Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!umd5!uvaarpa!mcnc!unccvax!dya From: dya@unccvax.UUCP (Edison Carter) Newsgroups: sci.electronics Subject: Re: low power license free packet? Message-ID: <918@unccvax.UUCP> Date: 4 Mar 88 16:02:09 GMT References: <17327@glacier.STANFORD.EDU> <1004@bcd-dyn.UUCP> <4726@ecsvax.UUCP> Organization: Univ. of NC at Charlotte, Charlotte, NC Lines: 133 In article <4726@ecsvax.UUCP>, urjlew@ecsvax.UUCP (Rostyk Lewyckyj) writes: > In article <5607@cit-vax.Caltech.Edu>, peting@cit-vax.Caltech.Edu (Mark Peting) writes: > > One solution for providing a packet band without taking anyone's spectrum > > is to allow the use of any unused UHF television channel in an area. No. No. No. No. No. And, NO! > > Even in large cities there are hundreds of megahertz available for this. > > Just make it clear that any channel can be taken away if needed for T.V. > > If the packet modems were able to switch to any channel then it would > > not be any trouble to go to a new channel, and anyone trying to send into > > a T.V. channel would never key up since the channel would always be busy > > with the T.V. signal. Also since UHF is rather line of sight there > > shouldn't be much problem with interference with other cities that have > > a different UHF assignment. This is a crock of pure, unadulterated bullshit. Simply because a UHF TV channel is unoccupied, does not mean that operating these low power packet radios on them will not cause inter- ference to duly licensed broadcasters of both full power and low power commercial and educational TV stations. In assigning UHF's to a community (or applying for a low power TV license in them) the following items are considered: 1) Blanketing and intermodulation on the 2,3,4,5 upper and lower adjacents (20 mile separation) 2) - upper and lower Adjacent channel interference (55 miles) 3) Protection of cochannel (for LPTV, a minimum of about 70 miles; for fullpower stations, I think it is 155 miles spacing) 4) Local oscillator blanketing-interference due to the 7th channel above (or theoretically, below, but most sets use high side injection) a given channel in a market. For example, if there is a channel 36 in a given market, channel 45 is not useable because oscillator reradiation from receivers tuned to 36 would blanket 43 if 43 were assigned to that market. This would also happen to packet radios. Thus, 7 above requires 65 mile spacing. 5) Sound image and picture image: (14, 15 channels below). These spacings are high. I forgot what they are. However, you can't operate 14 or 15 channels below a given assignment in a given market, because the image of this would beat with the local oscillator to fall in the desired assignment if you were tuned to the other assignment. For example, you have a 28 assinged to Anywhere, USA. You can't assign 14 or 15 there because if you did, the visual and/or aural of 28 would fall in 14 or 15 and cause objectionable interference. At least 14 other channels are precluded in a given market because of a given allotment. (However, the 2,3,4,5 adjacents are usually assigned to nearby cities). Of these, at least 6 are highly critical. On cochannel allotments, suppose you live in Moore County, N.C. and are trying to recieve your local NBC affiliate, channel 28 in Durham (WPTF). The signal strength there is 64 dBuV, the minimum protected signal for grade "B". Now, along comes some packet radio jerk say, outside that contour. The minimum protection ratio for UHF TV is 45 dB (28 dB with precision offset, but that is another story). A signal of (64-45) or 19 dBuV would cause noticeable interference. 19 dBuV is very easily achieveable by a bunch of yahoos with their packet radios. One packet radio could take out a few hundred square miles of reception at the 64 dBuV contour. This is unacceptable. In the proposers' defence, they did bring this point up. > > > I most heartily agree with this proposal. I hope that somebody > will start work on a proposal based on this to the FCC. > In order to have a better chance of success, the proposers need > to take care of the following items in advance of their approach > to the FCC. > Develop plans for a transmitting system which would > not inadvertently cause interference to an occupied channel. > This means more than just a check for existing carrier before blasting > out your own transmission. Currently channels are allocated > so that reception coverage areas will not overlap with at least > one reception area's worth of buffer area between assigned locations. Obviously, the poster doesn't understand a damn thing about the nature of the UHF allotment procedure. For one thing, the FCC have already established "low power" (1 kw carrier input, unlimited antenna gain) TV stations in the UHF band. There are thousands of translators already bringing TV service to rural areas which also must be protected. Why should I (a LICENSED low power TV station owner) have to put up with having my service area chewed up by a bunch of hackers? How much risk are they taking with their interference "studies" (a so-called procedure which would NOT work)? The determination of interference to UHF allotments, both full and low power, is a matter for professional engineers to determine, not a bunch of computer hobbyists. > If the proponents of this plan can come up with solutions for these > difficulties, then there may be a chance for getting the FCC to > consider it. However you should be aware that other commercial > interests have surely cast their covetous eyes at all that "unused" > spectrum. You are damn straight. Forget this. You can be assured that the Community Broadcasters Association, the Association of Maximum Service Telecasters (AMST), the NAB, the AFCCE (Association of Federal Comm- unicaitons Consulting Engineers), the SBE, major televison networks, station group owners, and yours truly will fight vigourously to keep this crap out of our spectrum. THE UHF SPECTRUM IS NOT A BUNCH OF UNUSED CAPACITY WAITING TO BE REAPED. It is a well engineered system for broadcasting. If there is any unused capacity, it is NEEDED for high definition television, further installation of translators, and low power TV stations. It is also needed (in some cases) for public safety communications (police, fire, etc.). Low power TV allows entrepeneurs who couldn't afford the $8 million to put a vehicle of local expression on the air for $300 k or so. There are hundreds (soon, thousands) of smaller markets which now have access to the television medium at an affordable level. Millions of dollars have been spent on translators to bring commercial annd public TV to remote areas. Television is an integral part of public service. It brings not only entertainment, but vitally important information in the form of news. Countless lives and billions have been saved (and made) because of broadcast television. What the hell good is packet radio? It pales by comparison. Besides all of which, I doubt you guys can do it at 500 mHz. Multipath interference is a big problem up there. Why don't you look down in the 11 meter band from some spectrum. Sorry about the harsh and sometimes profane nature of this flame. However, I own two LPTV stations about to go on the air, and interference is the last thing we need. David Anthony DataSpan, Inc. Owner W28AC W06AM Charlotte, N.C. Concord/Kannapolis, N.C.