Why is video inverted for transmission?

[Joel Kolstad]

Spark-gap transmitters of any purity are illegal in US jurisdictions because
the FCC says so.

Ah, ok. Interesting... I suppose such a rule probably made a lot of sense at
one point.

I suspect that if one managed to build a spark gap transmitter for, say, the
HF amateur bands that had good enough filtering to splatter no worse than a
typical commercial radio, you would at least be pretty low on the FCC's list
of people to prosecute.

Likewise illegal, no matter how stable it may be, is an AM modulated
oscillator.

As opposed to a leveled oscillator with a separate modulator? Aren't things
like 49MHz kids (100mW) walkie talkies something like three transistors that's
someone's very creative kludge (the same transistors work for transmitting and
receiving) but that is still some sort of "amplitude modulated oscillator?"

 

[Martin Griffith]

He also apparently operated a _legal_ land based spark gap transmitter.
[I was once challenged on that statement - Checking with rep of Antique
Wireless Association of Holcomb NY showed claim was _feasible_.]

Absolutely... something a lot of people don't realize is that spark-gap
transmitters did have resonant circuits almost immediately after the first few
were built. Heck, strictly speaking I don't believe there's anything
inherently illegal about a spark-gap transmitter today -- it'd just that you'd
probably have to filter the daylights out of it to meet mordern emission
standards, so it wouldn't exactly be an "authentic" setup.

Spark-gap transmitters used tank circuits. Even Hertz's original
microwave transmitter used a resonant circuit, the tuned transmitting
antenna. Each spark excited the tank to ring for a few cycles, with
heavy damping. (What we now measure in time constants was called
"logarithmic decrement".) Most had no way to keep the phase of one burst
coherent with the preceding one, so splatter was heavy. (Various ways to
achieve coherence were truly ingenious.)

Spark-gap transmitters of any purity are illegal in US jurisdictions
because the FCC says so. Likewise illegal, no matter how stable it may
be, is an AM modulated oscillator.

Jerry

Somewhat OT, an 1895 demonstartion of microwaves
http://www.tuc.nrao.edu/~demerson/bose/bose.html


Martin

 

[Jerry Avins]

Ron Hunter wrote:

...

Now there is a great idea, uranium glass for radiation shielding....

It might be good shielding. Uranium is far heavier than lead, and
"spent" uranium is less radioactive than many other elements.

Jerry

 

[Michael A. Terrell]

GADS
I think my Father could top your stories.

He told of making capacitors.
The rule of thumb was "1 micro farad" / "gallon of 'fish tank' "

I have a roll of metaized mylar film from the Sprage plant that was
closed in teh Orlando area, years ago, along with a 20 pound spool of
component lead. Capacitors aren't hard to make, but why bother, these
days? Try keeping a 50 year old broadcast transmmiter on the air when
there are no spare parts availible.

He also apparently operated a _legal_ land based spark gap transmitter.
[I was once challenged on that statement - Checking with rep of Antique
Wireless Association of Holcomb NY showed claim was _feasible_.]

WHEN did he operate it? Spark is not a legal mode, and hasn't been
for a LONG LONG time. Even with a tuned circuit to couple the RF to the
antenna, the broadband noise will wipe out other communications. Spark
was replaced by Alexanderson generators.

When more uses were found for the radio spectrum, spark was made
illegal.

http://en.wikipedia.org/wiki/Ernst_Alexanderson


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jerry Avins]

Ah, ok. Interesting... I suppose such a rule probably made a lot of sense at
one point.

I suspect that if one managed to build a spark gap transmitter for, say, the
HF amateur bands that had good enough filtering to splatter no worse than a
typical commercial radio, you would at least be pretty low on the FCC's list
of people to prosecute.


As opposed to a leveled oscillator with a separate modulator? Aren't things
like 49MHz kids (100mW) walkie talkies something like three transistors that's
someone's very creative kludge (the same transistors work for transmitting and
receiving) but that is still some sort of "amplitude modulated oscillator?"

If the power is low enough, they don't care. But the rules definitely
apply to a 5W, or even a 2W set. Those are crystal controlled -- perhaps
via a PLL -- and the modulated stage is not the oscillator.

Jerry

 

[Richard Owlett]

Michael A. Terrell wrote:



GADS
I think my Father could top your stories.

He told of making capacitors.
The rule of thumb was "1 micro farad" / "gallon of 'fish tank' "

I have a roll of metaized mylar film from the Sprage plant that was
closed in teh Orlando area, years ago, along with a 20 pound spool of
component lead. Capacitors aren't hard to make, but why bother, these
days? Try keeping a 50 year old broadcast transmmiter on the air when
there are no spare parts availible.

He also apparently operated a _legal_ land based spark gap transmitter.
[I was once challenged on that statement - Checking with rep of Antique
Wireless Association of Holcomb NY showed claim was _feasible_.]

WHEN did he operate it?

Probably circa 1920. When he told me the stories I wasn't much
interested in dates.

In the mid-50's the AWA Museum had a operating permit for a spark gap
transmitter that allowed them to operate for up to 5 minutes with no
antenna attached. At that time nothing within 10 miles except farms.
Definitely impressed me as a teenager.

