I am trying to find out if the performance claims on the GAM SS-2
antenna could be accurate. http://www.gamelectronicsinc.com/mini.html
I found 2 reviews that rated this antenna #1 for a vhf short marine
antenna.
One was by Powerboat Reports
http://www.powerboat-reports.com/pub...es/4722-1.html .
And the other was by Practical Sailor
http://www.gamelectronicsinc.com/practical.html

I spoke with the manufacturer and he said the gain on this antenna is
6db or 5.1dbi. Is this possible or not possible from a 35" whip base
load antenna? If it could be possible, then under what conditions
would it be possible to get that type of gain from an antenna this
size?

I plan on calling the manufacturer back. What would be some good
questions to ask to find out the true performance of this antenna?

Thanks,
Doug

On 10 Jan 2004 21:29:12 -0800, (SDNomad) wrote:

I am trying to find out if the performance claims on the GAM SS-2
antenna could be accurate. http://www.gamelectronicsinc.com/mini.html
I found 2 reviews that rated this antenna #1 for a vhf short marine
antenna.
One was by Powerboat Reports
http://www.powerboat-reports.com/pub...es/4722-1.html .
And the other was by Practical Sailor
http://www.gamelectronicsinc.com/practical.html

I spoke with the manufacturer and he said the gain on this antenna is
6db or 5.1dbi. Is this possible or not possible from a 35" whip base
load antenna? If it could be possible, then under what conditions
would it be possible to get that type of gain from an antenna this
size?

I plan on calling the manufacturer back. What would be some good
questions to ask to find out the true performance of this antenna?

Thanks,
Doug

Doug,
Their 6db claim is in reference to a "coaxial antenna" and not against
a dipole; which would read dbd, or against an isotropic source which
is the dbi rating. Basically it's a marketing ploy. What they have
is essentially an end-fed half wave antenna which should perform
fairly much like a 'reference' dipole. You might want to ask them to
describe their "coaxial antenna" and what it's performance is in
comparison to a dipole and isotropic source (you should find about 2.1
db difference between the two - if not you are being hit with
'marketing science'). Gain in an antenna is a relative not an
absolute measurement, if they compare it to a wet string I'm sure the
gain would be enormous - it's all in how you represent a product.

I looked at the site and what I saw is your basic end fed half-wave
antenna - the lack of need for radials is what clued me in. The gain
should be about the same as any other antenna of same/similar design.
That being said, if they are rated as being more durable than other
manufacturers that is a plus -especially in the marine environment -
but don't expect more gain.

Good luck, but I am skeptical that you will get the 'true' performance
of this antenna from the manufacturer.

Howard

I am trying to find out if the performance claims on the GAM SS-2
antenna could be accurate. http://www.gamelectronicsinc.com/mini.html
I found 2 reviews that rated this antenna #1 for a vhf short marine
antenna.
One was by Powerboat Reports
http://www.powerboat-reports.com/pub...es/4722-1.html .
And the other was by Practical Sailor
http://www.gamelectronicsinc.com/practical.html

I spoke with the manufacturer and he said the gain on this antenna is
6db or 5.1dbi. Is this possible or not possible from a 35" whip base
load antenna? If it could be possible, then under what conditions
would it be possible to get that type of gain from an antenna this
size?

Anytime I see a gain of around 6 db at a frequency around 150 mhz the
antenna beter be about 20 feet tall. If not it could be refferanced to a
dummy load or most anything else. An antenna around 36 inches long is
usually rated about 3 db of gain at 150 mhz. That is not even refferanced
to a dipole. About 18 inches of antenna is a 1/4 wave whip. It is minus a
db or so refferanced to a dipole.

You might get an antenna modeling program to show the 6 db of gain if it is
isotropic and also you add some ground reflection in. This is not usually
done on vhf.

I would not even fool with the manufacturer that makes a claim like this.

