Which is it, RG59 or RG6?

[Jeff Liebermann]

On Sun, 06 Dec 2009 22:51:17 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Part of the extra .5 dB loss is in the cast aluminum 'F' connectors.
I ran Q. A. I ran tests on hundreds of samples to qualify them for our
MSO to purchase the best quality we could find. We bought splitters by
the thousands, and coax by the pallet

Also, eight way splitters are listed at -10 dB, not 10.5.

Agreed. However, I never had much trouble with the aluminium F
connectors. It was the chrome plated zinc castings that drove me
nuts. The RF skin depth at 1GHz was terrible making the connectors
rather lossy. Combined with an aluminum F connector, I had a few
millivolts of electrolysis and noise.

For entertainment, I like to string all the adapters in my collection
in series, and measure the loss. According to numerous luminaries,
the attenuation would be attrocious, sky high, dismal, or anything
except nominal. I don't have photos of my last song and dance in
front of the local radio clubs, but one person agreed to reproduce the
experiment with decent test equipment:
<http://802.11junk.com/jeffl/antennas/connector-loss/>
The display photos are rather difficult to read. The loss through
about 20 adapters is about -0.3dB at 450MHz and -2.0dB at 2.4GHz.
That's approximately the loss of an equivalent length of LMR-240. I've
done similar tests with assorted F adapters with similar results. The
chain a created for the local radio clubs was about 6ft long. I got
lazy and just used a wattmeter at each end of the coax, and a handheld
radio. Hardly any loss at 446MHz.


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

 

[Jeff Liebermann]

On Sun, 06 Dec 2009 23:11:22 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Ingression is external signals getting into the CATV plant. You are
describing radiation' where the signal is lost to being radiated from
the outer conductor, due to poor connections. It is monitored on a
continuous basis on most cable systems using 'Sniffer' or other brands
of monitoring equipment. While the signal is on the video carrier
frequency, it is FM modulated with annoying audio to make it easy to
identify.

Well, the leak or ingress goes both ways. While ingress from ham,
commercial, and broadcast radio xmitters are irritating, the
regulatory requirement is to prevent cable leakage from interfering
with public safety, aircraft, and of course, OTA broadcast. Lots of
nice toys to measure this leakage:
<http://www.trilithic.com/Broadband%20Instruments>

Personally, I prefer visual inspection, a TDR (time domain
reflectometer), signal level measurements, or just a pre-emptive
replacement.

Those are OK if you can shut a system down for repairs. Poor
connections in the trunkline can be detected by reading the voltage drop
between the coax and the amplifier housing, splice block or any other
splice in any powered cable. 60 volts modified sine wave AC @ 30 amps
from a CVT doesn't tolerate much resistance without causing hum
modulation or burning up a connector.

Ummm... the OP is trying to troubleshoot his home installation, not
the trunk line (or cable drop). I think it's a safe bet that he can
unplug his spaghetti without difficulties.


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

 

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sun, 06 Dec 2009 23:11:22 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Ingression is external signals getting into the CATV plant. You are
describing radiation' where the signal is lost to being radiated from
the outer conductor, due to poor connections. It is monitored on a
continuous basis on most cable systems using 'Sniffer' or other brands
of monitoring equipment. While the signal is on the video carrier
frequency, it is FM modulated with annoying audio to make it easy to
identify.

Well, the leak or ingress goes both ways. While ingress from ham,
commercial, and broadcast radio xmitters are irritating, the
regulatory requirement is to prevent cable leakage from interfering
with public safety, aircraft, and of course, OTA broadcast. Lots of
nice toys to measure this leakage:
http://www.trilithic.com/Broadband%20Instruments

The idiot manager of one system ordered the wrong midband modulator
that was right in the aircraft band. Rather than admit it, over 10,000
converters had to be modified to tune the new channel. It was used to
add 'The nashville Network' which had just been launched. The system was
in the Cincinnati area where people claimed that they didn't listen to
'shit kicking music'. I tested the mew modulator & c-band equipment for
less than 30 seconds, and after 2 am. We had over 100 phone calls
waiting the next morning, wanting to know when it would be back.

Personally, I prefer visual inspection, a TDR (time domain
reflectometer), signal level measurements, or just a pre-emptive
replacement.

Those are OK if you can shut a system down for repairs. Poor
connections in the trunkline can be detected by reading the voltage drop
between the coax and the amplifier housing, splice block or any other
splice in any powered cable. 60 volts modified sine wave AC @ 30 amps
from a CVT doesn't tolerate much resistance without causing hum
modulation or burning up a connector.

