On Fri, 10 Jan 2014 22:55:41 -0500, Jerry Stuckle
wrote:

That's theoretical. Reality is much different.

I think I'll print that on a large piece of paper and have it framed
for my office wall.

Have you ever worked
with a TDR? It's one of the tools we use regularly (and an expensive
one, also).

Sure. Also OTDR for fiber. I don't use the expensive stuff, unless
you include the Acterna HST3000 tester that was stolen from my office
a few years ago. Mostly, I built my own using a pulse generator and
an oscilloscope.

You stated that the losses come primarily from the "impedance bump"
presumably produced by the non-50 ohm connector or adapter in the
line. Well, time to put that to the test.
1. Take a length of RG-6/u coax with good connectors. Apply signal
on one end from a generator. Measure the signal level on the other
end with a spectrum analyzer that has a 1dB per division scale. I
want to be able to see small changes.
2. After establishing a reference level, either beat on the coax
cable with a hammer, squash it with a C-clamp, or flatten it with a
bench vise. Squash it just enough to obtain an "impedance bump", but
not a short between the center conductor and shield. Note the change
in level, if you can see it.
3. Now, either un-squash the cable, or find another length of RG-6/u
and attach a TDR. It can be open, shorted, or terminated. Doesn't
matter.
4. Flatten the cable in the same manner as before and note the TDR
display.

What I expect that you'll see is that there will be almost no change
in attenuation, while the TDR display will show a rather radical
"impedance bump". That's because the only thing that the change in
impedance along the cable length can do is create reflections. Those
are a serious problem in a CATV system, but really don't involve
serious signal level losses.

That's theoretical. Reality is much the same.

So? Dipoles aren't 50 ohm antennas. They're typically closer to 75 ohm.

I guess you missed my point. If you can tolerate the 1.5:1 VSWR, the
reduced attenuation and cost of 75 ohm coax makes the effort
worthwhile.

As for handling more power - rubbish. The current in 75 ohm coax is
lower than that in 50 ohm coax, for the same power rating.

Please re-read the article:
www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm
http://www.microwaves101.com/encyclopedia/why50ohms.cfm

We use RG-59 where appropriate, like from an outlet to the set top box.
But our in-wall coax runs are all RG-6 quad-shielded.

RG-59/u doesn't have a foil shield, so it's more flexible. So, I
guess that might work. For short lengths, the increased leakage,
higher ingress, and higher attenuation can probably be tolerated.
However, I use extra long RG-6/u, which somewhat compensates for the
lack of flexibility.

But we're also doing less and less coax and more and more Category cable
nowadays.

No MoCA installations?
http://www.mocalliance.org

They're OK for the hobbyist, but I don't know of any professionals who
use them. In fact, checking our main wholesalers, they aren't even
available through them (but other Beldon products are).

Find a different distributor or ask for it by part number.
Thomas and Betts SNS1P6U.

Quick check: Stocked by Allied, Newark, Tessco, Farnel(UK), MCM.
Not stocked by Digikey, Mouser, Arrow.

T&B distributor search:
http://www.tnb.com/ps/dls/dls?ca=corp

--
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 1/12/2014 12:29 AM, Jeff Liebermann wrote:
On Fri, 10 Jan 2014 22:55:41 -0500, Jerry Stuckle
wrote:

That's theoretical. Reality is much different.

I think I'll print that on a large piece of paper and have it framed
for my office wall.

Have you ever worked
with a TDR? It's one of the tools we use regularly (and an expensive
one, also).

Sure. Also OTDR for fiber. I don't use the expensive stuff, unless
you include the Acterna HST3000 tester that was stolen from my office
a few years ago. Mostly, I built my own using a pulse generator and
an oscilloscope.


I'm not talking about fiber, and I'm not talking about some half-assed
gadget cooked up in your basement. I'm talking about a real,
professional-grade TDR.

We use expensive stuff because it gives accurate results.

You stated that the losses come primarily from the "impedance bump"
presumably produced by the non-50 ohm connector or adapter in the
line. Well, time to put that to the test.

I didn't say anything about a non-50 ohm connector. The connector can
be 50 ohm and still get an impedance bump. With a TDR you can see every
connector on the cable (as long as they are far enough apart - typically
3-4 feet).

1. Take a length of RG-6/u coax with good connectors. Apply signal
on one end from a generator. Measure the signal level on the other
end with a spectrum analyzer that has a 1dB per division scale. I
want to be able to see small changes.
2. After establishing a reference level, either beat on the coax
cable with a hammer, squash it with a C-clamp, or flatten it with a
bench vise. Squash it just enough to obtain an "impedance bump", but
not a short between the center conductor and shield. Note the change
in level, if you can see it.
3. Now, either un-squash the cable, or find another length of RG-6/u
and attach a TDR. It can be open, shorted, or terminated. Doesn't
matter.
4. Flatten the cable in the same manner as before and note the TDR
display.

