How about two antennas on board?

[Expidia]

I'm picking up a fixed mount VHF for my 15 foot boat.

I've found my new handheld was pretty useless the first time I actually needed to use it due to it's limited range.

I was thinking of going with a 4 foot antenna for day to day use and maybe keep an 8 foot antenna in my rod locker for an emergency situation where I might need more range.

I don't go off shore, but the lakes and rivers I do go on are pretty big (Champlain is 10 miles wide at some points and 132 miles long).

Anyone know of an antenna brand that has a coax connector at the base of the antenna. Most of the ones I've seen have straight coax coming out of the antenna and it would be a pain to have to unhook it from the back of the radio and re thread the cable just to swap antennas out when I venture out onto bigger waters.

I fear if I leave the 8 footer on and have it down on the deck at times like when fishing or someone boarding on and off, someone is sure to step on it and break it as I've read in other posts.

 

[m&m252]

Re: How about two antennas on board?

try shakespeare brand...

 

[tashasdaddy]

Re: How about two antennas on board?

i have a shakespeare 8'. mount so it is more out of the way.

 

[ziggy]

Re: How about two antennas on board?

if yer in an emergency situation. i'd think ya wouldn't have time to be putting up yer 8'er. quick connect or not...... i suppose if the emerengcy is bad enough, ya might not even have time to flip it up if it was folded down...... out of the way is the ticket i'd think. on a 15' boat i suppose that could be a challenge though.... not what ya wanted to hear i don't suppose, but ya are on a pretty big body of water in a fairly small boat.....give yerself the best chance ya got is all ya can do.... a 8'er......

 

[Boatist]

Re: How about two antennas on board?

Range difference between a 4 foot and 8 foot antenna not that big a difference.
With both antennas mounted 2 feet above the water:
The 8 foot would have a height of 10 foot and a range of 4.49 miles.
The 4 foot would have a height of 6 foot and a range of 3.47 miles.
Now that is the range of your signal before it is block by the water and the curve of the earth. This range is added to the range of the other station.
So taking to another boat with an 8 foot antenna mounted 3 feet off the water his range would be 4.70 miles. So your total range would be 4.7 miles plus what your antenna can do.

Only good news is if your talking to the coast guard and their antenna is mounted on top of a 2000 foot high montain like many along the pacific coast then the Coast Guard range is or 63.5 miles.

Bottom line is the 8 foot antenna will have 1.02 miles more range than the 4 foot.

Distance is equal to the (square root of your antenna's height times 1.42.
Then you add the range to the other stations height, useing the same formula.

 

[JMRuth72]

Re: How about two antennas on board?

The other thing to watch out for when switching between an 8' and 4' is the SWR (Standing Wave Ratio). If all you do is switch antenna's then odds are really good that you are going to change your SWR. The higher the SWR the less efficient the transmission. The antenna's that have the coax preset are also generally pretuned for optimum performance. You can use a meter with the adjustment ability built in, but they are still not as efficient as hard setting it and using a meter to verify it. Follow the directions for the meter to calibrate it then you are looking for anything less then 1.5. I used the power meter on a CB to tune a hidden antenna (a converter that used the cars AM/FM antenna for the CB), because I didn't have a SWR meter yet. When I got the meter I had managed to set it to 1.1 using the CB power meter. If you need to know how I did that just ask it is a bit tedious, but not hard. That is just about perfect. By the way when you buy a SWR meter I believe that you have to buy one for the frequency range it will be used on. I am pretty sure that I could not use my CB meter to check a VHF/UHF radio installation. Like a couple of the others said mount the 8' out of the way somewhere and be done with it. The only good reason to have a quick disconnect type mount is to prevent theft. However make sure that you keep the socket clean of all corrosion and when you put the antenna up make sure that it is tight. To do this simply put some dieelectric grease on the socket. You can get this at any auto parts store pretty cheap.

 

[Texasmark]

Re: How about two antennas on board?

Next thing (along with the good info already supplied) is to consider is receiver sensitivity.

This transmission-reception thing is a closed loop. For a given set of circumstances, all environmental conditions, including distance, weather, topography, and anything else that plays into this thing, it takes a given amount of signal gain at the given frequency for you to get info from the transmitter's modulator to your radio's speaker.

