Joining coax cable

[crackle]

I am moving my shack to a room at the other end of the house.
I was wondering what the general opinion was about extending and joining coax cable outside in the elements.
I wanted to ask opinion on the benefits if any of splicing the cable as opposed to using conventional PL259 type plugs and joiner piece.

When splicing the cable the braid will be pealed back, the centre conductors soldered, the centre solder joint will then be insulated with pvc tape. Then the braids will be folded back and overlapped and gently soldered in 3 or 4 places around the braiding.
The whole joint will then be covered in a layer of self amalgamating tape and that will be over covered in a layer of silicon sealant to waterproof the joint.

The alternative is to fit 2 PL259 plugs and use a joiner and place all that in a weatherproof box so it can remain outside.

Which do you think will give a better joint.

Thanks
Mike

[Electronpusher0]

I think it depends on what you are putting down the co-ax.
I have had good results splicing co-ax at TV frequencies and in theory splicing should be lower loss than plug and socket joins.

Peter

[Radio Wrangler]

I wouldn't use PL259/SO239 for a few reasons.

They aren't actually 50 or 75 Ohm connectors, they are a mismatched interruption in the cable.
They aren't seen as a 'serious' connector where quality is important, so the quality of many on the market is dubious.
The method of connecting to the braid is very unsatisfactory.
They have a tendency to come loose.
Back to back connectors are usually cast out of zinc-based dodgy metal.

You can find ones made by Greenpar if you look around, and ones with gland cable fitting rather than the soldered braid horror.

I'd much rather use Type-N. With care over the assembly of the gland, you even get a rubber water seal to the cable jacket. The N connector itself has a seal between the male and female parts when mated. So you start out with a layer of sealing, and any you add outside increases sealing from a good starting point.

David

[red-duck]

Agree with Radio Wrangler - use a male & female N connector. Just as easy - if not easier than a PL259 to make up ( watch the youtube videos if unsure how to make one up.)
You might not notice a splice if its only for Rx. But for TXing .. its asking for trouble, first to solder it, then to secure, it then to waterproof it.

[eddie_ce]

I agree wholeheartedly with David. When having to do similar joints on commercial installations we used good quality N-connectors and wrapped these with a layer of self-amalgamating tape, to protect this from UV degradation, the whole lot was then wrapped with a layer of black UV resistant electrical tape.

Possibly a bit OTT for amateur installations, but even after 10 years or more in challenging environments at 250m above ground, the unwrapped connectors looked as if they had just come out of the packet.

Just my two euro cents worth.

I have some N's that have been outside for 20 years, still waterproof.

[crackle]

Do N connectors rely on a dry joint for the braid connection?
Would a quality soldered splice be better or worse than N type connectors.
thanks
Mike

[Jon_G4MDC]

Definitely worse at any frequency above a few MHz.

[GrimJosef]

I'm a bit surprised at the negativity over splices. We used to send high-voltage trigger pulses down 50ohm coax and with a bit of care we could splice that (concertina the braid back, slide 2-3cm of thinnish heatshrink insulation over one inner and ~8mm of adhesive-lined heatshrink over the other, solder the inner conductors together over a total 8mm exposed length, shrink the adhesive-lined tube over the exposed copper, shrink the thinnish tube over the whole lot, reinstate the braid maybe over a turn of copper tape if we were worried about stray braid wires, close up the slit outer sheathing and tape and/or heatshrink over the whole lot. That didn't seem to degrade the rising edge of our trigger pulses, at least on a timescale of 5-10ns. Dispersion in the cable could be more of a problem.

The impedance disruption would only apply over a short length - 2-3cm - which should really only be significant as we approach GHz shouldn't it ?

Of course we weren't putting kilowatts down the cable and, perhaps importantly, we weren't working outdoors (the environment was more like an aircraft hanger). But weather-sealing the cable happens entirely on its outside. That ought to be possible, surely ?

