| Author |
Message |
    
Slowhand
Intermediate Member
Username: Slowhand
Post Number: 103
Registered: 7-2005
| | Posted on Monday, June 19, 2006 - 5:00 pm: | 
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I'm installing a radio in my conversion van. It has a fiberglass top. A 102" whip is too tall for me. I've been running an old Solarcon 20K large coil type antenna on another vehicle and I may swap it to the van. I'm just concerned about the lack of ground plane due to the fiberglass top.
Any ideas appreciated. |
Tech237
Moderator
Username: Tech237
Post Number: 384
Registered: 4-2004
| | Posted on Monday, June 19, 2006 - 8:12 pm: |
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Slowhand,
look around there are several antennas (mainly for marine applications) that will work with a fibreglass roof. Either that or use a 6ft whip with an area of aluminium under the roof at least 3ft x 3ft. Mount the base thru the aluminium and you should not have much trouble in getting everything to work.
I think I have the design of a ground-independent antenna for 27Mhz but I think it's not much smaller than the 102" whip. |
Milkman21218
Member
Username: Milkman21218
Post Number: 54
Registered: 1-2004
| | Posted on Tuesday, June 20, 2006 - 8:04 am: |
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Slowhand,I installed a ball mount w/spring on the side at the rear.Which is about 1 foot below fiberglass cap.This way I still have a good ground plane. Removed a speaker for access to metal (drilled holes from this side out) and back of mount,ran 8X coax and a SP-3000 ant. Swr 1:2 on ch.1 and 1:3 on ch.40. Gets out VERY WELL I often 20 or miles mobile to mobile (2950 no amp). Talked from Baltimore to Chicago on AM several times.I'm sure this will work for your 20K ant. |
Dale
Advanced Member
Username: Dale
Post Number: 502
Registered: 12-2002
| | Posted on Tuesday, June 20, 2006 - 9:08 am: |
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antenna on your roof wont work on fiberglass.unless its a ground antenna witch i found they dont handle power at all and have only poor to average results.do you have metal mirriors or they plastic coated?if metal id get something like a wilson 2k trucker with the longer shaft believe its 18 inches you must get wilsons coil above the roofline to achieve good swrs.if not maybe a 102ss whip on front bumper
then go on your roof and tie it back when height issues arise.or last the no ground type antenna
id only use this type of antenna if ALL else fails |
Jameslarson
Intermediate Member
Username: Jameslarson
Post Number: 220
Registered: 4-2006
| | Posted on Tuesday, June 20, 2006 - 10:37 am: |
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Hi. Isn't there metal underneath the fiberglass? In other words, you still have the regular metal roof underneath the fiberglass correct? If so, wouldn't the antenna "see" the metal underneath and through the fiberglass? Isn't fiberglass a "transparent" material when it comes to antenna waves? Just curious. Thanks. |
Tech237
Moderator
Username: Tech237
Post Number: 385
Registered: 4-2004
| | Posted on Tuesday, June 20, 2006 - 10:43 am: |
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Actual dale a properly designed, built and installed no-ground antenna should not work any worse than an antenna needing ground. After all a dipole is a no ground antenna, a longwire is a no ground antenna, the Imax 2000 and A-99 are no-ground antennas.
In several countries that use 27MHz for marine radio ( where lives can depend on contact) most boats need to use a no-ground antenna. Like any other antenna the power a no-ground antenna can handle depends on the construction of teh antenna and the material used. |
Milkman21218
Member
Username: Milkman21218
Post Number: 55
Registered: 1-2004
| | Posted on Tuesday, June 20, 2006 - 1:46 pm: |
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I think he would do better just mounting on the vans body just like I did. The vans body is metal.The metal makes a ground plane. Using a ball mount on the side up hi get tip of antenna a few feet above the roof using your 20K.Why worry about the fiberglass roof? You mount on metal(below the fiberglass) not the fiberglass roof. No need to buy A no gound plane antenna. I am using A antenna with A BIG COIL on a conversion van with low swr,and I get out very,very well.Just think metal body mounting not fiberglass roof. |
Slowhand
Intermediate Member
Username: Slowhand
Post Number: 104
Registered: 7-2005
| | Posted on Tuesday, June 20, 2006 - 5:52 pm: |
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I'll probably try the ball mount.
thanx!
slowhand |
Dale
Advanced Member
Username: Dale
Post Number: 505
Registered: 12-2002
| | Posted on Tuesday, June 20, 2006 - 10:07 pm: |
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yea your right tech 237.a properly designed built should work the same as one not needing ground.but ya didnt mention the important part in a perfect world.ive personally mounted a coulpe of these myself yea they worked ok but thier was a compermise in performance my opion.most marines around here i think use either vhf/or uhf and a coulpe hundred watts |
Tech237
Moderator
Username: Tech237
Post Number: 388
Registered: 4-2004
| | Posted on Wednesday, June 21, 2006 - 12:47 pm: |
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Here in the US they do not have the 27 Marine band but in Australia, where I used to live and work they do.
Give me over the weekend to look for it and I'll post the design of a ground-indepenent 27MHz antenna that I used to make and sell. |