Ummm... the OP is trying to troubleshoot his home installation, not
the trunk line (or cable drop). I think it's a safe bet that he can
unplug his spaghetti without difficulties.

Then it is very unlikely he will have access to a TDR, sniffer or any
other equipment. Even a field strength meter isn't likely.


--
Offworld checks no longer accepted!

 

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sun, 06 Dec 2009 22:51:17 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Part of the extra .5 dB loss is in the cast aluminum 'F' connectors.
I ran Q. A. I ran tests on hundreds of samples to qualify them for our
MSO to purchase the best quality we could find. We bought splitters by
the thousands, and coax by the pallet

Also, eight way splitters are listed at -10 dB, not 10.5.

Agreed. However, I never had much trouble with the aluminium F
connectors. It was the chrome plated zinc castings that drove me
nuts. The RF skin depth at 1GHz was terrible making the connectors
rather lossy. Combined with an aluminum F connector, I had a few
millivolts of electrolysis and noise.

the tap plates were cast aluminum if they were Jerrold, or plated
brass threads bolted to an aluminum plate in Lindsay taps. Both cause
problems in areas where road salt was used. Just as bad were the
unplated brass cable connectors someone tried to sell us.

For entertainment, I like to string all the adapters in my collection
in series, and measure the loss. According to numerous luminaries,
the attenuation would be attrocious, sky high, dismal, or anything
except nominal. I don't have photos of my last song and dance in
front of the local radio clubs, but one person agreed to reproduce the
experiment with decent test equipment:
http://802.11junk.com/jeffl/antennas/connector-loss/

Run the tests again after a 48 hour salt spray test.

The display photos are rather difficult to read. The loss through
about 20 adapters is about -0.3dB at 450MHz and -2.0dB at 2.4GHz.
That's approximately the loss of an equivalent length of LMR-240. I've
done similar tests with assorted F adapters with similar results. The
chain a created for the local radio clubs was about 6ft long. I got
lazy and just used a wattmeter at each end of the coax, and a handheld
radio. Hardly any loss at 446MHz.

--
Offworld checks no longer accepted!

 

[Jeff Liebermann]

On Mon, 07 Dec 2009 02:59:30 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

the tap plates were cast aluminum if they were Jerrold, or plated
brass threads bolted to an aluminum plate in Lindsay taps. Both cause
problems in areas where road salt was used. Just as bad were the
unplated brass cable connectors someone tried to sell us.

Again, this is for outdoor use. The OP is doing indoor.

http://802.11junk.com/jeffl/antennas/connector-loss/

Run the tests again after a 48 hour salt spray test.

<http://en.wikipedia.org/wiki/Salt_spray_test>

Actually, I have. I used to design marine radios and the salt fog
test was one of the hazards of the business. None of the equipment
survived 100%. We were just checking for problems that might occur in
a marine atmosphere. As I recall, the silver plated brass connectors
did quite well, while the cadmium plated pot metal died a horrible
death. Dissimilar metals and connector materials were also bad.
Unless you watch TV in the shower, I don't think any of these will be
a problem with an indoor installation.

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

 

[mm]

On Sun, 06 Dec 2009 20:49:12 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sun, 06 Dec 2009 22:51:17 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Part of the extra .5 dB loss is in the cast aluminum 'F' connectors.
I ran Q. A. I ran tests on hundreds of samples to qualify them for our
MSO to purchase the best quality we could find. We bought splitters by
the thousands, and coax by the pallet

Also, eight way splitters are listed at -10 dB, not 10.5.

Agreed. However, I never had much trouble with the aluminium F
connectors. It was the chrome plated zinc castings that drove me
nuts. The RF skin depth at 1GHz was terrible making the connectors
rather lossy. Combined with an aluminum F connector, I had a few
millivolts of electrolysis and noise.

So is there any value in getting gold-plated F connectors (if they
have them) or gold-plated A/B switches (which I know they sell)?

It's the A/B switch I'm particularly curious about because at one
store, that was all they had, and some antenna signals are so weak, I
figured any little thing might help.


Or other gold plated connectors?

 

[Jeff Liebermann]

On Mon, 07 Dec 2009 13:15:19 -0500, mm <NOPSAMmm2005@bigfoot.com>
wrote:

So is there any value in getting gold-plated F connectors (if they
have them) or gold-plated A/B switches (which I know they sell)?

