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Poor range on CB

 
 
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Tue Feb 03, 2009 10:34 am    Post subject: Poor range on CB Reply with quote

I have an Intek M-760 CB with a springer type aeriel ( 600mm long ). As the aeriel mount is on the top offside corner of the motor, I dont want to increase the length of the twig as it gets knocked enough as it is.
This leaves me with fitting an amp but I have heard that they can amplify the background noises as well as what I want to hear.
What is the best way forward?

Roger
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.
Difflock Royalty


Joined: 19 Jun 2002
Odometer: 40007
Location: Northern Ireland's Gold Coast


2009 Land Rover 110 CSW

PostPosted: Tue Feb 03, 2009 11:48 am    Post subject: Reply with quote

Linear amps are illegal
__________________________________
Bert the Defender 110 XS - because it's Cool (work it out yourself!)
Lolita the Lightweight
???? the V8 90 CSW
Suzuki DL1000 V-Strom - yes that's right, I have a Zook!
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idratherbesurfing
Just got MTs


Joined: 06 Nov 2008
Odometer: 434
Location: In my garage with a cup of tea and the heating on


1985 Land Rover Defender

PostPosted: Wed Feb 04, 2009 10:21 pm    Post subject: Reply with quote

is the SWR ok? I bought a brand new CB and it wouldnt pick anything up, SWR was reading off the scale!

turned out the inner core of the co-ax had snapped off the bit where it meets the twig. stripped it down, soldered it back on and nw SWR is just under 2 and she works like a good un Very Happy
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jonkem
Just got MTs


Joined: 25 Sep 2007
Odometer: 389
Location: Bedfordshire, UK


1989 Isuzu Trooper

PostPosted: Thu Feb 05, 2009 8:28 pm    Post subject: Reply with quote

From memory (when I bought mine)...There's 2 types of amp. One of them only amplifies the outgoing signal which is the one to go for (obviously only when you're not in the UK Wink ).

Do check the SWR 1st though Roger as it makes a massive difference. You need the best earth for the aerial that you can possibly get before trying to set the aerial up.

Rocket Radio in Letchworth (01462 675481) are happy to talk for hours about getting the best range possible from your CB, very, very helpful people and they sell online as well.

And NO.....Linear amps are not illegal but their use in the UK is Very Happy
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Tue Feb 17, 2009 10:30 pm    Post subject: Reply with quote

oops, only just got back on this one!

Differ's failed to tell me I had replies.

SWR is approx 1.2 and I check it regularly as in the old position ( spare wheel bracket ) I used to get breakdown's in the co-ax due to continual bending and stretching each time the back door was opened.

The aeriel is now fitted to the rear quarter panel, just under the roof gutter, so I don't have the same problem.

It would appear that I can fit either a longer twig---but that would suffer probable damage from trees etc or fit an amp---the problem there being that most will amplify the background noise as well as the signal.

For the time being I will leave well alone as the system works well for the relatively short ranges I use it for. On the somewhat cheaper system I had on my Suzuki I could get ranges of 5 miles regularly, something my current set-up hasn't a hope of emulating, 300m would be nearer the mark!

On one occasion, whils't camping on the top of a mountain on the Isle of Mull my old system picked up a guy in the South of France!

Many thanks for the help.

Roger
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.
Difflock Royalty


Joined: 19 Jun 2002
Odometer: 40007
Location: Northern Ireland's Gold Coast


2009 Land Rover 110 CSW

PostPosted: Wed Feb 18, 2009 1:17 pm    Post subject: Reply with quote

Is the poor performance on the receive or transmit?
__________________________________
Bert the Defender 110 XS - because it's Cool (work it out yourself!)
Lolita the Lightweight
???? the V8 90 CSW
Suzuki DL1000 V-Strom - yes that's right, I have a Zook!
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TheClunk
Off-Road Guru


Joined: 26 Jan 2009
Odometer: 1159
Location: Chippenham


1997 Vauxhall Frontera

PostPosted: Wed Feb 18, 2009 2:27 pm    Post subject: Reply with quote

5 miles isn't far either.
20 miles is possible with any aerial if you get the SWR spot on.
I have a Modulator on a mag mount, using a 1980's Harvard CB, and I get between 15 to 25 miles depending on terrain.
If you are in a town, you will struggle to get anywhere nowadays. Wireless internet, mobile phones, and all sorts of stuff creates a lot of background noise.
If possible, set your swr in the middle of nowhere.
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Wed Feb 18, 2009 3:14 pm    Post subject: Reply with quote

The question as to which is OK or better than is vexing because I don't know.

I do know that the quality of the kit carried by other people in my group is on the low side as they are all based on the principle of " throw it all together and hope it works" and " SWR--what's that? " so it may be that my range is OK and it's just their systems that cant receive and vice versa.

