How to test coax end-to-end?

[eorange]

I have a 90 foot run of RG-8X mini. One end is in the basement. It routes through a hole in the house to outside and up to a discone mounted on the side of the house. Both ends have a PL-259, attached by me and I think I did a decent job weatherproofing the outside connection.

So I'm thinking about replacing discone with a 2m/440 antenna and since I'll be using it more for transmit...I'm wondering how I can test the integrity of the cable. In general it's in great shape but I do wonder about moisture ingress (if any). This is just due diligence since I'll be making an antenna change.

What tools and or methods could I use to ensure my coax & connectors are still in good shape?

 

[dave3825]

What tools and or methods could I use to ensure my coax & connectors are still in good shape?

Testing CB Antenna Coax

This guide describes how to test CB antenna coax cable for continuity and shorts.

www.wearecb.com

 

[serial14]

I've used a NanoVNA to test coax before.

• SWR sweep the antenna to ensure the expected results.
• Scan the coax terminated into a dummy load
• Scan the coax open.

Using these tests on an antenna with degraded performance, I was able to determine the coax had gone "bad" from water ingress.

I'm away from my notes now, but on the NanoVNA I used both SWR and Return Loss plots in the above tests to determine appropriate and bad behaviors.

 

[eorange]

Testing CB Antenna Coax

This guide describes how to test CB antenna coax cable for continuity and shorts.

www.wearecb.com

Thanks, but the ends of the cable are nowhere near each other.

 

[eorange]

I've used a NanoVNA to test coax before.

• SWR sweep the antenna to ensure the expected results.
• Scan the coax terminated into a dummy load
• Scan the coax open.

Using these tests on an antenna with degraded performance, I was able to determine the coax had gone "bad" from water ingress.

I'm away from my notes now, but on the NanoVNA I used both SWR and Return Loss plots in the above tests to determine appropriate and bad behaviors.

Perfect, that's a great starting point!

 

[a417]

Thanks, but the ends of the cable are nowhere near each other.

They don't need to be.

 

[eorange]

They don't need to be.

They do per the "Testing CB Antenna Coax" link. My multimeter doesn't have 40 foot leads!

 

[kg4ehv]

Use a good piece of wire the right length.

 

[a417]

They do per the "Testing CB Antenna Coax" link. My multimeter doesn't have 40 foot leads!

So?

What do you think your multimeter is sending down that wire? Test packets? Magic unicorn tears? It's sending electricity. Send your own. You don't need your multimeter to do it for you.

How would I do it without access to both ends? Simple. I'd test for no shorts to ground at each end. If I found none, I would connect a current limited low voltage source (ie lantern battery or something if you don't have one) and go to the other end and look for appropriate voltage. Taking distance and impedance into account, I would know what voltage to expect at the other end.

 

[G7RUX]

Testing coax single-ended can be a bit problematic.
Water ingress can tend to increase the losses so will tend to make SWR look better as the loss goes up. A VNA of some sort is a worthwhile and can be (especially if it’s a nanoVNA) a cheap piece of test kit with many uses. Using a multimeter from one end is doable if you have some resistors to pop on the other end and a dummy load fits this quite nicely. An electrician with an insulation tester can be a useful addition!

If you are just concerned about water ingress you have a couple of simple options.
First, just check for continuity and for short circuits…this is crude but a reasonable start. You can check continuity from one end by introducing a short circuit at the far end.
Second, if you are still concerned then examine the outdoor end of the feeder. Look for corrosion of metals and damage to the coax outer sheath; damage virtually guarantees that water has got in there and the braid will wick water surprisingly quickly. Consider removing the connector and stripping back a small amount of the cable to check condition before refitting it all properly.

If you have access to the kit you could inject a signal of a known amplitude and measure it at the other end. This would give you a way to find the attenuation of your coax at frequencies you choose which can be very useful.

 

[G7RUX]

They do per the "Testing CB Antenna Coax" link. My multimeter doesn't have 40 foot leads!

You can check continuity of both inner and outer at the same time by setting a short at the far end. Then remove the short and the meter should then show an open circuit. It’s crude but it is a start.

 

[buddrousa]

Simple answer WATT METER and DUMMYLOAD and a TRANSMITTER.

 

[ems55]

I've used a NanoVNA to test coax before.

• SWR sweep the antenna to ensure the expected results.
• Scan the coax terminated into a dummy load
• Scan the coax open.

Using these tests on an antenna with degraded performance, I was able to determine the coax had gone "bad" from water ingress.

I'm away from my notes now, but on the NanoVNA I used both SWR and Return Loss plots in the above tests to determine appropriate and bad behaviors.

Hi, which NanoVNA do you have ? I've been thinking about getting one..

 

[eorange]

Testing coax single-ended can be a bit problematic.
Water ingress can tend to increase the losses so will tend to make SWR look better as the loss goes up. A VNA of some sort is a worthwhile and can be (especially if it’s a nanoVNA) a cheap piece of test kit with many uses. Using a multimeter from one end is doable if you have some resistors to pop on the other end and a dummy load fits this quite nicely. An electrician with an insulation tester can be a useful addition!

If you are just concerned about water ingress you have a couple of simple options.
First, just check for continuity and for short circuits…this is crude but a reasonable start. You can check continuity from one end by introducing a short circuit at the far end.
Second, if you are still concerned then examine the outdoor end of the feeder. Look for corrosion of metals and damage to the coax outer sheath; damage virtually guarantees that water has got in there and the braid will wick water surprisingly quickly. Consider removing the connector and stripping back a small amount of the cable to check condition before refitting it all properly.

If you have access to the kit you could inject a signal of a known amplitude and measure it at the other end. This would give you a way to find the attenuation of your coax at frequencies you choose which can be very useful.

All great advice, thank you!

I am very familiar with continuity checks and have made a decent number of coax cables, checking for shield to center shorts and the like.

I replaced my HF vertical a bit ago and redid the whole thing - added a radial plate, radials, and other improvements. I lopped off the end of that coax to start new and not surprisingly there was about a foot of moisture ingress because the shield wasn't good, and I hadn't done a good weatherproofing job at that time.

I'm this case, however, my instinct tells me the coax should be in better shape, so I'd rather not start by opening things up, except if absolutely necessary. I just ordered a NanoVNA-H4 and have been looking for a need to get one. But I am curious how it's doing so will do the sweep + testing.

 

[Ubbe]

For professional use I measure a coax and antenna at the time of its installation, or get the result from the installer guy that needs to do a measurement to see that everything looks okay, to be used as a reference. Every tiewrap and coax bend and connector will show on that measurement and also the antennas return loss, its SWR, will be seen within its frequency range and how it degrades outside its frequency band.

I haven't had much water ingress problems but if I remember correctly it will take upp all the power like a dummy load so that it looks like a good SWR but it will flatten out and extend to cover almost any frequency and not only within the frequency range of the antenna.

/Ubbe

 

[buddrousa]

In the old days we used to use old line.
In this order Transmitter Watt Meter Coax Dummy Load if that checked good we would move Watt Meter to the end of the Coax and put it between the Coax and the Dummy Load to see what we had for a loss compared to what we should have.