No. The plating is so thin, that at UHF frequencies, the skin depth
is less than the plating depth. If you want good RF conductivity, get
silver plated connectors. The real problem with gold is dissimilar
metals. Although gold will not corrode, oxidize, or rot, it will
create an electrolytic junction when wet. The result is some noise,
and possibly some corrosion of the other junction metal. What that
means is that gold is a fair idea if you use all gold connectors,
everywhere. It's not so great an idea if you mix materials.

However, that's really only for exterior installations, where water
can get into the connectors and devices. For indoor use, it's not so
much an issue unless you live in the tropics, on a boat, or in a
swamp.

It's the A/B switch I'm particularly curious about because at one
store, that was all they had, and some antenna signals are so weak, I
figured any little thing might help.

Or other gold plated connectors?

Ok, so we're off cable TV and onto OTA (over the air) issues.

The biggest improvements you do for signal strength are (in order of
importance):
1. Location, location, location, location, line of sight, etc.
2. Selection, design and construction of the antenna(s).
3. A tower mounted amplifier.
4. Everything else.
If you've done the first 3 items, to the best your abilities and
finances, then tinkering with plating materials and A-B switches is a
waste of time and money.

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

 

[mm]

On Mon, 07 Dec 2009 11:46:16 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Mon, 07 Dec 2009 13:15:19 -0500, mm <NOPSAMmm2005@bigfoot.com
wrote:

So is there any value in getting gold-plated F connectors (if they
have them) or gold-plated A/B switches (which I know they sell)?

No. The plating is so thin, that at UHF frequencies, the skin depth
is less than the plating depth. If you want good RF conductivity, get
silver plated connectors. The real problem with gold is dissimilar
metals. Although gold will not corrode, oxidize, or rot, it will
create an electrolytic junction when wet. The result is some noise,
and possibly some corrosion of the other junction metal. What that
means is that gold is a fair idea if you use all gold connectors,
everywhere. It's not so great an idea if you mix materials.

However, that's really only for exterior installations, where water
can get into the connectors and devices. For indoor use, it's not so
much an issue unless you live in the tropics, on a boat, or in a
swamp.

I've been told it's a swamp, but I disagreed.

It's the A/B switch I'm particularly curious about because at one
store, that was all they had, and some antenna signals are so weak, I
figured any little thing might help.

Or other gold plated connectors?

Ok, so we're off cable TV and onto OTA (over the air) issues.

The biggest improvements you do for signal strength are (in order of
importance):
1. Location, location, location, location, line of sight, etc.
2. Selection, design and construction of the antenna(s).
3. A tower mounted amplifier.
4. Everything else.
If you've done the first 3 items, to the best your abilities and
finances, then tinkering with plating materials and A-B switches is a
waste of time and money.

Good to know. Thanks.

 

[Jeff Liebermann]

On Mon, 07 Dec 2009 02:56:48 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

The idiot manager of one system ordered the wrong midband modulator
that was right in the aircraft band. Rather than admit it, over 10,000
converters had to be modified to tune the new channel.

Ouch. However, the aircraft band is from 108 to 136Mhz. That covers
channels 98, 99, 14, 15, and 16 that have to be protected. Comcast is
using 14 and 15 locally, but I've noticed that the signal levels are
much lower than the adjacent channels.

It was used to
add 'The nashville Network' which had just been launched. The system was
in the Cincinnati area where people claimed that they didn't listen to
'shit kicking music'. I tested the mew modulator & c-band equipment for
less than 30 seconds, and after 2 am. We had over 100 phone calls
waiting the next morning, wanting to know when it would be back.

Chuckle. There's no accounting for taste. For the last year or so,
I've been erratically trying to convince DirecTV to carry UCTV:
<http://www.uctv.tv>
It's currently carried by Dish and Comcast locally, but not DirecTV.
So far, my efforts have been futile. So, I watch UCTV on the
computah.

Ummm... the OP is trying to troubleshoot his home installation, not
the trunk line (or cable drop). I think it's a safe bet that he can
unplug his spaghetti without difficulties.

Then it is very unlikely he will have access to a TDR, sniffer or any
other equipment. Even a field strength meter isn't likely.

If he can borrow an oscilloscope, a TDR is very easy to build. I've
built several similar to:
<http://www.epanorama.net/circuits/tdr.html>
If he knew the test frequency, a simple scanner with aircraft band
should work. Every cable operator seems to use a different frequency.
I usually find it by connecting my scanner to the cable, and scanning
the aircraft band for the obnoxious tones.