After all the problems I did have, I took a lot of trouble to see that I dotted all the "Is" and crossed all the "Ts".

So my choices seem to be:-

a) Park on a motorway bridge and see if I can strike up a conversation with some truck driver who can accurately tell me where he is, without too much of the " Rubber duck " and "That's a good 10-4"

or

b) Find someone who has a decent system and know's how to use it and is willing to help by sitting in his motor whils't I drive off into the blue yonder.

On reflection I think (b) is the best option but I will check my SWR somewhere out in the wilds. My current reading is approx 1.2 on band 20 but that was in the middle of a housing estate.

Would a longer twig ( mine's only 600mm long) make that much of a difference?

Roger
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TheClunk
Off-Road Guru


Joined: 26 Jan 2009
Odometer: 1159
Location: Chippenham


1997 Vauxhall Frontera

PostPosted: Wed Feb 18, 2009 3:51 pm    Post subject: Reply with quote

A longer aerial makes little difference. They are all the same length anyway. Just that the coil takes up the length of the aerial. An optimum length for a CB aerial needs to be around 20 feet (I could be wrong, it has been a long time).
If your SWR is 1.2, this is an OK figure. 1 is best, and 1.5 is the worse I would accept.
Another thing to check, is attenuation. A lot of newer CB's don't have this feature any more. But with older ones, you had the option to attenuate the power from 4watts, to 0.4 watts. This was to reduce your range for convoys, or groups modulating in close proximity. If your CB has this switch, make sure it is off.
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northumberlad
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PostPosted: Wed Feb 18, 2009 4:17 pm    Post subject: Reply with quote

The attenuation switch is probabbly marked local/DX if your radio has it
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TheClunk
Off-Road Guru


Joined: 26 Jan 2009
Odometer: 1159
Location: Chippenham


1997 Vauxhall Frontera

PostPosted: Wed Feb 18, 2009 4:20 pm    Post subject: Reply with quote

northumberlad wrote:
The attenuation switch is probabbly marked local/DX if your radio has it
Ahh, I wondered if newer rigs had it. Thanks.
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Wed Feb 18, 2009 5:31 pm    Post subject: Reply with quote

OK guys, listen up because I will say this only once, Very Happy

I have dug out the owner's manual and the rig does have a low power mode but the sign to say it is on is off and as the meter indicates 4 watts when on transmit I will assume all is OK on that score.

I will be out with my team this week-end, so I will do some more checking.

Roger
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jonkem
Just got MTs


Joined: 25 Sep 2007
Odometer: 389
Location: Bedfordshire, UK


1989 Isuzu Trooper

PostPosted: Thu Feb 19, 2009 5:43 pm    Post subject: Reply with quote

Roger, can you borrow an aerial that is centre loaded which will move the coil away from the roof?
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Thu Feb 19, 2009 8:30 pm    Post subject: Reply with quote

Jonkem

I have checked the SWR in the middle of a field ( nearest tree 100ft away ) and outside my house in the middle of an estate.

Both reading's were 1.25.

I have also re-set the controls to increase the mic. gain and increase the RF gain.

I can't do anything about the aeriel position at the moment and in truth it is extremely unlikely that I would contemplate moving it. It took a lot of fiddling to position it on the O/S corner, a position I picked to get it as far from the engine as possible.

I hope to be able to do some testing this Sunday.

As a further aid to testing, does anyone have any views on the SWR figure I have achieved? Would it be worthwhile trying to achieve a lower figure and would it show a significant improvement?

Roger
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TheClunk
Off-Road Guru


Joined: 26 Jan 2009
Odometer: 1159
Location: Chippenham


1997 Vauxhall Frontera

PostPosted: Thu Feb 19, 2009 10:36 pm    Post subject: Reply with quote

If your SWR is 1:1.25, and you are still getting no further than 5 miles, then I do not know what else to suggest. I would start pointing fingers at the rig next. Try a different rig in your car to see if it improves any.
Or, try a different SWR meter.
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jonkem
Just got MTs


Joined: 25 Sep 2007
Odometer: 389
Location: Bedfordshire, UK


1989 Isuzu Trooper

PostPosted: Thu Feb 19, 2009 11:05 pm    Post subject: Reply with quote

I reckon 1.25 is fine. Is it even on channel 1 & 40?

It looks in your pic that the coil isn't very far away from the rear quarter and not above the roofline, is that right or is it a camera angle thing?

I read somewhere about the position of the coil in relation to the bodywork when I was doing my bumper mount and just thought that as yours is base loaded it might be worth trying it with the coil higher but on your existing mount.

Could you borrow a mag mount for the weekend and try it with your antenna on that, right on top of the roof temporarily.
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Mon Feb 23, 2009 10:35 am    Post subject: Reply with quote

Went out with 2 other motors on Sunday, into the Derbyshire Dales.

