joinng coaxial

[wiggy]

Im in the process of installing a new VHF and need to extend coaxial by about 6 inches. Can I simply solder core and outer and insulate for a permenant join?

 

[Hoolie]

Yes you can. Use self-annealing tape to insulate the inner and make sure the screen braid is spread evenly before spot soldering. Finish with shrink sleeving over the joint, though of course it has to threaded on before starting!

 

[CPD]

Second that.

 

[Sneds]

Any join will be a weak link, in probably the most essental life saving bit of kit on board.
Can't you replace the whole co-ax? Use the old one to pull the new one through?
IMHO that would be the better job.
Don't buy cheap co-ax, get the correct one (RG58?) and preferably one made in Europe.

 

[glenndraper]

the main problem is that you will lose gain - by far the best thing to do is change wire for the correct length - if this is impractical I suggest that you use a male and female joint designed for the job

 

[glenndraper]

although on second thorghts I vote with sneddon replace the whole length

 

[brianrunyard]

Soldering is not recommended, if you can't avoid a join, use a proper connector, see photo
PL259

Must learn to type faster.

 

[wiggy]

Problem is it runs under the floor moulding and down inside mast compression post.When one end is pulled it seems to go no where.

 

[Sneds]

Good point, in that instance use a proper in line connector, as others have said.
Take your time making the ends off so its done properly.

Cheers

 

[wiggy]

Any problem using maplin for parts as generally they seem to be about 1/3 the price of the swindlery, anyone know maplin part numbers, i always get lost and distracted on their site by all the great stuff!!!!!!!!!!!!!!

 

[emnick]

I have soldered before and not had a problem, although in an ideal world one cable is always better, forgot to add that when soldering inner core try and stretch insulator to cover the solder joint,insulate with tape, then solder braid, if this is gone black due to moisture ingress I would suggest changing whole cable.
PS I usually wrap the joint in alcan foil then use SA tape over whole joint

 

[Oldhand]

[ QUOTE ]
Yes you can. Use self-annealing tape to insulate the inner and make sure the screen braid is spread evenly before spot soldering. Finish with shrink sleeving over the joint, though of course it has to threaded on before starting!

[/ QUOTE ]

Such a joint will cause an impedence step in the cable which will cause some of the transmitted power to be reflected back into the transciever - definitley not to be recomended. You should only use proper RF coaxial connectors (like BNC type) but it would be best not to have joint at all.

 

[iangrant]

If you solder the joint properly and heat shrink seal the inner, then re-plat the outer and heat shrink that'll be OK, as for two connectors, then you have mating surfaces prone to green stuff, you'll have solder joints in the pins anyway (unless you have crimps and the proper tool, will cause more problems than a proper solder joint,

new cable better though!

ian

 

[lw395]

Suggest using a male and a female BNC, make sure ithey are for the correct size cable, which is typically RG58. Properly done, clamp type bnc's, where you use a spanner to compress a gasket around the jacket, will keep moisture out of the coax better than those 'orrible 259 series plugs, and the loss and vswr at VHF will be fine, if you follow the instructions.
Other people's comments about selft amalgamating tape are good, as moisture and corrosion in the braid cause loss.
Cheers,
Chris

 

[William_H]

As a techie from way back I reckon the biggest problem with just soldering the wires together is not the impedance mismatch but simply the loss of integrity of the cable to resistance to moisture etc.
I don't really think connectors would be any better defence against corrosion.
Best is to replace with RG8U large sized low loss coax. In a run of 15metres you can lose something like half transmitted power in the smaller RG58 coax. (and about 5% with large cable) Hence my claim that impedance mismatch of a join won't make much difference.
(regardless of the theoretical losses many people still get good radio operation with the RG58)
olewill

 

[Sneds]

Large RG58 is also known as "Thick Ethernet" and is usually yellow.

 

[gi7kmc]

[ QUOTE ]
Large RG58 is also known as "Thick Ethernet" and is usually yellow.

[/ QUOTE ]
For "Thick Ethernet" they used either RG5 or RG8 cable.

 

[Salty John]

If you only need to extend the cable by 6" I assume it is in the cabin at the radio end. In this case joining it as others have described should be fine. Be certain that the core and braid cannot meet!
You could also make up a short lead with a PL259 at each end (one for the radio, one to connect to the existing cable), add a PL259 to the end of the existing cable and join with a barrel connector (PL258).
If you do change the cable, use RG8X for runs up to about 20m and RG8U for longer runs.

 

[MarkGrubb]

I agree. the system will tolerate loss with out a noticeable change in performance. Losing half your transmitted power sounds terrible, but its only a few dB, which is nothing to worry about for marine VHF, and think how the SWR will improve with that extra return loss added by a length of lossy cable.

 

[Oldhand]

[ QUOTE ]
If you solder the joint properly and heat shrink seal the inner, then re-plat the outer and heat shrink that'll be OK, as for two connectors, then you have mating surfaces prone to green stuff, you'll have solder joints in the pins anyway (unless you have crimps and the proper tool, will cause more problems than a proper solder joint,

new cable better though!

ian

[/ QUOTE ]

So, in the above process, how do you maintain the ratio between the diameters of the inner and outer conductors and the dielectric strength of the insulator in between in order to preserve the 50 ohm impedence of the cable?