Thank you all for your replies. As I should have guessed, a simple
question leads to a long and complicated answer!
Peter
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In message [EMAIL PROTECTED], John Day writes:
So 75 ohms as we
know it now is a compromise between the low attenuation 77 ohms and
the 73 ohm dipole feed-point.
I can confirm that the choice of 75 Ohm for telecom use indeed
is because of the low attenuation. The first use of coax was
for
measurement
Subject: Re: [time-nuts] 50 vs 75 ohm cables
In message [EMAIL PROTECTED], John Day writes:
So 75 ohms as we
know it now is a compromise between the low attenuation 77 ohms and
the 73 ohm dipole feed-point.
I can confirm that the choice of 75 Ohm for telecom use indeed
is because of the low
At 02:52 AM 5/11/2007, Peter Vince wrote:
Thank you all for your replies. As I should have guessed, a simple
question leads to a long and complicated answer!
Of course!
One of the truly fun things about groups such as this one is that we
have people with an enormous wealth of knowledge. I know
In a message dated 5/10/2007 20:27:33 Pacific Daylight Time,
[EMAIL PROTECTED] writes:
Fortunately we are seeing more and more DVI and HDMI around here and
they seem to have much better characteristics, the S-Video
interconnec system is, to put it mildly, worthy of the junk bin!
Yeah,
[EMAIL PROTECTED] said:
I can confirm that the choice of 75 Ohm for telecom use indeed is
because of the low attenuation. The first use of coax was for
Carrier Frequency systems, where a number of telephone conversations
were AM modulated on individual carriers, usually 4 kHz apart.
What's
As the impedance goes up, the current drops for a given power level drops.
John WA4WDL
- Original Message -
From: Hal Murray [EMAIL PROTECTED]
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Sent: Friday, May 11, 2007 3:26 PM
Subject: Re: [time-nuts] 50 vs
At 03:26 PM 5/11/2007, you wrote:
[EMAIL PROTECTED] said:
I can confirm that the choice of 75 Ohm for telecom use indeed is
because of the low attenuation. The first use of coax was for
Carrier Frequency systems, where a number of telephone conversations
were AM modulated on individual
In message [EMAIL PROTECTED], Hal Murr
ay writes:
[EMAIL PROTECTED] said:
I can confirm that the choice of 75 Ohm for telecom use indeed is
because of the low attenuation. The first use of coax was for
Carrier Frequency systems, where a number of telephone conversations
were AM modulated on
I came across some telecom equipment the other day which had
reference outputs marked as 75 ohms. I work in television, not
telecoms, and we use 75 ohm connections for video, but with most RF
stuff being (I believe) 50 ohms, and certainly all the HP and other
counters seem to have 50 ohm
From: Peter Vince [EMAIL PROTECTED]
Subject: [time-nuts] 50 vs 75 ohm cables
Date: Thu, 10 May 2007 13:39:27 +0100
Message-ID: [EMAIL PROTECTED]
I came across some telecom equipment the other day which had
reference outputs marked as 75 ohms. I work in television, not
telecoms, and we use
] On
Behalf Of Peter Vince
Sent: 10 May 2007 13:39
To: time-nuts@febo.com
Subject: [time-nuts] 50 vs 75 ohm cables
I came across some telecom equipment the other day which had
reference outputs marked as 75 ohms. I work in television, not
telecoms, and we use 75 ohm connections for video
Peter-
Maybe others have hard historical evidence, but my understanding is that the 50
ohm cables were selected because of better power handling capability in high
power RF applications and the 75 ohm standard was used for lower loss
applications. That's why CATV folks use 75 ohm cables. It
Danielson [EMAIL PROTECTED]
To: time-nuts@febo.com; [EMAIL PROTECTED]
Sent: Friday, May 11, 2007 12:53 AM
Subject: Re: [time-nuts] 50 vs 75 ohm cables
From: Peter Vince [EMAIL PROTECTED]
Subject: [time-nuts] 50 vs 75 ohm cables
Date: Thu, 10 May 2007 13:39:27 +0100
Message-ID: [EMAIL PROTECTED]
I
Sure,
If you factor in all of the ohmic losses, ~70 ohm is the
lowest loss ratio of inner to outer conductor diameters
in an air dielectric coaxial transmission line.
The original 70 ohm line, invented by Western Electric,
was air dielectric with a thin polyethylene disk every foot.
50 ohm
Hi Peter,
If you make a dipole (not folded) antenna for any frequency it will have
a characteristic impedance of 72 Ohms in free space. It will also have,
essentially, the same impedance until you get real close to the ground.
A properly made electrical 1/4 wavelength vertical antenna will have
At 11:00 AM 5/10/2007, WB6BNQ wrote:
Hi Peter,
snipped
In an effort to standardize, the industry selected the mid point between
the 35 Ohms and the 72 Ohms, that being 50 Ohms. This forced the antenna
manufacturers to design their antennas for 50 Ohms or provide a matching
network.
Nice
John Day wrote:
At 11:00 AM 5/10/2007, WB6BNQ wrote:
Hi Peter,
snipped
In an effort to standardize, the industry selected the mid point
between
the 35 Ohms and the 72 Ohms, that being 50 Ohms. This forced the
antenna
manufacturers to
Hi guys,
some practical comments:
* 50 Ohms transmission lines are much easier to fabricate on standard 4,
6, or 8 layer PCB's. 75 Ohms traces are very thin and thus have issues in
manufacturing accuracy.
* Feeding a 50 Ohm source into a 75 Ohm load gives a VSWR of 1.5, a
At 01:50 PM 5/10/2007, WB6BNQ wrote:
John Day wrote:
At 11:00 AM 5/10/2007, WB6BNQ wrote:
Hi Peter,
snipped
In an effort to standardize, the industry selected the mid point
between
the 35 Ohms and the 72 Ohms, that being 50 Ohms. This
At 02:31 PM 5/10/2007, [EMAIL PROTECTED] wrote:
Hi guys,
some practical comments:
* 50 Ohms transmission lines are much easier to fabricate on standard 4,
6, or 8 layer PCB's. 75 Ohms traces are very thin and thus have issues in
manufacturing accuracy.
* Feeding a 50 Ohm source into a
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