Can you offer comments to my proposed VHF setup?

[Pedro -Dawn-]

Hello All!

I can’t seem to pass page 8 of the VHF threads. Not sure if this is a problem with the forum settings, etc. I am currently refitting a 35ft monohull with a 40ft mast.

Once I step down the mast I will run the following cables: (i) 1x 5-way 16 awg cable for the nav light; (ii) 3x 2-way 16awg cables for spreader lights and wind instrument; (iii) 1x CAT5e cable for mast top camera.

Here are my concerns:

1 - If i were to run a VHF cable (preferably a RG-213 although very expensive), to the mast top this would need to be bundled with the above mentioned electric cables. I am very afraid of the possible interference in the coax signal;

2 - I am not sure if my navigation light will interfere with the VHF signal (manufacturer didnt offer any comments on that);

3 - I am not willing to run the coax cable outside the mast (not sure even how this would be possible)

The current alternative I am looking into:

I am building a very sturdy solar arch. All in the top of my arch from the water line would be 10ft. If I were to attach a VHF antenna there, I think I could have the following benefits:

1 - I can run a completely isolated run of coax in its own conduit from the unit to the arch top, limiting interference;

2 - Having a shorter cable run avoiding power loss, as well as fitting better with my budget (then I could really go for a RG-213 cable);

3 - ease of maintenance;

4 - possibility to running another 2 separate cable runs for (i) a dedicated AIS antenna in the future; and (ii) a higher gain antenna - so I could have a broader bandwidth antenna for regular usage and the possibility to switch to a higher gain if needed. Although I am not sure if running this antennas at 10ft (antenna base height) would negate the higher gain advantage.

On a final note, here in Brazil I can’t seem to find 1/2 wave dipole antennas dedicated to marine environment (e.g. Shakespeare, Belden), at least not ones costing less than USD400, nor can I find Amphenol connectors.. What seems to be readily available are mostly vehicular 1/4 wave antennas. Any thoughts on that as well?

I have seen many great discussions on the topic here, and some fantastic people helping each other. I am looking forward to any comments you may have about this setup. If you think negatively of this, please let me know as well, no problems at all.

Thank you all for your time in advance!!

Cheer from Brazil

Pedro @dawnexpedition

[Hartleyg]

As far as mounting on the stern arch, I would say you will get good service - not maximum range, but more than adequate for 99% of VHF usage. I have one of each on our Tayana 48, and I seldom even turn on the radio with the masthead antenna because it hears traffic from far away and is annoying at best.

The end-fed 1/2 wave antenna is the best (also called a "36 inch whip") such as a Tram 1603 (easily found on Amazon), as it is independent of the ground/counterpoise - if you have a large metal arch, this may work with a quarterwave vertical, but remember it was designed to work over a car roof

On a sailboat, a high gain antenna only works well when you are not sailing, so of limited usefulness in my opinion, but maybe your environment is different from ours.

Good Luck!

Hartley
S/V Atsa

[Brian.D]

With regards to running at mast top, running an RF cable with other cables is usually not a problem, except when the RF cable in question is "leaking". We call that RF Shield Leak, or Common Mode Current. This happens when an unbalanced antenna starts to use the shield of the coax as part of the antenna. When that happens, RF gets into everything because the coax is a radiating element.

There is a simple fix, called a Common Mode Choke. This will be placed at the input on the antenna and is designed to attenuate these stray currents. The device us usually a toroid snap-on that is comprised of Mix 31. When this device is attached to the cable at the antenna, it will exhibit a high impedance to the currents running along the shield of the coax, thus blocking them. Mix 31 is good up to 300 MHz.

Now, you may look on the net and find lots of sellers of RFI and EMI toroid snap-on devices, but they may not be suitable for VHF RF applications. I would highly recommend finding the Mix 31 snap on.

This is just my opinion as I am sure some other will also chime in with there opinions.

[Pedro -Dawn-]

Originally Posted by Hartleyg

As far as mounting on the stern arch, I would say you will get good service - not maximum range, but more than adequate for 99% of VHF usage. I have one of each on our Tayana 48, and I seldom even turn on the radio with the masthead antenna because it hears traffic from far away and is annoying at best.

The end-fed 1/2 wave antenna is the best (also called a "36 inch whip") such as a Tram 1603 (easily found on Amazon), as it is independent of the ground/counterpoise - if you have a large metal arch, this may work with a quarterwave vertical, but remember it was designed to work over a car roof

On a sailboat, a high gain antenna only works well when you are not sailing, so of limited usefulness in my opinion, but maybe your environment is different from ours.

Good Luck!

Hartley
S/V Atsa

Hello Hartley,

Thank you very much for the reply. I forgot to ask about the counterpoise part, but you did that for me. I have a friend in the US and the Tram 1603 is small enough that it won't bother him to bring back to Brazil (a 36" antenna no, that is impossible haha).

