UHF Coax Cable Joining

Dougwe · Chief one feather

UHF Coax Cable Joining

Baz421 · Guru

Dougwe wrote:
Hi fellow GN's,
To keep this short I have a UHF Radio fitted in my Prado and need to redirect the coax cable under the hood, my question is,
Can you join the Coax Cable successfully? I would use correct fittings if available and solder where possible.

Edit....Sorry, forgot to ask, with the join mentioned, would there be signal loss?

-- Edited by Dougwe on Saturday 31st of August 2013 01:35:53 PM

Hi Doug Can join OK if careful, shouldn't lose signal.

I just bought and extension coax (plugged in) when I had my antenna on the bull bar,,, Jaycar/Dick Smith sell em. If not specialist UHF radio sellers have em OR a single longer one with no join.

Cheers Baz

-- Edited by Baz421 on Saturday 31st of August 2013 02:53:53 PM

Yendorane · Senior Member

If it were me i would just desolder the plug that's already on the coax & reattach when

all back in place Taking care not to melt the insulation on the center pin when soldering

the center wire back in

Cheers Yendorane

Mark · Senior Member

Hi Doug Can join OK if careful, shouldn't lose signal.

I just bought and extension coax (plugged in) when I had my antenna on the bull bar,,, Jaycar/Dick Smith sell em. If not specialist UHF radio sellers have em OR a single longer one with no join.

Cheers Baz

Hi Dougwe

As Baz states, and just to add confirmation.............. "no problem with joining at all"
I personally use joiners when installing a new aerial so I don't have to run a new cable through the fire wall, never had an issue with signal loss.

Mark

justcruisin01 · Guru

Doug, I just bought a joiner from jaycar to extend the coax on the new tug, small a compact ,has a center section with two screws for the center wire a clamp for the outer shield. Haven't fitted it yet will do this week.

Cloak · Guru

All joining will have signal loss but given it's a low power unit I doubt it will be noticed, unless you do a complete hash of it.... lol

Mark · Senior Member

Cloak wrote:
All joining will have signal loss but given it's a low power unit I doubt it will be noticed, unless you do a complete hash of it.... lol

Not according to my meters it doesn't!!

VKPORTABLE · Senior Member

Cloak wrote:
All joining will have signal loss but given it's a low power unit I doubt it will be noticed, unless you do a complete hash of it.... lol

Sorta right and sorta wrong.

Yes, any join or adapter will induce loss into the line - RG-58 is awful lossy at 477 MHz, not to mention PL-259 connectors.
The best solution would be to start from the antenna with a new lump of coax then terminate at the radio end with the appropriate connector.

As for low power, if you are using low power you want as much of that power to be getting to the antenna, the lower the power you are running the more you will notice loss.

At the end of the day soldering it together and using heat shrink to insulate is going to work just fine, and probably less loss then an adapter.

03_troopy · Guru

VKPORTABLE wrote:
Cloak wrote:
All joining will have signal loss but given it's a low power unit I doubt it will be noticed, unless you do a complete hash of it.... lol

Sorta right and sorta wrong.
Yes, any join or adapter will induce loss into the line - RG-58 is awful lossy at 477 MHz, not to mention PL-259 connectors.
The best solution would be to start from the antenna with a new lump of coax then terminate at the radio end with the appropriate connector.
As for low power, if you are using low power you want as much of that power to be getting to the antenna, the lower the power you are running the more you will notice loss.
At the end of the day soldering it together and using heat shrink to insulate is going to work just fine, and probably less loss then an adapter.

Hi VKPORTABLE, in the highlighted text it looks like you're suggesting a solder joint in the cable as opposed to a connector joint? ( or am I misreading this?) Surely a male/female BNC would be a better way to join the cable if you really had to join it? Personally I'm another one for replacing the cable complete. Any joint will cause losses however minor, but also, every joint is a possible future source of failure due to corrosion or mechanical degradation of the joint.

VKPORTABLE · Senior Member

soldering it together and using heat shrink to insulate is going to work just fine, and probably less loss then an adapter.

Hi VKPORTABLE, in the highlighted text it looks like you're suggesting a solder joint in the cable as opposed to a connector joint? ( or am I misreading this?) Surely a male/female BNC would be a better way to join the cable if you really had to join it? Personally I'm another one for replacing the cable complete. Any joint will cause losses however minor, but also, every joint is a possible future source of failure due to corrosion or mechanical degradation of the joint.

