary123
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RFI-EMI-GUY
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Correct, mixing wide and narrow band radios will either cause weak received audio or potentially garbled, over modulated audio.
I am not sure what model radios you mention. However the best idea is to read the FCC Certification number from the tag on the radio. Look it up on the official FCC OET site or unofficial FCC.IO site. Then find the FCC grant which shows the frequency of operation, power output , emission designator, applicable rules. Part 90 Commercial or Part 95 FRS/GMRS. (Part "9" is bogus). The emission designator for a wide band radio will usually be 16K0F3E or 20K0F3E. A narrowband radio will be 11K0F3E or 11K3F3E .
A radio can be type accepted for both wide and narrow band capability. Most are not.
If the numbers for your particular radio are different, lower, then they are modulating with a lesser modulation index and will sound weaker than a standard radio.
A huge number of cheap Chinese radios (Low parts count) have inferior modulation.
I am not sure what model radios you mention. However the best idea is to read the FCC Certification number from the tag on the radio. Look it up on the official FCC OET site or unofficial FCC.IO site. Then find the FCC grant which shows the frequency of operation, power output , emission designator, applicable rules. Part 90 Commercial or Part 95 FRS/GMRS. (Part "9" is bogus). The emission designator for a wide band radio will usually be 16K0F3E or 20K0F3E. A narrowband radio will be 11K0F3E or 11K3F3E .
A radio can be type accepted for both wide and narrow band capability. Most are not.
If the numbers for your particular radio are different, lower, then they are modulating with a lesser modulation index and will sound weaker than a standard radio.
A huge number of cheap Chinese radios (Low parts count) have inferior modulation.
Understood RFI-EMI-GUY. I was hoping some pone had simply tested it out in the field to see how bad the newer FM approved radios reacted to the 'over modulated' FM from earlier "all mode 11-10m" radios.
I may have to visit a truck stop and see if anyone has a approved AM/FM radio installed. I can test with a anytone 6666 and a old 148GTL-DZ superstar radio.
I will post results.
I may have to visit a truck stop and see if anyone has a approved AM/FM radio installed. I can test with a anytone 6666 and a old 148GTL-DZ superstar radio.
I will post results.
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The context of my reply was with respect to Part 90 and Part 95 radios in VHF and UHF.
If you are asking about HF and Low Band VHF radios; there was never any narrow band mandate for VHF Low band radios. Those radios like Motorola, and GE/Harris will likely have 16K0F3E or 20K0F3E wide band +/- 5.0 KHz deviation / modulation.
HF ham radios have no standardized FM deviation. CB radios that are now certified are narrow band FM, +/- 2.5 KHz deviation. There were some older ham/cb radios that were narrow as well.
Mixing the wide and narrow will have the effects you describe. In some cases it is as easy as turning the volume up and in other cases, one party will have to back away from the mike.
mmckenna
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I have a few Superstar 3900 radios that have FM. Might have to fire one up and see if any new FM cb is in use near me. I have to look at its FCC id tag and verify its a legal radio. After all these years, who knew...
mmckenna
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If it has FM and it's not minty fresh out of the box within the last few months, it won't be a type accepted CB radio. Likely an "import" radio or a ham radio that's been modified to work on CB.
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Right you are, worse than I said.
mmckenna
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Yeah, I really want to hear how bad that sounds.
Last time these were minty fresh out of a box was late 80's, early 90's. My lord, I can not believe I committed acts frowned upon by the FCC. Seriously tho, back then I had no idea and figured since it was bought mail order, that it was good to go.
This is actually what I just saw that suggested they were not on the up and up
It wont let me link it. Its the first 2 choices.
RFI-EMI-GUY
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Its sad US CB cannot have FM improvement (capture) as Major Armstrong intended. Maybe there is room for "peak and tweak" in the FM CB world!
mmckenna
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Should be interesting the first time someone tries to crank up the deviation...
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I have done so on FRS radios. ICOM IC4008A. Measured the RX bandwidth and tweaked the deviation to 3.5 so they would play well with my Saber's on the GMRS interstitials.
mmckenna
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If you wanted to toe the FCC line, that would be out.
But we all know how closely the FCC watches CB.
None the less, if it's running wider deviation on FM that the 2KHz allowed, everyone else is going to think your radio sounds like poop.
I had the opportunity to do some testing. I found a trucker using a President Thomas who was interested in using FM for the first time to talk to some one. We used Ch29 and stock power (10w on the 6666). I positioned myself about a half mile away and did some testing while monitoring the RF with a spectrum analyzer.
Here is what I found. His FM audio was about 70% as loud as it was on AM but did sound crisper. My audio back was the same volume between AM and FM with 1.5.Khz deviation. When I upped the deviation to 2khz he started to get chopping as I 'over deviated' his receivers limiter. When I set my deviation to 1.25Khz my audio dropped to about 70% volume. The other interesting result is whan I slected a PL (151.4Hz) 600Hz deviation his radio heard the noticeable hum of the PL tone. This indicates there is no low pass filter on the audio.
Conclusion: The radios are fully compatible but if using an "export" type radio back off the mic or turn the mic gain down so you dont over modulate and get chopped up by the other radios circuitry.
One more thing a range test. At just over a mile distance the AM was starting to get motion flutter and weak signal 1-2 bars on the Thomas and 3-4 bars on the 6666 but the FM was solid with just a bit of flutter. Both radios lost comms at about 1.5 miles. I would say FM was clearer and held the communication legibility better than AM even though the range was about the same.
I would like to thank everyone for contributing to this thread. I hope this will give everyone a bench mark to use when in FM mode.
Here is what I found. His FM audio was about 70% as loud as it was on AM but did sound crisper. My audio back was the same volume between AM and FM with 1.5.Khz deviation. When I upped the deviation to 2khz he started to get chopping as I 'over deviated' his receivers limiter. When I set my deviation to 1.25Khz my audio dropped to about 70% volume. The other interesting result is whan I slected a PL (151.4Hz) 600Hz deviation his radio heard the noticeable hum of the PL tone. This indicates there is no low pass filter on the audio.
Conclusion: The radios are fully compatible but if using an "export" type radio back off the mic or turn the mic gain down so you dont over modulate and get chopped up by the other radios circuitry.
One more thing a range test. At just over a mile distance the AM was starting to get motion flutter and weak signal 1-2 bars on the Thomas and 3-4 bars on the 6666 but the FM was solid with just a bit of flutter. Both radios lost comms at about 1.5 miles. I would say FM was clearer and held the communication legibility better than AM even though the range was about the same.
I would like to thank everyone for contributing to this thread. I hope this will give everyone a bench mark to use when in FM mode.
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