Help CB fitting - SWR meter needed in Nott's

Post by **sevy** » 24 Apr 2007, 08:46

Anyone help , and some intructions for a Kernow beta 2100, used to own a cb years ago but just got one for van , any help gratefully recieved. Got loads of advice on poarts aerial and mount ordered. trucker 80 mini aerial and gutter mount kit from king radio !!

Post by **hembo666** » 24 Apr 2007, 15:28

sevy, you should have said something at the weekend, i had the swr meter in the van and was parked near enough next to you.

not that i really know what im doing to set it up, still waiting for help with mine on that one.

Post by **"WEAZLECHIN"** » 24 Apr 2007, 21:21

email king radio and ask them if the antenna is pre-tuned, if it is - - carry on, if not get an swr meter. job done

Post by **hembo666** » 24 Apr 2007, 21:48

our aerial is supposed to be pretuned but i pick up very little on it

Post by **Dan Wood** » 25 Apr 2007, 05:51

Every car/van/truck is a different size and shape to every other one, so an antenna can't really be pre-tuned to match it.

Now, call me cynical but I wonder if these pre-tuned things actually have a 50 ohm resistor between centre and outer, so that they always give a good match on the SWR meter. (Despite turning all your CB chat into heat!)

Perhaps someone who has a 'pre-tuned' antenna could measure the resistance between inner and outer of coax (at the plug that goes into the CB aerial socket will do) with a reasonably accurate multimeter and see if they get a reading around 50 ohms....

(A 'proper' vertical antenna mounted on a vehicle should have an infinite resistance...)

Post by **"WEAZLECHIN"** » 25 Apr 2007, 06:58

my icom has a built in swr and i bought a pre tuned antenna (my own coax and mount)its tuned to 11m fine (well about 450khz of it)whether its on my sprinter, van or an artic, its not the ground plane you tune , its the length of the ant. i use a magmount so its a capacitive ground and could not get it to tune in at all on my old ldv because there was some kind of radio signal booster in the roof/ceiling.if there was a 50ohm resister in line i would be transmitting into a dummy load and the returning standing waves would be nil all of the time and swr would stay down whether on 11m or 20m(and there is no way i would be doing DX on it)imagine the size of the resister too 100w. if you cant hear anything there is a problem somewhere?? if you have one of those 13inch antennas bin it, the the longer the antenna the more catchment area it will have and will be closer to a true 1/4 wave(50ohm). if you live in the sticks with a 13inch antenna your knackered

ps - who is king radio ? a cb or ham radio dealer, haven`t heard of them.

Post by **Mocki** » 25 Apr 2007, 13:46

its more important to have a good earth than anything, the "spring type coil" antenna's such as the orbitor or alike are near enough pre tuned not to worry, IF you have a good earthing.......

proper antenna's that fit on a so239 mounting are a different kettle of fish all together from the 11m rubbish that fit on a 3/8 unf thread mount......

if its one of those stupid short toy antennas ( that come in the starter kits, mostly on a crap magnet) with a torpedo coil in the center of it wont hear naff all unless you can see the person you are hearing .

the longer the better........

Post by **Rozzo** » 25 Apr 2007, 18:37

"WEAZLECHIN" wrote:my icom has a built in swr and i bought a pre tuned antenna (my own coax and mount)its tuned to 11m fine (well about 450khz of it)whether its on my sprinter, van or an artic, its not the ground plane you tune , its the length of the ant.

actually the two are related as is the length of the coax. for cb the coax should ideally be in multiples of 9ft. to say you dont tune the groundplane is naive as it makes up the other "quarter wave" to make the half wave that presents the required impedence of 50 to 75 ohms. you actually tune the length of the whip against the other half and relative to it and since all vehicles are different, even if the same model the aerial will benefit from tweaking.
aerials are not pre-tuned unless designed for a spot frequency in a fixed, known installation and this is not the case with mobile installation. they'll probably work but won't be ideal without a bit of tweaking.

Post by **"WEAZLECHIN"** » 25 Apr 2007, 21:14

no well like i said, you can buy tuned antennas set to a certain frequency because i have one tuned to 11, if i want to use 10 i shorten it to marks i put on it. it is tuned to that set frequency regardless of the vehicle im in. dipoles use a mirror image, but that cant be said for gps. i can show you if you dont believe, wouldnt say i was naive, i was a g7 about 17 years back and a m0 for about 10 (18 wpm) dont know why i bothered.but when we were dxing we often swapped antennas between our different vehicle (never a problem) its a good quality ground that you need, not the shape of it!!!. oh, then theres marine antennas(capacitive) no gp.

Post by **Rozzo** » 25 Apr 2007, 21:51

"WEAZLECHIN" wrote: oh, then theres marine antennas(capacitive) no gp.

but normally sited over water, the best gp in the world

Post by **"WEAZLECHIN"** » 26 Apr 2007, 12:52

and work equally well in attics!!!!! fibreglass mounted

no water

Post by **Dan Wood** » 26 Apr 2007, 15:13

Ah, but they are half-wave verticals, so do not need any ground plane.

I'm a big fan of end-fed halfwaves. I've one for 70cm, and one for 2m. Their only snag is that they have to be single band antennas...

Post by **"WEAZLECHIN"** » 26 Apr 2007, 17:15

absolutely, but thats why the bands run as so= 10, 20, 40, 80,mtrs etc etc so a full L on 10 can be a 1/2L on 20, or a 1/4L on 40. back when g5rv(louis varney) was still at primary school!! i suppose someone found out about 5/8L and 3/4L useability later on, when they learned about antenna loading and stuff, and actually had all the "modern" ahem, test equipment. never been into vhf except 50mhz when theres a window.

Post by **BrokenSlider** » 27 Apr 2007, 07:34

I was really keen on getting myself a cb but after reading this which has all gone whoosh over my head I'm not so sure!!!

Is it really that complicated? Are there places that would fit it all and tune it in for you

Post by **Mocki** » 27 Apr 2007, 09:26

setting up a cb is really as simple as fitting a broadcast wirless in your van, ignore all the tech stuff above, all you need to know , in reality, is

RED to +12vdc
Black to -12vdc
antenna in the back od the cb
antenna mounted onto METAL with an elctrical connection to the vehicle body and away you go, 90% of cb'ers dont even know what SWR is, nevermind how to adjust its results.......

the best tip when looking to get a cb set up in your van is "dont mess about buying second hand antenna systems" buy a new antenna set up, buy the longest antenna you dare put on the van, and make sure its connectedd to a metal part of the body......
its only a cb, its not rocket science, and its going to reach only as far as the person you are listening to can transmit, dont expect anymore than 2-3 miles mostly mobile to mobile.