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hello YouTube Preppers this is the comms prepper with the video about bandwidth and channel spacing I've received a lot of messages and comments about this so I've done a dedicated video to it I'm gonna pick on the three comments radio services that are popular with Preppers because they serve as good examples on the first slide here on the upper left hand side is gmrs and you can see I highlighted in red that that's a 25 kilohertz service and then below that I have FRS which is a 12.5 kilohertz service and then on the right hand side I have MERS which is a mixed bag of non-standard bandwidth and that's the first three channels is 11.25 and the last two is 20 kilohertz so I'm gonna start off with channel spacing first and I'm gonna use a ruler here as an example 25 kilohertz channel spacing this is what's typically known as wideband and what that is is every 25 kilohertz in an assigned spectrum they'll issue a frequency or a channel and they're spaced out at 25 kilohertz apart and this is how it's been for quite some time and looking at the ruler below you can see I'm drawing an analogy to every inch they issue a frequency and and the non-free services like Public Safety a business ban where the FCC can sell these frequency is for money you can see how much money they're making there make it some money every inch and as technology has improved and radios have being come a little bit better they came up with a solution to make more money and that was to double the number of channels issued in the same amount of space so instead of issuing a channel every inch they cut that channel spacing down by half and now they issue a channel every 12.5 kilohertz and if you look at the ruler you can see you double your money but if you cut your channel spacing in half you have to cut the bandwidth of the channel in half as well or you'll overlap on each other and we'll get into this a little more later but to help provide some perspective here I have an example here with some math so you can see how it's done so for this example I use gmrs channel 1 460 255 0 and if I add 12 kilohertz to that or looking at the math here point 0 1 2 5 megahertz the answer is 462 5 6 2 5 which is channel 2 in the gmrs radio service and this pattern repeats itself at least all the way through the 462 piece of gmrs and this is channel spacing this is not the bandwidth of a channel this is just how they issue the frequencies so now we'll get into the bandwidth of a channel on this slide it's a spectrum analyzer print or screenshot and you see a blue bell curve and a red vertical line runs down the center that red vertical line is the actual assigned frequency so when you program your radio and you put the frequency in that red line represents what you put in the display of your radio and again I used a ruler analogy the one-inch mark being let's say frequency 1 now the bandwidth for that frequency is determined by the FCC and what they're saying is you're assigned this frequency in the display of your radio but as you're transmitting you can't deviate any further to the left of the right of that or below or above that frequency then what's specified for that channel and that's what bandwidth is this bell curve and in this ruler example it's you can't go any further than three quarter inches below the frequency or three quarter inches above the frequency that's the bell curve but here I've highlighted the actual bell curve and I'm going to go into depth here on the bell curve a little bit more with this slide so wideband or 25 kilohertz you'll see this in your software and your programming your radios and what this actually means is this is a designation assigned by the FCC that they say the bell curve or the bandwidth of a wideband 25 kilohertz channel shall not exceed 16 kilohertz in totality from the left side to the right side of the bell curve and you can divide this in half eight kilohertz on the left or 8 kilohertz on the right when you add them together your bell curve your bandwidth cannot exceed 16 kilohertz the f3 e means analog frequency modulation but the 16 K 0 is the important piece here 16,000 kilohertz is the max deviation you can have for this wideband bell curve now radios aren't set to this max they shrink that in a little bit to account for possible frequency error in the radio to higher or lower frequencies so at a factory or when you take your radio in for service the technician on a wideband channel will set the deviation or the max deviation for your bell curve at 5 killer plus or minus 5 kilohertz on the left and the right side of the center frequency and in this case it's 462 5 5 0 for channel one of the gmrs service and they do this like I said you'll see on this next slide if your radio is out of alignment as you see the bell curve shifts to the left if it shifts a little bit and it's off center as indicated by the top arrow red arrow if you look at the lower left red arrow you're still within the tolerances for that channel assignment as issued by the FCC so here's how it looks when you look at more than 125 kilohertz wideband channel with 25 kilohertz channel spacing these little blue bell curves fit nicely evenly spaced across a radial spectrum and like I said there's a little bit of buffer space between each one to accommodate frequency error but it's a nice even consistent pattern you have a wideband bell curve on a wideband channel spacing and everything fits in nicely and what they do is they go to narrowbanding and this is what it looks like you cut that channel spacing down in half and you can double the number of channels but what they also did is they cut the maximum allowable bell curve from 16 kilohertz to 8 cutting in 1/2 and the vendor is when they set the modulation level cut it from 5 plus or minus 5 KC's to plus or minus 2.5 kilohertz and that's how you fit double the amount of channels in the same amount of space you're deviating half as much and you're not going out as far when you're assigning these channels one after the other and that's how narrowbanding is achieved and that's the difference between wideband and narrowband how much modulation you have and how those channels are spaced in a specific chunk of spectrum now I'm going to pick on gmrs here because that's what we're familiar with as preppers a lot of us have these radios oddly enough gmrs channel spacing is every 12.5 kilohertz boom-boom-boom-boom-boom and you'll see that highlighted here in green in the middle those are actually the channels that are shared with the FRS radio service so gmrs is spaced at 12.5 kilohertz but as the FCC website indicates they're still using 25 kilohertz of bandwidth so these channels are actually overlapping a little bit so if you've ever used radios and heard some Co channel or adjacent channel interference on your radio it could be that there was somebody right next to you on the next channel transmitting and their bell curve was entering into your bell curve in your receiver you're picking up some of their transmission and this is why because you have a 25 kilohertz channel assigned at 12.5 kilohertz of channel spacing and if that's not bad enough for it confusing enough as I covered in previous videos 7 of the channels of the gmrs radio service are shared with the Family Radio Service and that's indicated with these little green narrowband bell curves because FRS is a narrowband service so they're only putting up half the modulation as gmrs if the radios are configured correctly so you can think that you're on a gmrs Channel and as you can see you might actually hear FRS users and that might cause some confusion but that's the reality seven of the gmrs channels are shared with the FRS radio service and here's actually one frequency example another anomaly you might experience as a prepper if you have a gmrs radio and an FRS radio trying to communicate with each other the gmrs radio is set for wideband now you can tell by the blue bell curve when the FRS radio transmitted to the gmrs radio the modulation is cut by half so it may sound like the FRS radio user is whispering or have low modulation you won't hear it as well in the gmrs radio because that radio is looking for a much wider bandwidth at the receiver just the opposite for the FRS user who has a narrow band width on the receiver the gmrs radio might sound like the user is screaming into the radio or be loud and distorted so again that's another anomaly Preppers might experience because of narrow band and wideband a third anomaly you might experience is co-channel overlap and here's an example of a gmrs channel it with the blue bell curve next to an FRS channel with the green bell curve and they cross and I highlighted that with the little red red circle so the modulation is interfering in each other check each other's channel so you might hear some distortion or some other signals out there that are breaking your squelch and you can't put your finger on it this could be the reason it's just enough of the adjacent channels bell curve encroaching on your space or your bell curve to trip your receiver so I hope I didn't confuse you too much and at the risk of losing subscribers for having a video that's too technical I appreciate your bearing with me here please leave a comment if you have any questions on this or you'd like see a specific topic covered in future videos and as always thank you for watching and thank you for subscribing this has been the Khans prepper