vhf antenna interesting info
Submitted by grayzeee on Thu, 2012-10-18 19:06
http://www.llelectronics.com/docs/awards/VHFAntennas.pdf
Just bought a new icom vhf from USA for quite a saving , and was looking into antenna's.
Found the above link which is a bit of an eye opener. Of the 8' whips tested , some managed a paltry 7nm while others got double the distance in test.
Makes me wonder if the obligatory gme antenna's are anything like their radio's.
I couldn't even find the Db rating on their 8' antenna.
Looks like shakespeare are well well worth a look into.
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If I spent half as long fishing , as I do reading this bloody forum , I'd be twice the fisherman I am.
till
Posts: 9358
Date Joined: 21/02/08
Good that they put the info
Good that they put the info about the higher the gain, the flatter the signal is, and the implications for boats. Most people don't really get it.
squidder
Posts: 457
Date Joined: 03/09/10
Height is mite
is the general consences with antennas.
The problem with a lot of aerials and antennas is they are placed up against windscreens and the like and in doing this it severely reduces the in/output of the antenna, what a tech would call tx,rx.
Plain and simple put aerials up as high as possible and buy the longer ones at that.
cheers
Brucesta
Posts: 1721
Date Joined: 29/05/09
It's got nothing to do with
It's got nothing to do with the length, just the design, look for the gain reading always
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till
Posts: 9358
Date Joined: 21/02/08
Well kinda. There are
Well kinda.
There are physical reasons the an omni antenna needs to be of a certain length to get the gain levels they're claiming, its based on the wavelength that they operate.
Gain isn't all good, as that document shows, higher gain means that the output donut is flatter, and possibly spending more time pointing at the water or the moon, depending on how your boat rocks.
Brucesta
Posts: 1721
Date Joined: 29/05/09
All depends if they tune to
All depends if they tune to a half wave length or 1/4 wave. Take 300 and divide 155, you get roughly 2, this is your wavelength in meters, a quarter wave antenna (this is your shorter versions) will have unity gain, half wave length versiozns have 3db more than the 1/4 wave versions. If manufacturers claim any more than that, they are full of poo. Let's face it your antenna is useless if your receiver is screwed. If in doubt get it checked and make sure your antenna cable is as short as possible, not crushed by cable ties and the connector is put on correctly. Adaptors take away 0.5db power away, crushed cables another 1db, longer run or poor cable another 0.5db. Your only transmitting 43 odd db (25w) in a perfect world, take those losses in and your only pumping 10 to 15w out the stick.
A good receiver is better than a good transmitter in the end. Positioning isn't too critical either as long as its vertical and unobstructed it'll work, mine is on the side of the boat not up high and works better than most because I'll move my boat into a prime position with the antenna side facing the target.
Its all smoke and mirrors in the end. Don't even bring atmospherics into it....
Las Vegas - Rolling the dice and trying your luck. 1M+ Barra summer target. 100kg Black Marlin winter target
Paul H
Posts: 2104
Date Joined: 18/01/07
Hell try reading that after
Hell try reading that after half a bottle (no offence Brucesta but it hurt a little just after the 300 bit not to mention the divide bit which is my pet hate)
- So in laymans terms if I wanted as good a possibility to get some one to hear me in an emergency what do I want.
Base of the antenna as high as reasonable on the boat
As short a cable from the unit to the antenna as feasably possible (ie on top the cabin infront of the windscreen on your average 5-7m cabin boat)
good connections
any corrections or other points (he asks after losing count of the glasses of bourXXX BorXXX F*&%$#@ Whiskey :-)
Cheers
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Brucesta
Posts: 1721
Date Joined: 29/05/09
have it high and have it
have it high and have it clear. good connections, not dodgy looking ones and as short of a cable length as you can, if they give you say 5m and you only need 2, don't coil it up and cable tie it away, that will create loss of signal.
all antennas are now ground independant so having it in the middle of your roof if you have the luxury is no different if it's on the side of the targa top. Then make sure you're switcghed to 25W not 1W.
