What is the difference between...

[Charlie]

TV and CATV? And why? I'm referring to the setting on modern sets and vcr's. I use a VCR/DVD combo as my cable box on my sets, but just for the hell of it, I connected a splitter to my CM roundie and connected the cable directly to it. Being that a roundie isn't "cable ready", the channels are different on the UHF dial. Cable channel 77 will be found somewhere near 29 on the 1966 UHF tuner... cable channel 78 somewhere near UHF 30. I have to say "somewhere near" because the UHF tuner is continuous. A little lower down the dial... let's say cable channel 20... won't be tunable on the UHF dial.

So what's the reason for this? Why not have cable channels the same on a digital tuner and an old fashioned tuner?

[tubesrule]

Hi Charlie,
This mainly has to do with how the FCC alloted slots for television. The final VHF band was assigned between approximately 55MHz (channel 2) and 211MHz (channel 13). When UHF became necessary in 1952 it was assigned 471MHz (channel 14) to 885MHz (channel 83). You can see there was a substantial gap between channel 13 and 14. Because cable does not come under the FCC allocations, they are free to pack every channel 6MHz apart unbroken. This is why standard cable channels above 14 appear at lower frequencies than there terrestrial counter parts. You can find some good charts on the web that will give the exact frequencies of each channel for the various systems.

Darryl

[southernguy]

Back in the early days of cable tv the channel capacity was limited to maybe a little over 13 channels. Cable companys only used channel locations near the Hi-Lo VHF Band including 2-13. As time went on so came more cable tv channels and more needed bandwith. They keep it as close to 2-13 as they could as there tends to be more signal line loss with the UHF Frequencys. The RF Amplifiers they used back then would only carry maybe 39 channels, such as cable channels 2 - 40. Also cable channels 23-64 is between VHF 13 and UHF 14.

[southernguy]

Here is how cable channels compare to the older tunners. If you look at it continuously it goes something like this. Cable channel 1 is between is between VHF 4 & 5. The FM band is right after VHF channel 6. Between VHF channels 6 and 7 you will find Cable channels 6,95-99,14-22,7. 7 through 13 is the same. After VHF 13, 23 through 64, then

CATV/UHF
65 14
66 15
67 16
68 17
69 18
70 19
71 20
72 21
73 22
74 23
75 24
76 25
77 26
78 27
79 28
80 29
81 30
82 31
83 32
84 33
85 34
86 35
87 36
88 37
89 38
90 39
91 40
92 41
93 42
94 43
100 44
101 45
102 46
103 47
104 48
105 49
106 50
107 51
108 52
109 53
110 54
111 55
112 56
113 57
114 58
115 59
116 60
117 61
118 62
119 63
120 64
121 65
122 66
123 67
124 68
125 69

[3Guncolor]

Channels 2-5 (skip 4 Mhz) 5-6 95-99 14-22 7-13 23-94 100-up this is the most common order of cable channels frq wise. Most up to date cable companies go to ch 116 750mhz to as high as 860 or higher. Most analog stops at 550Mhz digital is ch79 and up.
Channel 2 would be 55.25mhz 5 77.2500mhz add 6 mhz for each channel above 5.

Steve

[Charlie]

Wow... so they cram quite a few cable channels in between the standard TV channels!

[wa2ise]

There's also channels below 50 or so MHz. Going all the way to about 7Mhz. But these are used mostly for sending video to the head end, stuff like town council meetings and high school sporting events.

Also many cable systems avoid putting channels on ham radio bands, like 144-148MHz, 222-225Mhz and 440-450MHz. Because hams are quite ternacious about leakage from the cable into the air. Also the areonautical band just above the FM broadcast band is also avoided. Both services expect to be able to communicate to weak signal stations. Police and fire are less fussy, as they are channelized and their signals are usually fairly strong (as they usually only talk to their guys in the same town).

[3Guncolor]

The return to the headend is 5 to 50mhz used for cable modem, phone and VOD access. Most systems try to stay away from using the return for video these days because it never seems to work well due to noise. The lowest channel used for forward is channel 2. Almost all cable systems use all the channels they can. Even the HAM bands etc... the FCC will shut us down if we have leakage over a set amount. Where I work we use every channel on the 750Mhz systems from ch2 to 117.