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Old 14-05-2024, 19:29   #1
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Choosing the the right VHF Coax

My mast is down due to repairs we did over the winter. I'm going to replace all of the wiring at is is 20-40 years old. I'm trying to sort out how crazy I need to go on the coax for the VHF.

We sail on Lake Superior, Tartan 27-2 with a 40' mast and about 12-15' feet from the base of the mast to the radio. I'm having a hard time understanding the potential range difference between using RG-58CU or RG-8X (due to signal loss over that distance). We also use a handheld. However, I want to be sure we have reasonable range for longer sails, further from shore.

Appreciate guidance on this.
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Old 14-05-2024, 20:14   #2
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Re: Choosing the the right VHF Coax

https://www.qsl.net/co8tw/Coax_Calculator.htm

For frequency use 156MHz
For power in use 25W

You will very quickly see why both RG58 and RG8x are considered poor except for very short cable runs, and why RG213 is often considered required minimum, and LMR400 preferable for very long runs or high performance. Note, LMR400 is aluminum and more sensitive to having the connectors installed correctly, and many recommend against it for that. If you opt for LMR400, you would be advised to have it professionally installed.

For your boat, unless you have some special requirements, use RG-213.
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Old 14-05-2024, 21:27   #3
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Re: Choosing the the right VHF Coax

RG213. Anything more is overkill and not warranted except in special circumstances. Anything less is 'underkill' and a waste of time and effort.

Do it once and do it right - use RG213.

As Whollybee mentions, if someone does manage to convince you to use LMR400, make sure it is a waterproof version such as LMR400-DB (i.e 'direct bury') and have it professionally installed by someone who really knows what they are doing - not all 'professionals' are equal...
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Old 15-05-2024, 06:15   #4
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Re: Choosing the the right VHF Coax

RG 213U. with drip loop(s)
1.Most rugged 50 ohm coax for general use.
2.Negligible loss for your purpose & length.
3. Can use one PL259-PL258-PL259 coupler inside boat(not inside mast).to allow for mast removal-without noticeable loss of performance in your application.
4. Seal the PL259 conn. at top of mast thusly:
a.2 layers of rubber weld tape +
b. 2 layers of Liquid Tape.
Note: I also recommend a Shakespeare 5215 (or equivalent) antenna for any sailboat. Rugged,compact,proven performance,easy to mount & connect to.


All above is based on 30+ yrs of commercial experience & practical ,real life performance vs the ?< 10%? that "the book" says,if you spend a lot more $$
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Old 16-05-2024, 09:31   #5
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Re: Choosing the the right VHF Coax

I could probably put RG213 in the mast (probably only 5" in diameter inside). I doubt I could run RG213 in the cabin from base of mast to the radio. I can see the signal loss numbers for Rg8x compared to rg213, but what does it really mean with respect to transmit and receive distance. Are we talking about a range of 5 miles vs 13 miles 9 vs 13? Hard to put a value on whether this is the right thing to do. Separately, I'm reading that the Shakespeare connectors are not great. DX engineering are much better quality. Any insight into this?
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Old 16-05-2024, 17:49   #6
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Re: Choosing the the right VHF Coax

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Originally Posted by Timccarpenter View Post
I could probably put RG213 in the mast (probably only 5" in diameter inside). I doubt I could run RG213 in the cabin from base of mast to the radio. I can see the signal loss numbers for Rg8x compared to rg213, but what does it really mean with respect to transmit and receive distance. Are we talking about a range of 5 miles vs 13 miles 9 vs 13? Hard to put a value on whether this is the right thing to do. Separately, I'm reading that the Shakespeare connectors are not great. DX engineering are much better quality. Any insight into this?

For the lengths of coax you are dealing with the signal loss is not that significant. As a rule of thumb for VHF larger diameter coax has less loss than thinner coax. VHF communications range is impacted more by height of antenna than the signal loss in the transmission line (coax).

More of an impact is good quality connectors and keeping them clean and dry. Here is where I agree that Shakespeare connectors are poor quality. They are no solder, aluminum and depend on the contacts being made by pressure made during assembly. Aluminum and copper are not good together, especially in a marine environment. Amphenol solder connectors are best. They are silver plated brass and will last a very long time. A properly crimped connector is also very good - many say better than soldered. Especially true for inexperienced connector installers. Crimped connectors use specialty crimping tools that for just a couple of connectors would be expensive. DX engineering has their own proprietary connectors that are also very good. If you can fit the connector through the mast pre-made cables are a good option for the relatively inexperienced. You could also get the coax with a good connector crimped on one end and feed the other end through the mast. This would ensure a good connection at the top of the mast where weather tight is more important than inside the boat.