Already added it to my amazon cart. So your suggestion was GOLD!

Cheers

[Pedro -Dawn-]

Originally Posted by Brian.D

With regards to running at mast top, running an RF cable with other cables is usually not a problem, except when the RF cable in question is "leaking". We call that RF Shield Leak, or Common Mode Current. This happens when an unbalanced antenna starts to use the shield of the coax as part of the antenna. When that happens, RF gets into everything because the coax is a radiating element.

There is a simple fix, called a Common Mode Choke. This will be placed at the input on the antenna and is designed to attenuate these stray currents. The device us usually a toroid snap-on that is comprised of Mix 31. When this device is attached to the cable at the antenna, it will exhibit a high impedance to the currents running along the shield of the coax, thus blocking them. Mix 31 is good up to 300 MHz.

Now, you may look on the net and find lots of sellers of RFI and EMI toroid snap-on devices, but they may not be suitable for VHF RF applications. I would highly recommend finding the Mix 31 snap on.

This is just my opinion as I am sure some other will also chime in with there opinions.

Hello Brian, thanks for the suggestion.

I found this on amazon RF Choke 31200 Ferrite Filter Core Material 31 Mix.

Seems inexpensive enough to give it a try. However is this something you suggest i do preemptively? This will be a fresh install.
Cheers!

[wholybee]

I don't think you will have any issues with coax, as long as you use good coax, and a good antenna. Needing a choke I think is a special case. Avoid at all costs RG8x- you will have problems with that cheap cable. Buy an antenna from a reputable company specific to Marine VHF. They can be a couple hundred dollars even in the US. If by "vehicular antenna" you mean for an AM/FM radio in a vehicle, that will not work. Same if for a CB, or a land based two way radio. It needs to specifically be a marine VHF antenna.

I know in Brazil buying anything that had to be imported is really expensive. I had to import a few dollars worth of parts while I was there, and it was quite the ordeal. But I suggest paying it if that is how you get good quality RF components.

What brand Navigation light do you have, so that someone might know if it has an interference issue? The ones that work well can be considerably more expensive than the cheap ones.

What nav light do you have that requires a 5 conductor wire? Usually you only need 3-Tricolr, anchor, ground. At the spreader another 3 conductor wire, spreader light, steaming light, ground. My wind instrument uses a 5 conductor wire, supplied with the instrument, with a special connector already on the end. Newer ones I think mostly use NMEA2000 cables.

[Pedro -Dawn-]

Originally Posted by wholybee

I don't think you will have any issues with coax, as long as you use good coax, and a good antenna. Needing a choke I think is a special case. Avoid at all costs RG8x- you will have problems with that cheap cable. Buy an antenna from a reputable company specific to Marine VHF. They can be a couple hundred dollars even in the US. If by "vehicular antenna" you mean for an AM/FM radio in a vehicle, that will not work. Same if for a CB, or a land based two way radio. It needs to specifically be a marine VHF antenna.

I know in Brazil buying anything that had to be imported is really expensive. I had to import a few dollars worth of parts while I was there, and it was quite the ordeal. But I suggest paying it if that is how you get good quality RF components.

What brand Navigation light do you have, so that someone might know if it has an interference issue? The ones that work well can be considerably more expensive than the cheap ones.

What nav light do you have that requires a 5 conductor wire? Usually you only need 3-Tricolr, anchor, ground. At the spreader another 3 conductor wire, spreader light, steaming light, ground. My wind instrument uses a 5 conductor wire, supplied with the instrument, with a special connector already on the end. Newer ones I think mostly use NMEA2000 cables.

Hello Warren!

I just managed to order a Tram VHF antenna.

Coax will need to be bought locally. Per my search, there is little to no information provided by the manufacturers down here. Hope it works decently.

My navigation light is made here in Brazil. Its Optolamp. It's a bundle of 5 cables: 2 for the tricolor lights, 1 for the anchor light, 1 for the strobe and 1 negative. The product seems really amazing, and also a bargain (it cost me less than USD100). There are Vendee Globe boats using the same lamp.

My wind instrument is a tentative one. It is made for cranes and I will hook it up with arduino sensors. The boat was completely stripped out. So I will only run Open Plotter navigation equipment (e.g. pypilot autopilot, sensors, etc).

Thanks for the message!!

[wholybee]

If you can't find any specs for coax you buy, that's a shame. Make sure it is the larger size (about 11mm) and 50 ohm. And I guess hope for the best, I would be *very* *very* uncomfortable buying coax without knowing exactly what I was ordering. There is a tremendous range in performance and intended use.

Given the difficulty in removing the mast to replace it if it is wrong, I would spend the money to order something from the USA and know I wouldn't have the wrong item.

