C b radio problems

Discussion in 'Motorhome Chat' started by froghopper, Mar 14, 2013.

  1. froghopper

    froghopper Read Only Funster

    Joined:
    Nov 29, 2009
    Messages:
    413
    Likes Received:
    176
    Location:
    winchester
    Morning all, have fitted a new cb, now I have had one in campers and trucks since the 60's so a bit of past use. Now this one will not transmit. Swr. 1.4 new thunder pole twig. Extra earth from base of twig to chassis.very good metal base. Have tried another set, same readings.. Help help help or any one want an outfit grrrrrrrrrrrrrrrrrr, oh yes... Thanks
     
  2. rainbow chasers

    rainbow chasers Read Only Funster

    Joined:
    Oct 30, 2009
    Messages:
    3,747
    Likes Received:
    1,720
    Location:
    Mid Cornwall
    what type of mount do you have and where is it?

    It is probably not transmitting due to aerial or ground plane issues.

    You have run a cable down to chassis earth - needs to be 10mm minimum size, so make sure it is suitable. You may required to add steel baseplate to aid it.

    If that fails you can purchase a ground plane kit for around £30 from thunderpole which is designed to get over the need for steel, though you will need to mount on ladder/mirror or similar as it requires a protrusion beneath the aerial base.
     
  3. Reallyretired

    Reallyretired Funster

    Joined:
    Apr 27, 2008
    Messages:
    5,706
    Likes Received:
    3,210
    Location:
    Eastbourne East Sussex
    I assume the output is what it's meant to be. Most SWR meters will show the transmitter output.
     
  4. reader

    reader Funster

    Joined:
    Apr 27, 2011
    Messages:
    177
    Likes Received:
    65
    Location:
    IO83rk
    If the thunderpole aerial is of the twisted spring design then the connection is the likely culprit, however you would see a higher SWR reading if it was the aerial.

    I havnt seen many "modern CBs" but the original 27MHz UK FM band rigs had a 0.4watt switch on an I wonder if fitted if this could be an issue although it should transmit.

    You need to test this rig on another aerial/psu and see if you get the same results.

    Has the rig been messed with in respect to power output levels by any chance and the pa blown ?
     
    Last edited: Mar 14, 2013
  5. Jaws

    Jaws Funster Life Member

    Joined:
    Sep 26, 2008
    Messages:
    18,325
    Likes Received:
    21,626
    Location:
    Narrfoook
    Ok,, couple of things..

    Just running a wire to a good earth may well not be good enough ( to say the least )

    Can I have a bit more info ?

    Where and how have you mounted the antenna ?

    What make ( and where did you get ) the CB ?

    Something often missed is that some cheaper rigs have a very poorly designed 'pye tank', which is the bit between the final output stage and the antenna.. On some cheapo rigs they are very poorly matched and have an impedance ( resistance to an AC signal basically, or in this case RF which is just extremely fast AC ! ) that is nothing like the 50 Ohms it is supposed to be.
    So even if the antenna is working great the standing wave ratio ( SWR ) can never be brought down to an acceptable level ! :Sad:
     
  6. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    More important than anything What is it mounted to? ie Metal or Fibre glass By metal I mean Steel not Aluminium.

    If it is GRP (fibreglass) you need a proper non ground plane antennae, It is not sufficient to attach a wire to its base and to the Chassis, If you do that it throws the ground plane way off as it is then at ground level virtually, I have tried approx 12 different methods of getting a CB to work on a MH and this way doesnt work, You will get a good SWR but as the ground plane is so low you do not get any distance at all.
     