Bob;

Obviously replacing the whole lot is the best way.
As with the benefits/downsides of soldering the coax together or using adapters it's a bit of a camp-fire discussion point isn't it?
Adapters are lossy, soldering as above is lossy.

Maybe we should do a test and see which gives the most loss, would be interesting to see actually. I am going to put my money on adapters been more lossy :p

Re every joint is a possible future issue - agree 100%, although with an adapter you are adding another connector in the line, so that would have to induce losses.

To show how pedantic I am about things, when installing the new stereo into the 4WD with the assistance of my mate, he was the nuts n bolts man that got the dash apart and back together again - last time I pulled a dash out I ended up with about 9 spare screws I had no idea where they went!

Anyway, he kinda likes toys and was busting his guts to get the stereo in - and I've seen his 'slap happy let's get it done as quick as I can so I can play with it' approach before with things, he was not to impressed when I made him solder all the speaker and power leads together and heat-shrink each one. He wanted to just twitch and tape, bugger that for a joke - not in my 4WD!!!

Then he asked how many radios (transceivers) were going in it, he went a bit pale in the gills when I said five :)

-- Edited by VKPORTABLE on Wednesday 4th of September 2013 10:13:18 AM

-- Edited by VKPORTABLE on Wednesday 4th of September 2013 10:17:06 AM

Dougwe · Chief one feather

Just sent you a PM VK.

Thanks all, sorry for the delay in replying, I have been a bit off colour, so to speak, interesting responses. I have decided to just relocate through the passenger side of firewall, then seal the entrance area and that will solve my problem. I think.

03_troopy · Guru

HI VKPORTABLE, the thing that concerned me most was that the impedance of the coax would be dramatically affected unless you were able to maintain the correct dimensions between centre conductor and braid with a suitable dialectric. You would have to somehow build up a new piece of dialectric between the two conductors to maintain integrity. That method is fine for joining a shielded wire, but coax is a transmission line, where the dimensions and properties of centre conductor, dialectric and braid are critical to performance. If you view a crushed coaxial cable (dimensions between conductors distorted) with a TDR you will see how much it will affect the cable.

VKPORTABLE · Senior Member

Yes, there will be a change in impedance. Yes, it will present loss into the transmission line.
Both these statements are true and correct.

Having said all this, what happens when you solder your coax onto a standard mobile antenna base, as shown below:

You have done exactly the same thing, you have separated the inner conductor and the outer conductor changing it's dielectric constant.
Therefore at this point you must also be introducing a change in impedance.

Crushed cable is a totally different thing compared to a cable that has been correctly joined. Soldered correctly, heat-shrink tube used on both the inner conductor and over the join. And if you want to get really pedantic, self-amalgamating tape over this again.

Also, at the end of the day we are not talking a 'mission-critical' application here, we are not talking high-power levels and if all been correct with the antenna, it's installation and VSWR then this will work as a 'fix'. Solder joining nor adapters should be considered for a long-term application, the best solution is to run new coax. Although with some antennas, particularly some GME models there is no way of getting the coax from the internals of the base, so this prohibits the 'run new coax' idea. The only viable way would be to chop the coax somewhere near the base, mount an inline N-Type female to it, then a N-Type male to your coax (coming from the radio). Why N-Type, due to their design they are waterproof and of much better quality then any other connector. Even with this arrangement you are still going to have loss.

The original questions were: 'Can I do it' (Solder or adapter) and 'Will there be loss'.
Yes, it can be done - Yes there will be loss.

When you say TDR I guess you mean a Time-Domain Reflectometer - not sure how many nomads or anyone not working in the high-end of the communications industry would have access to one of these and know how to use it. At a price tag of between $1800 for a low-end on to over $4000 for an AEA, very few I would suspect.

Anyway, I think we are getting far to deep into technical theory here and resulting in just confusing people.

Dougwe · Chief one feather

Phew, who said confusing? I'm not confused. I'm just all mixed up and lost the plot, I'm sitting here waiting on the man in a white coat to arrive. biggrin

I must say though, thanks for the interesting discussion, so many different views on the subject, just why this forum is good providing it's in the correct section, as this topic is, thankyou guys.

As I said above I have decided to just drill a hole in the firewall and enter near the glovebox area, I will then actually shorted the coax by about 1.5mts so should be better that way. I actually have one of the GME type antenna's where the coax goes up through the bottom of the antenna and I can't see a way of getting to it so it all has to be removed.

Gee, all this because of a black cat biggrin biggrin :)) :)). Sorry CC.

