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Old 05-01-2011, 16:43   #1
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Coax for VHF

Hi, I have an old boat, and intend to pull the mast for several improvements, one of which is to replace the vhf antenna and coax cable. I am about sold on a Morad VHF-156 deluxe antenna, however I am a bit confused about the coax choice.

Morad sells a LMR240 high sensitivity coax cable, and while this cable is nice and light relative to RG213 or RG8X, but with good performance, it is not tinned. I worry that over time this might be a problem on saltwater boat.

Should I go with the heavier, but tinned cable, or the lighter untinned cable? I will also probably install a spare second cable for future AIS receiver.

Any comments welcome.
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Old 05-01-2011, 18:48   #2
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I've used various types of coax outside in numerous ham radio antenna installations for almost 50 years and moisture isn't that much of a problem, IF you properly install and waterproof the connectors.
To the point, LMR240 has a loss at 150 MHz exceeding 3 dB. RG8X is even worse. Both are a bad choice for your VHF.
There are a number of low loss coax cables but the most reasonably priced one for a marine antenna is Belden 9913 or it's equivalent which has a loss half that of the 240.
Properly solder all coax connectors, don't crimp them as it just deforms the dielectric, seal them with any of a number of available sealants, one of which is called coax seal and don't allow the coax to hang from and thereby put strain on a connector.
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Old 06-01-2011, 05:27   #3
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Not sure what is meant by "Properly solder all coax connectors, don't crimp". If it means do not attempt to crimp a solder type connector, then I agree, however, crimp type connectors are perfectly fine if installed properly. Iv'e been in this business for 35 years and use them all the time. Waterproofing is a must but I do not recommend coax seal. It is messy, gooey stuff to work with. I recommend silicone tape. It is a non-sticking self fusing silicon tape that when stretched on properly, will completely seal all voids and can be simply removed with a longitudinal slit with a razor knife. I use to use a combination of rubber tape and vinyl tape but this silicone tape has come on the market recently and is proving to be an excellent product.

Eric
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Old 06-01-2011, 08:17   #4
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A trivial point not worth debating further but crimping ANY PL259 can easily deform the dielectric which is why it's always a bad idea, regardless of what type PL259 you have.
I would agree Coaxseal is messy but is an option for those who don't routinely have to "mess" with changing connections and it is idiot-proof.
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Old 06-01-2011, 10:18   #5
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Not a trivial point at all. Your information is incorrect. Crimp connectors are used almost exclusively by professional's in the communications world. The shield of the coax gets crimped between the solid portion of the connector body and the crimp ferrule. There is no crimping of the dielectric. Here's some pics I took of a pl259 on rg8x. Works the same on all coax.






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Old 06-01-2011, 11:15   #6
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Okay, I'll play. Commercial applications, broadcast transmitters, high power applications in industrial use and all microwave uses are a very specific type of coax - hardline. None of these commercial grade (hardline) coax use crimping on anything.

Boaters don't use hardline as you may know; they use retail grade coax with dielectric material of either foam or plastic, both of which easily deform charging the characteristic impedance of the coax or worse. I won"t debate the point further except to say crimping can easily cause far more damage than the few minutes time saving it saves over soldering.

What you show are not commonly used by DIY'ers on coax installs, Regardless, the crimp in your pics covers the dielectric. Just because you can't see it doesn't make the problem created disappear.

Further discussion is both pointless (to me) and not helpful to other boaters here.
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Old 06-01-2011, 12:15   #7
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Alleged professional use crimps instead of soldering because pros get paid by the minute, and crimping is WAY FASTER than soldering. End of discussion.

Soldering a PL259 takes time and is in many ways still a craft that not everyone can master. Crimping? Zip, zip, zip, done. Although some fools still screw it up.

String, do a little web search, there are plenty of older threads on how to choose coax, the pros and cons of different types, and PROPER INSTALLATION.

Buy the cheap stuff and install it without knowing how, and you can redo the job every 2-4 years. Buy the premium stuff and take the extra time to install it to spec, and you'll probably sell the boat before the job needs to be redone.
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Old 06-01-2011, 12:17   #8
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Yeah...OK...whatever And the crimp does not affect the dielectric.

To the OP. Iv'e been doing this professionally for 35 years. Crimp. clamp, solder or combination thereof, will all work equally well for your coax as long as they are properly installed and weatherproofed. Most DIY'ers have neither the experience or tools to do it well although crimping would be far easier for them to get good results.

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Old 06-01-2011, 13:04   #9
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Just to prove my point, I just crimped a ferrule directly over the coax cable jacket. There is no noticeable deformation of the dielectric, and this is foax dielectric. Normally, the solid part of the connector body, which is much thicker than the ferrule, slides under the shield and the dielectric is well protected inside the thick connector body. Yes, a small portion of the ferrule goes over the cable jacket and an even smaller portion of that gets crimped over the jacket but it is of no consequence to the dielectric and actually provides a bit more strain relief to the connection as I am unable to pull this ferrule off by hand.

