Disco 2 CB Radio installation and set-up

Just started to install CB set-up in My 2004 Disco 2 - put the main unit in yesterday all powers up and working fine, aerial in on a gutter mount on the back of the vehicle.

The CB is a Jesan KT-4004, bought 2nd hand from eBay but seems to be working fine (powers up, does what it should, PA system works when speaker connected). The remote speaker and PA speaker that came with it were rubbish so went in the bin, the coax was old and split and the mount was some weird sort of long bayonet fitment - or half a one anyway (so I binned that too!). What my £5 plus postage got me then was the CB unit, a gutter mount and an aerial of unknown brand - 3.5 foot (roughly - can't find tape measure at the moment) and consists of a small "coil" section with 3/8th mounting on the bottom end and a small hole in the top with hex key lock, this take a short section of whip type aerial, of about a foot, then there's another coil (hex lock connection top and bottom) and a further section of whip aerial of about another 2 foot.

To be honest I've got to idea whether the aerial is working - other than that i'm not receiving anything on any channels currently - I'm guessing it's either not properly earthed through the gutter mount (does Disco 2 body construction create and special issues here??) or it's not tuned, or it's simply old and broken somewhere inside the coil bits - or maybe a combination of these issues.

As you can probably tell, i'm new to all this radio stuff. I've got no issues with wiring up the electrics side of things (fitted enough car stereos in my time!!!) but not sure what i'm doing with the aerial stuff. I've read lots of website "advice" (some seems much more realistic than others and of course, there's always differences in opinion and lots and lots of American advice which seem to be written by people trying to sell stuff - so not sure how true it is). Most importantly it seems I need to either buy or borrow an SWR meter thing and "tune" the aerial - I can understand some of the site that say I might need to snip bits off the type of aerial I've got to make it the right length, that sort of makes sense. What I can't get my head around is that the same websites say if I buy one of those nice pretty fibreglass ones then I still need to tune it - but can't see how that's done (that's the bit when they go very vague about it all).

What i'm wondering is:

Is there anyone one here that can give me a guide on what I need to do to make it work fro where I'm up to? Is there anyone local that can check the aerial I've got works and maybe lend me an SWR meter and show me what to do?

Or maybe, possibly, there's someone out there in my neck of the woods that would like to waste some of their precious time setting it up for me? Of course if that's at my place then tea / coffee / biscuits / etc. are plentiful - if you'd prefer I came to you then I can do that too.

Various other bits I need to get sorted in time for Stamford Hall so want to get this sorted and ticked off the list and then I can move on to the next (or fix the next bit that breaks!!).

I do have all the test gear required and I'm about 30 miles or so from you, but that's the short route. Unless you want to get the Disco very, very wet, you'll have to come across the Severn Bridge! It's 70 odd miles over the bridge .
Seriously, you're not going to get very far with fully setting up your CB transmitter and aerial without a reflectometer or VSWR bridge. What you'll be trying to achieve when you do get hold of one is measuring the power travelling along the coax to the aerial and then measuring the power apparently being reflected back from the aerial towards the transmitter.
Obviously what you want is the situation where the aerial is absorbing and radiating all the power being sent into it without wasting any by sending it back.
By lengthening or shortening the top element of your aerial the tuned condition can be attained as closely as possible. In a normal practical world, a perfect match to an aerial doesn't really exist, just as close as possible. In my experience of radio circuits and transmission lines, a "perfect" VSWR reading would be somewhat troubling and probably indicate a fault condition exists somewhere along the line.

Where have you put your CB inside Paul?

brian47 said:

I do have all the test gear required and I'm about 30 miles or so from you, but that's the short route. Unless you want to get the Disco very, very wet, you'll have to come across the Severn Bridge! It's 70 odd miles otherwise .
Seriously, you're not going to get very far with fully setting up your CB transmitter and aerial without a reflectometer or VSWR bridge. What you'll be trying to achieve when you do get hold of one is measuring the power travelling along the coax to the aerial and then measuring the power apparently being reflected back from the aerial towards the transmitter.
Obviously what you want is the situation where the aerial is absorbing and radiating all the power being sent into it without wasting any by sending it back.
By lengthening or shortening the top element of your aerial the tuned condition can be attained as closely as possible. In a normal practical world, a perfect match to an aerial doesn't really exist, just as close as possible. In my experience of radio circuits and transmission lines, a "perfect" VSWR reading would be somewhat troubling and probably indicate a fault condition exists somewhere along the line.

