SWR is a killer! Are roof racks a problem?

General Mobile CB antenna advice and troubleshooting

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soydemadrid
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Thu Mar 26, 2015 12:07 pm

Hi I hope someone can help.

I have a S Mini CRT CB radio and a mini springer style antenna. First I mounted the antenna on the wing of my Land Rover but had very high SWR readings. I had a good earth and even made a metal bracket for underneath the mount to give a better ground plane but it didn't help.

So I bit the bullet and ordered the PSM1 mount which a lot of Land Rover owners use and find a great mount.

I spent lots of time carefully installing, making sure I had a great earth and an earth wire also to chassis. Made the ground plate touch bare metal and tuned and cut my aerial until I had matching SWR on 1, 20 and 40 but I still can't get below 2.9, 2ish SWR reading. Which is about borderline in the red. (I've cut as much as I can off as I had to then make 5mm longer again due to SWR going up slightly, now it is as low as I can get and very even on all channels...).

It's driving me bonkers - I thought the PSM1 would work well even though I do have a big old galvanised roof rack. Does anyone know if a roof rack would cause this problem?

I've included a photo of my aerial installation, but I'm getting a bit frustrated as I don't want to keep making wholes in the old land rover (it's leaky and rusty enough as it is!). As far as I can tell I've got great earth, good connections, good antenna and good CB. I know that roof rack is close to the aerial, but the aerial IS up high and at the back, and I've seen other CB antenna's in close proximity to roof bars and racks like this... Surely I should able to get a better SWR even with the PSM1 next to the roof rack??
antenna_land_rover.jpg
antenna_land_rover.jpg (82.37 KiB) Viewed 3087 times
Any suggestions please are welcome... Thanks.

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stampman
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Thu Mar 26, 2015 12:37 pm

change the antenna to an omega 27 for a start and that should drop your SWR the orbiter you are useing dose not like ANY metal alongside it and picks up reflection for fun you may get a lower swr even useing a center loaded orbiter so its your choice or even mount the orbiter on a mirror mount on the top bar of the roof rack


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if it anit broke dont fix it

soydemadrid
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Thu Mar 26, 2015 12:47 pm

Hi thanks for the reply - so the Omega 27 will really make a difference? If I just order that antenna, will it screw into the PSM1 thread in the same way or will I need some kind of adapter?

Thanks once again for the help!

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stampman
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Thu Mar 26, 2015 12:51 pm

just tell colin when you order you need a reverse banjo with a butterfly nut and bolt and explain to him what you are doing and he will sort you out


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if it anit broke dont fix it

soydemadrid
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Thu Mar 26, 2015 3:12 pm

Hi I just had a thought, and wondered if it was worth a try before buying the other antenna...

After emailing Thunderpole, Andy mentioned I might be better off with a centre-loaded antenna, so that the spring coil is higher up and clears the roof rack...

I then wondered though if there is a way to centre-load my current antenna. Could I add a Quick Disconnect / Quick Release and that would help my SWR and push the antenna spring up? I've seen some that are 10cm long so that would push the base loaded spring/coil up half way over the roof rack possibly?

Or is there an extension piece you can get to try this?

Maybe I'm just dreaming?!

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wildfire
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Thu Mar 26, 2015 7:10 pm

Hi soydemadrid,

personally mate i would go with stampmans idea as it could be your side mount what could be coursing you high SWR readings & for a bar mount i would suggest this one http://www.thunderpole.co.uk/mirror-bar ... it.htmlfor the antenna i would suggest one of the following Discovery 2 http://www.thunderpole.co.uk/large-cb-a ... ry-ii.html Thunderpole Orbitor HD | Centre Load http://www.thunderpole.co.uk/large-cb-a ... -load.html Thunderpole Red Rocket http://www.thunderpole.co.uk/large-cb-a ... ocket.html Medium sized antennas are alright but if your looking for long distance contacts then your better of with one of the larger antennas above,

& i wish you all the best of luck.

soydemadrid
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Thu Apr 02, 2015 3:07 pm

Hi thanks for all the help and thanks too to Thunderpole!!

In the end I just ordered the centre-loaded big stinger, screwed it in and as soon as I checked the SWR it was down at 1.5 and under!! Without cutting it down or anything!! So Thunderpole are excellent and it was just my old antenna that was causing the issue and possibly making it worse that it was base loaded.

Glad to finally be sorted and talking on the road! Thanks again

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andy@thunderpole.co.uk
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Wed Apr 08, 2015 11:32 am

Glad you managed to get it sorted! :D :D :D

Andy :wink:

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