What I expect that you'll see is that there will be almost no change
in attenuation, while the TDR display will show a rather radical
"impedance bump". That's because the only thing that the change in
impedance along the cable length can do is create reflections. Those
are a serious problem in a CATV system, but really don't involve
serious signal level losses.

That's theoretical. Reality is much the same.


First of all, we don't crush cables to try to emulate something we can
easily see in real life.

Second of all, you can gimmick up something all you want with signal
generators, spectrum analyzers, crushed cables, all you want.

We SEE the results in real time in real installations with the
appropriate test equipment.

So? Dipoles aren't 50 ohm antennas. They're typically closer to 75 ohm.

I guess you missed my point. If you can tolerate the 1.5:1 VSWR, the
reduced attenuation and cost of 75 ohm coax makes the effort
worthwhile.


No, it's worthwhile because your coax will more closely match the
antenna. And you can easily match the coax to the transmitter with a tuner.

As for handling more power - rubbish. The current in 75 ohm coax is
lower than that in 50 ohm coax, for the same power rating.

Please re-read the article:
www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm
http://www.microwaves101.com/encyclopedia/why50ohms.cfm


I read the article. Unlike you, I understand what it is saying.

We use RG-59 where appropriate, like from an outlet to the set top box.
But our in-wall coax runs are all RG-6 quad-shielded.

RG-59/u doesn't have a foil shield, so it's more flexible. So, I
guess that might work. For short lengths, the increased leakage,
higher ingress, and higher attenuation can probably be tolerated.
However, I use extra long RG-6/u, which somewhat compensates for the
lack of flexibility.


You don't know our installations. We've been in business for several
years, with lots of satisfied customers. Trying to tell a professional
what their job is only makes you look stupid.

But we're also doing less and less coax and more and more Category cable
nowadays.

No MoCA installations?
http://www.mocalliance.org


Nope. It's used by few professionals. Coax ends up with too many
problems. Category cable for runs under 100M or so and fiber for longer
runs.

They're OK for the hobbyist, but I don't know of any professionals who
use them. In fact, checking our main wholesalers, they aren't even
available through them (but other Beldon products are).

Find a different distributor or ask for it by part number.
Thomas and Betts SNS1P6U.


We use several distributors - both U.S. and international companies.

Quick check: Stocked by Allied, Newark, Tessco, Farnel(UK), MCM.
Not stocked by Digikey, Mouser, Arrow.

T&B distributor search:
http://www.tnb.com/ps/dls/dls?ca=corp


These are consumer (retail) outlets. They are not used by most
professionals.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

On Sun, 12 Jan 2014 11:48:13 -0500, Jerry Stuckle
wrote:

I'm not talking about fiber, and I'm not talking about some half-assed
gadget cooked up in your basement. I'm talking about a real,
professional-grade TDR.

Make and model please?

I used to drag around a Tek 1503 but rarely used it. It was most
useful for find broken cables, usually where the rats chewed through
the wires. Also, for measuring the length of cables on a roll that
didn't have ft markers. One day, I needed it, and it was dead,
probably from bouncing around in my truck. Rather than fix it, I sold
it as-is.
http://www.ebay.com/itm/131091152872
I was already carrying a scope, so I saw no reason to buy another
scope just to get a TDR. So, I designed and built a TDR, mostly
checking CAT5 and telco wires, not coax. Something like this:
http://www.epanorama.net/circuits/tdr.html

We use expensive stuff because it gives accurate results.

I use cheap stuff because I know its limitations and can work within
those limitations. Much as I value my money, old test equipment is
good enough for most things.
http://www.learnbydestroying.com/jeffl/pics/home/slides/test-equip-mess.html

You stated that the losses come primarily from the "impedance bump"
presumably produced by the non-50 ohm connector or adapter in the
line. Well, time to put that to the test.

I didn't say anything about a non-50 ohm connector. The connector can
be 50 ohm and still get an impedance bump. With a TDR you can see every
connector on the cable (as long as they are far enough apart - typically
3-4 feet).

If the connectors were a prefect 50 ohms, you wouldn't see any
reflection. Therefore, either the connectors are not quite 50 ohms,
your coax is not quite 50 ohms, you have a high resistance shield
connection, or this is one of your cases where theory fails to
accommodate your reality.

That's theoretical. Reality is much the same.

