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Author Topic: Okay to lengthen coax with a pair of connectors?  (Read 4223 times)
ES1TU
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« on: October 01, 2012, 01:04:01 AM »

Hi guys,

I need to rearrange my antenna cable a bit. Unfortunately, new run of coax will be a bit longer.
It would be quite inconvenient to take the antenna down in order to install longer, one-piece coax.

Now I'm thinking about appending a piece with a pair of connectors. What do you think, is it okay to do so?
What would the attenuation be compared to uninterrupted run?

Freq is 21MHz, RG213, about 75ft of coax.

Thanks!
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G3RZP
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« Reply #1 on: October 01, 2012, 01:07:41 AM »

Provided you use decent connectors, you won't notice the difference. With good lab equipment, you might  JUST see a difference.
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KA4POL
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« Reply #2 on: October 01, 2012, 02:59:06 AM »

No problem, the loss at 21 MHz will be very low, about .007 dB provided you are using decent ones.
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WX7G
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« Reply #3 on: October 01, 2012, 05:38:40 AM »

"Decent" connectors? I don't think one could buy connectors that were not "decent" at 21 MHz. So, no need to worry.
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K2DC
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« Reply #4 on: October 01, 2012, 05:40:55 AM »

With a decent quality adapter, the average Ham could not even measure the difference.  Using laboratory equipment, I once measured in-series and between-series adapters at an average 0.006 dB at 1300 MHz.  And it took quite a bit of averaging to drive the noise floor down far enought to repeat the measurement.
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K7RBW
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« Reply #5 on: October 01, 2012, 06:21:43 AM »

Just be sure to wrap them so they stay dry. Moisture or corrosion could change the nominal insertion loss to something quite noticeable.
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KCJ9091
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« Reply #6 on: October 01, 2012, 06:24:30 AM »

Now would be a good time to insert a PolyPhaser type protection device in the cable if you do not have one in place.   
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G3RZP
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« Reply #7 on: October 01, 2012, 09:05:53 AM »

WX7G

I got caught quite a few years back with a cheap in line SO239 back-to-back type coupler that actually melted with 400 watts at 10 MHz. That with an SWR of around 1.5:1.  The two female sockets were just pushed against each other rather than being one piece or screwed together.


The right angle ones can even have a coiled spring in them as the connection.
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K0CBA
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« Reply #8 on: October 02, 2012, 08:21:14 AM »

Coax can be spliced!  They didn't start the machine back in the 40's and it's been putting out one unspliced piece of coax ever since.

I came across an old military radio school 'how to' manual and there it was.   
It is a bit tedious the first time or two you do it but with a little practice you will have a near perfect splice.

Compared to soldering up two connecters and buying a barrel connecter it certainly is less expensive and probably faster.

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W5DQ
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« Reply #9 on: October 02, 2012, 12:08:19 PM »

"Decent" connectors? I don't think one could buy connectors that were not "decent" at 21 MHz. So, no need to worry.

Maybe not RF reference wise but I have seen some barrel connector that actually fell apart. Also not all PL-259's are created equal. The point here is using quality connectors should reduce any issues mechanically. Like most have stated, you would be hard pressed to see any difference with or without a 'splice' in the coax run at 21Mhz. Now 2M or 440Mhz, that's a different animal.

Also I would not recommend using 'solderless' RF connectors for anything short of an emergency repair. I've seen many new hams use these as they were easy to use without a soldering iron, which many new hams have either never used or don't own.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
AC5UP
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« Reply #10 on: October 02, 2012, 03:27:29 PM »

If I were starting my tool collection and experimenter phase today I'd invest in a good quality crimp tool.

A few years back you'd never convince me that anything was superior to a properly soldered RF connector, but experience has shown me that crimp-on connectors are both cost effective and reliable (*).  Plus, they have a shorter learning curve and that's important to me as I don't work with them often enough to stay in practice. Best way to get your nickel out of a tool like that is to buy it when you're young and take care of it for a long. long time.........

(*) = and, like their solder-on cousins, if you buy cheap-ass connectors you will get what you paid for.
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W0BTU
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« Reply #11 on: October 02, 2012, 03:53:19 PM »

If I were starting my tool collection and experimenter phase today I'd invest in a good quality crimp tool.

A few years back you'd never convince me that anything was superior to a properly soldered RF connector, but experience has shown me that crimp-on connectors are both cost effective and reliable ... and, like their solder-on cousins, if you buy cheap connectors you will get what you paid for.

I fully agree. There is nothing sacred about soldering (or for that matter, all-copper coax), although I once thought that crimping always was a slipshod way to do it.

For one example, examine a good snap-and-seal type fitting for aluminum shield CATV coax with a magnifying glass, and you'll be amazed at how well they make electrical contact with both the center conductor and shield (not to mention make a waterproof seal). Try soldering that kind of coax. You can't. But that's OK. :-)
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W5DQ
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« Reply #12 on: October 02, 2012, 09:37:46 PM »

If I were starting my tool collection and experimenter phase today I'd invest in a good quality crimp tool.

A few years back you'd never convince me that anything was superior to a properly soldered RF connector, but experience has shown me that crimp-on connectors are both cost effective and reliable ... and, like their solder-on cousins, if you buy cheap connectors you will get what you paid for.

I fully agree. There is nothing sacred about soldering (or for that matter, all-copper coax), although I once thought that crimping always was a slipshod way to do it.