[Pedro -Dawn-]

Originally Posted by wholybee

If you can't find any specs for coax you buy, that's a shame. Make sure it is the larger size (about 11mm) and 50 ohm. And I guess hope for the best, I would be *very* *very* uncomfortable buying coax without knowing exactly what I was ordering. There is a tremendous range in performance and intended use.

Given the difficulty in removing the mast to replace it if it is wrong, I would spend the money to order something from the USA and know I wouldn't have the wrong item.

Sure thing. Honestly, it has been like that throughout all my boat refit. I imported most of what I used, but my budget us just really on its last legs right now.

Can you imagine there is only one manufacturer of tinned wire here? And they only supply the offshore industry at outrageous prices. And this is just one example.. but it happened like that for everything I had to consider buying for the boat.

[rslifkin]

I'd decently put an antenna on the mast for the longer range. A second antenna on the arch or a spreader would be a nice bonus, as having 2 VHFs is handy at times. And if it's on the arch, it'll still work if the mast or main antenna is damaged.

[Brian.D]

The mix is right, but the size (I.D.) is too small. You will need to know the diameter of your cable and get the correct size. Most cables like LMR400, RG8 or other types of that rating are about .5" (11~12mm) in diameter. LMR240, RG-8X is about .24" (5~7mm) in diameter.

Now, as mentioned, good quality cable with good quality connectors and a top brand VHF antenna on the mast should not be a problem. But, some like to go budget and that is not a problem. This is why I recommend the Common Mode Chokes at the base of the antenna.

If you go this route, make sure you protect the choke(s) with shrink wrap. This will ensure they remain in tack for a long time.

Good luck and I see you have lots of options.

[mitiempo]

Originally Posted by Pedro -Dawn-

........I have a friend in the US and the Tram 1603 is small enough that it won't bother him to bring back to Brazil (a 36" antenna no, that is impossible haha).

Already added it to my amazon cart. So your suggestion was GOLD!

Cheers

The Tram 1603 is 38" in length.
https://www.amazon.ca/Tram-1603-Vhf-...10946671&psc=1

Also, with your vhf antenna on the stern arch the future Ais antenna should be on the masthead as they shouldn't be close together.

[stormalong]

Originally Posted by mitiempo

The Tram 1603 is 38" in length.
https://www.amazon.ca/Tram-1603-Vhf-...10946671&psc=1

Also, with your vhf antenna on the stern arch the future Ais antenna should be on the masthead as they shouldn't be close together.

That should be just the opposite. VHF antenna should be at the masthead and AIS on the arch. You only need 5 to 10 miles range on AIS bit want as much range as possible on the VHF.

As for coax choice RG-213 is good. For VHF frequencies thicker coax has significantly less loss. One thing you will find on cheap coax is the shield braid has poor coverage. Get a sample of what you are buying or go to the store where it is sold. The braid should completely cover the insulation. RG-213 specification is 96%. In the U.S. you can get marine grade RG-213 (both conductors tinned) from a company named Davis RF. They also carry Amphenol connectors. Silver plated is the best.

I know you are at a disadvantage having to bring in materials (been there, done that), much worse today with high shipping rates and import duties. It may be cheaper to have your friend pay an extra luggage fee than getting things shipped.

[mitiempo]

Originally Posted by stormalong

That should be just the opposite. VHF antenna should be at the masthead and AIS on the arch. You only need 5 to 10 miles range on AIS bit want as much range as possible on the VHF.

As for coax choice RG-213 is good.

I agree, that is what I would do.

[IOM]

Being at the top of the mast will always be better for range

LMR400 is a lot better than RG213 at VHF, but more expensive. (check the 213 is tinned wire, not all are. if its not tinned it will 'dissolve' in the sea environment quite quickly compared to tinned wire) It does definitely improve the Radio range in test I did. It is also double screened, so less chance of RF in or out the coax.
Vehicle style VHF antenna could be made to work, only issue might be the ground connection with corrosion. To add a wire for a ground plane cant be difficult , but in all probability not needed, and vehicle antennaes are usually made of stainless steel anyway. just the mounting hardware is not always stainless steel.


If you concerned about the LED Nav lights creating RFI , then place a few turns of the nav light wire through a mix 31 choke at the top of the mast. This will help suppress any interference from the switch mode supply in the LED base traveling down the wire. Same with the camera wire, but I doubt at VHF especially on FM you will have any issue.


If you running a raspberry pi, and powering it with a switch mode supply, then be warned the noise from the supply can be so bad it can destroy even a wifi system on the boat. I changed to a linear supply , which is less efficient, and created more heat, but a lot less RFI. Alternatively spend a lot of time on RFI suppression and screening on the Supply.