I can also connect a VHF radio in a bench test using my IFR communications monitor and strip the end of the coax, fold over the center conductor enough so that it stays in the jack on the radio and just tape some of the shield over the ground part of the jack and there is no noticeable difference in power out or receiver sensitivity. This just to show how a botched connector or damaged cable can still give no actuall use evidence of performance degradation. Now, I can connect my really high dollar analyzer to an installed cable and show you impedance bumps all over the place, but it has no affect on performance in actual use by the operator.

I think most DIY'ers don't use crimps because of the expense of the tools required.



Now here's what one of those Shakespeare CenterPin idiot-proof connectors for DIY's can do. Talk about dielectric distortion. But did it make any difference in real world performance? No. Does it show any performance degradation using a mid-dollar ($10,000) communications monitor? No. Even, so, stay away from these. Iv'e got a whole box full of ones Iv'e replaced due to shield connection problems.

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Old 06-01-2011, 17:02   #10
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and you think telling people "This just to show how a botched connector or damaged cable can still give no actuall [sp] use evidence of performance degradation." isn't misleading?????????

among all the RF lab testing done over the decades to design, improve and perfect these connectors, the one test never done previously with which I am aware is the laugh test.
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Old 06-01-2011, 18:17   #11
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What's misleading, and quite laughable IMO, is your statement "crimping ANY PL259 can easily deform the dielectric which is why it's always a bad idea, regardless of what type PL259 you have". Do you have any source of information to support this besides your say-so? I guess all the manufacturers who make these crimp connectors didn't know about this problem? I initially thought you might have meant trying to crimp a solder type PL259 because there was a ham who invented and marketed a tool for doing just that, and with nothing between the braid and dielectric, it could certainly deform the dielectric.

For those who ARE interested in trying crimp connectors, here is a nice article by Paul Peters who had a 30 year career in the telecommunications industry and now works exclusively in the field of commercial radio applications that support emergency services.

Eric
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Old 06-01-2011, 18:31   #12
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This is getting childish. I don't expect a self-proclaimed expert to admit he might be wrong but do expect someone who claims to have some experience recognize others may have more.
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Old 06-01-2011, 18:55   #13
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Crimp type PL259 connectors are ubiquitous. They are an industry standard. They do not "easily deform the dielectric". I have proven that, you have proven nothing in defense of your statement.

Eric
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Old 06-01-2011, 20:18   #14
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It seems you two have hijacked the thread, to little gain for others. My take: either solder or crimp work fine if executed well, are waterproofed, and carry no mechanical load. The problem is that an awful lot of people don't know how to solder the solder-type PL-259, and few people have the proper tools for a good crimp (not to mention the training to use the tools). Getting this right is critical for long term performance. If not entirely confident a skipper should seek help. And avoid the quick-connect type...

Now, back to the thread. The question was which coax is best. The best coax will be 50 ohm, have low loss and low leakage. The low loss lets out most small diameter coax like RG-58 (about the worst but most common choice) and mini-8 (RG-8X). LMR-240 is a bit better but still higher loss than the 0.4" diameter flexible cables: RG-8 and RG-213 have half the loss of RG-8X. RG-213 is the traditional high-end choice and is a safe bet. The foam core is an advantage over air core in the event of water intrusion. I have no experience with Belden 9913 but the loss specs are impressive.

Tinning will only matter if you wish to cut off the end and put on a new connector, only to find the shield corroded; not likely to be a problem if waterproofing was correctly applied. And if there is water intrusion then it needs to be replaced anyway.

On an anecdotal note, I put RG-213 in the boat while building her in 1980. It still seems to be working well. I did seal some coax at the masthead with liquid vinyl to protect against sun damage however. Even though Carina was one of the smallest boats at anchor in Playa del Coco, Costa Rica, I was the only one who could consistently contact the boats in Playa Flamingo (1994). It pays to get it right.

BTW, until last year I was using the Morad antenna as well. It had the best SWR of any antenna I tested, and did well on 2m ham as well.

I would not mount the AIS antenna close to the communications antenna, particularly if they are at the same height. They will interfere with each other. And it isn't needed. AIS is fairly low power (1W IIRC) but really reaches out (although I can't explain it). My antenna is mounted just above my radar, on a pole at the transom, perhaps 12' off the water. I can watch the Coast Guard ships maneuver at the mouth of the Columbia 100 miles away. At sea it is not unusual to pick up ships 80 miles off. I don't see any advantage to putting it up high. And remember, while the line of sight is better at the masthead there is a lot more attenuation with the longer cable run.

I hope this helps.

Greg
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Old 07-01-2011, 05:51   #15
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Quote:
Originally Posted by CarinaPDX View Post
It seems you two have hijacked the thread, to little gain for others.
Excellent post. The thread was not hijacked and I hope others that are reading this thread have gained a little knowledge about crimp connectors to make there own decision on there use, even if it was not the main topic of the thread. The OP did say "any comments welcome". My response was not to argue back and forth with S/V Illusion, but to quell the notion, for others reading this thread, that crimp connectors deform the dielectric, cause far more damage than soldering, and are always a bad idea. I did this with the use of pictures, that show how they are installed and show evidence that they do not crimp the dielectric, based on my extensive experience with installing and using these types of connectors.

Eric
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