For one example, examine a good snap-and-seal type fitting for aluminum shield CATV coax with a magnifying glass, and you'll be amazed at how well they make electrical contact with both the center conductor and shield (not to mention make a waterproof seal). Try soldering that kind of coax. You can't. But that's OK. :-)

Having never actually installed a crimp-on connector myself, I can easily say that many of the commercially acquired coax assembly using a 'crimp-on' (at least as far as the shield was concerned) I ever dealt with had issues with the connectors - either from the get-go or sometime early in the life of the cable. Yes there were a few that didn't leave me tracking down problems but enough to scar me from going that route anymore. One so-called big name company's 100 foot coax assembly that was ordered by a buddy to do his installation with actually had one of the connectors fall off in his hand.  He paid big dollars to have crimp-on connectors put on by this REPUTABLE company and had to send them coax back to have it replaced before he could complete his antenna install. He can't install his own connectors due to physical dexterity problems ... and the fact he usually ends up going to the burn ward when he tries to use a soldering iron. I keep telling him if he smells flesh burning when he picks up the soldering iron, he has it by the wrong end  Grin

To avoid the issues with unknown quality of connector installations, I have just made it a routine to put on my own connectors that way I know for a fact they are done correctly and should never give me any problems. Once they are installed and checked I have never have any issues with my coax connections - in as far as reliability of the connector installation is concerned. Regardless, to each their own way, but I'll take solder on type and do it myself.

And yes, you can't solder aluminum but since I don't use aluminum hardline it isn't a problem for me. If and when I should ever do use AL cable, I'll most likely have to go to crimp-on style connectors  ..... and hope the best Smiley
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
NR4C
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« Reply #13 on: October 03, 2012, 06:37:47 AM »

Lots of talk about using good quality connectors.  Great idea.

But, a word about weather-proofing.

To make life easier and still provide a water-resistant connection, I used the following procedure to extend a feedline at my old shack.

Notes below assume a coax running vertically wit one end onTOP and the other end on BOTTOM.  For a horizontal run, think of TOP as end ONE and BOTTOM as end TWO.

Also, start and end each layer of the following about an inch above/below the previous layer.

1) One wrap of Scotch 33 TOP to BOTTOM with "Sticky" side out and overlapping about 1/3rd to 1/2 the width of the tape.  This is a bit of a challange to get started, but after that it's easy.  You will appreciate this step when it comes time to remove all this stuff to take the joint apart.

2) Apply one layer of "RainCoat" or some form of self-sticking waterproofing material.  CoaxSeal is another possibility.

3) Apply two wraps of Scotch 33, one layer from TOP to BOTTOM and the other BOTTOM to TOP.  This puts the exposed edge of the overlap pointing down so it doesn't trap water.  Make sure to relax the tension of the last few 'turns so the end doesn't want to pull back after you cut it.

This should provide good weather proof connection.
...bill  nr4c
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AA4HA
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« Reply #14 on: October 03, 2012, 01:41:44 PM »

WX7G
I got caught quite a few years back with a cheap in line SO239 back-to-back type coupler that actually melted with 400 watts at 10 MHz. That with an SWR of around 1.5:1.  The two female sockets were just pushed against each other rather than being one piece or screwed together.
The right angle ones can even have a coiled spring in them as the connection.

In a moment of insanity (ok, the $1.99 each pricing on eBay) I bought a bag of adapters (N to PL-259). When they arrived I was disappointed to find out that they were poorly nickel flashed, pot-metal. Last week I had a PL-259 come completely apart in my hands, the snap ring that retains the threaded nut portion was held in place with "magic" (or spit). Working on commercial stuff for so long I had forgotten how badly the amateur radio community gets "junk" foisted off on us. (whoever made the barely shielded RG-8 should be wrapped in 5000' feet of it and dropped into the deepest spot in the Pacific).

I too have just barely seen the "bump" on a TDR (time domain reflectometer) of coax connectors. Generally I do not mess with PL/SO-259 stuff but even really high quality connectors are visible on an analyzer. Really PL-259 connectors are not all that well matched for 50 ohms (little known factoid)  but the losses are going to be so low that you would not see it in the HF band.

Meaning "high quality" would be pins and spring fingers that are possibly gold coated with really tight spring fingers where all four grasp the pin. Look inside of some SO-259's and you will frequently see scorching, maybe a broken off or bent spring finger. If you can get a teflon insulator all the better, you can test that, teflon is not going to melt if you touch a soldering iron to it. One time I had some really old PL/SO-259's that had a ceramic insulating body (some sort of mil surplus stuff).

Non-crimped connectors are all over the place in the technique to install them. As a young child I was taught to fan out the copper braid and make two twisted rabbit ears and feed those through and pull them through the little holes with a hemostat (or really tiny needle nose pliers), get the biggest soldering gun we had and to melt about a quarter pound of solder to the body to the braid and then to use the same technique on the center pin. It was not uncommon to end up with a shorted out connector (darned little copper strands go everywhere). The attempt to repair the problem was to jumper a car battery across the cable to vaporize the shorted out copper shield strand. If that did not work, unsolder the entire mess and start over.

LMR-400, burial rated is the way to go, with real crimp connectors and a real crimp tool. I will not get started on my "Heliax and Type-N is God spiel" (off topic).
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
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