  7. Shuggy68

    Shuggy68

    Joined:
    Apr 25, 2012
    Messages:
    625
    Likes Received:
    296
    Location:
    Birmingham
    cb

    do u really still use cbs:Rofl1:
     
    • Like Like x 1
  8. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    No That's why he is asking about them. :Doh:
     
  9. buyer

    buyer Funster - Life Member Life Member

    Joined:
    Jun 29, 2008
    Messages:
    215
    Likes Received:
    69
    Location:
    leicestershire
    I would very much like to fit a cb radio in my camper,but I don't no which one or what twig to use.my motor has a grp roof with an ally roof rack,both of which are no good to get a ground plane.i would like ctcs I think it's called so I can block out what I don't want to listen to when travelling in convoy. And I also want a hand held So it can be used when we get to a show etc.. I would be very gratefull for some GOOD advice on the best way to get good results because I don't want to waste my time or money buying crap that will not work as I can't afford to waste either,but I am prepared to buy quality if it works right.many thanks. Steve.:thumb:
     
  10. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    First off let me tell you about ctcss, It is a great system, BUT it will only work good if ALL the people you want to talk to have it. Sorry :Sad:

    Hand helds I would sugest a small cheap 446 band as these will suffice in the situation you describe.

    Now as for the others It IS possible to get a good service But it depends how far you are prepared to go, I have a fairly large plate bonded to my roof on which I have a Mag Mount with a Sirio Mythos 900s and I get great service, My plate is 70" X 34" But they dont need to be that size, I have plenty of room and weight available so I went large, a Plate 36" X 36" would be great But even as small as 24" X 24" would also be good, You can then attach a wire to the base as described earlier and this would work, a Firestick or similar or one same as Mine would be good, The plate doesnt need to be thick a 1mm plate would be Ok, If afterwards you want to remove the plate it comes of pretty easy.

    The Radio :BigGrin: well an average mid range rig will be good, But if you want to travel through Europe you need one that will work on the European channels, also look for one which has the new "Export" channels on as these are coming legal later this year and already are in some European countries, This "Export" frequencies will mean that all Europe will be on the same frequencies and have the facility of AM, FM, SSB and not soon enough.

    I hope I have helped and I hope it is what you wanted, I have tried to keep it as simple as possible.
    :thumb:
     
  11. Jaws

    Jaws Funster Life Member

    Joined:
    Sep 26, 2008
    Messages:
    18,325
    Likes Received:
    21,626
    Location:
    Narrfoook
    Actually, there is another option.
    If the antenna is mounted high up there is nothing wrong with using a 1/4 wave length of wire as a counterpoise.. You could put a couple of windings in the drop to reduce the total length a little but the more coils that you use, the lower the Q of the set up, the narrower the band width it will work over and the harder it will be to tune the top half of the antenna system ( This method would work best with a base loaded antenna such as the Z27 but may work ok with a helically wound antenna such as a largish firestick .. Absolutely no chance or using a top loaded stick such as the DV27 types though, and a centre loaded stick would be a real bitch to set up but COULD in theory be used )

    The reason it it rarely mentioned is because we ( as in motorhomers ) are in a fairly unique situation. We have a large ( tall ) fibre glass body behind us.. Soooooo
    You could mount the stick on the edge of the roof ( do remember it is up there and DO remember to add the size to your over all height ) and attach a lump of copper wire ( or indeed several all twisted together ) to the earthy side of the mount that is 2.595* mtrs long and sort of hide it somehow down through a cupboard, and onward in as vertical direction as possible.. If ( as is likely ) you cannot run a cable that long vertically, make a coil close to the base mount to reduce the length.

    *
    2.595 mtrs is found thus:

    (Σ / f)/4 x.95

    where :
    Σ = light speed which for the sake of this app is considered to be 300 M / S

    f = frequency ( which I have take as 27.45 megs. I chose that as channel 1 of the newer ( CEPT ) UK legal channels is 26.965 megs and the highest of the old UK channels is 27.99125

    and the .95 is to account for the velocity factor of the cable not in free space

    A bit long winded and I am sorry about that, but it IS an option so oft over looked due quite simply, as said, to out rather unique vehicle type.
     
  12. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire

    Basically an NGP Antennae uses the same theory BUT it is easier for someone who does not understand all the technical side to BUY an Antennae that will do the job, It is extremely easy for people who understand to rattle all the mathematics and theory off, BUT I wonder how many who read it will understand it?

    I have a method which I call KISS = Keep It Simple Stupid.