Antennas are just part of that and vertical dipoles are 360 degree radiator/receptors so you loose a lot of antenna gain that you would otherwise get in going to a more sophistocated antenna, like on your TV (non-log periodic to keep it simple) where you have directors preceding the dipole and reflectors behind it. These elements shape your "beam" and concentrate your signal transferring ability by increasing the gain of the signal.

Since all that fancy stuff is not real practical on a small boat you're pretty much stuck with a simple dipole, and on a small boat I don't think I would be fooling around with an 8' when the gains can be made elsewhere.

So the system consists of the transmitted radiated power, the antenna gains (in your direction) of both tx-rx, and your receiver sensitivity (measured in microvolts) in particular the signal-to-noise ratio (measured in decibels...dB) of your receiver's "front end". You're not going to change the transmitter part, nor either antenna (using the 4') , so you are left with working on your receiver.

To overcome the "elements at hand" it takes a certain amount of these things to get the modulation (information) from the mouths of the transmitter folks, into your ear. The biggest part of that is how well can your receiver pick out that info amongst the "white noise" (hiss-static) that is always there and the two things I mentioned about your front end are how you do that. Once your receiver captures that signal, the rest of the processing (if and audio amps) have no problem in getting it to your speaker/headset.

So the best thing is a Low Noise Amplifier (LNA) up front, between the radio and antenna. Again this is probably prohibitive so you have to look at a different radio with the best front-end you can afford. Simple as that.

Your radio retailer will know what you are talking about when you discuss the above with him.

HTH

Mark

 

[thurps]

Re: How about two antennas on board?

I don't know what your boat layout is but I have both 8' vhf and 4' cb mounted about 18" apart on my 13' Whaler with excellant results. Maybe theres a place on your boat you can mount them with minimal obstruction for your usage. Ziggy is right, if you are in trouble the last thing you need is having to mess with the antenna.

 

[Texasmark]

Re: How about two antennas on board?

Well Thurps, with a 13' boat you can't be venturing very far out, much less have the weight capacity to tolerate multiple communications facilities. So, I guess, to get us skeptics to accept your rhetoric, you might want to supply some more pertinent information.

 

[Expidia]

Re: How about two antennas on board?

Thx to all who responded . . .

And thanks for several of those well covered explanations. One wrinkle is that I have already decided on the radio. It's going to be the Standard Horizon PS 2000. This decision is being made due to space considerations. This radio is a black box that can go under the dash and the only thing that shows on the dash is the mike on it's hook. It's the mike that has all the controls and the digital screen to show the channel.

And the best part is when the boats on the trailer or unattended (like when in a restaurant) I just unplug the mike and the radios secure.

Back to the antenna. I could lean towards the 4 footer digital if as another poster has said said that I'd get about 3/4's of the range that I'd get with the 8 footer. Just seems to me that a 4 footer is better suited for placement up high on a higher boat like on top of a center console's hardtop rail or maybe on a sailboat's mast.

The 8 footer mounted to the right of my console (best place to be out of the way) still would hang off a foot or two. It would also lay on top of the lockers when down awaiting someone to step on it.

The 4 foot one could stay inside the enclosure when it's up. The 8 footer would have to be mounted on the starboard railing just in front of the enclosure and it would also not hang off the back when down.

It's a quandry on which way to go. Still would like a detachable one too for those nights the boats out in the parking lots of those sleezy motels . I was quoted by a dealer today on a Conrad antenna that has the detachable feature, but it was 200 clams

The 4 foot digital was about $63.

Would also like one in black!

Quite the shopping list?

 

[Boatist]

Re: How about two antennas on board?

I would not worry much about someone stealing an antenna if you have it on a normal mount. I would worry about the radio, GPS, Depth Finder, Poles and tackel.

If you buy a normal Marine antenna it will be tuned to 1/2 wave and you will not need to worry about Standing Wave (SWR). Do not cut the cable shorter than 6 feet and make sure when you attach the pl259 coax connector that you do not short the center conductor to the outer braid and the SWR will be good. Still when done check it with a VHF SWR Bridge just to be sure.

If you attach the antenna to a permanate mount no one will steal the antenna. A good quality antenna will make a difference as the antenna gets older. Cheap antennas use low quality radiors. Some even used a tune section of coax. Quality antenna use Brass, Copper, Silver radiators and the receive better from start to finish.

In an 8 foot antenna I really like the Shakespears Galaxy 5225. It is 6 db gain and a quality antenna. It is also available in Black, but it not a cheap antenna.

