Obtaining a CB...

Co-Pang-Yang said:

Just getting mine to work at all would be a bonus. :lol:

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I am off next week, we could play with it next week.

Cheers for that fellas, I'll run a good earth to it and get a swr meter off eBay.

Thanks for the link

Hello again!

I have problems

I have just tested my SWR and get a reading just over 3...

The other day i bought a new SWR meter off ebay, was new old stock, £9.95 delivered. It is branded Altai. Looks good enough to me! (i assume it isnt broken)

Whilst i was waiting for it to arrive, i tested my gutter mount, and found it was not earthed. So, i ran a length of 25amp single cable to the body, and screwed it to the inside of the roof section, near the grab handles.

I now have a good low resistance earth connection with the body, and i have tested the outer collar of the aerial cable where it screws to the back of the radio and there is good connection to earth there aswell.

i have also tested the aerial cable itself, there is no connection at all between the inner and outer contacts.

The aerial cable is new as i recently snapped my gutter mount and the cable was damaged, so i replaced it with a 14 quid complete mount and cable set off ebay.

SO, my question is why such a high SWR?

The radio does work and i can send and receive clearly, but i do get a lot of noise sometimes, and sometimes i have to turn the RF gain down as i cant cut out the noise with squelch.

Is there any way of deciding what's up?

Maybe i should try a mag mount in the middle of the roof??

Cheers, Sam.

have you tuned the aerial with the vehicle parked in the open away from any buildings with doors all shut? failing that try mag mount in middle of roof, it is a disco? tin roof? i reduced my SWR reading from about 3 or so to around 1.4 just by adjusting the length of the aerial with the manufactures adjustment and by moving mag mount from bootlid to roof.

paulkelly50 said:

have you tuned the aerial with the vehicle parked in the open away from any buildings with doors all shut? failing that try mag mount in middle of roof, it is a disco? tin roof? i reduced my SWR reading from about 3 or so to around 1.4 just by adjusting the length of the aerial with the manufactures adjustment and by moving mag mount from bootlid to roof.

Click to expand...

as above in red, you should have a grub screw at the bottom, adjust the aerial mm at a time till u get about 2 lower if better

Hi fellas

Thanks for your help on that.

It is a disco with a (now earthed) gutter mount.

I tested it down a country lane, wide open space, with the doors closed yes.

The adjustment in the antenna was seized up, I have stripped it down and cleaned it all up, it now adjusts smoothly. There is about an inch of adjustment available.

I will check it again later, the previous setting was about half extended, I'll shorten it and see what happens.

Cheers, sam.

Hello, me again!!

Calling all CB gurus, over!

More help please, over!

I rechecked SWR today. Improvement!!

I have a reading now of about 2-2.5 ish on ch20. I have a lower reading on ch1 than ch40.

This is with the aerial at it's shortest adjustment, about 15mm shorter than when I got SWR 3+ the other day.

The aerial I have is damn long tbh, longer than a lot of whips I have seem, probably around 1.5mtr or more.

According to cb radio guides, my results mean I might have to shorten my aerial a bit.

The bit I don't know is how much. Are we talking inches, centimetres or millimetres??

Obviously I can fine tune with the built in adjustment, but I need to know how much I should be looking at shortening first off.

Also, it was dark before so I didn't get involved trying different lengths. Is it possible that I need to lengthen the aerial by a few mm to get a lower SWR on ch20. Or do my ch1 and ch40 results mean it defo needs shortening...?

OR do I leave it as is, and try a mag mount...?

Any help appreciated, the radio gear is all new stuff to me!!

Thanks, sam

it definitely needs shortening if the SWR reading is lower on channel 1 than it is on channel 40. As for how much it needs shortening, we're probably talking mm or cm at most.

Easiest thing is to shorten it by 1cm, for example, then test SWR again. If it's still lower on channel 1 than channel 40, shorten it further. If channel 40 is now lower than channel 1, lengthen it a bit. Repeat this procedure until it's the same (or very close) on channel 1 and channel 40.

For what it's worth, here's a graph showing an example of how the readouts should be...



Needless to say, 26MHz on the graph is nearest channel 1, and 28MHz is nearest channel 40.

The best SWR guide i've read is this one: SWR Meters & Readings Explained

As for your antenna, a "Long Springer" is a 1.5m aerial. This is what I have. I think it works out to be 1/4 of a wavelength at 27MHz. The longer the better really. Shorter aerials are half the length and work out to be 1/8 of a wavelength.

By changing the length of the aerial, what you are doing is getting it as close to 1/4 wavelength as possible. 0.25 wavelengths is perfect. If your aerial is too long, it could be equal to 0.26 wavelengths, which is not giving the best reception etc...

Hope this all makes sense!

It still sounds like your SWR reading is a bit high though.

You said the adjustment on the aerial was seized up. Could there be corrosion in there preventing the aerial from making a good electrical contact with the base perhaps?

You obviously need good electronics throughout the system. Any exposed coax core, or bad electrical contacts can affect things a lot.

Hope this helps!

Many thanks mate, yeah that's a super explanation.

It was seized up yeah, but I sanded down the aerial whip to clean it nicely, and ran a drill down the aerial base part to try to clean up the hole.

I'll give it another clean up, and then measure it and see about taking it down a little at a time.

Thanks again buddy - I'll be back!!

Woohoo!

Success, finally.

i gave up trying mounts, so i decided to remove the stud mount from my gutter mount and drill a hole for it in the roof.

i cleaned up the underside of the roof so it had a nice shiny earth to bond to.

this is what i came up with. it was dead easy to fit cos i simply removed the rear interior light and drilled the hole directly above there, and then ran the wire to it under the headlining.



result: an swr reading of between 1.05 and 1.1 on channels 1, 20 and 40.

yeehaa!

fantastic! congratulations!