Motor "A" hadn't been set up as regards SWR so could not be relied upon.

Motor "B" had SWR meter build in and a quick check indicated a reading of 2.25, which I believe to be way to high. This would surely reduce his transmit range. From tests we did in the hills and on the way home he could pick us up way beyond the point at which his transmits to us were brocken and garbled.

I surmise that my rig is OK but the other's are not.

With motor "A" between motor"B" and myself, transmission to "B" appeared blocked by "A", unless I had direct line of sight. This has happened before with "A" and other members of the group have noted this in the past.

For the moment I will endeavour to reduce my SWR reading to as close to 1 as possible. If i get a chance to test it agains't a rig of known abilities, I will do so.

Thanks for all your suggestion's

Roger
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TheClunk
Off-Road Guru


Joined: 26 Jan 2009
Odometer: 1159
Location: Chippenham


1997 Vauxhall Frontera

PostPosted: Mon Feb 23, 2009 1:16 pm    Post subject: Reply with quote

Sounds like motor 'A' has a burner, or is tweaked. If he is blocking while not transmitting, I would say the burner.
So to surmise, from what you are saying, there is nothing wrong with your set up, just everyone else's is bad.
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.
Difflock Royalty


Joined: 19 Jun 2002
Odometer: 40007
Location: Northern Ireland's Gold Coast


2009 Land Rover 110 CSW

PostPosted: Mon Feb 23, 2009 1:26 pm    Post subject: Reply with quote

Motor A obviously has a sticky PTT from what you describe
__________________________________
Bert the Defender 110 XS - because it's Cool (work it out yourself!)
Lolita the Lightweight
???? the V8 90 CSW
Suzuki DL1000 V-Strom - yes that's right, I have a Zook!
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Mon Feb 23, 2009 2:12 pm    Post subject: Reply with quote

Owner of "A" reckons he had it tweaked to give 6 watts output.

Whats a sticky PTT?

Roger
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TheClunk
Off-Road Guru


Joined: 26 Jan 2009
Odometer: 1159
Location: Chippenham


1997 Vauxhall Frontera

PostPosted: Mon Feb 23, 2009 3:01 pm    Post subject: Reply with quote

Press to talk.
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Jeepster
Gate Opener


Joined: 26 Jan 2009
Odometer: 25
Location: Aberdeenshire



PostPosted: Thu Mar 05, 2009 11:04 am    Post subject: Reply with quote

It is worth checking the CB. some had hi and lo power switches, it gave either full 4 watts or 0.5 watts. I think this feature was like a privacy for convoy stuff.
if yours is stuck on low power that would tie in with 5 miles or less and 20 on 4watts

Also you did not mention what vehicle, if it is a glass fibre top you have mounted the ariel to, you will not have the earth to create a ground plane. That would make the range probably about 300 metres.
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Roger
Mud Obsessed


Joined: 25 Feb 2008
Odometer: 2050
Location: Redditch Worcestershire



PostPosted: Thu Mar 05, 2009 11:56 am    Post subject: Reply with quote

Thanks for the comments Jeepster. I am getting the full 4 watt, as confirmed by the on rig power meter and my SWR meter ( it can also read power ).

The aeriel is mounted on the rear o/side quarter and with an SWR of 1.2, I dont think there is anything wrong with it. One of my group has an SWR of 2.25, so I want to get that fixed and then we can do a few more tests.

Roger
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wildsmith
Just got MTs


Joined: 05 Feb 2003
Odometer: 123
Location: West Midlands



PostPosted: Sat Mar 07, 2009 12:21 am    Post subject: Reply with quote

An SWR of 1.2 is quite a good match, I wouldn't worry about trying to get it lower. IMO the size of antenna will be having quite a big effect - 600mm is very short for CB frequencies and will be quite inefficient. The only other thing to watch out for is poor quality coax that due to its losses will give you a lower SWR reading than is really the case. If Stourbridge isn't too far away you're welcome to try option B over here.
__________________________________
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www.way-finder.co.uk
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Giovanni
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Joined: 01 Dec 2006
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Location: Enderley,Hamilton,North Island,New Zealand,South Pacific.


1988 Lada Niva

PostPosted: Mon Mar 30, 2009 6:24 am    Post subject: Reply with quote

If possible keep well clear of short antennas.
They are inefficiant and very narrow in band width.
SWR is not everything but is desireable.
Think of a dummy load,it gives a good SWR but radiates very little.
Field strength metering is a good test of how your radio station is getting out.

__________________________________
"Make love to a Niva owner.We need more of them,OVER!"

73 de 41-HN3800 / CEF-195 / SAS-1173 / ZL1PO / ZMT5152
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YotaDave
Articulating


Joined: 12 Nov 2007
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Location: Bristol


1994 Toyota Landcruiser

PostPosted: Mon Mar 30, 2009 11:48 am    Post subject: Reply with quote

I got my CB setup on Friday and went out on Friday night to test it. Went to the top of big hill out of town and even without the antenna adjusted I could communicate with people 30 miles away.

