The courage to start drilling......

General Mobile CB antenna advice and troubleshooting

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Matt C
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Location: Nairnshire, Scotland.

Sat Jun 10, 2017 4:34 am

Well, the time has come to do my very fist every roof-mounted antenna, and to be honest I'm a little bit scared! My setup will be:

Sirio Super 9 'blue line' antenna (DV body-mount)
Thunderpole T2000 CB
A 57-plate, immaculate, low-mileage Suzuki Jimny!

So, I've bought a 12.5mm drill-bit especially for the job, will completely and carefully remove the headlining, and plan to mount as centrally in the roof as possible. Given how thin the roof sheet-metal is, I'm toying with cutting out the tin base of a biscuit-tin, drilling through the centre of it and sandwiching this also between the roof and mount to give extra thickness (it will, after all, be completely invisible when the headlining is refitted!)

For drilling itself, I'll put masking-tape on the roof to prevent scratches, use a centre-punch to get my mark, and will prop with wood underneath to reduce flexing, which I'll drill straight through and into, to hopefully get a tidier hole. I'll treat the hole with 'Kurust' prior to fitting, and use the opportunity of having all the B-pillar panels and sill-plates removed to give a good spray of 'Dinitrol' along any sill-joints....

So, for the experienced among you, I have the following questions:

1. Is there any merit in taking any paint off the inside of the roof metal, to ensure earthing-contact between the roof-metal and biscuit-tin metal, or will the fact that the mount is passing/clamping through both be enough?

2. When laying out the coax, should I remove any excess, or keep with the manufacturers length? (I would be careful not to coil the excess)

3. I intend to use a thin smear of silicone-sealant on the upper and lower sides of the rubber grommet, clamp in place whilst still wet, and immediately wipe-away the extrusion (again whilst wet). I toyed with the idea of using 'Sikaflex' rather than standard clear-sealant, or is this simply 'going overboard'?

Any other advice/suggestions gratefully received. I've been plucking up the courage to do this one, and keep telling myself that the benefits are that it will be the best performing and most robust install, and once done like this, I can swap between the 'Super 9' and 'Omega' by doing one DV wing-nut.

(Oh, and general observations are that I don't do 'green-laning'/off-road, don't have too much of a problem with low-branches, don't use multi-storey car-parks, and I live in the Scottish Highlands where we don't have motorways or high-speeds)

Thanks folks!
Call sign: 2H2SQ
Handle: 'Turtle'
Home is where you park it!...

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Asterix
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Location: Sanderstead, Surrey

Thu Jun 29, 2017 7:14 pm

Hi turtle
I will tell you of an experience I had with putting an antennas directly on the roof, I fitted mine about 8 inches away from the rear window centrally on the roof and it worked a treat, the only thing I found is that the wind resistance tends to drag the antenna backwards as your driving resulting in a very slight dip in the roof, I know you are fitting and bit of tin underneath the fittings which might be ok ( which I never did ) but maybe use something a little more stronger than thin tin and shaped to your roof line. Where mine was fitted Farley close to an edge I wouldn't of thought it would of made a dip but there you go. Just a little thought to consider maybe !!

SuperMike
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Sat Jul 01, 2017 6:30 pm

On thin sheet metal, I would not use a drill, preferring a fine tooth hole saw, having first drilled a tiny pilot hole. Lots of revs at the drill and with only gentle pressure. Let the tool do the work, not you shoving. :!:

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stampman
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Location: lancaster

Fri Aug 18, 2017 11:53 am

guess its done now so if you give me your phone num then i can send any customers i get who want one fitting in the roof :evil:


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