 

[JMRuth72]

Re: How about two antennas on board?

If you read this link West marine does a wonderful job of describing the things that you should be looking at when selecting a VHF antenna. I was a Fire Controlman before crossrating to Avionics Technician and both rates deal intensely with RF transmission/reception and from what I remember from FC A school they are dead on. They hit on things that I had forgotten about.

http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/VHFAntennas.htm

Why spend all that money on that transceiver just to cut it off at the knees with a less than optimal antenna. Pick a quality antenna, use quality connections with the largest coax you can as high as you can and you should get years of use with good range.

By the way radios do not work by meeting at the ends. What I mean by that is that if your radio is only putting out enough power for the most sensitive receiver to pick up at 10 miles you will only be heard out to 10 miles. Similarly if another station is only putting out enough power for your radio to pick them up at 10 miles you will only hear them out to 10 miles. The 2 stations will not talk at 20 miles like one of the other posters suggested. They will only talk out to 10 miles. Sorry to dissappoint you on that one.

 

[Expidia]

Re: How about two antennas on board?

Thx for the replies . . .

What are thoughts on the Digital VHF Marine Antenna 529VB (black) vs the Shakespeare Galaxy 5225Xt (black)? How wide is the Shakespeare? Until I get up to West to see one, I remember they are pretty wide towards the base. I'm trying to stay small as possible. I don't want a wide diameter 8 foot antenna that really belongs on a 22 foot boat. I'd like to stay slim, but of strong construction, so I'm willing to pay up for one.

They are both around $120. I had one marine store tell me why get an 8 footer when the top area in many antennas are only filled with epoxy. That I'd be better off getting a 4 foot Digital since it's all antenna parts inside rather than filled epoxy. They had both the 4 and the 8 in the Digital brand.

When looking at the reviews on the Galaxy seems they stopped winning awards around 2004 (they had a run of 5 years in a row I think) Does this mean the Digitals are taking over as the antenna's of choice. It does seem one is buying old technology with the Galaxy.

I don't know, that's why I'm asking since I don't trust what an online retailer is telling me and many marina's are worse. As are stores like West where most of their salespeople are not very knowledgeable.

I'm going to review that West link now to pick up some more knowledge, thank.

Note: just read the article. I've read that before in my searching around. One wonders how old that article is cause there is no mention of the newer digital antennas or is the word Digital just that particular company's name?

In any case, from that article it says an antenna located 5 feet high might give you 7 miles line of sight. Mine would be mounted at least 3 feet above the water line so wouldn't that give me a working height of 7 feet. That would give me around a 7-8 mile range which would me plenty for me. Much more than my handheld now. Maybe I could use only a 4 footer?

 

[JMRuth72]

Re: How about two antennas on board?

Don't know alot about either one yet as I am just getting into boating. I like the fact that both are 6db gain. I am leary of the fact that Digital Antenna used a mini-UHF connector then you have to use an adapter to connect it to a PL-259 connector. The more connections in the system the more chance of corrosion and reduction in output power at the antenna. Just on that information alone I would probably go with the Galaxy of course since I know how to I could always just cut the mini-UHF connector and install a PL-259 to the other antenna. So I guess that wasn't alot of help.
They do not use 4ft of epoxy in the end of the antenna's. It is almost all radiator inside, there is enough epoxy and fiberglass to provide strength and protection and that is about it. The longer the elements inside the antenna the more energy it transmits and receives because of the higher surface area of the radiator element. This in turn gives you the higher gain. For the most part the old technology is still practical. The only advance that I can see is better soldering which then caries the energy more effeciently between parts.
Antenna design is based on the operating frequency, not analog or digital. The carrier wave is still at a set frequency and that is what counts on an antenna not the type of modulation. If someone tells you other wise they are selling you a line. A digitally encrypted secure radio will use the same basic antenna as a normal analog radio. Digital in this case is just part of the name of the company.
As for the transmitting distance it sounds like you have got it to me.

 

[Wotam]

Re: How about two antennas on board?

"The 8 foot would have a height of 10 foot and a range of 4.49 miles.
The 4 foot would have a height of 6 foot and a range of 3.47 miles."

There's more to it than that. The 'gain' of an antenna is a critically important factor in the marine environment. Think of 'gain' as the ability of an antenna to focus energy into a pattern desirable for the application.

