Can I replace a 6ft piece of RG-58U between my VHF radio and the mast? With an 8 ft p

[s/v Jedi]

When you have one continuous cable and have to cut it to unstep the mast, I recommend to either replace the cable if it’s time anyway, or to splice it using N-type connectors which are waterproof and have better HF specs as well

[n5ama]

N connectors are great and provide a reduced impedance bump than UHF connectors but my boat requires a fitting to go thru the cabin at the base of the mast. I have a UHF connector at that point but so far I’ve been unable to find the equivalent N connector.

[Wotname]

Originally Posted by n5ama

N connectors are great and provide a reduced impedance bump than UHF connectors but my boat requires a fitting to go thru the cabin at the base of the mast. I have a UHF connector at that point but so far I’ve been unable to find the equivalent N connector.

Something like a thru bulkhead N type adaptor?

https://au.element14.com/multicomp/1...ING-CONNECTORS

or

https://au.element14.com/amphenol-rf...ING-CONNECTORS

[n5ama]

Thanks Wotname!!
That may do the job. I'll pull the old UHF connector and see if the length will work. The last owner didn't bother to wrap the connection at the mast base so the connector really needed to be changed anyhow.

[Brian.D]

N connectors are great, and are found on professional installations such as government and military, but not so on recreational boats. One will note that no consumer grade RF equipment are equipped with N connectors. That should tell you something.

Stay with what is considered standard in the RF field, and that is UHF (PL-259/SO-239) connectors with a good dosage of dual wall 3:1 heat shrink tubing.

[n5ama]

Thanks Brian
I would only replace the UHF connectors with N connectors where I go thru the cabin top. I would do this because the added water proofing benefit. I will continue to use UHF connectors on the antenna and radio.

Heat shrink is great but I find the size necessary to go over the connector is difficult to fit and seal well when it steps down to the much smaller diameter coax.

I use Temflex 2155 rubber sealant (kind of like butyl tape) to seal and completely water proof the connection and then wrap that with 3M Super 33 electrical tape to protect the Temflex. I keep those two products on board and can reseal the connector in less than a minute.

[Discovery 15797]

I agree with Brian. While the PL-259 is a non-constant impedance connector, it is quite fine for applications up to 300 Mhz without any appreciable degradation. (In HF freq. range there is virtually zero.) And here is a good write up about actual measurements at UHF frequencies.

N connectors for a marine application are simply overkill. If you're really worried about performance then you should probably change your antenna cable to LMR 400 and go with BNC connectors and a full wave length antenna.

Also, unless you have full and easy access to the entire run of your cable from the mast base to the radio (and if you are running this behind the headliner it doesn't sound like that's the case) then you definitely want a disconnect at the mast for ease of stepping/unstepping the mast.

The simple truth is that while PL-259 is a non-constant impedance connector...you simply will not notice any difference in performance and if you are using high quality cable and connectors that are properly fitted.

Don't use nickel plated connectors for VHF & above, and other tips found here for PL-259 (UHF) connectors.

[s/v Jedi]

You are wrong. N-type is waterproof, PL259 is not. That alone is good enough reason. It’s also not true that N-type is only for military as every serious HAM uses it, as well as all commercial ships. It is not that hard to find an antenna with N-type connector and it is the antenna connection and mast base connection where it matters most. There is no overkill for those applications.

You can also buy Home Depot plywood to make bulkheads and coat with epoxy to make it waterproof so does that make meranti marine plywood overkill? Not even when you coat that with epoxy imo.

PL259 is fine behind the radio where other connections are not waterproof either. In the bilge, at the deck step and at the masthead N-type is the gold standard for VHF. I don’t know why BNC is brought into the discussion and think that is not useful at all.

[Cheechako]

A vhf works on a 30 foot mast or on a 70 foot mast.

[n5ama]

As I stated earlier, I have no concern about the impedance bump of the UHF connector at our VHF frequencies.

