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Old 12 January 2003, 16:49   #1
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Where to mount aerial ?

I have purchased an Icom 401 and aerial at the boat show and need some advice. My Zodiac pro 550 will not take an A frame so I think that the aerial will have to be mounted on the center console. Any thoughts or help would be appreciated.
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Old 12 January 2003, 17:43   #2
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Scotty

Although my boat has an A-frame it always prudent not to have long wires scatered on the boat.
Both the GPS and VHF aerials are mounted on the port and startboard side of the consol of the boat as is shown in the attached photo.
Hope this info helps.

PS Since then I also put a compass in the middle but there is not interferance by either the GPS or the VHF.
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Old 12 January 2003, 18:44   #3
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Reception ?

Will the reception be ok if the aerial is only as high as the console ?
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Old 12 January 2003, 18:51   #4
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Scotty

So far no probs with reception.
Until transmits and receives 100+1%!!
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Old 12 January 2003, 19:28   #5
scm
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Scotty

Have the same problem myself at the moment. I have a Selva 460 which can take an a-frame but i am against putting any more weight at the back. I also have the 401 which was fitted by the dealer but not put into the console. It was just put on the bracket and fitted to the console with a very small whip AE. I have found this to be very poor indeed.

I have therefore been to to my local shop and bought one of those big AE's as seen on bigger boats. I think this will provide a far better AE. I don't see the point of having a fitted VHF and losing the power available with a poor AE. To that end i have invested in a bracket to fit the AE to the centre console. I have decided to fit here as i think this will give me more height which is better for VHF. I could have put it on the back where the A-frame goes but not as high and is still putting weight at the back.

The AE and bracket is made by Glomex which i found a bit expensive but worth it as it sorted my problem. Their web is www.glomex.it and the bracket i got is the RA166.

I will post a pic when i have finished the job.

Hope this helps.
Regards

Stuart
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Old 13 January 2003, 09:31   #6
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Aerial,

Stuart,
What aerial do you use with this bracket ?
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Old 13 January 2003, 15:02   #7
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Scotty, I've got a 485 Cherokee and, although it's got an A frame I (for various reasons) decided to mount the aerial on the consol. I've got a 6ft f/g aerial on a ratchet mount on the starboard side, just above the tubes. No probs. Remember that some aerials don't like the wire being shortened, so plenty of room to coil it inside the consol.
Phil
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Old 13 January 2003, 19:11   #8
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Scotty,
Attached a pic of where i put it. (just got to wire it up!)

The whip i got i just asked the bloke for their advise and got the one that is about 2m in length. The higher the better for VHF but not big as to look stupid !
Rgds
Stuart
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Old 13 January 2003, 20:41   #9
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Hi folks

For my 2p's worth

Where Manos has mouted the antennas might be good for cable routing but ALL antennas MUST be mouted away from conductive items, which includes items which hold water as salt water is conductive. (dont forget people are maily salt water . )

To work correctly and idea siuitaion would be where no conductive items are within a wavelength of the antenna, on the same level, about 1.9 meters for VHF and about 25cm for GPS. If items are placed closer than this they tend to de-tune the antenna making it a poor antenna. This leads to poor GPS fixes, shorter VHF range etc.
This can be hard to obtain but most of the loss if when you go below half these values, a half wale length.

The other key thing mainly for VHF is height. The higher an antenna the better the reception.
Mounting on a pole is good, but you must get a antenna that does not need a groundplane, which most do, if you going to pole mount it.

If i didnt have a A frame i would go for a transom mounted pole about 3-4 foot high and go for a antenna with about 3dBi gain (the ones about 3-4 foot long).

A good check but not always 100% is to use a SWR meter the reflected power should be 1.5:1 or less.
This is only a guide as a dummy load with give you 1:1 but will not radiate much !!.

Also Phil, there should no reason not to shorten a coax feed antenna as long as you make good job of fitting the coax plug.