First of all, we don't crush cables to try to emulate something we can
easily see in real life.

I crush, chop, dissect, and set fire to cable to see how they're
built. Amazing what you find if you look inside of things. However,
since you have an aversion to crushing coax able, you can get the same
effect with a short length of different impedance coax cable and some
adapters. Just insert where I suggested you crush the coax, and you
should see it clearly on the TDR. Then replace it with an identical
length of the correct impedance cable and compare the losses. At
worst, the loss difference will be fractions of a dB. That suggests
that your "impedance bump" isn't really responsible for much loss.

Of course, you have set fire to plenum, non-plenum, and riser CAT5
cables to see how they burn. I think you might be surprised. Learn
by Destroying(tm).

Second of all, you can gimmick up something all you want with signal
generators, spectrum analyzers, crushed cables, all you want.

For those that believe theory, proof by bench testing is possible. For
those who do not believe or understand theory, no amount of test
equipment will ever prove anything. Theory and testing go hand in
hand. If there's a discrepancy, then either one of them is wrong, or
the procedure is flawed.

We SEE the results in real time in real installations with the
appropriate test equipment.

You see the results, but for some odd reason, I haven't seen your
results or list of appropriate professional test equipment. Why
always so vague and non-specific? FoN (Fear of Numbers)?

So? Dipoles aren't 50 ohm antennas. They're typically closer to 75 ohm.

I guess you missed my point. If you can tolerate the 1.5:1 VSWR, the
reduced attenuation and cost of 75 ohm coax makes the effort
worthwhile.

No, it's worthwhile because your coax will more closely match the
antenna. And you can easily match the coax to the transmitter with a tuner.

Tuners can be lossy. Try this T-tuner Java app on the lower bands.
http://fermi.la.asu.edu/w9cf/tuner/tuner.html
The starting values (hit the AutoTune button) produce a 2dB loss at
160 meters. The losses are much less on the higher bands. Q=100 for
the inductor seems a bit high.

Please re-read the article:
www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm
http://www.microwaves101.com/encyclopedia/why50ohms.cfm

I read the article. Unlike you, I understand what it is saying.

What part of the following do you disagree with and why? (It's all in
the above articles). Please try to be specific:
1. Loss for approximately equal size is less for 75 ohm cable.
2. 50 ohm cable will tolerate a higher power due to a higher voltage
breakdown.
3. Maximum power is with about 30 ohm coax cable.
http://www.microwaves101.com/encyclopedia/coax_power.cfm
4. Mismatch loss from 75 ohm cable in a 50 ohm system is 0.18dB.
5. If the mismatch loss from using 75 ohm cable is less than the
difference in attenuation for a comparable 50 ohm cable, and there are
no high power levels involved, then it is better to use 75 ohm cable
and tolerate the mismatch.

You don't know our installations. We've been in business for several
years, with lots of satisfied customers. Trying to tell a professional
what their job is only makes you look stupid.

I only debate a persons ideas and never attack them personally. If
you are unable to do that, you lack "professionalism" which presumably
goes with your professional title.

No MoCA installations?
http://www.mocalliance.org

Nope. It's used by few professionals. Coax ends up with too many
problems. Category cable for runs under 100M or so and fiber for longer
runs.

Fiber is generally better and much more expensive. I also do fiber
where possible. However, when faced with a large apartment complex,
with no possible way to economically rewire the building, I was forced
to consider what could be done with the existing wiring. The building
had CAT3 going to all the apartments, but CAT3 is useless (no twists).
Even DSL had crosstalk problems. I tried to use the CAT3 as a pull
line to drag in CAT5, but that also failed (no smurf tubes in the
walls). I also tried 2.4/5.7 wireless, which proved erratic because
of aluminum foil backed insulation, untouchable firewalls, and
interference from existing Wi-Fi systems.

So, I tired MoCA and it worked.
http://www.netgear.com/service-providers/products/in-home-connectivity/moca-bridges/
http://www.netgear.com/service-providers/products/in-home-connectivity/moca-bridges/wm2500rp.aspx
They're now bringing in Comcast TV, internet, and phone via coax,
using MoCA to distribute internet around each apartment. Depending on
wiring, Jperf shows about 100-300 Mbits/sec between clients (16
maximum). Speedtest shows whatever was ordered from Comcast from/to
the internet, typically 22/2 Mbit/sec.