My concern is with the UHF connector not having the water sealing ability of the N connector. Also mentioned earlier, the previous owner didn’t properly seal the connector at the base of the mast. It is exposed to a lot of weather and I found the thru connector had leaked water (minor amount but never the less some corrosive water) thru that fitting and onto the cabin where it fed thru..

A “N” connector is certainly overkill with respect to the frequency, but for the very minor cost difference over the UHF connectors, I feel the additional cost is justified if I’m getting a tighter and more moisture proof connection.

[Wotname]

Originally Posted by Brian.D

N connectors are great, and are found on professional installations such as government and military, but not so on recreational boats. One will note that no consumer grade RF equipment are equipped with N connectors. That should tell you something.

Yep, it tells me they are built to the lowest possible cost.

Stay with what is considered standard in the RF field, and that is UHF (PL-259/SO-239) connectors with a good dosage of dual wall 3:1 heat shrink tubing.

Brian D, I have no wish to change your mind - your boat, your rules.

However in the RF field, UHF connectors are not the standard. I accept they are ubiquitous in the recreational sail boat market in the USA (presumably and perhaps elsewhere) but in the real RF world, there are simply dozens of different style connectors and they all have their place.

I tend to use a connector commensurate with the cable size e.g. for a RG58 size coax, that would be a BNC below decks and a TNC above decks while using N type for larger coax like RG8. Not that I particularly like RG58 or RG8, just using this as example of coax diameter.

The first thing I stick on the back of any recreational boat radio is a UHF male to either a BNC / TNC / N type female adaptor.

YMMV.


FWIW, here is everything (almost) you ever wanted to know about RF connector design and materials.

https://www.fclane.com/sites/default.../rfguideen.pdf

From the preface - After having been in the RF Interconnection Market for more than fifty years, we felt the need to provide our business associates around the world with a booklet containing key information on coaxial connectors.
Today, key concepts behind RF technology have not changed much - and this is what this booklet, the HUBER+SUHNER RF CONNECTOR GUIDE, is all about. It contains HUBER+SUHNER know how and experience in the field of connectors. Primarily, we aim this booklet at non-technically and technically skilled people who are daily confronted with purchasing, distributing or maybe installing RF connectors.
The Guide is a reference to coaxial connectors, which embraces the underlying theory, design technology and performance features behind RF connectors. It should enhance the understanding of possible usage, so that people with no or little RF knowledge are able to consider or even select the best suitable connector for their application problem. However, we have to stress that the Guide cannot stand alone as a definite solution to all connector problems. .

[Discovery 15797]

Originally Posted by s/v Jedi

You are wrong. N-type is waterproof, PL259 is not. That alone is good enough reason. It’s also not true that N-type is only for military as every serious HAM uses it, as well as all commercial ships. It is not that hard to find an antenna with N-type connector and it is the antenna connection and mast base connection where it matters most. There is no overkill for those applications.

PL259 is fine behind the radio where other connections are not waterproof either. In the bilge, at the deck step and at the masthead N-type is the gold standard for VHF. I don’t know why BNC is brought into the discussion and think that is not useful at all.

I thought I was a pretty serious ham operator, DxPeditioner, and occasional contester. But, I would never use N-type connectors on HF frequencies. There is zero value add. In fact, I can't think of anyone I know that uses N-type connectors on HF rigs.

My Icom 9700 UHF/VHF radio uses N-type connectors, as do the antennas and I agree for high end UHF/VHF and higher freq. transceivers the N-type connector is the gold standard. But, this is a high end radio. For marine use, I don't believe there is a discernible difference between N-type and PL-259s in performance on VHF for most marine rigs.

I brought up BNC because the BNC is a constant impedance connector (unlike the PL-259). They are widely used in HF radios, and also precision electronic test equipment and some vhf rigs. They are also better at UHF frequencies. But, you're right...I would not likely use a BNC connector in a marine application, although they are theoretically better compared to PL-259s.