I am using a 2' K40 1000w Power whip on the rear gutter, Thw SWR is about 1.5 - 2 at the moment as I havent been able to get out to a clear area to adjust the antenna fully. The hill is quite densely wooded too.

Goes to show, length isnt everything! Razz I think its the quality of the components that makes or breaks something. In this case the best quality coax cable and the best antenna I could get (I love K40 antennas ever since I saw a demo and used a rig with one in America).

__________________________________
Dave (the Young Fart)
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mlines
Off-Road Guru


Joined: 12 Sep 2002
Odometer: 1467
Location: Reading, Berks



PostPosted: Tue Mar 31, 2009 6:18 am    Post subject: Reply with quote

Roger wrote:
From tests we did in the hills and on the way home he could pick us up way beyond the point at which his transmits to us were brocken and garbled.

I surmise that my rig is OK but the other's are not.


...or your rig is deaf, less sensitive on receive. People concentrate too much on getting every last bit of their 4 watts out of the aerial without looking at the various performances of the receivers.

Around 1.5 microvolts for 10db S/N average
1.0 microvolts for 10db S/N is good
0.75 microvolts for 10bd S/N is excellent

Not something you can test without the right kit but you can look up the basic specification for your rig.

A dodgy front end transistor in either the T/R switching mechanism or the first RF amplifier can deafen a receiver.

Martin

__________________________________
SUZUKI MEET - 19th October 2014 - Borden, Hants
See www.bigjimny.com
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Kitesurf
Difflock Royalty


Joined: 28 Feb 2005
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Location: Luton, Beds


1994 Toyota Surf

PostPosted: Thu Apr 09, 2009 12:21 am    Post subject: Reply with quote

TheClunk wrote:
A longer aerial makes little difference. They are all the same length anyway. Just that the coil takes up the length of the aerial. An optimum length for a CB aerial needs to be around 20 feet (I could be wrong, it has been a long time).
If your SWR is 1.2, this is an OK figure. 1 is best, and 1.5 is the worse I would accept.
Another thing to check, is attenuation. A lot of newer CB's don't have this feature any more. But with older ones, you had the option to attenuate the power from 4watts, to 0.4 watts. This was to reduce your range for convoys, or groups modulating in close proximity. If your CB has this switch, make sure it is off.


The length of the antenna does make a difference. On receive capture effect comes into play - the more antenna the higher the signal at the receiver. The loading coil on an antenna adds, "artificial length," to the antenna, merely acting as a load, which makes the transmitter see the correct impedence and, therefore, the correct VSWR. The other problem with short antennas is that they tend to radiate the signal at a high angle.

The optimum length for a mobile CB antenna is approx' 2.6M or 8'6" in old money.

IMHO, the short length of the antenna, plus its mounting position on a vertical component of the vehicle body (I am assuming that the roof of the vehicle is fibre glass) is the problem.
In an ideal world a short mobile antenna needs to be mounted as near to the centre of a metal roof as possible. Putting the antenna at the corner of a roof can make it directional. i.e. It will radiate/receive in a favoured direction opposite to the corner on which it is mounted. An easy to understand analogy is to imagine a pencil stood on a small rectangular mirror. When the pencil is in the centre of the mirror, you can see the whole of the pencil, plus its reflection, at a reasonably low angle from any direction. Stand it on the corner of the mirror and you can see it at a very low angle in one direction but not at all in the other. The direction from which you can see more of the pencil is the direction in which the antenna it represents will radiate.
Personally I use an 8ft 6" whip antenna, with a heavy duty shock spring, mounted on the front bumper of my vehicle, not only because it radiates a good signal at CB frequencies but because it can also radiate a good signal on the ham radio 10M Band. Mounting it in the centre of the bumper makes it radiate best towards the front and to the rear of the vehicle, which is useful in a convoy situation.

Roger,
I would:
A. Test the coax by removing the antenna and replacing it with a dummy load. Check with a VSWR meter and if the reading is 1.1:1 it is a fair indication that the coax is in good nick.

B. Try a longer antenna. There is not a lot wrong with short loaded antennas but I feel that 2 Ft is a little short at 27 MHz, as it is only 1/16 of a wavelength long at the frequency in use. I would not use anything under 4Ft in length.

C. Try the antenna in a different position on the vehicle. In the absence of a tin roof I would say that on top of one of the wings or the front bumper is the next best option as it would provide the best ground plane or mirror for the antenna.

Good luck.

__________________________________
Motorist who drove his 4x4 up Snowdon sentenced to appear on Top Gear.
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