On 1/10/2014 7:01 PM, Ian Jackson wrote:
In message , Jeff Liebermann
writes
On Thu, 9 Jan 2014 21:08:11 -0800, "Sal" salmonella@food
poisoning.org wrote:

Another experiment I ran (back around 1975) was to take 100 feet of
cable
and measure the loss, then repeat the measurement using a different
100 feet
made from ten different pieces. Yup, the loss was about 3 dB more,
indicative of an average 0.3 dB loss per joint, neatly within the
range you
specified.

0.3dB per connector at what frequency?

This is more fun:
http://802.11junk.com/jeffl/antennas/connector-loss/index.html
Just take every connector that you can find, put them in series, and
measure the loss. In this case, it was done at 2.4Ghz and 450MHz. End
to end loss at 2.4GHz was 2dB for about 25 adapters or about 0.08dB
per adapter. At 250MHz, the loss was about 0.2dB or 0.008dB per
adapter.

I've done similar demonstrations using two wattmeters at the local
radio club meeting. The results are typically that the adapter string
has the same loss as an equivalent length of small coax cable. I had
a surplus of BNC T connectors, so a strung about 50 of them in series
and obtained similar results.

Bottom line: Connectors and adapters aren't as evil as the data
sheets and literature suggest.

I've always assumed that the loss measured through connectors and
adapters was mainly
(a) because they have unavoidable length (ie not a lot), and
(b) because the impedance match through them is less than perfect (ie
not a lot).
The ohmic contact resistance may also be a tiny tad higher than the same
length of coax (even less).

The main loss in a connector is due to the impedance bump at the
connector. This can be easily seen on a TDR (Time Domain Reflectometry)
display.

Some connectors are better than others; for instance, the older F
connectors which are crimped down with a ring are the worst. Next is
the connector where the crimp is a hex crimp - it doesn't give a
consistent impedance around the connector.

The best (and the ones we use) compress the entire base of the connector
evenly, creating a smooth crimp. The end of the coax is evenly covered
by the connector.

The other problem is the technician installing the connectors. I've
seen great ones, and not-so-great ones. There are a lot of chances for
going wrong - for instance, it's easy to screw up the braid when trying
to insert a crimp-on connector under the outer jacket and shield. And
soldering connectors (i.e. PL-259 and N) is almost sure to give you a
huge bump (and loss) because it's almost impossible to solder the shield
without melting the inner insulator to some point. It may not short
out, but that doesn't mean you don't have loss there.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

On Fri, 10 Jan 2014 19:36:59 -0500, Jerry Stuckle
wrote:

The main loss in a connector is due to the impedance bump at the
connector. This can be easily seen on a TDR (Time Domain Reflectometry)
display.

Rubbish. Let's pretend that I mix in a 75 ohm coax connector into a
50 ohm system. Depending on the location of this "impedance bump",
the VSWR is no more than 1.5:1 which is generally considered marginal.
That's 0.18dB of mismatch loss.
http://www.microwaves101.com/encyclopedia/calvswr.cfm
If you're doing satellite or microwave DX work, then 0.18dB might be
important. However, for most other applications, it's a trivial
amount.

You might be amused to know that most of my rooftop antennas are fed
with 75 ohm coax and that my favored antenna designs are also 75 ohm.
There are various reasons, but the main one is that coax cable losses
are less at 75 ohms, than at 50 ohms. 50 ohms can handle more power,
but 75 ohms has less loss.
http://www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm
The only problems I have with 75 ohms is finding the proper connectors
and dealing with the pads needed to make my 50 ohm test equipment look
like 75 ohms. (Actually the real reason is that the 75 ohm stuff is
mostly CATV surplus, which tends to be really cheap).

Mo
http://www.qsl.net/n9zia/wireless/75_ohm_hardline.html

Some connectors are better than others; for instance, the older F
connectors which are crimped down with a ring are the worst. Next is
the connector where the crimp is a hex crimp - it doesn't give a
consistent impedance around the connector.

I rip those out wherever I find them, even if they're on the ends of
commercially crimped cables (usually RG-59/u which is another
nightmare). However, the loss mechanism with the old CATV coax and
associated crappy crimp connectors was radiation, not mismatch loss.
The ground connections would fall apart, turning the coax shield into
an impressive antenna.

The best (and the ones we use) compress the entire base of the connector
evenly, creating a smooth crimp. The end of the coax is evenly covered
by the connector.