A good analog to help understand gain is a focusing flashlight. Turn the beam to 'wide' (low gain) and you cover a lot of area, but the beam isn't as strong. Turn the beam to 'narrow' and the light is very bright, but doesn't cover a broad area.

Why would you ever want a low-gain antenna? It provides better coverage in a boat that is heeling (like a sailboat) or moving around a lot (small powerboat in rough water). If you can imagine holding a tightly focused flashlight on a pitching boat, you can probably visualize the beam spending much of it's time shining out into space or down into the water.

Most 8' VHF antennas will have 6db gain... Shorter whips, 3db. To get higher gains (9-12db) in VHF antennas you usually have to go to much longer antenna lengths.

 

[Expidia]

Re: How about two antennas on board?

Thx JM . . . I figured it was just their name. One thing I've read, some people like the Digital brand antenna for it's connector since it is a "mini" it allows for a smaller hole having to be cut in your boat!

 

[Expidia]

Re: How about two antennas on board?

Thx Wotam . . . that flashlight analogy was a good one. Might as well go for the 8 footer since I didn't think the range would only be 4.49 miles with an 8.

One would think I'd see at least 5 miles (line of site). I certainly don't want less then 4.5 miles if I only use a 4 footer.

 

[JMRuth72]

Re: How about two antennas on board?

If you go with the galaxy then you have to install the connector from what I read. The nice thing about that is that you can drill a small hole, install a grommet to protect against chafing and route the cable very easily then install the connector as the last step. The down side is that if you don't install it correctly you can ruin the gain of the antenna and the ability to receive weaker signals because of a poor connection.
On the other hand if you use the digital you can still make a small hole for routing purposes and install a grommet. The down side is that you have more connections to worry about either corroding or loosening. Either way you can ruin the gain of the antenna and the ability to receive weaker signals because of a poor connection. In that case some ways to protect against these problems you can use a dieelectric grease to coat the connection, make sure that it is tight and then wrap it with something to make it water tight. There is a tape that is similar to electrical tape except that it is self-vulcanizing ( IE it seals to itself), or you could try that liquid electrical tape to seal it. The key is a tight, clean and dry connection.
In either case I would personally recommend using a dieelectric grease at all connections including the back of the transceiver, and the connection for the mike. Good luck on whatever you decide and I hope that we have been able to help.

BTW there is a really good textbook on antenna's called Practical antenna handbook by Joeseph J. Carr. It covers just about anything that you would want to know about antenna's of all types. It discusses RF propogation, transmission, and the practicals of antenna's from mobile to stationary VHF/UHF. I am just now getting around to reading it. I have over a dozen books on electronics that were given to me including this one, but I have a problem with math and they are pretty intense so I can only take small doses. Thanks to the Navy it makes more sense than it did when I got them, but I am still looking foward to getting out in a few months.

 

[Expidia]

Re: How about two antennas on board?

Thx JM . . . yes, everyone has been very helpful here on the in's and out's of antenna 101 for me.

Like you I've always been interested in this stuff. My Father was an Electronic Engineer for Raytheon and was involved with the space program.

I can remember building crystal radios that I used to ground on my homes radiators when I was about 7 yrs old. I then got into some ham radio stuff as a teenager.

I'll use the dielectric on the connections. My boats never on the water overnight or around salt water or left uncovered so corrosion should not be an issue. The radio will be up under the dash too away from the elements.

I might just wind up snaking the coax thru a slot so when and if for the few times I might need to remove the antenna all I will have to do is unscrew the connector at the back of the radio and probably just pull the ratchet mount apart so I don't have to unscrew the ferrule of the ratchet.

I'll definitely go with an 8 footer now. Probably a Shakesphere Galaxy with a stainless steel ferrule and brass elements.

Thx again for all the input.

 

[Expidia]

Re: How about two antennas on board?

So far I just ordered this antenna today online . . . SHAKESPEARE 5226XT Galaxy 8' VHF ANT BLK W/ SS FERRULE 6DB

Paid $108 with shipping to NY.

Still waiting on the PS 2000 with a black Mike. About $169 when it comes in plus shipping.

** Anyone have any experience hooking up the Shakespeare AM/FM splitter with this type of antenna? It's about $52. I'm using a 12v powered $20 AM/FM antenna now which is under the dash. I just figured I might also get great FM reception using this splitter and the 8 foot antenna.

But I don't want to hurt the VHF reception and transmission with extra connections and this add on device.