What are the physical characteristics of this antenna that would keep
it from having a gain of 5.1 dbi? Is the height the determining factor
for the amount of gain from an antenna? Could the coil be wound in
such a way to get the increased gain from a 3' whip?

SDNomad wrote:
What are the physical characteristics of this antenna that would keep
it from having a gain of 5.1 dbi? Is the height the determining factor
for the amount of gain from an antenna?

Yes, for a base-loaded whip like this one.

Could the coil be wound in
such a way to get the increased gain from a 3' whip?

No, blood out of the proverbial turnip comes to mind.

Since this is a marine antenna, I suspect they are talking about gain
over salt water, i.e. close to a perfect ground. The antenna is a 1/2WL
vertical. EZNEC says the gain of a 1/2WL vertical over average ground is
about 0.5 dBi and over perfect ground is about 7.5 dBi. In free space,
it is, of course, about 2.14 dBi.

The gain of an ordinary 1/4WL monopole over perfect ground is about 5-6 dBi.
So this antenna has essentially no advantage over a 1/4WL monopole or even
a coaxial antenna. They obviously didn't model the "coaxial antenna" over
perfect ground or they didn't fold back the braid to furnish the other
half of the coaxial antenna.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

I would not even fool with the manufacturer that makes a claim like this.

That's what I was thinking, but what about the ratings tests from
Powerboat Reports and Practical Sailor. Are these reputable magazines?
Also, someone told me they have had good performance from a Maxrad
MHB5802 vhf antenna. It is the same type of antenna and claims 1/2
wave, 2.4db with ground plane and unity without ground plane. Would
this be a better choice? I know Maxrad is a more well known
manufacturer.

That's what I was thinking, but what about the ratings tests from
Powerboat Reports and Practical Sailor. Are these reputable magazines?
Also, someone told me they have had good performance from a Maxrad
MHB5802 vhf antenna. It is the same type of antenna and claims 1/2
wave, 2.4db with ground plane and unity without ground plane. Would
this be a better choice? I know Maxrad is a more well known
manufacturer.

I don't know anything about those magazines. Does the company advertise in
them ? If so do you think they would print anyting negative about them ?
I have almost never seen any magazine print anything negative in the reviews
for any product that was advertised in them.
Most let anybody write anything that will sell the magazine.

For most antennas of that type it is best to just look at how well they are
put together mechanically..They should all have about the same absolute gain
for the same length. I look for a stiff antenna that will not flop around.
Too many people do not understand that to get gain from an antenna for a
given type it must be so big. To double the gain ( such as going from 3 to
6 db) you must doubel the size , minimum. I assume that for a boat most of
the stations they will be transmitting to will be low altitude antennas on
shore or another boat. You want an antenna that will keep the signal toward
the horizon. The 5/8 wavelength antenna usually does that. They are
usually around 34 to 36 inches in length in that frequency range. The 1/4
wave antenna at about 16 to 20 inches will tend to put much of the signal
toward the sky like a round ball would look laying on the water. The 5/8
antenna will spread it out like you put your hand on the ball and mashed it
flatter.
On land for mobile antennas it depends on the area you are in as to which
antenna will work the best. I have compaired amny kinds of antennas over
the years by switching with friends of mine and looking at signals from
transmitters at all differant directions. There was no clear winner on all
stations.

Ralph Mowery wrote:
"The 1/4 wave vertical at about 16 or 20 inches will tend to put much of
the signal towards the sky like a round ball would look laying in the
water."

The mental image Ralph`s statement creates in my mind is mistaken. The
1/4-wave vertical antenna over a reflecting plane has a pronounced null
at its tip. The pattern is no hemisphere.

See Fig 3 on page 3-5 of the 19th edition of the ARRL Antenna Book for
the vertical radiation pattern of a 1/4-wave vertical antenna over
earth. Over a ground plane antenna at any elevation, the pattern is
similar, that is, there is a pronounced null at its tip.

Best regards, Richard Harrison, KB5WZI