OT: Checking coax jumpers before soldering

[Frank Precissi]

This is along the same lines of the PL-259 connector soldering.  Although
off topic for this group some collective wisdom might help someone other
than myself in the future.

How can you check to see if coax is still "good"?  Sure we can test for
shorts with a multimeter, but if the coax has been crushed and the
dielectric has been deformed, obviously things will be wonky when we put RF
through it.

Is it possible to short one connector with a 50ohm resistor, then on the
other end attaching an antenna analyzer and sweep the ham bands looking for
obvious SWR changes?  I mean to me (read: newbie when it comes to this) it
should show a flat 50ohms across the bands, correct?

I have a few spools of 100' RG8X that I'm sure have been slammed in a
sliding glass door more than once.  No sign of any trauma on the jacket or
shorts, but I cant tell if the dielectric has been mangled inside.  I
really don't want to blindly ditch perfectly good coax.

Any tricks of the trade when it comes to this?

73

Frank
KG6EYC


--
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[W4JBB]

Frank,

I use an Anritsu SiteMaster at work to detect such things with hardline
and coax. It comes with a 50 ohm load for testing feedline. I don't know
how you'd set up an amateur-style antenna analyzer to do such. When I'm
looking for faults, I specifically set it to " Return Loss - DTF
(Distance To Fault)."

If you have a station dummy load, you could use that. The one I built
from Oak Hills Research is a little bulky, but would do the trick I think.

73,
Joel - W4JBB

On 11/12/13, 12:41 AM, Frank Precissi wrote:

> This is along the same lines of the PL-259 connector soldering.  Although
> off topic for this group some collective wisdom might help someone other
> than myself in the future.
>
> How can you check to see if coax is still "good"?  Sure we can test for
> shorts with a multimeter, but if the coax has been crushed and the
> dielectric has been deformed, obviously things will be wonky when we put RF
> through it.
>
> Is it possible to short one connector with a 50ohm resistor, then on the
> other end attaching an antenna analyzer and sweep the ham bands looking for
> obvious SWR changes?  I mean to me (read: newbie when it comes to this) it
> should show a flat 50ohms across the bands, correct?
>
> I have a few spools of 100' RG8X that I'm sure have been slammed in a
> sliding glass door more than once.  No sign of any trauma on the jacket or
> shorts, but I cant tell if the dielectric has been mangled inside.  I
> really don't want to blindly ditch perfectly good coax.
>
> Any tricks of the trade when it comes to this?
>
> 73
>
> Frank
> KG6EYC
>
>

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[Nr4c]

I have used 50 ohm BNC 'terminators' with adapter to verify coax.  Start with terminator on analyzer, should be flat VSWR over wide band.  When at other end of coax should be same.

...bill nr4c


Sent from my Verizon Wireless 4G LTE DROID

Joel Black <[hidden email]> wrote:

>Frank,
>
>I use an Anritsu SiteMaster at work to detect such things with hardline
>and coax. It comes with a 50 ohm load for testing feedline. I don't know
>how you'd set up an amateur-style antenna analyzer to do such. When I'm
>looking for faults, I specifically set it to " Return Loss - DTF
>(Distance To Fault)."
>
>If you have a station dummy load, you could use that. The one I built
>from Oak Hills Research is a little bulky, but would do the trick I think.
>
>73,
>Joel - W4JBB
>
>On 11/12/13, 12:41 AM, Frank Precissi wrote:
>> This is along the same lines of the PL-259 connector soldering.  Although
>> off topic for this group some collective wisdom might help someone other
>> than myself in the future.
>>
>> How can you check to see if coax is still "good"?  Sure we can test for
>> shorts with a multimeter, but if the coax has been crushed and the
>> dielectric has been deformed, obviously things will be wonky when we put RF
>> through it.
>>
>> Is it possible to short one connector with a 50ohm resistor, then on the
>> other end attaching an antenna analyzer and sweep the ham bands looking for
>> obvious SWR changes?  I mean to me (read: newbie when it comes to this) it
>> should show a flat 50ohms across the bands, correct?
>>
>> I have a few spools of 100' RG8X that I'm sure have been slammed in a
>> sliding glass door more than once.  No sign of any trauma on the jacket or
>> shorts, but I cant tell if the dielectric has been mangled inside.  I
>> really don't want to blindly ditch perfectly good coax.
>>
>> Any tricks of the trade when it comes to this?
>>
>> 73
>>
>> Frank
>> KG6EYC
>>
>>
>
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>

