Splicing RG58

[Brian McVickers]

Splicing RG58 Coax Cable for a radio

During a recent vehicle project I found my CB cable and decided to follow it.
The previous owner installed the CB and its two antenna mounts, one front and one rear. Along the length going to the rear mount I found two taped up connections that turn out to be splices joining three separate lenghts of cable to make one.

These splices are done by twising the center braided wires together and then the outer braded wires together, then it's all taped up!

Seems a bit sketchy to me. Does this work or should it be done another way?

What is the proper way to splice RG58 together?

 

[DaveInDenver]

Funny! You most certainly can not treat coax like regular wire. Splices are no good pretty much under all conditions. There is absolutely no way to guarantee your impedance at the splice by striping, twisting and soldering the connection. That will be a huge discontinuity and probably will result in a horrible reflection. Have you ever tried checking the VSWR of your feed? Bet it's ridiculous.

If you must join two lengths, the only way to do it reasonably is putting connectors on each section and adding a bulkhead in the middle. This is less than perfect, but far better than trying to join them like regular wire.

Your best bet is buy a roll of cable and run new, unmolested feeds.

 

[BajaTaco]

I can't understand what the purpose of splicing 3 cables together would be. Do I understand correctly, that basically, this is a "strand" of 3 cables all terminating at a single point at either end (where the splices are)?

As far as I know, the proper way to splice RG58 would be to use a barrel connector and then two PL-259 connectors at each end of cable. Process the connectors and cable ends as shown HERE.

 

[Brian McVickers]

That's what I figured, these twisted splices are just ugly!

I have terrible transmit and receive, maybe a 1/2 mile!!
I just got an SWR meter and was going to try and tune the system but then found the splices and decided that needs correction before worrying about the SWR.

I’ll need to look into replacing it with a solid length, Radio Shack seems to be my only convenient option and they have 20 and 50 foot lengths with connectors on the ends but I will most likely have to cut the connectors off of at least one end to run it, and then replace the connector.

Now with my other project, I am needing to run a second coax but one end has a special soldered connection that I can’t duplicate. This coax is not long enough so I have a 20’ extension that I will have to connect with a bulkhead. Hopefully It wont result In too much loss.

All of the CB type shops near me keep inconvenient hours so they are hard for me to get to. Any other ideas besides Radio Shack?

 

[Brian McVickers]

I can't understand what the purpose of splicing 3 cables together would be. Do I understand correctly, that basically, this is a "strand" of 3 cables all terminating at a single point at either end (where the splices are)?

Correct. It seems as if the installer needed a 20 foot lentgh of cable but only had a 7', 8' and 5' lengths to work with so he connected them end to end!

 

[DaveInDenver]

I can't understand what the purpose of splicing 3 cables together would be. Do I understand correctly, that basically, this is a "strand" of 3 cables all terminating at a single point at either end (where the splices are)?

One reason people try to splice coax is to feed two antennas from one source. There are probably correct ways to build a harness to do that, but other than truckers with their CBs I'm not personally aware of anyone who does that (other than commercial broadcasters, but that's a little more sophisticated). It's hard enough optimally tuning a single antenna, forget dealing with two radiators! With co-phased antennas you need to be super careful about the distance between the two whips and it'll really only works well at a relatively narrow bandwidth. The two whips probably should not be flopping around in the wind, either...

 

[DaveInDenver]

I have terrible transmit and receive, maybe a 1/2 mile!!
I just got an SWR meter and was going to try and tune the system but then found the splices and decided that needs correction before worrying about the SWR.

Since you haven't yet burned up your radio, keying it one more time is probably not a big deal. I'd measure the SWR of the feed as it is, just to see. But I'm curious in that way.

I’ll need to look into replacing it with a solid length, Radio Shack seems to be my only convenient option and they have 20 and 50 foot lengths with connectors on the ends but I will most likely have to cut the connectors off of at least one end to run it, and then replace the connector.

Now with my other project, I am needing to run a second coax but one end has a special soldered connection that I can’t duplicate. This coax is not long enough so I have a 20’ extension that I will have to connect with a bulkhead. Hopefully It wont result In too much loss.

All of the CB type shops near me keep inconvenient hours so they are hard for me to get to. Any other ideas besides Radio Shack?

A bulkhead-type splice is fine. You do get some loss, but it's not horrible and in a mobile rig it's really not enough to bother worrying about.

As far as rolling your own, don't shy away from crimped connectors. They are not as good as solid soldered connections, but if you take time and keep things tidy and organized, they can work fine. I carry crimp connectors and coax tools in my spares kit, never know when you might need to make a repair. Your feed is going to be better if trimming off one pre-made connector allows a cleaner installation and trimming the coax to the right length is better than coiling up extra cable.

 

[Brian McVickers]

One reason people try to splice coax is to feed two antennas from one source. There are probably correct ways to build a harness to do that,

Ok so here's the kicker,
this setup has one connection that goes into the back of the radio as normal. That connector has a rubber boot on it with two holes. Out of each hole comes one cable to there are two cables going to the one connection that attatches to the radio. One cable runs forward to the front bumber antenna mount and the other runs to the back to the spare tire carrier antenna mount.

Thing is I only have one antenna. I believe this set-up was to allow the one antenna to be positioned for driver preference, in the front or in the back. So one antenna mount is always empty.

Does this make sense???

 

[DaveInDenver]

Ok so here's the kicker,
this setup has one connection that goes into the back of the radio as normal. That connector has a rubber boot on it with two holes. Out of each hole comes one cable to there are two cables going to the one connection that attatches to the radio. One cable runs forward to the front bumber antenna mount and the other runs to the back to the spare tire carrier antenna mount.

