In-line joining of coax

[ZS6GST]

Hi Collin

I love the magic of stubs (1/12th wave, 1/8 wave, 1/4 wave & 1/2 wave) and do a lot of work with them.

The 1/12 wave is used to make matching transformers between feedlines with any choice of impedance.such as RG58 to RG59. (Email me if you need more info on these natty transformers). I have an HP 8713 3GHz network analyser to test my joints with and have yet to see a direct inline joint I made that has a degrading impedance bump even at VHF frequencies. Also keep in mind that many beautifully made commercial folded dipoles have inline joints for their matching transformers that are cunningly hidden inside the dipole itself.

Here is the method I use to make direct (connector less) in line joints:-

Step 1; Prepare the ends of the coax you want to join by trimming the outside back by ~ 1 cm. This leaves ~ 1 cm of the inner insulation and then
expose 3 to 4 mm of the inner conducters and comb the braiding back over coax it belongs to with a suitable awl or scriber.

Step 2; The conductors can then be lid next to each other and soldered but a better method would be to source some "bootlace ferrules" of a size to fit snugly over two parallel inner conductors from your local electrical wholesaler. These consist of very small diameter plated soft copper ferrules with a larger end piece. Next cut some 3 mm sections of the ferrules with a Dremmel tool armed with a high speed cut off disk. This is a delicate operation, the disk can split and the ferrule can fly off - so please use safety glasses!

Step 3; Position the exposed inner conductors to be joined into the ferrule and crimp lightly with a suitable plier. (I use a high quality low cost medical artery clamp bought from a medical supply company) then solder the joint as rapidly as possible. If the inner insulation should become watery and melt, just support the cables being joined until the insulation cools down and sets.

Step 4; Wrap white teflon tape (of the sort commonly used by plumbers) around the joint jou just made until the wrapped joint has the same diameter as the original inner insulation. The dialectric constant of the teflon and inner insulation is near identical and in addition the teflon can withstand high soldering temperatures.

Step 5: Comb the braiding from one of the coaxes over the joint and then comb the braid from the other over it.

Step 6: You are now ready to solder the two braids together but remember it must be done by means of quick jabs with a clean soldering iron, Do not apply the iron so long as to melt your joint. Cover the completed joint with 3m tape or shrink tube. You did remember to slip some shrink tube over one of the cables before joining them did you not?

QED & 73 de Pine, ZS6GST - from the land where the big five roam around.

[ZL3OZ]

Ahh. David.

Did you not read the rest of my tongue in cheek posting? I didnt do 80mtrs.

I used it for long haul VHF 2mtr into VK and was and still am (with better coax now) in the ZL forward pack when it comes to SpE DX on 2mtr.

Yes I know its awfull but the loss produced was less than the gain of the SpE with QSB on the day and i might have lost the weak one in the noise now and then but when the propagation was there so was I.

I know of a very good tech who once tried to show me how to find a fault in a small portable radio. He laboured for some time with the oscilloscope and could not find what he wanted to show me, till I pointed out the black wire had come off the battery holder.

Sometimes we can get lost in the forest trying to find a tree to pee behind.

Ken OZ.

[VK2XSO]

There's really not a problem with joining coax. It's not uncommon for something like a mobile phone tower to use 5 joins between the transmitter and the antenna.

So nothing said about your choice of coax
The connectors do not have very much loss even for crappy connectors, but as mentioned you might not want to see what they look like on a TDR

So assuming that you can terminate the RG58 to a connector, it's not going to make much difference between solder or crimp.
I was going to say consider the connector quality, but we're talking about RG58.

OK.... lets remove RG58 from the equation and just consider it's magic coax.

N type would be my first choice because it's reasonably cheap and good quality.
BNC if you need quick disconnect
PL259 if you need cheap
DIN 7/16 if you have OCD issues about quality.