I've had problems with some of those push-on connectors. I also don't
want to stock a zillion different connector variations from different
vendors. So, I've standardized on the "red" univeral T&B SNS1P6U
RG-6/u connectors:
www.ebay.com/sch/i.html?_nkw=SNS1P6U

The other problem is the technician installing the connectors. I've
seen great ones, and not-so-great ones. There are a lot of chances for
going wrong - for instance, it's easy to screw up the braid when trying
to insert a crimp-on connector under the outer jacket and shield. And
soldering connectors (i.e. PL-259 and N) is almost sure to give you a
huge bump (and loss) because it's almost impossible to solder the shield
without melting the inner insulator to some point. It may not short
out, but that doesn't mean you don't have loss there.

Actually, it's not the crimp job that kills the connection. It's the
stripping of the coax that causes the most problems. I use various
rotary contrivances that have razor blades to make the cuts at the
correct spacing. Those work well initially, but after about 50
connectors, the blades become dull and useless. Of course, nobody has
spare blades or knows how to adjust them. They either continue to use
a dull razor or steal my new stripper.

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

"Jeff Liebermann" wrote in message
...
On Fri, 10 Jan 2014 19:36:59 -0500, Jerry Stuckle
Actually, it's not the crimp job that kills the connection. It's the
stripping of the coax that causes the most problems. I use various
rotary contrivances that have razor blades to make the cuts at the
correct spacing. Those work well initially, but after about 50
connectors, the blades become dull and useless. Of course, nobody has
spare blades or knows how to adjust them. They either continue to use
a dull razor or steal my new stripper.


I don't know the quality of the cutters you use, but I have bought several
from China off ebay for about $ 2 each including shipping. For the very few
connectors I do, they work. At that price, you could order a lot of them
and not worry about the replacement blades. Just like the disposiable
razors. They seem identical to the ones that sell in stores for $ 10 to $
15 .



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On 1/10/2014 10:23 PM, Ralph Mowery wrote:
"Jeff Liebermann" wrote in message
...
On Fri, 10 Jan 2014 19:36:59 -0500, Jerry Stuckle
Actually, it's not the crimp job that kills the connection. It's the
stripping of the coax that causes the most problems. I use various
rotary contrivances that have razor blades to make the cuts at the
correct spacing. Those work well initially, but after about 50
connectors, the blades become dull and useless. Of course, nobody has
spare blades or knows how to adjust them. They either continue to use
a dull razor or steal my new stripper.


I don't know the quality of the cutters you use, but I have bought several
from China off ebay for about $ 2 each including shipping. For the very few
connectors I do, they work. At that price, you could order a lot of them
and not worry about the replacement blades. Just like the disposiable
razors. They seem identical to the ones that sell in stores for $ 10 to $
15 .



Ralph,

They may seem identical, but they aren't. The $10-15 ones last much,
much longer. However, unless you're doing it full time, it probably
doesn't pay to get the more expensive ones.

We tried one of the cheap ones. After about 3 weeks the tech threw it
as far as he could because he was so frustrated. The ones we have now
typically last a year or more (we don't really track them).

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

"Jerry Stuckle" wrote in message
...
,

They may seem identical, but they aren't. The $10-15 ones last much, much
longer. However, unless you're doing it full time, it probably doesn't
pay to get the more expensive ones.

We tried one of the cheap ones. After about 3 weeks the tech threw it as
far as he could because he was so frustrated. The ones we have now
typically last a year or more (we don't really track them).


You probably do more connectors in a week than I will ever do. For me , it
won't pay, but for you it will if they last that much longer. Must be the
quality of the blades as I can not tell any differance in the couple I
bought from China for $ 2 and the one I bought here for $ 15.
I just bought one for each size and type of cable I use.
I don't do the TV connectors, just the BNC,N,PL259 types.




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On 1/10/2014 11:39 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
,

They may seem identical, but they aren't. The $10-15 ones last much, much
longer. However, unless you're doing it full time, it probably doesn't
pay to get the more expensive ones.

We tried one of the cheap ones. After about 3 weeks the tech threw it as
far as he could because he was so frustrated. The ones we have now
typically last a year or more (we don't really track them).


You probably do more connectors in a week than I will ever do. For me , it
won't pay, but for you it will if they last that much longer. Must be the
quality of the blades as I can not tell any differance in the couple I
bought from China for $ 2 and the one I bought here for $ 15.
I just bought one for each size and type of cable I use.
I don't do the TV connectors, just the BNC,N,PL259 types.



Yup, one tech can do upwards of 50 connectors a day on a large project.
Mostly F and RJ-45, but also some RCA and others. It counts up
quickly!