I also suggest tinned coax. I bought tinned rg-213 marine grade coax from Davis RF about 15 years ago and it is still good. I don't know if they offer other types of marine grade coax.

Installation is very important. Keeping the masthead connector dry and keeping water out of the coax are critical for long installation life. I suggest heat shrink tubing with glue inside to keep the connector dry.
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Old 16-05-2024, 19:14   #7
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Re: Choosing the the right VHF Coax

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Originally Posted by Timccarpenter View Post
I could probably put RG213 in the mast (probably only 5" in diameter inside). I doubt I could run RG213 in the cabin from base of mast to the radio. I can see the signal loss numbers for Rg8x compared to rg213, but what does it really mean with respect to transmit and receive distance. Are we talking about a range of 5 miles vs 13 miles 9 vs 13? Hard to put a value on whether this is the right thing to do. Separately, I'm reading that the Shakespeare connectors are not great. DX engineering are much better quality. Any insight into this?
It is difficult to quantify the distance changing to a higher loss cable would be. A good installation would between 2 boats reliably have a range of almost 30 miles. Beyond that you are over the horizon and higher power won't increase range. A poor installation would have that range with a boat with a good installation, or might have intermittent and unreliable communication at that range with another boat with a poor installation.
I have a very good installation, and it is pretty common for other boats to hear me clearly, but not get out well enough for me to hear them, I would say typical would be they have about 10 miles. But it is really difficult to say what about their installation is causing that.
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Old 16-05-2024, 19:31   #8
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Re: Choosing the the right VHF Coax

This is all very helpful, thank you for the input. I made the decision to move forward with RG8X. Almost all of our sailing is within a few miles of our harbor (day cruising). For our purposes this will be fine. I also went with the DX Engineering soldered connectors. I would have done crimp connectors but as Stormalong mentioned, doesn't make sense when you only need to do a couple of connections.

Any other brands that are good for a barrel connector? I would order DX Engineering but they only come in packs of 4 and I need 1.
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Old 17-05-2024, 01:44   #9
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Re: Choosing the the right VHF Coax

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RG213. Anything more is overkill and not warranted except in special circumstances. Anything less is 'underkill' and a waste of time and effort.

Do it once and do it right - use RG213.

As Whollybee mentions, if someone does manage to convince you to use LMR400, make sure it is a waterproof version such as LMR400-DB (i.e 'direct bury') and have it professionally installed by someone who really knows what they are doing - not all 'professionals' are equal...
LMR-400 of any type is better avoided on a boat. Too many things to go wrong with it. Aluminum parts are subject to corrosion in the marine environment; foam insulator subject to being crushed in boat installations.

Use RG213 or 214 if you have space for the fat cables, which is very rugged with solid insulator and copper conductors; LMR-400 is total overkill for VHF frequencies. And there's nothing wrong with RG-8X if the fatter cable is hard to pull.

As someone else said -- effective VHF comms is NOT nearly so much about total power as it is about antenna height, antenna quality, and, especially, quality of the installation. 25 watts is overkill for line of sight communications, in fact that power level was specifically designed to give a large reserve for antenna cable installation.

I have a really good installation which I did myself with RG-214, a really good antenna (Shakespeare Little Giant, internal dipole), really good connectors soldered myself, and no connector at all at the mast base -- continuous coax feedline from radio to masthead.

I have gotten "weak but readable" signal reports at more than 60 miles. USING 1 WATT TRANSMISSION POWER. In fact, my radio is normally set at 1 watt.

Install it well and use good connectors and good antenna, and RG-8X is plenty. RG-213 is luxe. Forget LMR-400.
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Old 17-05-2024, 01:47   #10
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Re: Choosing the the right VHF Coax

Quote:
Originally Posted by Timccarpenter View Post
This is all very helpful, thank you for the input. I made the decision to move forward with RG8X. Almost all of our sailing is within a few miles of our harbor (day cruising). For our purposes this will be fine. I also went with the DX Engineering soldered connectors. I would have done crimp connectors but as Stormalong mentioned, doesn't make sense when you only need to do a couple of connections.

