Gam Electronics VHF Antenna

T

tpbrady

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I have been using a Gam Electronics SS-2 VHF antenna for the past month and so far haven't seen any difference between its performance and the performance a a Shakespeare 8 foot antenna I had on my last boat. The SS2 is mounted on top of the radar arch on a 24 inch extension mast, and has about 15 feet of transmission line between it and the radio. On paper the difference between the two antennas should be about 3 dB (half the gain on transmit and recieve). Gam advertises it as a 6 dB gain antenna as compared to a coaxial antenna. I am not sure how to interpret that as the gain of a VHF antenna is normally a function of its length, the longer antenna has a higher gain. I think the main difference between the Gam and the Shakespeare is the loading coil on the Gam and the stainless whip. The loading coil helps to match the operating frequency to the length of the antenna helping to reduce signal losses due to mismatches (I think this is commonly referred to as SWR or standing wave ratio). The stainless whip is probably slightly more efficient as a collector and radiator of energy as it is a heavier guage.

All the technical issues aside, the performance seems to be as good as a Shakespeare 8 foot antenna. The best example came a week ago, when I was able to talk to another boat approximately 10 miles away with intervening terrain while the boat next to me, with an 8 foot Shakespeare could not. The installation on this particular boat was marginal (it was mounted on a gunwale not on the roof) making the antenna only 3 feet above the water while mine was 9 feet. At $49 at Defender Marine, so far it has proven to be a good investment as I don't expect it to wear out over time.
 
All of the base loaded 35 to 36" whips should work about the same. They are 1/2 wave end loaded antennas. The advantage is that they are more rugged than the fiberglass antenna. The thickness of the SS whip is of little consiquence. That being said, the 36" whips are generally 3 dB gain antennas. The 6 dB gain over what? This is a marketing ploy. The Shakesphere antennas are not my favorite. I do antenna testing on any antenna I buy looking for one which has the best resonant frequency and the lowest SWR. SWR being low will fool a radio into putting out its full 25 watts. You can load up a coat hanger or a fence, with a proper tuner--that does not mean that it is an effective radiator.

There are many other factors in antennas--the coax size and quality. The connections; both in the antenna sleeve, and the PL 259 connector. For example a good soldered PL 259 will beat a crimp on every day.

10 miles in not unusual--nor is 300 miles or more--depending on atmospheric conditions.

If the antennna works for you --great. But I doubt that the "Gam" is any better than other 36" antennas. There is no magic--of course unless you let the smoke out of the radio--and then the magic is gone!
 
Performance versus which 8' Shakespear Antenna? Their base model (5206) is little more than a coat hanger in a fiberglass sleeve.

I'll never forget rigging a new high end antenna on my friend's 48' Motoryacht, and finding out the previous owner had rigged the previous high end Icom radio with a $29 Shakespear 5206 antenna.
 
Matt Gurnsey":79nzuos3 said:
Performance versus which 8' Shakespear Antenna? Their base model (5206) is little more than a coat hanger in a fiberglass sleeve.

I'll never forget rigging a new high end antenna on my friend's 48' Motoryacht, and finding out the previous owner had rigged the previous high end Icom radio with a $29 Shakespear 5206 antenna.
Click to expand...

What are some recommendations for "high-end" antennae?

Warren
 
I have found that the higher end "Digital" (brand name) antenna are better than the Shakespeare Galexy series (which are better than the lower cost units). Comrod is also a high end antenna manufacturer which has an excellent reputation.

Remember that the coax is important-RG 58 is the minimal, then RG 8x and best (over kill for a C Dory, but necessary for a long run on a sail boat mast)-is RG 8U. (There are also Belden mil spec equivilants).

The coax fittings reduce the power--you loose about 1 dB for each fitting, so if you put in a barrel fitting with two PL 259's, rather than a continous run, you loose 2 dB. Also put a little conductive grease on the Pl 259 coax fitting as it goes into the female connector in the radio.
 
I am pretty sure the comparison is to the low end Shakespeare antennas. I disassembled one Shakespeare that was broken and the antenna element inside was simply the center conductor of RG-58 and it wasn't very straight. As a second antenna on a boat for a second radio, this would be a pretty good choice. For an AIS receiver this would also be good if you didn't want to split the output a single antenna. As with almost all antennas height is everything.
 
Antennas are rated with respect to an isotropic radiator, that is, a radiation equally in all directions (spherical surface.) The power density is in watts per square meter. An isotropic radiator has a gain of 1.

Also, antennas do not create power, but focus the available power in a given direction. If, in a certain direction, an antenna focuses twice as much power as the isotropic reference, it has a gain of 2 IN THAT DIRECTION, which is equivalent to 3 dB. Since no power is created , less power is transmitted in other directions. An antenna which focuses 4 times the reference power has a gain of 4 or 6 dB.

Antenna patterns are as shown:

antenna_pattern.jpg


The distance from the origin represents power radiated in a particular direction. The line labeled "isotope" shows power equal in all directions (actually a spherical surface, but we're limited to 2 dimensions on this page.) The half wave dipole radiates power horizontally, with a toroidal surface, and radiates more power in the 90 deg direction. Now, shorter ( in wavelength) antennas don't focus the power as tightly as longer antennas.

