🚀 go-pugleaf

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.