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Ok, well that sorta makes sense - just sounds a little above my techy-knowledge abilities! The thing that's puzzling me is that I can't seem to find anything the same as the aerial I've got listed anywhere - i'm wondering if it's old, foreign, or simply not supposed to be used with the kit I've got? The outfit came as a package from eBay but from a charity shop seller (so they had no idea what they were selling), hence some of it not working and the aerial not fitting the mount. Before I go any further, does it sound like it should work or would it be best if I just bought a new aerial first?

RyanDay1 said:

Where have you put your CB inside Paul?

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I've got a dash-mount switch pod and it's mounted to the top of that - pretty much top centre on the dash. Then on the back of the car there's about 3 inches of gutter either side of the rear door so I've got work lamp fitted passenger's side and aerial fitted driver's side - both mounted with CB type gutter mounts (I like symmetry ), should be a reasonably safe location as it's round on the back not sticking out on the side where it can snag on branches and stuff.

I bought the mount complete with new length of co-ax with the fittings already connected at both ends (ideally could have been a meter longer but it does the job and the install isn't too untidy so I can live with it).

I'm toying with the idea of an SWR Meter... partly because I want to be able to add a magmount aerial to the handheld CB i've just bought and dont want to find all the power is bouncing straight back at it... and partly because i'm looking at options for a VHF base station at work.

Until then... if you need someone localish (Bristol/Bath) to just try transmitting from one CB radio to another to see if it works then more than happy to see if we can meet up somewhere at some point.

It's very difficult to give an opinion on your aerial without actually seeing it. The coils which some people think are just springs are usually placed to electrically lengthen a radiating element. It's using a property of inductance.
The first thing I'd like you to check is whether or not there a big chunk of what looks like a braided flat cable inside the bottom coil. If there is then we can forget it since it's electrically shorted out and just acting as a shock absorbing spring.
If that is the case, then you're looking at a type of aerial which is known as a "Centre Loaded Whip" and that is a technique often used in CB or 27Mhz mobile vehicle aerials. Although I have in my time heard of aerial which are both base and centre loaded in the same construction. Centre loading tends to be more efficient than base loading.
However in the absence of any information about the aerial you have, you might be better off buying a new one of known performance. If you go to a local specialist CB shop, I dunno, maybe up in Bristol, they would possibly do the tuning for you as part of the deal.

brian47 said:

However in the absence of any information about the aerial you have, you might be better off buying a new one of known performance. If you go to a local specialist CB shop, I dunno, maybe up in Bristol, they would possibly do the tuning for you as part of the deal.

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I dont know if they do CB kit, but having used them for VHF kit in the past, I can definitely recommend Co-Channel in Avonmouth - the guys there are extremely knowledgeable and have always been very friendly and helpful.

As I said earlier, I'm fully kitted out with the test gear needed for CB, Amateur HF, VHF and UHF and PMR446 radio kit. Including reflectometers, frequency counter, RF power meter, AM/FM Modulation meter and a signal generator (a rare Marconi TF2950/8 bench test set).

brian47 said:

As I said earlier, I'm fully kitted out with the test gear needed for CB, Amateur HF, VHF and UHF and PMR466 radio kit. Including reflectometers, frequency counter, RF power meter, Modulation meter AM/FM and a signal generator (a rare Marconi TF2950/8 bench test set).

