Is there a quad band antenna I could put on my roof?

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Is there a quad band antenna I could put on my roof?

Postby Southwales » Mon Feb 05, 2018 6:03 pm

Is there an antenna you would recommend for cb FM that I could also use for my scanner and baofeng. I will only be allowed one antenna on my roof, why I know it may not be perfect for all bands but would a silver rod be my best? And if so can you just use the bracket supplied to mount to the chimney or should it go on a metal pole first?
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Re: Is there a quad band antenna I could put on my roof?

Postby m0lsx » Mon Feb 05, 2018 8:31 pm

I really do not know anything about CB. But a CB antenna will work to a certain extent as a RX antenna. But put decent 50 ohm coax between the antenna & the radio if you are going to be using it for VHF/UHF RX. RG-58 will do on 27 mhz, but not above.
From what I have read there are plenty of gullible CB enthusiast out there who believe all this, it's got gain bulldung. But real gain is something over & above a half wave centre fed dipole & no vertical without a decent earth is going to do that, or not in the real world & without a good dose of imagination it's not. So what you want is the best wavelength, or design, for putting the RF at the horizon, instead of warming the clouds.
Quarter waves are not bad, but a 5/8th is good unless you can find a 7/8th wave, which are as good as you can get without going to collinear lengths. Ignore that. I have rubbished my own advice :dizzy: :dizzy: . the 5/8th wave fires at the horizon the 7/8th at 45 degrees. So not what you want for FM. Look for a 5/8th wave..
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Re: Is there a quad band antenna I could put on my roof?

Postby Southwales » Tue Feb 06, 2018 12:58 am

Hi, so guessing I would need to stick with 50ohm what is a good transmitting coax as an upgrade over rg58? Also can it mount straight to the chimney or does it need to go on a scaffolding tube first? I thought I read it would need to be on a piece of metal tube to get the swr down.
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Re: Is there a quad band antenna I could put on my roof?

Postby m0lsx » Tue Feb 06, 2018 9:21 am

Often the antenna it's self is the cheapest part of the system when setting up that part. A £40 antenna can easily cost £150 to get into place & that is assuming you do it yourself & do not get a contractor to do it. And yes you will need a mounting pole to mount an antenna.
If you get a contractor to mount the antenna make sure they know what they are doing as most antenna erectors know almost nothing about antennas & only know how to attach them to walls, chimneys etc.
A badly mounted antenna can be useless.
There are a number of options open to you for Coax & which you choose will depend upon length & where the run goes. But assuming you are using less than 20 -25 meters & do not need any sharp bends in it, then reasonable quality RG-213 is a minimum choice. It is much thicker than RG-58 & much less flexible, but it also looses you much less signal. Normally. HOWEVER poor quality RG-213 can be no better than good RG-58.
As much as anything what you need is reasonable quality coax. Not cheap & nasty. Ignore the likes of Maplin & buy something that will last a few years & keep the signal in. Because not all coaxes are of the same quality & thus some coaxes loose more signal than others. Although RG means it was once a military specification. RG coax is no longer used by the military & thus it is a meaningless specification. So RG-58's, 213, mini 8's etc can all be of different qualities & it's only the number that means anything & that is it's size.
In fact RG is such a meaningless prefix that RG-8X was never used by the military, so should not really have a military RG prefix.
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Re: Is there a quad band antenna I could put on my roof?

Postby G4RMT » Tue Feb 06, 2018 9:26 am

That particular antenna design doesn't need anything from it's support, other than stability - so you could use a small crank arm and bolt to a wall, or plonk it on a 50mm thick walled tube - NOT a scaff pole because they are just too heavy for antenna supports and the bracketry to keep those safe is very large and chunky. You could mount it on a chimney but it rather depends on the size of chimney. A 12 stack mammoth on a Victorian terrace would be fine, but a smaller chimney serving just a few fireplaces would be far less strong - your best guesss really. RG58 really isn't much cop as feeder even on CB - While spending money on low loss feeder for 27MHz may be not necessary, if you intend using the antenna for a scanner - as a lump of metal in the sky - then for UHF it's going to be a bit feeble - so what it does capture needs to get out the other end into your scanner. Being very honest, HF antennas on VHF, let alone UHF are pretty useless. They get the strong stuff of course, but so does a correct length whip. I fear you need to prioritise here. I wonder if you could be clever? A Twenty foot aluminium tube could be insulated with plastic tubing from the supports, and with a bit more insulation at the top, you could install a dual band white stick on the top, and with an ATU, load up the mast as your CB antenna. I've no idea how good it would be as an antenna, but the idea intrigues me? If you want an off the shelf solution - I suspect it will be picking one or the other and accepting one as pretty naff.
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Re: Is there a quad band antenna I could put on my roof?

Postby m0lsx » Tue Feb 06, 2018 11:07 am

G4RMT wrote:I wonder if you could be clever? A Twenty foot aluminium tube could be insulated with plastic tubing from the supports, and with a bit more insulation at the top, you could install a dual band white stick on the top, and with an ATU, load up the mast as your CB antenna. I've no idea how good it would be as an antenna, but the idea intrigues me? If you want an off the shelf solution - I suspect it will be picking one or the other and accepting one as pretty naff.


A quick thought. Anything is going to be a compromise. So what do you think about this idea?
https://www.ebay.co.uk/itm/SQBM4010P-Quad-Band-10-4-2-70cm-Base-Antenna/391771326461?hash=item5b376407fd:g:nf0AAOSww9xZBwMp

It's a moonraker antenna & normally I would not go near them. But it's compromise that looks like it requires a ATU on 10 meters & as CB frequencies are only just below 10 meters, it should only a little extra compromise over the amateur bands & it will, or should work better at VHF & UHF.
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Re: Is there a quad band antenna I could put on my roof?

Postby Southwales » Tue Feb 06, 2018 12:33 pm

m0lsx wrote:
G4RMT wrote:I wonder if you could be clever? A Twenty foot aluminium tube could be insulated with plastic tubing from the supports, and with a bit more insulation at the top, you could install a dual band white stick on the top, and with an ATU, load up the mast as your CB antenna. I've no idea how good it would be as an antenna, but the idea intrigues me? If you want an off the shelf solution - I suspect it will be picking one or the other and accepting one as pretty naff.


A quick thought. Anything is going to be a compromise. So what do you think about this idea?
https://www.ebay.co.uk/itm/SQBM4010P-Quad-Band-10-4-2-70cm-Base-Antenna/391771326461?hash=item5b376407fd:g:nf0AAOSww9xZBwMp

It's a moonraker antenna & normally I would not go near them. But it's compromise that looks like it requires a ATU on 10 meters & as CB frequencies are only just below 10 meters, it should only a little extra compromise over the amateur bands & it will, or should work better at VHF & UHF.


Hi, It certainly looks along the lines of what I am after, what do you make of this part in the description though ( VSWR on 50-52 Mhz and 28-30 Mhz may exceed 2:1 ) I have to admit apart from knowing you want you swr low I don't know much about setting it or how low is important, I do have a combined Moonraker 125 power meter and swr meter being delivered in the next few days. If the swr does exceed 2.1 is this harmful to the CB?
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