Hi guys!
I am not a telecom guy and my knowledge about frequency is basically zero.
My question is about channel spacing. I am currently reprogramming all (internal and external) of my UHF radios so they'll see each other. I created a channel table with constant frequency width of 25khz and 1mhz channel spacing. Is the 1mhz channel spacing a regulatory factor? Is there any possible hardware related effect using wider spacing? How about operating temperature effect?
Any idea guys? Thank you.
Regards.
I'm not up on the rules, but there has been a lot of talk about narrowbanding that I thought dictated a maximum width of 12.5 kHz for this service in the US. Other countries may have other rules, and 25 kH used to be quite common.
The spacing is important only in avoiding interference between links. If you are receiving a desired transmitter signal on one frequency and there is a stronger (e.g. considerably closer) transmitter on an adjacent frequency, the radio may not be able to separate them. In this circumstance more spacing is better. I'd guess 1 Mhz is plenty. So long as all your frequencies fall in an allowed band and you aren't regulated to specific frequencies, I don't think there is any regulation on the frequency spacing of your transmitters.
I'm not a radio guy either, but in the ham bands the spacing typically increases with frequency. In the 2-meter band (144 to 148 MHz) anywhere from 15 to 30 kHz is common, in the 70-cm band (420 to 450 MHz) it seems to go to 500 kHz.
Ham repeater offsets between transmit and receive are 600 kHz and 5 MHz, respectively, for those frequencies, and by the time you get to the 23-cm band (1240 to 1300 MHz) the offset goes to 12 MHz.
amdomag, post: 360042, member: 1683 wrote: Hi guys!
I am not a telecom guy and my knowledge about frequency is basically zero.
My question is about channel spacing. I am currently reprogramming all (internal and external) of my UHF radios so they'll see each other. I created a channel table with constant frequency width of 25khz and 1mhz channel spacing. Is the 1mhz channel spacing a regulatory factor? Is there any possible hardware related effect using wider spacing? How about operating temperature effect?
Any idea guys? Thank you.
Regards.
I know radios enough to tell you if you are in the US you must narrow band to 12.5 bandwidth. It's been the law a few years now. You are in violation of federal law, the FCC has the ability to find you when youre transmitting. It's my understanding first offense is a slap in the hand.
The only way of legally using wideband radio (25khz) is to be transmitting 19.2 kbps data rate. That would be equivalent to using two adjacent channels at 9600 bps on narrowband (12.5khz). Your FCC license has to have the proper emissions designator which (if my memory is correct) is 19k6. Narrowband would show an emissions designator of 11k2.
The problem with using wideband, even legally, in a populated area is that any of three different narrow band channels can cause interference. If you were using 461.100 then you are transmitting from 461.0875 to 461.1125. All three of those are the center of a narrowband channel.
James
The OP is not in the US.
Good point, I missed that.
Here is a pdf that should answer some of your questions. Heat being one of them.
I could be wrong. My wife says I usually am.
James
What's the difference between frequency width and channel spacing by the way?
My channel table consists of the following:
0 - 450mhz
1 - 451mhz
2 - 452mhz
. . .
. . .
15 - 470mhz
Frequency width is set at 25khz and baud rate at 38400.
Did I miss something?
Thank you guys!
Regards.
Even in the USA there's a difference between channel spacing and channel width. Some of you are getting them mixed up. Please don't get them mixed up guys.
The channel spacing is the distance (for lack of a better term) between channels. The current standard for UHF is 12.5 khz but will eventually go to 6.25 khz
Example of 12.5 khz
461.025
461.0375
461.050
461.0625
You can't enter 461.030 because it is not a channel. Those listed are the center of the frequency width or bandwidth.
VHF will be 15 khz spacing eventually going to 7.5 khz spacing. I haven't kept up with is lately but VHF may already be at 7.5 khz spacing even though the bandwidth is 12.5 khz. Thats kinda like a running track with 3 foot wide lanes on 2 foot center to center.
154.400
154.415
154.430
James
Programming a Pacific Crest radio using PDL Configuration Manager allows you to specify any channel spacing provided it is a multiple of 6.25khz. Same is with Satel Configuration Manager for satel radios. In each environment, the bandwidth is set at either 25khz or 12.5khz depending on your choice. This bandwidth is not same as channel spacing as you can specify channel frequencies of your choice for as long as it is divisible by 6.25khz. In my case, my channel frequencies are 450mhz, 451mhz, 452mhz, and so on. My channel spacing is 1mhz but bandwidth is at 25khz as set by the system during programming. If the idea is illegal or not workable then it would have not been allowed in PacCrest or Satel environment to begin with. I am currently in testing mode and my GNSS is working well.
My concern is the possibility of running over frequencies of noble use and I don't want to be in that situation.