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May well drop you a PM at some point when i'm more awake if thats ok

private penguin said:

May well drop you a PM at some point when i'm more awake if thats ok

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OK, no problem.

brian47 said:

It's very difficult to give an opinion on your aerial without actually seeing it. The coils which some people think are just springs are usually placed to electrically lengthen a radiating element. It's using a property of inductance.
The first thing I'd like you to check is whether or not there a big chunk of what looks like a braided flat cable inside the bottom coil. If there is then we can forget it since it's electrically shorted out and just acting as a shock absorbing spring.
If that is the case, then you're looking at a type of aerial which is known as a "Centre Loaded Whip" and that is a technique often used in CB or 27Mhz mobile vehicle aerials. Although I have in my time heard of aerial which are both base and centre loaded in the same construction. Centre loading tends to be more efficient than base loading.
However in the absence of any information about the aerial you have, you might be better off buying a new one of known performance. If you go to a local specialist CB shop, I dunno, maybe up in Bristol, they would possibly do the tuning for you as part of the deal.

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Image below shows the kit I bought - aerial does seem to have bottom and centre load (from what I can tell with my limited knowledge) but, as I said, I can't find anywhere that sells anything the same so didn't really know what it was and whether it's any good or not?? It's certainly not springs in either section, they both look like they're solid and at least wrapped in coiled cable then covered in black rubber coating. There's some writing (or once was) on the rubber bits but I can't actually read any of it so that gives no help as to finding more info.

The aerial you've shown does appear to have a matching coil at the bottom and a loading coil in the middle. As I've said, it is a technique which I've seen in the past.
However, as I also said, in the absence of any information and in your case test equipment, I'd say that your best way forward is to purchase a new aerial.

brian47 said:

The aerial you've shown does appear to have a matching coil at the bottom and a loading coil in the middle. As I've said, it is a technique which I've seen in the past.
However, as I also said, in the absence of any information and in your case test equipment, I'd say that your best way forward is to purchase a new aerial.

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Cheers Brian, i'll do that and see how things go. Might come back to you if that's ok? Maybe arrange to pop over and see you sometime if I can't get things set up properly?

Paul Leinichen said:

Cheers Brian, i'll do that and see how things go. Might come back to you if that's ok? Maybe arrange to pop over and see you sometime if I can't get things set up properly?

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No problem. Just drop me a PM.

brian47 said:

No problem. Just drop me a PM.

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Cheers for the offer - popped down to my local shop that sells CB stuff (well, they sell just about everything you can imagine - just not a huge selection of anything!). Managed to pick up a nice little springer aerial which is apparently pre-tuned - popped it on, drove up to the top of the nearest hill and started to pick stuff up so it's obviously working ok now. I appreciate pre-tuned probably goes against the grain with many (and, in honesty, i'd have preferred to have it set specifically) but no point trying to learn something new in order to set it up for something special considering the small amount of use it will get - "working" is good enough for me for now.

I'll probably bring the other aerial to Landyzone 13 and see if there's someone there who can show me how to tune it as, if it's going to work for longer distances than the little one I've bought then it'll be good to have both.

Hi Paul,

If you do not get it done before, then I am sure a few will have SWR meters at LZ13, I can bring mine,

My "pretuned" aerial was sold as a kit with my CB, and it still needed to be tuned using an SWR meter. So it is worth doing to get the best from the unit.

Cheers

yeah i'd read elsewhere that pre-tuned was never 100% but thought it would do me for now - not actually got much use for it before LZ13 so will bring both aerials with me an see who wants to do a little tuning in exchange for a beer on Friday afternoon (gotta help get the beer tent set up first though I guess)

Paul Leinichen said:

Cheers for the offer - popped down to my local shop that sells CB stuff (well, they sell just about everything you can imagine - just not a huge selection of anything!). Managed to pick up a nice little springer aerial which is apparently pre-tuned - popped it on, drove up to the top of the nearest hill and started to pick stuff up so it's obviously working ok now. I appreciate pre-tuned probably goes against the grain with many (and, in honesty, i'd have preferred to have it set specifically) but no point trying to learn something new in order to set it up for something special considering the small amount of use it will get - "working" is good enough for me for now.

I'll probably bring the other aerial to Landyzone 13 and see if there's someone there who can show me how to tune it as, if it's going to work for longer distances than the little one I've bought then it'll be good to have both.

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No problem Paul. Glad you got it on the air.
As @neilly said, even though it's "pre-tuned", it's always a good idea to check it out with a reflectometer just to make sure that you're getting the best from the installation.