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

 

[Michael A. Terrell]

Jeff Liebermann wrote:

On Mon, 07 Dec 2009 02:56:48 -0500, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

The idiot manager of one system ordered the wrong midband modulator
that was right in the aircraft band. Rather than admit it, over 10,000
converters had to be modified to tune the new channel.

Ouch. However, the aircraft band is from 108 to 136Mhz. That covers
channels 98, 99, 14, 15, and 16 that have to be protected. Comcast is
using 14 and 15 locally, but I've noticed that the signal levels are
much lower than the adjacent channels.

It was used to
add 'The nashville Network' which had just been launched. The system was
in the Cincinnati area where people claimed that they didn't listen to
'shit kicking music'. I tested the mew modulator & c-band equipment for
less than 30 seconds, and after 2 am. We had over 100 phone calls
waiting the next morning, wanting to know when it would be back.

Chuckle. There's no accounting for taste. For the last year or so,
I've been erratically trying to convince DirecTV to carry UCTV:
http://www.uctv.tv
It's currently carried by Dish and Comcast locally, but not DirecTV.
So far, my efforts have been futile. So, I watch UCTV on the
computah.

The system added TNN at my insistence. We picked up about 500 new
customers by adding it. The number one country music station in the US
was in Cincinnati for several years.

Ummm... the OP is trying to troubleshoot his home installation, not
the trunk line (or cable drop). I think it's a safe bet that he can
unplug his spaghetti without difficulties.

Then it is very unlikely he will have access to a TDR, sniffer or any
other equipment. Even a field strength meter isn't likely.

If he can borrow an oscilloscope, a TDR is very easy to build. I've
built several similar to:
http://www.epanorama.net/circuits/tdr.html

I preferred my homebrew return loss bridge. I used a surplus video
modulator module for the Atari 2600, and built the bridge in a Pomona
diecast box. It was a lot more useful than a TDR in troubleshooting the
MATV systems in dozens of schools.

If he knew the test frequency, a simple scanner with aircraft band
should work. Every cable operator seems to use a different frequency.
I usually find it by connecting my scanner to the cable, and scanning
the aircraft band for the obnoxious tones.

United Video always used the video carrier frequency of the first
channel past what the system used.


--
Offworld checks no longer accepted!

 

[Ian Jackson]

In message <W4idnbUfmb694IHWnZ2dnUVZ_gudnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes

The 20 dB isolation means that the return loss is more than 20 dB.

No it doesn't. It means that the isolation - the loss between two
outputs (with the input terminated) - is 20dB.

This is to prevent the local oscillator from one TV causing interference
to another TV.

True - but, more generally, it is to minimise the effects of something
connected to one output affecting another output. As well as protecting
against local oscillators, it also protects against incorrect loading
(ie if an output port is not correctly terminated in a 75 ohm load). It
should not matter (too much) if an output is left open circuit, short
circuited, has a length of cable connected to it but going nowhere, etc
etc.

I was the engineer at a CATV system with over 10,000
active drops. There are hundreds of myths and half truths about the
hardware used for CATV systems.

Was your statement above (about RLR) one of these? [Sorry. The Devil

made me say that! ;o))]

I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes
more sense. (Actually, it should be -7.0dB loss).

While most 3-ways are typically 3.5/7/7, there are one or two around

with equal outputs, of appx 5.5dB (although, personally, I can't really
see much need for them).
--
Ian

 

[Michael A. Terrell]

Ian Jackson wrote:

In message <W4idnbUfmb694IHWnZ2dnUVZ_gudnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes


The 20 dB isolation means that the return loss is more than 20 dB.

No it doesn't. It means that the isolation - the loss between two
outputs (with the input terminated) - is 20dB.

Sigh. How do you think you measure that isolation?

This is to prevent the local oscillator from one TV causing interference
to another TV.

True - but, more generally, it is to minimise the effects of something
connected to one output affecting another output.

What are you connecting that doesn't have a TV tuner? FM radios are
supposed to use a single port -20 dB tap.

As well as protecting
against local oscillators, it also protects against incorrect loading
(ie if an output port is not correctly terminated in a 75 ohm load). It
should not matter (too much) if an output is left open circuit, short
circuited, has a length of cable connected to it but going nowhere, etc
etc.

Unterminated ports are not allowed in properly designed systems.
PERIOD.