To be honest, things did not go smoothly. MoCA is expensive. The
isolation between apartments on the main Comcast splitter was not
enough to prevent leakage between bridges. Using couplers instead of
splitters were a big help. I also needed to select a different
channel, which is not allowed by every MoCA unit. I started with
Actiontek, which was cheaper, but does NOT offer channel selection and
was therefore useless. Some of the apartments had satellite TV, which
had to be accommodated with diplexers. However, the worst problem was
that I rapidly became the single point of contact for any problem with
the system. Fortunately, I was conveniently underbid for the
maintenance contract by another service company, which has taken over
the system. To the best of my knowledge, it's still running nicely
after about 18 months.

Next time you run into a situation that does not economically allow a
retrofit of fiber or CAT5/6, and there's existing coax, think about
MoCA.

Find a different distributor or ask for it by part number.
Thomas and Betts SNS1P6U.

We use several distributors - both U.S. and international companies.

Did you any of them if they specifically carry T&B or stock T&B
SNS1P6U connectors? Where we left off, you were having difficulties
finding a stocking distributor. Are either of your unspecified
distributors on the T&T distributor search page?
http://www.tnb.com/ps/dls/dls?ca=corp
Within 25 miles of your location, it shows 5 stocking distributors
with 13 locations.

Quick check: Stocked by Allied, Newark, Tessco, Farnel(UK), MCM.
Not stocked by Digikey, Mouser, Arrow.

T&B distributor search:
http://www.tnb.com/ps/dls/dls?ca=corp

These are consumer (retail) outlets. They are not used by most
professionals.

None of those listed above have a retail (brick and mortar) store.
Many do sell online and from catalogs, but even the largest
distributors do that. Legally, if they charge sales tax, they are a
"retail" operation. Offhand, I can't think of a single large
distributor that does not accept taxable sales or requires a resale
permit in order to process an order. There used to be those as B2B
(business to business) operations, but not any more, because the
growth of internet commerce has made retail processing a necessity.

--
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 1/12/2014 7:24 PM, Jeff Liebermann wrote:
On Sun, 12 Jan 2014 11:48:13 -0500, Jerry Stuckle
wrote:

I'm not talking about fiber, and I'm not talking about some half-assed
gadget cooked up in your basement. I'm talking about a real,
professional-grade TDR.

Make and model please?


It's in my office, and not my lap. And quite frankly, I'm not about to
go out of my way to follow up because it's none of your business.

You're trolling now, and I don't respond to trolls.

rest of garbage snipped because it just proves you have no idea what
you're talking about.

One other comment. No, you won't go back to school not because you
don't need another piece of paper on the wall. You already think you
know everything. And it just might ruin your day to find out how wrong
you are.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

On Sun, 12 Jan 2014 21:10:17 -0500, Jerry Stuckle
wrote:

On 1/12/2014 7:24 PM, Jeff Liebermann wrote:
On Sun, 12 Jan 2014 11:48:13 -0500, Jerry Stuckle
wrote:

I'm not talking about fiber, and I'm not talking about some half-assed
gadget cooked up in your basement. I'm talking about a real,
professional-grade TDR.

Make and model please?

It's in my office, and not my lap. And quite frankly, I'm not about to
go out of my way to follow up because it's none of your business.

No doubt a private label TDR made especially for professionals and
considered a trade secret by it owners. Gosh, I want one of those.

You're trolling now, and I don't respond to trolls.

Not exactly trolling but close. I'm asking you to substantiate your
claims and to supply specific makers and model numbers.

rest of garbage snipped because it just proves you have no idea what
you're talking about.

One other comment. No, you won't go back to school not because you
don't need another piece of paper on the wall. You already think you
know everything.

I'm not sure I can decode your comment with it's 3 negations. I said
that I *DO* need another piece of paper for my wall. My 2013 calendar
expired last week, and I need something to fill the wall space.
Obtaining a new 2014 calendar is both costly and time consuming. It's
easier to just fill the space with another diploma.
www.ebay.com/sch/i.html?_nkw=fake+university+diploma

And it just might ruin your day to find out how wrong
you are.

You first, then you can cross examine me. You stated that I don't
understand the two articles on 50 versus 75 ohms. You also stated
that you do understand the articles. Then please explain them to me.
The following are my claims, all derived from the articles. Where in
the following am I wrong and why?

1. Loss for approximately equal size is less for 75 ohm cable.
2. 50 ohm cable will tolerate a higher power due to a higher voltage
breakdown.
3. Maximum power is with about 30 ohm coax cable.
http://www.microwaves101.com/encyclopedia/coax_power.cfm
4. Mismatch loss from 75 ohm cable in a 50 ohm system is 0.18dB.
5. If the mismatch loss from using 75 ohm cable is less than the
difference in attenuation for a comparable 50 ohm cable, and there are
no high power levels involved, then it is better to use 75 ohm cable
and tolerate the mismatch.


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