 

[Jerry Avins]

Michael A. Terrell wrote:

...

I have a roll of metaized mylar film from the Sprage plant that was
closed in teh Orlando area, years ago, along with a 20 pound spool of
component lead. Capacitors aren't hard to make, but why bother, these
days? Try keeping a 50 year old broadcast transmmiter on the air when
there are no spare parts availible.

I was once so far out in the Atlantic that the Coast Guard, who were
looking for us in Long Island Sound, found us only by accident and that
only after five hours of motoring closer to shore. The motor had quit
the afternoon before, then a storm came up. We drifted as far as we did
because of the tide pulling us out with a sea anchor I gas improvised to
keep from getting swamped by waves.

Come first light and a calm sea, I got the flywheel off and figured out
that the condenser was shorted. I made a replacement from four sheets of
foil-lined paper from cigarette packs -- smoking saved our lives -- that
worked well enough to get us under way. There are plenty of reasons to
make capacitors.

He also apparently operated a _legal_ land based spark gap transmitter.
[I was once challenged on that statement - Checking with rep of Antique
Wireless Association of Holcomb NY showed claim was _feasible_.]

WHEN did he operate it? Spark is not a legal mode, and hasn't been
for a LONG LONG time. Even with a tuned circuit to couple the RF to the
antenna, the broadband noise will wipe out other communications. Spark
was replaced by Alexanderson generators.

Marine spark equipment was grandfathered for a long time after it was
banned on land. You didn't need a BFO to read it precisely because it
wasn't CW. A late friend was a passenger in a two-seater in Alaska that
broke up on making an emergency landing. He improvised a spark-gap
transmitter using the battery and spark coil, as well as other wires
ripped out of the plane. For two hours he alternated between tapping out
his best-guess position and keeping fire going. Then a plane dropped
survival equipment and food. Two hours later yet, a helicopter landed
and picked them up. He asked the crew if his signal had been heard of if
they had been found by accident. "Hear you" came the answer. "You were
all over two bands. Nobody could hear anything else." To quote the Edda,
"Even the black dog will have its day."

When more uses were found for the radio spectrum, spark was made
illegal.

http://en.wikipedia.org/wiki/Ernst_Alexanderson

Jerry

 

[G]

Michael A. Terrell wrote:



Jerry

When I was fairly young I got a remote control bus for Christmas. it used a
spark gap transmitter. The receiver used a powered carbon detector.
Every time a signal was found, the carbon would start to conduct and fire a
relay setting up action on the preprogrammed mechanics and motor. When
an action ws complete, a arm would come down a hit the carbon detector
to break conduction and get ready for another command. it used to trigger
on lightning. I got my first real shock when i unscrewd the insulated antenna
out, and stuck my finger in the hole and pushed the button. I guess
that was my first electronic project, except my mother used to tell me about
the time when I poured water into a lamp socket. It goes buzzz.

greg

 

[Gene E. Bloch]

No wonder Thunderbird's spell checker flagged it. I assumed the word was just
too big. Silly me!

Jerry

Oh - Thunderbird. I use it for e-mail. Its spell checker is very
bizarre, IMHO

Luckily I also use the organic spell checker after a pass or three of
Thunderbird's. When I remember to do it, that is...

I use a bunch of spell checkers (not by choice - each program seems to
have a checker of its own), and they *all* are bizarre - it's just that
what one screws up the next does fine, etc

 

[Joerg]

Joerg wrote:
(snip)



Living in big cities is always expensive, and basic cable should
be less than $30.

Now, for people living away from big cities, can a large antenna and
amplifier get enough signal? I believe the current DTV signals
are in the UHF region where high gain antennae aren't so hard to
build and low noise transistors are more affordable than ever.
Multipath should be a small problem relative to signal strength.

Multipath is extreme here. I don't know yet but I have heard that DTV
quickly falls apart under those conditions. When you watch "All in the
Family" out here you sometimes have 3-4 Archie Bunkers in there. When a
Fedex Cargo jet lumbers in that increases to almost 10 of them. And we
have a rather large Yagi antenna on a mast, low noise preamp, head
distribition amplifier and all that. The distribution has been carefully
designed, calculated and built by yours truly and causes no reflections.
Yet there is only one channel (Ch19) with no ghosting at all. It's
Spanish only ...

In Seattle, I can get plenty of signal with an antenna in the attic
(installed by the previous owner) and two splitters on the way down.
I can see the transmitters out the window. (I don't know if they
are TV or radio, though, but I can see them.)

The Seattle area is much easier. My first employer's HQ is there, in
Bothell. AFAIR the RF situation doesn't become nearly as tricky until
you get to somewhere significantly east of Issaquah.

 

[glen herrmannsfeldt]

Jerry Avins wrote:

(snip)

Come first light and a calm sea, I got the flywheel off and figured out
that the condenser was shorted. I made a replacement from four sheets of
foil-lined paper from cigarette packs -- smoking saved our lives -- that
worked well enough to get us under way. There are plenty of reasons to
make capacitors.

Trying to remember non-electronic ignition systems, I thought they
would work without the capacitor. (or condenser as I remember it.)