Las Vegas - Rolling the dice and trying your luck. 1M+ Barra summer target. 100kg Black Marlin winter target
Paul H
Posts: 2104
Date Joined: 18/01/07
Cheers pretty well what I was
Cheers pretty well what I was thinking
Paul
Youtube Channel - FishOnLine Productions
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Brucesta
Posts: 1721
Date Joined: 29/05/09
And that gain can go
And that gain can go straight out the window if you crimp it wrong, crush the cable, bad VSWR etc
Las Vegas - Rolling the dice and trying your luck. 1M+ Barra summer target. 100kg Black Marlin winter target
squidder
Posts: 457
Date Joined: 03/09/10
Longer
antennas usally always have a higher db than short ones. Short antennas have the windings done in an attempt to gain higher db's.
The long antenna's on commercial boats are usually 9DB and the shorter ones decrease in DB's, roughly 3DB.
Surely antenna's are put highup on hills for a reason.
Cheers
meglodon
Posts: 5981
Date Joined: 17/06/10
what has been said above is right height is might
the reason they put repeater stations etc up in the hills is to get as much height above sea level as possible in Mandurah channel 82 is inland above the Alcoa site at pinjarra and the reception is great a long way out to sea
Willlo
Posts: 1490
Date Joined: 07/10/11
Sorry to semi hijack thread,i
Sorry to semi hijack thread,i have been thinking of putting either a VHF or a 27 meg radio in at home behind my bar (i live 1 street back from the ocean).Was wondering how you would go about it? would be cool to listen in to whats happening on the days i am not fishing,any ideas?
Call Sign - BZ785
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tim-o
Posts: 4657
Date Joined: 24/05/11
Could just get a cheap 12v
Could just get a cheap 12v battery charger, connect the radio's power and earth wires to the aligator clips, dunno about antenna location, on the roof?
I am, as I've said, merely competent. But in an age of incompetence, that makes me extraordinary.
Willlo
Posts: 1490
Date Joined: 07/10/11
Yeah the antenna wont be the
Yeah the antenna wont be the problem,got a spot for that.Wanted to run it of the house power,what would you use to bring it down to 12 v?
Call Sign - BZ785
Haynes Hunter Prowler CC
squidder
Posts: 457
Date Joined: 03/09/10
If
you wish to "Listen" only then a very small power supply, not even 1 amp will do the job.
It's only when one wants to Transmit is when you require a decent supply.
If you already have an antenna, then all you need is , whats called a stand off bracket attached to your existing antenna, if not then acquire a length of pipe/tubing and attach this to something solid with your antenna to the top.
Cheers
meglodon
Posts: 5981
Date Joined: 17/06/10
try a 12 volt/240 volt
i don't know if you can get a 12v/240v transformer that would do the job ok
tim-o
Posts: 4657
Date Joined: 24/05/11
Yes, yes the old school
Yes, yes the old school chargers are transformers but no longer cheap, but this is http://www.ebay.com.au/itm/New-AU-AC100-240V-DC-12V-5A-60W-Power-Supply-Adapter-Transformer-/330719115718?pt=AU_Travel_Acc&hash=item4d006539c6
Just check the fuse rating for the radio, if it is 5amp then it wont draw more than 5 amps.
WOOHOOO 1000 POSTS finally, btw wtf happened to FW for the last 5 hours??????
I am, as I've said, merely competent. But in an age of incompetence, that makes me extraordinary.
Willlo
Posts: 1490
Date Joined: 07/10/11
That looks like it might be
That looks like it might be the go,cheers fella's.
Call Sign - BZ785
Haynes Hunter Prowler CC
hooty
Posts: 198
Date Joined: 25/05/10
Radio to small sealed 12 volt
Radio to small sealed 12 volt battery. Battery to battery charger all the time or when needed.
Brucesta
Posts: 1721
Date Joined: 29/05/09
you canvget 240AC to 12DC
you canvget 240AC to 12DC supplies from jacar and dick smiths bout 100 bucks, to transmit you'd need something with about 5A to be sure. GME do a 7A unit that we use a lot at work.
Las Vegas - Rolling the dice and trying your luck. 1M+ Barra summer target. 100kg Black Marlin winter target
crasny1
Posts: 7003
Date Joined: 16/10/08
Jeez Brucesta
You have me totally blown away with this radio techno talk. Next time I see you Ill remember to blow you away with my techno talk. LOL.
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