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[Dave Aslin, G3WGN]

I use a RigExpert antenna analyser in Time Domain Reflectometer mode.  This will show 'distance to fault' amongst other coax parameters.  More reliable than just doing an SWR sweep.  Since the analyser tells you where the faults lies, you can inspect the cable for trauma at that point or cut out the poorly performing part and use the rest.
The RigExpert AA-230 is one of several amateur antenna analysers that have this function, so checking coax in amateur stations is easy-peasy these days!  No need for megabucks test gear (even though it may be nice to have for other reasons).
73
Dave G3WGN M6O WJ6O

[Don Wilhelm-4]

The MFJ-259 and 269 also can determine distance to fault.  Look in the
instructions to see how to get to it.

73,
Don W3FPR

On 11/12/2013 8:15 AM, Dave Aslin, G3WGN wrote:

> I use a RigExpert antenna analyser in Time Domain Reflectometer mode.  This
> will show 'distance to fault' amongst other coax parameters.  More reliable
> than just doing an SWR sweep.  Since the analyser tells you where the faults
> lies, you can inspect the cable for trauma at that point or cut out the
> poorly performing part and use the rest.
> The RigExpert AA-230 is one of several amateur antenna analysers that have
> this function, so checking coax in amateur stations is easy-peasy these
> days!  No need for megabucks test gear (even though it may be nice to have
> for other reasons).
> 73
> Dave G3WGN M6O WJ6O
>

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[Charlie T, K3ICH]

I remember seeing a chart somewhere that listed cable loss vs. SWR into an
open (or was it shorted?) coax.  Just open or short one end, measure the
SWR,  plug that value and the length into the chart to read the loss.
Admittedly, this would be difficult for a cable already installed, but it
would be an easy way to check an unknown piece in the junk box.

Anybody remember where that chart was published?

73, Charlie k3ICH


----- Original Message -----
From: "bill conkling" <[hidden email]>
To: "Joel Black" <[hidden email]>
Cc: "elecraft" <[hidden email]>
Sent: Tuesday, November 12, 2013 7:16 AM
Subject: Re: [Elecraft] OT: Checking coax jumpers before soldering


>I have used 50 ohm BNC 'terminators' with adapter to verify coax.  Start
>with terminator on analyzer, should be flat VSWR over wide band.  When at
>other end of coax should be same.
>
> ...bill nr4c
>
>

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[DL6OAP]

That kind of chart is e. g. in the ARRL antenna book (I have two older editions but am sure it is in both of them). Since the measurement assumes that the fraction of the power that is put into the line and not being converted into heat in the coax is completely reflected at the far end, it should work equally well with shorted or open end. I have a MiniVNA network analyzer that relies on this method for determining the electrical length and the loss of coax. Normally I leave the end open.
However, I am not sure if it works very well with short pieces of low loss coax because of the difficulties of precisely determining a high s.w.r.

73, Ralf, DL6OAP

Am 12.11.2013 um 14:47 schrieb "Charlie T, K3ICH" <[hidden email]>:

> I remember seeing a chart somewhere that listed cable loss vs. SWR into an open (or was it shorted?) coax.  Just open or short one end, measure the SWR,  plug that value and the length into the chart to read the loss. Admittedly, this would be difficult for a cable already installed, but it would be an easy way to check an unknown piece in the junk box.
>
> Anybody remember where that chart was published?
>
> 73, Charlie k3ICH
>
>
> ----- Original Message ----- From: "bill conkling" <[hidden email]>
> To: "Joel Black" <[hidden email]>
> Cc: "elecraft" <[hidden email]>
> Sent: Tuesday, November 12, 2013 7:16 AM
> Subject: Re: [Elecraft] OT: Checking coax jumpers before soldering
>
>
>> I have used 50 ohm BNC 'terminators' with adapter to verify coax.  Start with terminator on analyzer, should be flat VSWR over wide band.  When at other end of coax should be same.
>>
>> ...bill nr4c
>>
>>
>
> ______________________________________________________________
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[Edward R Cole]

I have one of the MFJ Antenna Analyzers which can be used to test
existing coax lines.  SWR can certainly be tested, but its not
intuitive how to measure line loss on cables connected to antennas.