The points would ark more and wear out faster, but probably not
so fast that you wouldn't get back to shore.

-- glen

 

[glen herrmannsfeldt]

Joerg wrote:
(snip)

No idea, I don't like to live in big cities. But cable has one downside:
$$$. Out here it starts at around $30-40. OTA is $0. Why pay that money
when all you want to see is the evening news? Ok, we'd have that money
but there are people who don't and they might become rather miffed in
early 2009.

Living in big cities is always expensive, and basic cable should
be less than $30.

Now, for people living away from big cities, can a large antenna and
amplifier get enough signal? I believe the current DTV signals
are in the UHF region where high gain antennae aren't so hard to
build and low noise transistors are more affordable than ever.
Multipath should be a small problem relative to signal strength.

In Seattle, I can get plenty of signal with an antenna in the attic
(installed by the previous owner) and two splitters on the way down.
I can see the transmitters out the window. (I don't know if they
are TV or radio, though, but I can see them.)

-- glen

 

[glen herrmannsfeldt]

Ron Hunter wrote:

(snip)

BTW, is there a warning on those lead glass bricks about not eating
them, or letting children play with them? More paranoia.

There are plenty of things in physics labs that do radiation
work that don't have warnings on them. I would expect lead glass
bricks to be less of a problem than solid lead bricks.

The usual problem with lead crystal goblets is acidic liquids
that can dissolve some of the lead out. Usually lead glass bricks
are not stored in acidic liquids.

-- glen

 

[glen herrmannsfeldt]

Jerry Avins wrote:

(snip)

I live about half way between New York and Philadelphia and receive
pretty good signals from each. (Antenna has a rotator.) Multipath was a
problem that showed up as ghosting until a nearby water tower was taken
down. The Verrazano-Narrows Bridge across the Hudson caused weaker
multipath on New York stations while the antennas were on the World
Trade Center. Multipath can happen anywhere.

I was thinking about farm houses in the plain states. Far from the
big cities, and fairly flat. There could still be water towers
around, though. It might be too far out for affordable cable.

I would hope that the receivers could handle simple multipath with
echo cancellation systems such as those that modems or ethernet use,
but for big cities it is likely too much.

-- glen

 

[glen herrmannsfeldt]

Jerry Avins wrote:

(snip on lead glass bricks)

Yellow: interesting. The best yellow glazes I've seen contain uranium.

As I remember them, lead glass would be a fairly light yellow.
You could look through a three or four inch thick brick and it still
looked light yellow. As a thin glaze, you might not notice it.

-- glen

 

[Joel Kolstad]

Multipath is extreme here. I don't know yet but I have heard that DTV
quickly falls apart under those conditions.

I had heard that "first generation" ATSC chipsets weren't designed to worry
about multipath, but that 2nd and 3rd generation chips did. So while I think
you have a very valid concern, at least the engineers were aware of the
problems and I'm hoping you're going to be pleasantly surprised come 2008.

My only experience with ATSC so far was in Portland, OR where about 90% of the
transmitters are all on a nice, high hilltop so it was a simple matter of
pointing the roof-mounted antenna that way and it all worked swimmingly.

---Joel

 

[Joerg]

I had heard that "first generation" ATSC chipsets weren't designed to worry
about multipath, but that 2nd and 3rd generation chips did. So while I think
you have a very valid concern, at least the engineers were aware of the
problems and I'm hoping you're going to be pleasantly surprised come 2008.

For some reason there is a dearth of info about it. And here I mean
serious "rubber meats the road" field test results. Side by side, analog
image, followed by the digital image from the same tower. Move 100ft,
then do it again. And so on. Like what we do (hafta do) in medical or
the FDA would read us the riot act. I know a perfect spot out here for
such tests ;-)

My only experience with ATSC so far was in Portland, OR where about 90% of the
transmitters are all on a nice, high hilltop so it was a simple matter of
pointing the roof-mounted antenna that way and it all worked swimmingly.

A hill surrounded by smoothly dropping terrain is ideal for any digital
comms. Multipath is hard on digital, not matter how much effort they put
into FEC and all that. Same with digital cordless phones. There is no
gradual decay when you walk towards the garage here, it completely cuts
out from one second to the next.

 

[ChairmanOfTheBored]

That's obviously the best you can do, so why not just wuit?

You obviously have zero capacity to make valid assessments.
Particularly in Usenet.

 

[ChairmanOfTheBored]

Multipath is extreme here. I don't know yet but I have heard that DTV
quickly falls apart under those conditions. When you watch "All in the
Family" out here you sometimes have 3-4 Archie Bunkers in there.

Then it ain't digital.

 

[marika]

Joel Kolstad wrote in message

If a technology is supposed to be

Give him... mmm... about a year and a bit: By Christmas session next year, I'm
willing to bet there's going to be a large pile of ATSC->NTSC converters
sitting in a noticeable pile, with price tags $99 or below.

probably just preoccupied

wondering what the odds are that he will get together with Rosie Odonell

Also, hmmm scientology hmmm

and yet also, all those rumors he was impotent and whatever

mk5000

"The selected Company,
determines which
departments are available for
selection"--jason smith