I was the engineer at a CATV system with over 10,000
active drops. There are hundreds of myths and half truths about the
hardware used for CATV systems.

Was your statement above (about RLR) one of these? [Sorry. The Devil
made me say that! ;o))]

I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes
more sense. (Actually, it should be -7.0dB loss).

While most 3-ways are typically 3.5/7/7, there are one or two around
with equal outputs, of appx 5.5dB (although, personally, I can't really
see much need for them).

You would, if the use of the 3.5/7/7 would require a second drop from
the line tap on the street.


--
Offworld checks no longer accepted!

 

[Ian Jackson]

In message <Q-2dnRjtm4MceILWnZ2dnUVZ_vqdnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes

Ian Jackson wrote:

In message <W4idnbUfmb694IHWnZ2dnUVZ_gudnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes


The 20 dB isolation means that the return loss is more than 20 dB.

No it doesn't. It means that the isolation - the loss between two
outputs (with the input terminated) - is 20dB.

Sigh. How do you think you measure that isolation?

Sigh as much as you like - isolation and RLR are definitely NOT the same

thing, and you don't measure them in the same way.

This is to prevent the local oscillator from one TV causing interference
to another TV.

True - but, more generally, it is to minimise the effects of something
connected to one output affecting another output.

What are you connecting that doesn't have a TV tuner? FM radios are
supposed to use a single port -20 dB tap.

That could make the FM level uncomfortably low. It's better to separate

the FM from the TV signals via a bandpass diplexer filter. This is/was
common practice in Europe. Of course, in the USA, you have always had
your Channel 5 (running right up to the LF end of the FM band). Also,
these days, you could have digital TV signals starting immediately above
the FM (and still meeting the 'no interference' regulations for Air
Traffic Control radio. Do any cable systems still actually carry FM
radio?

As well as protecting
against local oscillators, it also protects against incorrect loading
(ie if an output port is not correctly terminated in a 75 ohm load). It
should not matter (too much) if an output is left open circuit, short
circuited, has a length of cable connected to it but going nowhere, etc
etc.

Unterminated ports are not allowed in properly designed systems.
PERIOD.

They may be installed correctly terminated, but you can bet your bottom

dollar a lot won't stay that way!

I was the engineer at a CATV system with over 10,000
active drops. There are hundreds of myths and half truths about the
hardware used for CATV systems.

Was your statement above (about RLR) one of these? [Sorry. The Devil
made me say that! ;o))]

I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes
more sense. (Actually, it should be -7.0dB loss).

While most 3-ways are typically 3.5/7/7, there are one or two around
with equal outputs, of appx 5.5dB (although, personally, I can't really
see much need for them).


You would, if the use of the 3.5/7/7 would require a second drop from
the line tap on the street.

When I said "much use", I meant "MUCH use". While a computerized CATV

system planner may flag up an out-of-spec condition, in practice, there
may be less than 1dB difference between a nominal 5.5 and 7dB.
--
Ian

 

[Michael A. Terrell]

Ian Jackson wrote:

In message <Q-2dnRjtm4MceILWnZ2dnUVZ_vqdnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes

Ian Jackson wrote:

In message <W4idnbUfmb694IHWnZ2dnUVZ_gudnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes


The 20 dB isolation means that the return loss is more than 20 dB.

No it doesn't. It means that the isolation - the loss between two
outputs (with the input terminated) - is 20dB.

Sigh. How do you think you measure that isolation?

Sigh as much as you like - isolation and RLR are definitely NOT the same
thing, and you don't measure them in the same way.

You use the same equipment, but connect the ports in a different
order.

This is to prevent the local oscillator from one TV causing interference
to another TV.

True - but, more generally, it is to minimise the effects of something
connected to one output affecting another output.

What are you connecting that doesn't have a TV tuner? FM radios are
supposed to use a single port -20 dB tap.

That could make the FM level uncomfortably low.

A 0 dB or higer signal will overload the front end of a FM radio. O
dBM is 1000 microvolts @ 75 Ohms. FM radios are supposed to work at full
quieting 10 microvolts. Some of the -20 dB taps were labeled as FM Taps
and were supposed to have a bandpass filter on the output port but none
of the ones I tested in the lab did.

It's better to separate
the FM from the TV signals via a bandpass diplexer filter. This is/was
common practice in Europe. Of course, in the USA, you have always had
your Channel 5 (running right up to the LF end of the FM band).