The standard method is with open coax runs (no load of any kind which
ensures total reflection at the far end;  the analyzer compares the
level of reflected signal with the original signal transmitted by the
analyzer to determine line loss).  The "TRICK" is to tune
significantly "OFF FREQ" with the analyzer so that SWR is near
maximum (appears to be open circuit).

Not as handy as a TDR or analyzer like the Anritsu Site Master which
will show distance to impedance "bump", but still useful for checking
the "health" of your cables.

73, Ed - KL7UW
http://www.kl7uw.com
[hidden email]
"Kits made by KL7UW"

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[ab2tc]

Hi,

The terminated loss in a coax is half of the return loss looking into the unterminated cable. RL is easily calculated using the formula:

RL = 20 * log (VSWR+1)/(VSWR-1) (dB)

The reason for the factor of two is that the wave has traveled the cable twice before being measured as return loss. But it is true that high SWR is diffucult to measure accurately so the method isn't used much. E.g. the LP100A is pegged at VSWR = 9.99 so cannot determine losses less than 0.87dB. The LP100A can also display the return loss directly but unfortunately that value is also pegged at the 1.74dB value corresponding to that SWR.

AB2TC - Knut

DL6OAP wrote

That kind of chart is e. g. in the ARRL antenna book (I have two older editions but am sure it is in both of them). Since the measurement assumes that the fraction of the power that is put into the line and not being converted into heat in the coax is completely reflected at the far end, it should work equally well with shorted or open end. I have a MiniVNA network analyzer that relies on this method for determining the electrical length and the loss of coax. Normally I leave the end open.
However, I am not sure if it works very well with short pieces of low loss coax because of the difficulties of precisely determining a high s.w.r.

73, Ralf, DL6OAP

Am 12.11.2013 um 14:47 schrieb "Charlie T, K3ICH" <[hidden email]>:
<sni>

[W7CS]

Bill, W0WFH,

For more than 20+ years I have been using various sizes of the heavy
duty shrink tubing with the sticky stuff sealant inside.

I've used it on the back shell to coax joints on up to 1 5/8" Heliax,
as well as smaller diameter coaxes.  I use another piece to cover the
type N joint  (or heaven forbid PL 259) after it's connected,
overlapping the first on both sides of the joint..  However to do
this on top of a 300' tower you need either a very long extension
cord or a battery operated heat gun.  No, I don't even know if they exist !

This type of shrink tubing (after even 20 years) generally comes off
cleanly, exposing bright connectors underneath.  The removal
technique involves cutting the shrink tubing longitudinally, through
to the connectors, with an Exacto or other quite sharp blade, and
then just pulling it apart.

Properly applied, this type of shrink tubing also provides a
stiffening type of support for the connector to coax joint.

Chuck,  W7CS

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[k6mrmagnet]

If you want to put shrink on a connector at the top of a tower, just use 3M cold shrink tubing. Seals the connector but no heat required…


Ken K6MR




From: Chuck Smallhouse
Sent: ‎Tuesday‎, ‎November‎ ‎12‎, ‎2013 ‎12‎:‎17‎ ‎PM
To: [hidden email]





Bill, W0WFH,

For more than 20+ years I have been using various sizes of the heavy
duty shrink tubing with the sticky stuff sealant inside.

I've used it on the back shell to coax joints on up to 1 5/8" Heliax,
as well as smaller diameter coaxes.  I use another piece to cover the
type N joint  (or heaven forbid PL 259) after it's connected,
overlapping the first on both sides of the joint..  However to do
this on top of a 300' tower you need either a very long extension
cord or a battery operated heat gun.  No, I don't even know if they exist !

This type of shrink tubing (after even 20 years) generally comes off
cleanly, exposing bright connectors underneath.  The removal
technique involves cutting the shrink tubing longitudinally, through
to the connectors, with an Exacto or other quite sharp blade, and
then just pulling it apart.

Properly applied, this type of shrink tubing also provides a
stiffening type of support for the connector to coax joint.

Chuck,  W7CS

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