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

On Fri, 10 Jan 2014 22:23:17 -0500, "Ralph Mowery"
wrote:


"Jeff Liebermann" wrote in message
.. .
On Fri, 10 Jan 2014 19:36:59 -0500, Jerry Stuckle
Actually, it's not the crimp job that kills the connection. It's the
stripping of the coax that causes the most problems. I use various
rotary contrivances that have razor blades to make the cuts at the
correct spacing. Those work well initially, but after about 50
connectors, the blades become dull and useless. Of course, nobody has
spare blades or knows how to adjust them. They either continue to use
a dull razor or steal my new stripper.

I don't know the quality of the cutters you use, but I have bought several
from China off ebay for about $ 2 each including shipping. For the very few
connectors I do, they work. At that price, you could order a lot of them
and not worry about the replacement blades. Just like the disposiable
razors. They seem identical to the ones that sell in stores for $ 10 to $
15 .

Those are the same cutters that I like to use. Good, cheap, easy to
use, and throw away when dull. (I've tried resharpening the blades
with poor results).

This style is my favorite:
http://www.ebay.com/itm/400525856013
but these also work and are usually cheaper:
http://www.ebay.com/itm/360806269903
There are other designs, but I haven't used them.

--
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 1/10/2014 9:06 PM, Jeff Liebermann wrote:
On Fri, 10 Jan 2014 19:36:59 -0500, Jerry Stuckle
wrote:

The main loss in a connector is due to the impedance bump at the
connector. This can be easily seen on a TDR (Time Domain Reflectometry)
display.

Rubbish. Let's pretend that I mix in a 75 ohm coax connector into a
50 ohm system. Depending on the location of this "impedance bump",
the VSWR is no more than 1.5:1 which is generally considered marginal.
That's 0.18dB of mismatch loss.
http://www.microwaves101.com/encyclopedia/calvswr.cfm
If you're doing satellite or microwave DX work, then 0.18dB might be
important. However, for most other applications, it's a trivial
amount.


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

You might be amused to know that most of my rooftop antennas are fed
with 75 ohm coax and that my favored antenna designs are also 75 ohm.
There are various reasons, but the main one is that coax cable losses
are less at 75 ohms, than at 50 ohms. 50 ohms can handle more power,
but 75 ohms has less loss.
http://www.belden.com/blog/broadcastav/50-Ohms-The-Forgotten-Impedance.cfm
The only problems I have with 75 ohms is finding the proper connectors
and dealing with the pads needed to make my 50 ohm test equipment look
like 75 ohms. (Actually the real reason is that the 75 ohm stuff is
mostly CATV surplus, which tends to be really cheap).


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

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.

Proper connectors are no problem when you can buy from commercial
distributors. But we don't typically sell them individually.

Mo
http://www.qsl.net/n9zia/wireless/75_ohm_hardline.html

Some connectors are better than others; for instance, the older F
connectors which are crimped down with a ring are the worst. Next is
the connector where the crimp is a hex crimp - it doesn't give a
consistent impedance around the connector.

I rip those out wherever I find them, even if they're on the ends of
commercially crimped cables (usually RG-59/u which is another
nightmare). However, the loss mechanism with the old CATV coax and
associated crappy crimp connectors was radiation, not mismatch loss.
The ground connections would fall apart, turning the coax shield into
an impressive antenna.


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.

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

The best (and the ones we use) compress the entire base of the connector
evenly, creating a smooth crimp. The end of the coax is evenly covered
by the connector.

I've had problems with some of those push-on connectors. I also don't
want to stock a zillion different connector variations from different
vendors. So, I've standardized on the "red" univeral T&B SNS1P6U
RG-6/u connectors:
www.ebay.com/sch/i.html?_nkw=SNS1P6U


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).

The other problem is the technician installing the connectors. I've
seen great ones, and not-so-great ones. There are a lot of chances for
going wrong - for instance, it's easy to screw up the braid when trying
to insert a crimp-on connector under the outer jacket and shield. And
soldering connectors (i.e. PL-259 and N) is almost sure to give you a
huge bump (and loss) because it's almost impossible to solder the shield
without melting the inner insulator to some point. It may not short
out, but that doesn't mean you don't have loss there.

Actually, it's not the crimp job that kills the connection. It's the
stripping of the coax that causes the most problems. I use various
rotary contrivances that have razor blades to make the cuts at the
correct spacing. Those work well initially, but after about 50
connectors, the blades become dull and useless. Of course, nobody has
spare blades or knows how to adjust them. They either continue to use
a dull razor or steal my new stripper.

Oops... dinner... gone.


Stripping is almost never a problem, unless you're a real klutz. Even
if you nick the braid a bit it isn't very critical.

We use the same type of rotary stripper - but just because it's much
faster. One of our techs can install an F connector in a minute or less
with one of them.

I never counted how many connections we get out of a stripper, but it's
got to be in the thousands. We replace some screwdrivers more often
than the strippers

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

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

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