Thing is I only have one antenna. I believe this set-up was to allow the one antenna to be positioned for driver preference, in the front or in the back. So one antenna mount is always empty.

Does this make sense???

Makes sense, although the preferred way to do this is an antenna switcher. Keep in mind that the coax is a part of the antenna system, so leaving it unterminated or poor connections have as much or more effect on the TX and RX as the whip itself. If I understand, you have at all times one of the feeds left without an antenna, right? That is basically, well, really bad. That looks like a very high impedance to the coax, which is best compared to a perfect mirror electrically and all the energy is reflected back from that leg. This is bad, bad, bad for the radio.

 

[Brian McVickers]

Thanks Dave, this is great info.

OK so the system has been this way since well before I had it. The radio still seems to TX and RX well within short distances so I don't think its fried.

I'm thinking of three solutions:

1 - Snip off the double connection going to the back of the radio and put a PL259 connector on each lead, one front and one rear. Then I would connect the lead coming from the active feed, mount with antenna, to the radio and leave the inactive feed, mount with no antenna, disconnected. That way I could just switch connections if I ever have the desire to swich antenna locations. --- Question, will each antenna location have it's own SWR reading ant therefore possibly need it's own antenna? Maybe I should just pick one location!?

2 - Get a second antenna so that each feed is active. However I would then need to tune the set and ther may be no benefit to such a setup.

3 - Get a dummy load to fill the inactive empty antenna mount.

I think I like Option 1, what do you think?

 

[DaveInDenver]

OK so the system has been this way since well before I had it. The radio still seems to TX and RX well within short distances so I don't think its fried.

Probably OK, at least not burned up. Probably not an ideal situation, but CB radios are usually pretty rugged units and can take quite a bit of abuse.

1 - Snip off the double connection going to the back of the radio and put a PL259 connector on each lead, one front and one rear. Then I would connect the lead coming from the active feed, mount with antenna, to the radio and leave the inactive feed, mount with no antenna, disconnected. That way I could just switch connections if I ever have the desire to swich antenna locations. --- Question, will each antenna location have it's own SWR reading ant therefore possibly need it's own antenna? Maybe I should just pick one location!?

2 - Get a second antenna so that each feed is active. However I would then need to tune the set and ther may be no benefit to such a setup.

3 - Get a dummy load to fill the inactive empty antenna mount.

I think I like Option 1, what do you think?

Option 1-
This would work just fine, kind of a pain but would work. Yes, the length of coax affects the SWR you'll get. So when you tune an antenna, the coax length determines ultimately the length of the whip. It's relatively unlikely that they'd be perfectly identical, but if the feeds are similar you might find that on one mount the SWR is good and the other it's not too bad, though.

Option 2-
If you have two whips, then tune each and then it's just a swap at the radio, that is fine. You could stick a switcher at that location and that would be easy.

Option 3-
This works, too. A dummy load, though, absorbs energy and so you'd be losing transmitter power just heating the resistor in the dummy load. This saves the radio at the expense of lost range. In real terms, this would be no worse than what you have now and might result in some increased range if your radio is designed to fold back its output when it see a poor load. Most CBs are dumb, but rugged enough to tolerate a bad SWR. Others are smart (most ham radios in the past decade or two operate this way) in that if they see too much reflection, they reduce their power. This protects the radio.

My $0.02 is to pick a convenient mount location, run fresh coax and tune it up (so, yeah, option 1). There is no perfect spot. The best ones electrically are rarely the best ones physically. I have mine on the roof and it works great, just bangs trees a lot. On the bumper it was less likely to hit stuff, but it did not do all that great facing forward.

 

[Brian McVickers]

Last night I pulled out the old spliced cable and ran a single piece of new cable about 18 feet long. This will connect the radio to the rear antenna mount wich will now be the primary antenna mount.

I attempted to put a connector on the leftover coax running to the front mount but it turns out to be RG-59 and it would not accept my PL259 connector since the cable is too thick.

I'm hoping to test the SWR today but this morning on the way to work the weather channel came through stronger than ever before. I tried a radio check but no one was listening!

Now my only concern with the CB antenna is its lenght in relation to its location. It is mounted on the spare tire carrier and the tip of the antenna does not clear the top of the vehicle -- so I'm concented that this clearance issue may act as a barrier to TX range.

Would it be better if the tip of the antenna cleared the top of the truck -- the signal is transmitted fromt the very tip of the antenna correct?

 

[DaveInDenver]

Would it be better if the tip of the antenna cleared the top of the truck -- the signal is transmitted fromt the very tip of the antenna correct?

Doesn't matter all that much. An antenna radiates along it's whole length, so getting just the tip above the roof will make a marginal difference. The more of the length above the roof the better. If the antenna is competely blocked, then you're getting very little going that way, but getting just a couple of inches above the roof line isn't going to suddently equalize the radiated energy in all directions. You'll still be getting very little energy radiated across the roof.

 

[Brian McVickers]

SWR Readings:

Ok, the antenna is completely below the roofline and about three inches off the back door's vertical plane.

I just checked the SWR readings:

Ch-20 = 7
Ch-40 = 4.8
Ch-01 = 12.5

The % of reflected power is in the red on the meter. Red starts at SWR of 3 and is equal to 25% of power reflected, so my readings are over 50% reflected.

According to the directions: If reading is higher at ch40 than ch01 antenna needs to be shorter. If readingis lower at ch40 than ch01 antenna needs to be longer.

So I need a longer antenna. Is there more to it that I am missing?

Oh, and thanks by the way this is great help!

 

[Brian McVickers]

Also note, I can hear the weather band bleeding over to the regular CB channels ever so slightly!????