Any other brands that are good for a barrel connector? I would order DX Engineering but they only come in packs of 4 and I need 1.
I didn't see this before writing the previous post.

You made the right decision! You would not have gained any noticeable range with different cabling.

What concerns connectors -- the Ampenol ones are a traditional choice of hams. DX is also great; and why would you mind having a few extra around?

What kind of antenna are you using? Is it new?
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Old 17-05-2024, 04:38   #11
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Re: Choosing the the right VHF Coax

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Ö.. DX is also great; and why would you mind having a few extra around

What kind of antenna are you using? Is it new?
I donít mind having a few around, the whole winter project has gotten far more expensive than planned! The nature of anything with ďmarineĒ in the name.

I ordered a new Shakespeare 5215 (but can change this plan - seems like still a great antenna) . I have a 20 year old one that Iíll test but suspect this is something I should just replace after doing all of the rewire.

I ordered an SWR meter to test the setup (at least from the base of the mast) before we re step the mast. Iíll need to haul a battery and radio to where Iím working on the mast for this as I donít have a dummy load. Of course, I could find issues with the radio! We shall see.
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Old 17-05-2024, 05:28   #12
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Re: Choosing the the right VHF Coax

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Originally Posted by deblen View Post
RG 213U. with drip loop(s)
1.Most rugged 50 ohm coax for general use.
2.Negligible loss for your purpose & length.
Just make sure you get RG-213U from a reputable source. RG-213U is a millspec number but there is no requirement to quality of cable to be called RG-213U when being sold to public. Buy from a coax company SKIP!!!! amazon for any coax, Most of it garbage Chinese made and they slap on any name they want on the cable and often its just rg8 with a 213 name.
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Old 17-05-2024, 07:49   #13
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Re: Choosing the the right VHF Coax

I will echo the RG213 recommendation everyone else is making. It will cost a bit more but you have the mast down. Now is the time to do it right.

I would recommend either buying a pre-terminated run or using quality crimp/soldered connectors and then waterproof the joint with tape. The push on "easy" connectors are trash. With quality RG213 you likely will never have an issue from the wire or antenna itself. Any issues will be from the connectors.
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Old 17-05-2024, 09:37   #14
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Re: Choosing the the right VHF Coax

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Originally Posted by Timccarpenter View Post
This is all very helpful, thank you for the input. I made the decision to move forward with RG8X.

RG8X uses a foam dielectric that loses strength when hot. Be careful about bend radius, and don't overtighten cable clamps. Tight bends and tight clamps can work at first and then fail once the cable has had a few hot days in the sun. I no longer use 8X for mobile or marine work. It's fine for temporary projects that aren't safety critical.

RG58 is lossier but more reliable. You would give up less than 1 dB on your boat compared to RG8X.

I have RG213 on my boat, which is what it came with and which is a good choice too. Also solid polyethylene dielectric. With a 60 foot mast it's roughly three pounds of extra weight above deck and maybe a 2 dB improvement over RG58.

Quote:
Any other brands that are good for a barrel connector? I would order DX Engineering but they only come in packs of 4 and I need 1.
Not sure where on Superior you are. I will be in Duluth on Sunday and if you're in the area you can stop by my boat and I'll give you one.

Digi-key will sell you what you need in any quantify and has many vendor's products in stock.
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Old 17-05-2024, 10:20   #15
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Re: Choosing the the right VHF Coax

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...reliably have a range of almost 30 miles. Beyond that you are over the horizon and higher power won't increase range
Lots of people repeat that but my personal experience and the many serious studies of VHF propagation don't agree. On open ocean there are tropospheric scatter effects. Where there is intervening terrain there are various diffraction effects. These are not unreliable outliers (like tropospheric ducting or sporadic E layer effects) but rather reliable phenomena that explain the limited over-the-horizon communications that can be achieved with VHF.

Any modern VHF propagation model incorporates these effects and you can see the predicted effects that increased power or gain have on coverage. One well known free site that performs this modeling is https://www.ve2dbe.com/english1.html

I have drive-tested coverage maps from that web site and found them to be remarkably accurate. Notably for this conversation some of the local higher-power VHF repeaters do in fact achieve the predicted broader coverage.

Whether or not it is necessary or desirable on a sailboat, power and antenna gain do in fact improve VHF coverage.
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