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BogMonster

CB, Ham & Communications etc

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I've been put off from any further interest by the CB experience of a whole load of swearing on the CB. That means I didn't want the set on in earshot of my kids. Hopefully a licensed set on different frequencies means better behaviour. I have a CB in the 110 which now never gets switched on :( The aerial is always unscrewed and slid along under the headlining in the back for what ever rainy day or pay and play might happen along.

G0TSH is mine and the wife is G7AYO have full HF,VHF,UHF in the 110 (Icom 7000) Antenna is a High Sierra for all HF, and a dual bander for VHF,UHF Just returned from a trip across europe and worked about 90 countries from the 110 including Australia, New Zealand and loads into the States

Keith

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It's ok to listen as long as you use receive only equipment.

It's ok to own a transmitter (with/without receive capability) as long as it's not installed (connected to a power source and to an antenna) or used.

See 'How licensing works' and 'Exemptions from licensing' at http://www.ofcom.org.uk/radiocomms/ifi/enforcement/law

My interpretation of the Ofcom rules is that you can use a Transceiver as 'Receive only equipment' if the Transmit is disabled.

On most mobile Amateur Radio's you can just remove the Mic and it will operate as 'Receive Only',unlike most CB's where removing the Mic disables receive as well. Just check you don't have any other buttons that can operate the Tx (like 1750Hz Tone or MOX).

My Callsign is M6XSD, hoping to upgrade to Intermediate in the New Year.

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OFCOM defines in several places that a receive only device is an "inherently incapable of transmission" apparatus.

I don't think there's room for interpretation here.

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Hi guys was just wondering if a roof light bar on a 110 would be gould enough as a ground plane or does it need to be bigger.

thanks in advance

Iain

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Worked for my Ham radio with a mag mount on my amber beacon bar rails before I fitted the mount I wanted direct to the roof.gutter mounts work OK

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Thanks for the reply Western , Just spent the day making a bracket and welding it to the bar then though is it good enough.

cheers Iain

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Ground planes, in the traditional sense, are ideally flat, with the aerial mounted in the centre. That said, people get away with all sorts of things.

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It shouldn't be, using a traditional base. Using a "no ground plane antenna", it will be fine. Having said that, it may well work just fine. Certainly worth trying it out to see. The rule of thumb is generally a square foot of steel is the minimum, but you could be just fine.

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Well checked the SWR and it off the scale , conections all ok no shorts and CB working fine . Im using a dome mount and a springer type ariel was going to get a psm-1 mount and put it at the back but have a roof rack and from what ive read the coil shouldnt be anywere near metal .

Would earthing the bar to the roof make any diference i have seen this when the ariel is on the roofrack.

Cheers Iain

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Would earthing the bar to the roof make any diference i have seen this when the ariel is on the roofrack.

It might have an effect, but in theory it shouldn't be much at all, 'earth' and 'ground plane' are not the same thing at all.

Is it a new aerial? I've had a few that have been overly long (they're always a bit over length) and taken a far amount of adjustment to get the SWR down.

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Yes its a new ariel will take a bit off tomorow and see how it goes a bit too cold and wet to try tonight.

cheers Iain

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IIRC on a springer, there is a smal allen screw at the top of the coiled section to allow adjustment, my one is on a gutter mount & it didn't need any trimming/adjustment.

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Hi mad pete thats the site i had looked at for the SWR readings must have missed that bit about taking 1-5 inch off . Thought it would only need a wee bit taken off will cut a bit off tomorow and see how it goes.

Western you are correct there is a allen bolt for adjustment.

Cheers Iain

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Hi guys well i took about three inches of a we bit at a time and the SWR still goes off the scale dont want to take anymore off incase there is a problem with the ground .

cheers Iain

p.s. is there anyone in the Edinburgh area that wouldnt mind giving up a wee bit of time to have a look.

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Slightly OT, but can anyone explain to me why people fit a foot square of steel to antennae which are mounted in the middle of an aluminium LandRover roof, or even why the roof bar attached to 2tonnes of LR underneath it isn't enough for a CB ground plane?

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I ran a dirty big earth strap on mine and that was good for a drop from 3 - 2.

3 and above should be earth fault I think. Check SWR meter is on right setting though.

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Slightly OT, but can anyone explain to me why people fit a foot square of steel to antennae which are mounted in the middle of an aluminium LandRover roof, or even why the roof bar attached to 2tonnes of LR underneath it isn't enough for a CB ground plane?

Dunno, but for best results (from a purely theoretical point of view, you understand) provided the metal surface is a) earthed well b) normal to the axis of the aerial and c) big enough to provide quarter of a wavelength-length of surface in any direction, it will work perfectly. At 27Mhz one wavelength is about 11m, so a 2.75m radius would be perfect :blink: . Middle of the roof then!

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Not sure why people add the steel plate - maybe for strength, or maybe it's a magnetic mount antenna?

The reason earthing via the roof bar is not ideal, is because the ground plane is supposed to start at the base of the antenna, not some electrical length away. As highlighted above, the distance along the roof bar, and then back to the centre of the antenna via the roof is a reasonably significant distance.

Mind you, I run mine from the roof bar, and the signal is pretty poor, and the SWR not that great, but not too damaging, I just live with poor range - like a mile or maybe 2 if I'm lucky. With my VHF antenna (for 2m HAM use) mounted 'more properly' on the same vehicle, I can get about 10-15 miles on the same RF output power.

Kev

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Slightly OT, but can anyone explain to me why people fit a foot square of steel to antennae which are mounted in the middle of an aluminium LandRover roof, or even why the roof bar attached to 2tonnes of LR underneath it isn't enough for a CB ground plane?

Aluminium doesn't work as a ground plane. Not sufficiently conductive/magnetic or something else. But aluminium is no better than fiberglass or wood. You need iron/steel. 1 square foot seems to be about the minimum it takes. A light bar won't do it either because it generally offers insufficient surface area.

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Aluminium doesn't work as a ground plane. Not sufficiently conductive/magnetic or something else. But aluminium is no better than fiberglass or wood. You need iron/steel. 1 square foot seems to be about the minimum it takes. A light bar won't do it either because it generally offers insufficient surface area.

Hmmmm, Works for my 35watt 2m ham radio dual band antenna & my MSA Rally radio gives me a good SWR reading on both units.

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Hi guys well i took about three inches of a we bit at a time and the SWR still goes off the scale dont want to take anymore off incase there is a problem with the ground .

You could try a lenghth of gash wire (similar diameter ideally and make sure you get a good connection) in place of the whip you have been cutting to see if it will tune by cutting that down further.

I would check all leads for a short from the centre of the co-ax to the outer braid too and if you'r sure they are ok check that the lamp bar has a good connection with the roof.

I used to run amauter HF from 10 to 80m mobile on a towbar mounted whip with no ground plane issues at all, but made good connections from the outer braid to car body with a heavy copper wire.

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Thanks for the reply guys , i checked the conections and no short , also checked with a tester and there is a conection between the conector (outer part ) and the earth of the body . but i dont think it great as i use a earth wire for the lamps to the battery and i think the only conection from the lightbar to roof is from the bolts , will a piece of welding wire be ok for using instead of the whip ? will also try an earth strap from lightbar to roof.

cheers Iain

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