The point of this whole discussion is that if any antenna is rated at 3 dB, it is only radiating 1/2 the power of a 6 dB antenna in that direction. For VHF antannae, the direction (=90 deg, above) is horizontal. So 3 dB is not as good as a 6 dB antenna, in terms or radiating power and providing communications over long distances. Period. If the antenna is shorter and claims the same gain as a full 1/2 wave length antenna, one should be suspicious and look at how its rated.

If you're on a sailboat, which heels, a 3 dB pattern may be better, since the power covers a wider area.

Now power has to get to the antenna, and that's where SWR comes into play as well as resistive losses. But to be blunt, Shakespeare's cheapest antennas is as good at radiating power as their more expensive. The more expensive ones a built sturdier and look better.

Boris
 
What Glomex antenna do they use? The have both 3 dB (36") and 6 dB (9 ft.) antennae. I assume it's the latter, but I don't know.

They also have a 9 dB antenna, at 23", but that pattern might be a little limited.

Note that their advertisements only extol the quality of the product, the radiated power gain is the same as others. I do appreciate quality, but I can't always afford it.

Boris
 
When I was actively working in the electronics end of the business, I almost always spec'd a Digital Brand antenna. Well built, with a mini connector factory installed, we had no problems with them.

Shakespeare's Galaxy is a good antenna, but the week point is how well does the connector get installed. I have been impressed with their Center Pin solderless connectors. Many problems happen at the connector, and the Center Pin installs easily and gives a good connection.

Comrod is a great high end antenna. For larger boats, especially using 16' or 23' models, these are rugger antennas.

Anytime I have a customer want to save money and go cheap on the antenna, I always remind them that the radio is only as good as the signal getting out. Customers would want to buy something like the Icom 604, and then order the $30 antenna.

That VHF may be your life line one day. Do you really want your life depending on a $30 VHF antenna?
 
I have had several VHF antennas, from el cheapo from West Marine, a Digital 4.5 ft, and now a Morad.

Morad is a company that makes a very tough series of antennas. They are used on most PNW fishing boats, Coast Guard patrol boats and other public service craft.

Here is a copy of the description from the web site.

Screen_shot_2010_06_08_at_10_31_24_AM.jpg

I visited the factory in Seattle and was impressed with the construction and employees. I have installed the 4.5 ft VHF 156 HD on my trawler on a 5 ft extension. The extension is 1in thick wall aluminium tube painted white. Very strong. Each antenna is tuned to a SWR of 1.15 during construction. There is a PL259 connector at the antenna base and any of the three sizes of antenna cable can be used.

Greg on Red Fox is running a Morad VHF 156 HD on a pole mounted on the cabin side. He uses the pole as a handhold!

The smaller antenna looks like it would be good on smaller boats.

I bought mine at Fisheries Supply, Seattle for somewhat less than the list price shown. Initial tests on receive only while my boat is under a metal roof are good. I cannot report range until later this summer.

And no, I don't own any stock in Morad!
 
My boat had 2 of the Shakespeare Continental antennas installed and I need to replace those, my old boat I spec'd Shakespeare 5225XT which was a nice setup, my question is if I change to a Digital or other antenna can I still use the Shakespeare mounts since they are very well installed with metal backing plates.
 
Larry,

We are running with 3 Morads. (2VHF + AIS) and functionally they have worked fine for 3 seasons now. Only problem we have had was one connector issue (mine) and now I have noted that some paint is flaking on the white mounting tube which is a minor thing to deal with.

We use one of them as the courtesy flagstaff when in Canada.

(And they don't break even if they hit the roof of the dock) :embarrased

Merv
 
Merv,

Nice to know other Brats have good results with the Morad.

The Morad company makes a gold anodized aluminum tube mount that probably keeps its finish longer than the paint, but doesn't look as 'yachty'. I wanted the anodized but it was not available at Fisheries.

I plan on using mine as a courtesy flag pole too.

Larry H
 
Larry,

A couple of plastic wire ties around the fat part of the body works fine for the courtesy flag and doesn't keep you awake at night by rattling when it's breezy.

I'm going to repaint mine with Rustoleum spray and see how that stands up.(Unless someone has a better idea to share).

Merv
 
Last year, I installed a 8' Shakespeare Galaxy 5225-XT. It has a RG-8X cable and used a Center pin solderless connector and paid $100 with shipping. I cant say it is high end but better than the previous one
 
I understand that there is draw to the solderless PL 259, but there have been a number of studies, especially with time, and corrosion of the braid, and place where it is pierced. Incidently any time you use a connection where the spray may get to the connection--and there goes your signal.

This is a link to THT article which is one of the best I have read on soldering a connector:

http://www.thehulltruth.com/marine-elec ... heavy.html

One of the "problems" with VHF radios is that if it works, people are happy, but never do any real objective testing--and when the time comes in an emergency they don't have the range that they may need (also clarity is important).
 
Bob, for years, I've been trying to get 2 units. One is an S-meter for the output (receive) of the antenna. Second is a field strength meter for the radiated field (transmit) of the antenna.

Do you know where I can get either of those at a reasonable price? From the above, it sounds as if you have those meters or a reasonable approximation.

Boris
 
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