No, it is Channel 6, with the aural carrier at 87.7 MHz. That is .3
Mhz below the bottom edge of the 88 to 108 MHz FM Broadcast band.

Also,
these days, you could have digital TV signals starting immediately above
the FM (and still meeting the 'no interference' regulations for Air
Traffic Control radio. Do any cable systems still actually carry FM
radio?

Are you kidding? They were dropped as soon as the franchises stopped
asking for FM and wanted more video channels. They gained three midband
channels without rebuilding the system.

As well as protecting
against local oscillators, it also protects against incorrect loading
(ie if an output port is not correctly terminated in a 75 ohm load). It
should not matter (too much) if an output is left open circuit, short
circuited, has a length of cable connected to it but going nowhere, etc
etc.

Unterminated ports are not allowed in properly designed systems.
PERIOD.

They may be installed correctly terminated, but you can bet your bottom
dollar a lot won't stay that way!

Not if it's maintained by morons. But then, those systems were never
in spec.

I was the engineer at a CATV system with over 10,000
active drops. There are hundreds of myths and half truths about the
hardware used for CATV systems.

Was your statement above (about RLR) one of these? [Sorry. The Devil
made me say that! ;o))]

I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes
more sense. (Actually, it should be -7.0dB loss).

While most 3-ways are typically 3.5/7/7, there are one or two around
with equal outputs, of appx 5.5dB (although, personally, I can't really
see much need for them).


You would, if the use of the 3.5/7/7 would require a second drop from
the line tap on the street.

When I said "much use", I meant "MUCH use". While a computerized CATV
system planner may flag up an out-of-spec condition, in practice, there
may be less than 1dB difference between a nominal 5.5 and 7dB.

So? If the franchise calls for all drops to be above 0 dB, one dB is
out of spec.


--
Offworld checks no longer accepted!

 

[Robert Macy]

On Dec 9, 3:46 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
....snip...

   A 0 dB or higer signal will overload the front end of a FM radio. O
dBM is 1000 microvolts @ 75 Ohms. FM radios are supposed to work at full
quieting 10 microvolts.  Some of the -20 dB taps were labeled as FM Taps
and were supposed to have a bandpass filter on the output port but none
of the ones I tested in the lab did.
....snip...

being a bit pedantic,
0 dBm in a 75 ohm system is 273,861 microvolts rms

 

[Michael A. Terrell]

Robert Macy wrote:

On Dec 9, 3:46 pm, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
...snip...
A 0 dB or higer signal will overload the front end of a FM radio. O
dBM is 1000 microvolts @ 75 Ohms. FM radios are supposed to work at full
quieting 10 microvolts. Some of the -20 dB taps were labeled as FM Taps
and were supposed to have a bandpass filter on the output port but none
of the ones I tested in the lab did.
...snip...

being a bit pedantic,
0 dBm in a 75 ohm system is 273,861 microvolts rms

I meant 0 dBmv, which is used in TV Land.


--
Offworld checks no longer accepted!

 

[Robert Macy]

On Dec 10, 8:56 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:

Robert Macy wrote:

On Dec 9, 3:46 pm, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
...snip...
   A 0 dB or higer signal will overload the front end of a FM radio. O
dBM is 1000 microvolts @ 75 Ohms. FM radios are supposed to work at full
quieting 10 microvolts.  Some of the -20 dB taps were labeled as FM Taps
and were supposed to have a bandpass filter on the output port but none
of the ones I tested in the lab did.
...snip...

being a bit pedantic,
0 dBm in a 75 ohm system is 273,861 microvolts rms

   I meant 0 dBmv, which is used in TV Land.

--
Offworld checks no longer accepted!

Understood. Thanks.

 

[Michael A. Terrell]

Robert Macy wrote:

Understood. Thanks.

I forgot to add the 'v' after 20+ years out of TV broadcasting, then
spending years building Telemetry gear.


--
Offworld checks no longer accepted!

 

[David Brodbeck]

Jeff Liebermann wrote:

On Mon, 07 Dec 2009 13:15:19 -0500, mm <NOPSAMmm2005@bigfoot.com
wrote:

So is there any value in getting gold-plated F connectors (if they
have them) or gold-plated A/B switches (which I know they sell)?

No. The plating is so thin, that at UHF frequencies, the skin depth
is less than the plating depth. If you want good RF conductivity, get
silver plated connectors.

But given that the center pin on an F connector is the bare copper
center conductor of the cable, I don't think I'd bother. If we were
talking BNCs or something plating might make sense.