    :thumb:
     
  13. buyer

    buyer Funster - Life Member Life Member

    Joined:
    Jun 29, 2008
    Messages:
    215
    Likes Received:
    69
    Location:
    leicestershire
    Many thanks for the above advice,I have some cheap hand helds but would like more range than they provide ,I have seen handhelds that connect to a fag lighter socket for power and to an external twig for more range,I think I would like these,they cost a lot more but I am prepared to pay for something that works right as we go to Cornwall in convoy with my son in his camper and we would like to be able to talk to him.do you think if I was to rivet a sheat of steel to my roof rack , aprox 6 feet x1 foot and earthed it to the chassis of the van with thick cable this would work.i also will nead a bendy twig as it will be on the roof and I don't want to snap it off ,and if I remember right a firestick is a thick fibreglass twig.:thumb:
     
  14. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    It would work, Which way would the length be ? front to back or crossways? The reason I ask is that the ground plane throws a pattern out, If it was front to back the most signal would be forwards and backwards if your antennae was in the middle, and if it was crossways the pattern would be sideways, The mythos 900S I use is a base loaded short twig with spring attached and it is excellent for on the roof of a MH as it is strong but flexible and 5/8 wave and only 75cm long, You can find them on ebay.
     
  15. Jaws

    Jaws Funster Life Member

    Joined:
    Sep 26, 2008
    Messages:
    18,325
    Likes Received:
    21,626
    Location:
    Narrfoook
    KISS.. yup.. completely agree which is why I did the maths already for anyone who wants to try it, quoting the correct length of counterpoise required

    No one needs to understand the maths side of it or have any technical know how at all.
    I just added that for anyone who is interested ( and of course to be a bit of a tart )

    If reading a tape measure is considered too technical then fair enough ! :Rofl1:

    An NGP is a completely different kettle of fish. It is a shunt fed thing that is then helically wound ( usually ) and is a total compromise .. at every level ! :Wink:
     
  16. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    Ok, How many will understand what a Counterpoise is ?

    The Everhardt NGP is totally opposite and is basically exactly what you described even down to the counterpoise
     
    Last edited: Mar 18, 2013
  17. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire

    Attached Files:

  18. Jaws

    Jaws Funster Life Member

    Joined:
    Sep 26, 2008
    Messages:
    18,325
    Likes Received:
    21,626
    Location:
    Narrfoook
    Ok.. an oversite of mine.. ( it has been a LOOOONG time since I lectured this stuff and am well out of practice at prepping in words .. thats my excuse and I am sticking to it :Wink: )

    Counterpoise = , in laymens terms, ground plane

    What your 2nd post points at is similar in theory only... it is, by virtue of the physical size severely compromised
    As mentioned in another post, and to misquote Scotty off of Star Trek, ya canna change the laws of physics ( but you can kid them, which is what has been done with that rather natty gizmo )
     
  19. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    No I wasn't pointing to that as same as your example, I have just found that, I have not tried one of them as I had not seen them before, If it works it looks a perfect solution for Motorhomers as it will clamp to the roof bars, The link I posted takes you to the page where it is attached to a Bull Bar clamp.
     

    Attached Files:

    Last edited: Mar 18, 2013
  20. LesAshmore

    LesAshmore Read Only Funster

    Joined:
    Jan 20, 2009
    Messages:
    283
    Likes Received:
    40
    Location:
    Chesterfield, Derbyshire
    Here we go There are 15 examples of this artificial ground plane and different brackets, It has to be worth a try, The company that is selling them is also a very good company and extremely helpful

    :cry:


    Wish I had found these sooner :Angry:

    :thumb:

    http://www.4x4cb.com/public/menu.cfm?Category=516
     
Loading...
Similar Threads
  1. gpz
    Replies:
    10
    Views:
    366
  2. ShiftZZ
    Replies:
    32
    Views:
    1,029
  3. Ovalball
    Replies:
    19
    Views:
    806
  4. robrace
    Replies:
    0
    Views:
    516
  5. Neckender
    Replies:
    7
    Views:
    609

Share This Page