Gordon wrote:
Well, I got an improvement, probably in spite of myself. The
setup gives better signal strength, and is less suseptable to
interfearence (people walking aroung the room) than just a
single bowtie.

A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Cecil Moore wrote:
Gordon wrote:
Well, I got an improvement, probably in spite of myself. The
setup gives better signal strength, and is less suseptable to
interfearence (people walking aroung the room) than just a single bowtie.

A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?

If its bad enough it will wreck the reception. But the latest
processors can tolerate multipath that is only 1 db down.

They are getting better as they try to debug HDTV for mobile reception.

-Bill

On Jun 1, 4:49*am, Cecil Moore wrote:
Gordon wrote:
Well, I got an improvement, probably in spite of myself. *The
setup gives better signal strength, and is less suseptable to
interfearence (people walking aroung the room) than just a
single bowtie.

A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

It puts 'ripples' into the passband. The ripples happen because of
phase cancelations. The ATI HDTV Wonder cards can handle variations to
around 8-10 dB. After that it just freezes up.

Near the bottom of the page in the link there is an example of the
ATSC spectrum. Add random dips into it.

http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html

G²

On Mon, 01 Jun 2009 06:49:20 -0500, Cecil Moore
wrote:

A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?

Your worst nightmare. From 10 years ago:
http://www.businessweek.com/bwdaily/dnflash/aug1999/nf90826b.htm
(Note the sales predictions, which were totally wrong).
All DTV chipsets now have ghost elimination circuitry, which does a
good job of reducing multipath problems. There's a spec for it but
I'm too lazy to look. Here's the patent:
http://www.google.com/patents?id=XNp3AAAAEBAJ&dq=7038732
with references to others in citations. I won't pretend to understand
how it works.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 01 Jun 2009 06:49:20 -0500, Cecil Moore
wrote:

Gordon wrote:
Well, I got an improvement, probably in spite of myself. The
setup gives better signal strength, and is less suseptable to
interfearence (people walking aroung the room) than just a
single bowtie.

A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?

In countries using COFDM (DVB-T), the symbol time is about 1000 us
(8k) or 250 us (2k), so in the worst case with minimal guard
intervals, you can still use mismatched coaxial cables longer than 1
km without problems :-).

With ATSC 8VSB it depends how well the equalizer is capable of
detecting the characteristics of the radio and coaxial path with a
known signal pattern.

Paul OH3LWR

A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?

Just as a point of interest (to me at least) I grew up within 3 blocks of
an airport, it
was a several times a day occurance to have the picture flutter as an
airplane flew by.
Mike

On Jun 9, 11:21*pm, "amdx" wrote:
A mismatch can cause ghosting in an analog TV.
What does ghosting do to a digital TV signal?

* Just as a point of interest (to me at least) I grew up within 3 blocks of
an airport, it
was a several times a day occurance to have the picture flutter as an
airplane flew by.
* * * * * * * * * * * * * * * * * * * * * * * * *Mike

It was identifying the reflection of radio signals from a flying
aircraft that led to the development and use of radar.
Radar was major factor in the successful defence of Britain (Britain
1940) against German bombing (The Blitz) early in WWII (1939-1945).
Although it was initially very crude, (It was called Radio-location or
RDF, Radio Direction Finding) at the time.
Unfortunately the first war time US use of radar was misinterpreted
when the Japanese attacked Pearl Harbour in Dec 1941!

stan wrote:

It was identifying the reflection of radio signals from a flying
aircraft that led to the development and use of radar.
Radar was major factor in the successful defence of Britain (Britain
1940) against German bombing (The Blitz) early in WWII (1939-1945).
Although it was initially very crude, (It was called Radio-location or
RDF, Radio Direction Finding) at the time.
Unfortunately the first war time US use of radar was misinterpreted
when the Japanese attacked Pearl Harbour in Dec 1941!

Actually it was blocking of a radio transmission by ships passing on a
river that led to the development of radar.

tom
K0TAR

On Mon, 15 Jun 2009 20:32:40 -0500, tom wrote:
stan wrote:

It was identifying the reflection of radio signals from a flying
aircraft that led to the development and use of radar.
Radar was major factor in the successful defence of Britain (Britain
1940) against German bombing (The Blitz) early in WWII (1939-1945).
Although it was initially very crude, (It was called Radio-location or
RDF, Radio Direction Finding) at the time.
Unfortunately the first war time US use of radar was misinterpreted
when the Japanese attacked Pearl Harbour in Dec 1941!

Actually it was blocking of a radio transmission by ships passing on a
river that led to the development of radar.

The Potomac -- I think that's what I read about it.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
* Killfiling google & XXXXbanter.com: jonz.net/ng.htm

On Mon, 15 Jun 2009 20:32:40 -0500, tom wrote:

stan wrote:

It was identifying the reflection of radio signals from a flying
aircraft that led to the development and use of radar.
Radar was major factor in the successful defence of Britain (Britain
1940) against German bombing (The Blitz) early in WWII (1939-1945).
Although it was initially very crude, (It was called Radio-location or
RDF, Radio Direction Finding) at the time.
Unfortunately the first war time US use of radar was misinterpreted
when the Japanese attacked Pearl Harbour in Dec 1941!

Actually it was blocking of a radio transmission by ships passing on a
river that led to the development of radar.

tom
K0TAR

RF blocking was used by both sides as a "burglar alarm" to detect
naval vessels passing through narrow straights. Germany tried to get
such a system working across the Straits of Gibraltar, but were foiled
by Spain's failure to cooperate.

Radar was officially "invented" in 1935 when Watson-Watt was asked by
the air ministry to calculate the possibility of using RF as a "death
ray" to cook an airplane pilot in flight. Some calculations were
performed which quickly determined that it was impossible. However,
he suggested that a similar system could be used to detect the
airplane by combining the range finding of ionospheric layers
techniques and the direction finding techniques used to detect
thunderstorms. At the time, there were also proposals for aircraft
detection using infrared and sound detection. Not wanting to lose
their funding, it was agreed that RF reflection was a good idea and
that research should continue on this different path.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558