Anyone wanting more info on specific instalation drop me a PM

Have fun

Regards Gary
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Old 14 January 2003, 20:53   #10
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antenna

Scotty its worth noting that good aerial connections are vital, transmitting on a vhf with no aerial connected can damage the unit , a bad connection will give the same result, as far as I can remember total impeedence of the aerial and cable is 50 ohms.Rember vhf is line of sight no matter how big your aerial is , a transom mounted Glomex might be the way to go for your Zodiac , also note that the fine for operating or posessing vhf radio equipment in the Republic without the licence is 25000 euro gav
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Old 14 January 2003, 21:14   #11
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Re: antenna

Quote:
Originally posted by gavin
, also note that the fine for operating or posessing vhf radio equipment in the Republic without the licence is 25000 euro gav
ho ho ho ho ho he heh heh heh heh ha ha hah .... jeez Gav when we catch all the tax evaders and put penalty points on our driving licences and lock up the car thieves that killed the taxi driver then they may catch up with me.

PS. I'm going to do my vhf course next month on d northside. But to be honest I couldn't give a flying ***k about that rule,if Im having a problem on the boat and my kids are with me then I'll use the radio.
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Old 16 January 2003, 20:11   #12
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licence

And you are right Scotty, The coastguard will not answer you without a callsign unless in an emergency situation but it is a rule nonetheless and its worth being aware of it, we were out in Howth on Nyears eve and got a lift out of the sea by Nickey, who operates the crane in the Marina, I didnt know that we could use the crane having no dealings with Howth Marina, he is most helpful and charged 37 euro if I remember for the lift ,and the hull wash, and better still so helpful and friendly pretty good for dnorthside in anyways
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Old 17 January 2003, 11:40   #13
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GareeG

I too will be looking to mount an arial shortly for vhf and interested in your comments re best postioning

It would certainly be easier for me to mount arial as SCM has shown in his attached pic earlier in thread ie on the console hand hold

Reason is cabling is easy & no cables running aft and arial will fold down nicely

I have however an A frame and I would think this is the logical place to put it ? (There is a navigation light mounted at the very top which is out of view and two on the side of frame)

Given attached pic of my boat setup where would you suggest mounting it for best performance ?

Cheers
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Old 17 January 2003, 11:53   #14
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I would always recomend on the top of the A Frame and as far away from other items as possible.

Your pic does not show the top of your A frame, but if its clear apart from the nav light you will get best results if its mounted in or close to the center giving as uniform a ground plane as is possible. If the groundplane is to one side, like it would be if you mounted the antenna on the side of the A Frame you would end up with bettter prformance in one direction and less in others, a non uniform radiation pattern.

If you do not want to not use the A frame I would suggest a pole mounted to you console, maybe on the handrail BUT high enough so the base of the antenna is above head height when seated.
This will lack a good groundplane but at lease will be clear of items which would de-tune it.

As a VERY GENERAL guide longer antennas are affected least by having a poor or no groundplane.

Hope this helps

Regards Gary
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Old 17 January 2003, 14:56   #15
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thanks garygee

another view of A frame:

by the sounds of it it will be best to purchase one of the small flexible wire arials mounted on A frame, the fibreglass ones would presumably be too high and not practical ?

I do need to bear in mind that the A frame only just goes under the car porch at present and I would need a removable arial or one that could fold down flat
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Old 17 January 2003, 15:43   #16
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matiboy

Attached the obvious p;lace for your aerial!!
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Old 17 January 2003, 17:58   #17
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Manos

wish fitting it would be that easy, dont look forward to having to drill stainless steel if thats whats required
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Old 17 January 2003, 18:04   #18
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Matiboy

Is not difficult you need special drill head for SS and cuts through it like butter. I have done it and it took me including fitting the cable about 1 hour.
Another way is to use a clamp but is not safe as it may become lose.
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Old 17 January 2003, 19:13   #19
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Drilling stainless

A simple and effective method I observed for drilling stainless steel is to pulse the drill trigger on off on off not allowing the surfaces to heat up whilist misting the area with wd40 this method actually works quite well cooling and lubricating, I have seen this done on a large stainless conveyer system where numerous holes were to be drilled.
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Old 17 January 2003, 19:35   #20
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matiboy - I have just drilled 5 holes in my s/s a-frame ,and it was a piece of cake. Use a decent drill at LOW speed ensuring you have 2 or 3 sizes of drill bits which are suitable for the job. Good ones are quite expensive! Stick a piece of gaffer tape over the area you intend for your hole to be (this stops the bit slipping) and drill a pilot hole with a small drill bit. Do not use much pressure as it will snap - I did not lubricate as Gavin suggested as it was not necessary, The drill it will literally cut through the steel. Proceed with the next biggest drill but and then finally the size required. Hope this helps.
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