Ok I have read a number of post about this interference for radios. SOme really lost me. To the point I am confused beyond belief.
I have used simple numbers here to represent the channels in use.
As I understand it if two radio are in use and the channel are 23 apart there will be glitchs.
sounds simple enough. So the first 22 channels can be used all at once. But what happens if channel 24 is used Will this affect the radios using channels 22 to 24 and channel 1 is not affected???
Does this affect FM radios also??
Also where is the best site to read about this that is in clear language that any one could understand
Hey Jeff,
Not sure where you got your information from, but you either read it wrong or someone was feeding you a line.
I think you might be referring to Third party modulation (3PM )
3PM is when 2 or more radio frequencies combine in to a 3rd frequency.
If you happen to be on this 3rd frequency, you will get “glitched” even though nobody is on your channel.
A brand new or properly tuned radio can still get interference from 3PM. It makes no difference if it is AM, FM, or PCM.
Simple rules of thumb.
~Keep off adjacent frequencies when sailing with others.
~Have your radio system re-tuned once a year.
~Always range test your system before going out for the first sail of the day.
~Keep fresh batteries or a full charge in your radio.
~Always ask others frequencies BEFORE turning on your transmitter.
The basic problem is that channels that are seperated by 23 channels are seperated by 455 kHz. So the two carrier waves from those two channels will “beat” at 455 kHz. As it turns out, 455 kHz is the de-modulation frequency, so the beating causes all the recievers on the pond to recieve a 455 kHz noise that they all interpret as being a signal from their radio and they “glitch”.
Most FM radios use dual conversion which means that in addition to the 455 kHz de-modulation frequency, they also use a second de-modulation frequency (can’t remeber the frequency off hand) that will filter out the 455 kHz noise.
You do need to know that the FM system still uses the 455 KHz frequency as one of its two modulation frequencies. So if you have an FM radio and an AM radio or even two FM radios seperated by 23 channels you will still get the interference. Only the AM recievers with single de-modulation will be affected by the glitching (the FM radio will not glitch).
The M3SC has a great chart to show the potential 23 channel conflicts that may exist. If you have two radios - one on channel 61 and the other on channel 84 - then all the single conversion recievers on the pond will be prone to glitching. Same with 62 and 85, 63 and 86, and so on.
I’ve heard some other people talking about this since the CR914 guys “found” this problem. A few clubs like M3SC have taken steps to avoid the problem by restricting certain frequencies. I have elected to invest in an FM radio that uses dual conversion.