Cheers,

GJ

[Radio Wrangler]

I'm assuming you used PTFE dielectric coax which doesn't melt when hit with soldering temperatures, GJ. If Mike's using ordinary polythene stuff, then, while soldering the braid, the inner can move within the molten dielectric.

Splices can be done, but doing them right needs a lot of care, and you still have to waterproof the outer.

Ian, G3ROO, showed me his trick of using hot-melt glue as a waterproofer for connectors and connections. It works remarkably well, though gobbing up the whole of the outside of a connector does look a bit repulsive. At least the heat drives water off of the jacket and allows good adhesion.

David

[ex seismic]

N or BNC for me. Both types quicker and easier to do than mess around with splices.

Gordon

[Refugee]

I would be very tempted to treat the installation to a nice new down lead so doing away with the splice.
Is there some prohibitive access problem at the far end?

[emeritus]

When I inadvertently severed the neighbour's coax with the hedge trimmers, I used 75 Ohm BNC plugs & free sockets covered with a length of heat shrink with some silicone rubber sealant inside for good measure.

[stevehertz]

Originally Posted by emeritus

When I inadvertently severed the neighbour's coax with the hedge trimmers, I used 75 Ohm BNC plugs & free sockets covered with a length of heat shrink with some silicone rubber sealant inside for good measure.

I'm thinking what is a downlead doing in a hedge? or at least, away from a wall or solid surface.

[Terry_VK5TM]

Even in a 'weatherproof box', PL259's are not waterproof, condensation will infiltrate the join.

N connectors or splice would be my options.

[GrimJosef]

Originally Posted by Radio Wrangler

I'm assuming you used PTFE dielectric coax which doesn't melt when hit with soldering temperatures, GJ. If Mike's using ordinary polythene stuff, then, while soldering the braid, the inner can move within the molten dielectric ...

Actually no. The trigger pulses we were using were tens of kilovolts (there was a spark gap at the far end of the cable) and even though they were short and infrequent, which increases the breakdown threshold very substantially, we still used big cable, typically URM67 or, if we were feeling flush, RG213. We straightened it out before we started and held it down on the bench with weights and under those circumstances the core tends to stay put in the polythene insulation as long as you don't faff too much with the soldering iron.

From a signal propagation point of view though the important factor was that the impedance disruption would be no more than 2.5cm long. At 5ns/m in polythene the transit time would be a little over 0.1ns and for the pulses we were using that was way too short to be 'visible'.

Cheers,

GJ

[Julesomega]

For receiving aerials I use two F-plugs with a back-to-back connector, which is then easy to wrap in self-amalg

[G6Tanuki]

I'd definitely recommend a N plug and free-socket as the way to go here. The compression-glands are about as waterproof as you can get at a non-bankruptcy-inducing price: I generally assemble them with a smear of Dow-Corning silicone grease worked well into the 'top-hat' and on the centre-core pin/socket before screwing them together, then a length of adhesive-lined heatshrink over the whole thing, extending 3 or 4 inches either side of the plug/socket.

In times-past I 'acquired' a load of about-10-Metre-long lengths of RG213/U - joined using back-to-back N-connectors and heatshrinked they ended up being used for a whole bunch of VHF/UHF commercial two-way radio and amateur-radio installs I did over a period of about five years. never had any water-ingress problems and my portable TDR couldn't 'see' the join!

[emeritus]

The coax was in the honeysuckle that had grown over the neighbour's side of the fence from the trellis on the wall of my house. The coax wasn't for the TV downlead but providing a connection from AV stuff in the living room to an upstairs bedroom and wasn't actually being used any more after his sons had left home.

I generally assemble them with a smear of Dow-Corning silicone grease

I use Vaseline, cheaper and available in your local bathroom! I popped out to the garden to have a look at the Ns there, they have gone a nice shade of black (silver plated ones) and fit in quite well. Upon separating a pair the contacts where still clean and bright.