03_troopy · Guru

Dougwe, there is usually a way to dissasemble the antenna to replace the cable. Unscrew the antena off the base and have a look at it. It may have a nut that can be removed to strip it down further to reveal how the cable has been conected. Often the centre conductor will be soldered through a hole in the antenna mounting stud.

Don't worry about the technical aspects I used, to try illustrate why joining coaxial cable by soldering the two ends together is a poor way of doing the job, that was for VKPORTABLE's benefit. But that advice is from more than 30 years experience in working with communications and instrument systems, installing anything from 20mm diameter HF radio coaxial cable to 3mm triaxial cable in aircraft GPS navigation systems. Joining cable can be done if absolutely necessary with the correct connectors, not soldering the two ends together.

from Wikipedia:
The characteristic impedance of the cable (Z_0) is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer and minimum standing wave ratio. Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality.[2

the rest of the article can be read here for a more technical explaination.

Coaxial Cable

PeterD · Guru

VKPORTABLE wrote:
Yes, there will be a change in impedance. Yes, it will present loss into the transmission line.
Both these statements are true and correct.
Having said all this, what happens when you solder your coax onto a standard mobile antenna base, as shown below:

You have done exactly the same thing, you have separated the inner conductor and the outer conductor changing it's dielectric constant.
Therefore at this point you must also be introducing a change in impedance.

People who know what they are doing do not use those bases above 200 MHz. The reason is the same one that is the same reasoning that you are erroneously using to justify why you can bodgy a cable together and get good results from it. If you want a good result from a CB antenna you should use a base like this one. It has an above ground mount as well as a much better cable termination. Yes you can get away with simple cable joining but if you want good efficiency you should terminate a cable jack on the cable leading to your set and a cable plug on the cable leading to the antenna. Anything less and you may as well forget installing a new antenna and just get a low powered hand-held (for probably the same price.)

Power losses increase as frequency increases. When you get over 200 - 300 MHz things start falling apart rapidly.

Mark · Senior Member

Dougwe wrote:
Phew, who said confusing? I'm not confused. I'm just all mixed up and lost the plot, I'm sitting here waiting on the man in a white coat to arrive.
I must say though, thanks for the interesting discussion, so many different views on the subject, just why this forum is good providing it's in the correct section, as this topic is, thankyou guys.
As I said above I have decided to just drill a hole in the firewall and enter near the glovebox area, I will then actually shorted the coax by about 1.5mts so should be better that way. I actually have one of the GME type antenna's where the coax goes up through the bottom of the antenna and I can't see a way of getting to it so it all has to be removed.
Gee, all this because of a black cat :)) :)). Sorry CC.

Dougwe..........

Just cut the thing and put a good quality joiner in it, I've done it a dozen times and it's not made a jot of difference according to the signal meter, and on my own vehicle have still managed a distance of 27 Km's (flat open ground) My assumption is that you use your UHF for a bit of a chit chat with the truckies and when local around town, backing onto a site maybe, your not gonna notice a loss of range/quality/reception etc.
Nothing to be sorry about, you ask a simple question and now you are confused with far superior communication knowledge.

Go for it and get chatting.
Over and Out.

Mark

Mark · Senior Member

Teddy wrote:
As with the benefits/downsides of soldering the coax together or using adapters it's a bit of a camp-fire discussion point isn't it?
Adapters are lossy, soldering as above is lossy
Re the above camp fire discussion it has been my experience that in the longer term there are more losses from the joiner than a properly soldered joint, as moisture and some degree of electrolysiswill set in on the push in type fittings whereas the soldered joint will (if done well) maintain its integrity

Heat shrink and amalgamation tape at the time of repair works wonders to stop the above concerns.

Edit was to correct: Shrink Wrap!! Duh!!

-- Edited by Mark on Friday 6th of September 2013 11:07:03 PM

Teddy · Member

As with the benefits/downsides of soldering the coax together or using adapters it's a bit of a camp-fire discussion point isn't it?
Adapters are lossy, soldering as above is lossy

Re the above camp fire discussion it has been my experience that in the longer term there are more losses from the joiner than a properly soldered joint, as moisture and some degree of electrolysiswill set in on the push in type fittings whereas the soldered joint will (if done well) maintain its integrity

VKPORTABLE · Senior Member

PeterD wrote:
People who know what they are doing do not use those bases above 200 MHz.

Peter, if you had read the post in context you would have seen the image was for explanation purposes. You would also be well aware there are two variants of this base type, one for HF and one that is used on VHF/UHF.

And of course there would be loss, as I indicated. Any join is going to create loss, regardless of it's mechanism.

Knowledge speaks, but wisdom listens.