The N-type connector is not waterproof...it is weatherproof (it is not totally impervious to water). Straight clamp plugs are better than crimp plugs.

To make PL-259 connections weatherproof you can use Coax-Seal. I use dielectric grease inside the connector, and Coax-Seal for external antenna connections. Coax-Seal is like a soft rubber in tape form. You wrap like tape then press into and around the connector shell. It's messy, but as close to waterproof as you can get.

BTW...I also do the above actions with N-type connectors.

Anytime I need to extend a cable with a female-female 'bullet' I will wrap the entire connection in silicone tape (Rescue tape). Again, about as close to waterproof as one can get. I use dielectric grease and silicone tape at the connection at the base of the mast where I couple the PL-259 and SO-239 connectors. At the masthead I use Coax-Seal.


Also, most problems with connectors (esp. the PL-259) is poorly installed connectors...especially when the shield is damaged or 'unwoven' while prep'ing the cable to attach the connector.

[Discovery 15797]

Originally Posted by n5ama

My concern is with the UHF connector not having the water sealing ability of the N connector. Also mentioned earlier, the previous owner didn’t properly seal the connector at the base of the mast. It is exposed to a lot of weather and I found the thru connector had leaked water (minor amount but never the less some corrosive water) thru that fitting and onto the cabin where it fed thru..

A “N” connector is certainly overkill with respect to the frequency, but for the very minor cost difference over the UHF connectors, I feel the additional cost is justified if I’m getting a tighter and more moisture proof connection.

The "moisture proof" connection is between the male and female N-Type connectors.

If you are leaking water through the connector at the base of the mast the problem is the bedding of the connector, not the connector per se.

Check out Coax-Seal or silicon tape for 'water-proofing' your connections. For the seal at the base of your mast....I am assuming that is some sort of female-female bulkhead connector? if so..you just need to rebed it.

[n5ama]

The “bedding” of the thru connector is ok. The flange on the connector has a nice flexible coating of some substance that appears to be waterproof. It is much better than the coax insulation and the PL259.

The moisture was coming down the coax and getting around the rear adapter of the PL259. At that point it ran thru the connector past the male pin (corroded) thru the double female bulkhead fitting (also corroded) and leaking into the coax fitting in the cabin (also corroded). The shield on the interior coax going to the radio was corroded for some distance. I presume this was from the water leaching thru the connector.

I use Temflex 2155 (very similar to CoaxSeal) and 3M Super 33 tape on top of that. I’ve never had a problem with this setup and although most of these connections are not in salt air, they are all outside and subjected to heating/cooling and the south Louisiana and south Texas climate that can get humid on occasion.

I use N connectors exclusively outside (even for HF applications) and feel that it is worth the little extra trouble and expense. I’m not fond of installing N connectors versus UHF connectors but deal with it.

I’ve ordered a N connector to replace the UHF. The only thing I’m concerned about is the length of the body. The body may be too short to allow both the retaining nut and the N connector in the cabin.

[continuouswave]

Originally Posted by AZ-Oldguy

I know very little about VHF and antennas[.] [I]s [the] length [of the transmission line between transmitter and antenna] critical?

The criterion "critical" is somewhat hard to assess in terms of the effect of a change in the length of a transmission line between a transmitter and an antenna. I will interpret your actual question as this:

Q: Does changing the length of the transmission line between a VHF Marine Band radio and its antenna affect the tuning of the antenna?

A: If the antenna input impedance is matched to the transmission line impedance, there won't be any change in the tuning of the antenna if the transmission line length is changed.

There is no magic length for the transmission line between a VHF Marine Band transmitter and its antenna.

In the context of the original question regarding increasing the transmission line length, and because a real transmission line is not a lossless transmission line, increasing the transmission line length increases the LOSS in the transmission line. In the context of changing to 8-feet from 6-feet, the change in transmission line LOSS will be so little that it could not be easily measured and won't be noticeable.