SBE CHAPTER 40
NEWSLETTER
MARCH 1998
SAN FRANCISCO
Roy Trumbull - Editor roy547@netcom.com
Bill Dempster -
Artist
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BABES/SBE LUNCHEON ON WEDNESDAY
MARCH 25th
This month our speaker will be Fred Jones, the
developer of the Ramsa DA7 digital audio mixer by Panasonic. Fred came into the
business as a user of equipment so he had a good idea of what people wanted. Our
thanks to Leo's Pro Audio for making the arrangements.
As usual our luncheon will be at Sinbad's. Sinbad's is just south of the
Ferry Building on the Embarcadero near the foot of Mission Street. Please
RSVP to Karen Prasek at Zack's: 408-324-0551 x126 as we've been running out of
tables and chairs. We meet at 11:30 and are seated at 12:30.
COMARK SPONSORS SEMINAR On feb 26th
Comark, Dolby, Divicom, Microwave Radio, and Dielectric Communications gave a
free day long seminar at Dolby Labs in San Francisco. It was an excellent
session. Dolby proposes building level information into digital content to
inform the receiver of the desired level settings appropriate to the content.
Dielectric and Comark have done joint tests on the S/N impact of uncorrected
group delay in filters. You get wiped off the map if you don't correct for it.
Even phase and amplitude ripple on transmission line are more troublesome than
you would think. Microwave Radio detailed the signal margin penalty of using
digital microwave. Dane Ericksen explained that you couldn't light up on a
channel without considering the effects on spillover from the digital signal
into adjacent channels. Divicom covered the encoding issues and the usage of the
digital bandwidth. In talking with Dielectric, I found out the 500khz resolution
of the DTV mask may make it somewhat easier to meet the spec.. Dane Ericksen
passed out a summery of the key features of the 6th Report and Order
Reconsideration.
PLANNING COMMISSION APPROVES SUTRO PERMIT
On the same day as the meeting at Dolby, there was a
marathon meeting at the San Francisco Planning Commission on the permit for the
construction work needed to mount the antennas at Sutro Tower. The permit was
approved but additional legal maneuvering is anticipated. Each broadcaster is
working out the details of modifications needed to their space in the Sutro
building. Some equipment has already arrived and it looks like the November 1
date will be met by several, if not all, of the stations
NAGLB PLANS NAB DINNER While the
straight SF broadcasters haven't been able to plan an NAB dinner for years, the
bent ones are doing fine. The dinner for the National Association of Gay and
Lesbian Broadcasters will have its NAB dinner April 7th at Sam's Town, 5100
Boulder Hwy. Social hour from 1830 to 2000 with dinner at 2000. For reservations
call 1-888-293-8454.
DON'T COUNT ON DTV FILTERS The
channel filters for digital television will have virtually no effect at the edge
of the channel. The reason it that the group delay would have a fatal impact on
the 8VSB signal. The filters don't kick in until 750 khz to 1250 khz away from
the channel. That means that the FCC mask has to be met by the transmitter.
That's something of a daunting task when you consider that values of -35 to -38
dB are typical of what a transmitter will do. The IOT has a very broad response
so there really isn't much rolloff near the channel edge.
The dynamic correction we've been hearing about may distort the peak to
average ratio of the signal and truncate peaks and effectively reduce system
S/N. The correction may provide little more than a carpet to sweep signal under
while simultaneously reducing power and coverage.
HOW'S YOUR ISI FILTER? Buried in
the 8VSB modulator is a filter which converts the 8 level digital signal to an
analog signal. It is the intersymbol interference filter (ISI). Without it the
required bandwidth would be infinite. With it, the system put 2 pounds of YNW in
to a one pound bag. Once in awhile 7 dB spills out. If you believe in perpetual
motion machines and alchemy, 8VSB should present no problem.
LONG HIKE AT NAB Please be advised
that you can't walk from the front of the LVCC to the LV Hilton. Construction is
underway. You have to go halfway back toward the meeting rooms and then go over.
Allow twice the amount of time.
WEB PAGE The chapter 40 web page is
at http://www.lns.com/sbe and is maintained
by Tim Pozar.
EMAIL MEISTER The keeper of the
chapter 40 email address list is Warren Reese his address is radions@jps.net.
Warren worked for the KPH in Bolinas which was one of the last coastal Morse
sites. He has photos of KPH on his web page at http://www.jps.net/radions.
Mountaintop Engineers Plan Annual Pre NAB Vanilla
Pudding Run at ZZYZX The 9th annual Vanilla Pudding contest
is on again in ZZYZX, which is between Barstow and Las Vegas. The April 1st sand
dune rock downhill ski run, done while balancing cups of vanilla pudding on the
skis is in the grand tradition of radio transmitter site sports. Check out the
details at www.nojohn.com.