CB Aerial for FM Radio

Stuballsed · Oct 1, 2012

Hi Folks

Right, based on research and advice from those whom I assume know what they are talking about, my idea of using a splitter has been binned on the grounds that it just aint very good.

So, Ive bought another CB aerial mount for t'other side of the roof above the rear door. CB bloke at Newbury 4x4 said no worries using a springer as an aerial (large thread on the mount) or the CB aerial lead (bought together), with a car radio plug on the end.

My question to you good folk is; is this going to be ok, i.e. better than my crap wing mount rubber duck?

I know the frequency stuff is all different, but will it really matter? Is the CB coax and different from a radio coax? Should I change it?

Cheers

Bump · Oct 1, 2012

coax will be fine - try and keep the number of adapters to a minimum.

You could tune the aerial (trim it) to the right frequency range you'll want.

It'll probably be an improvement on the standard as it is higher up, though, it does depend what it has as a ground plane.

Stuballsed · Oct 1, 2012

Hmmm.

Hell, how would I know what length to trim the aerial too?

If I could get a rubber duck type aerial with the right size thread, I guess that would deal with the aerial frequency thing and being up high, would definately be an improvement on now.

Coax will be from mount to Radio so minimum links.

ratty · Oct 2, 2012

Zetagi DX27 CB Radio Car Stereo Splitter Box dx 27 | eBay

Stuballsed · Oct 2, 2012

Cheers Ratty, but like first post sayeth, I decided not to use a splitter as I can't find anyone with anything goood to say about them.

Bump · Oct 3, 2012

Put it all together and see how it works.

If the reception is rubbish then find someone who is a radio engineer who can plug in some fancy kit for you and tune the aerial.

Stuballsed · Oct 3, 2012

Bump said:
Put it all together and see how it works.

Tis the current plan.

However, if anyone knows of an FM car aerial with a 3/8" thread, or an adaptor, then I could put a regular car aerial on the thing in the first place. Two hours on tinterweb searchin and I can't find a thing

Nigel-S · Oct 3, 2012

ratty said:
Zetagi DX27 CB Radio Car Stereo Splitter Box dx 27 | eBay

Tried one of these and it was rubbish, you end up with a weak radio signal and very poor CB transmission. Yes, it does work but at a big compromise.

Freelaner · Oct 3, 2012

I used to use one of these back in the day

K40 CB Antenna Video Review - YouTube

dunno if you can still get them though

with a 100W burner and a Melos

timtheenchanteruk · Oct 3, 2012

K-40 Antenna

Stuballsed · Oct 10, 2012

Well, got the CB aerial up and running. Signal is pretty good, but not hit any of my old black spots yet.

Seem to have lost front speakers. Im's assuming I just pulled some wire plugging in the new aerial lead. Surely this has nothing to do with the new aerial and lead?????????

Clarky130 · Oct 11, 2012

Stuballsed said:
Hmmm.

Hell, how would I know what length to trim the aerial too?

If I could get a rubber duck type aerial with the right size thread, I guess that would deal with the aerial frequency thing and being up high, would definately be an improvement on now.

Coax will be from mount to Radio so minimum links.

The aerial length has to be a defined fraction of the wavelength you intend receiving. 1/4 wave is common, as are 1/2, 5/8, and 1/8. Full wave less so, as the antenna would be quite large for the FM broadcast wavelengths.

IIRC, the formula for antenna size is 984/frequency in MHz. Since The CB spectrum centres around 27MHz, this is what the antenna lengths are tuned to... It equates to about 36ft for a full-wave antenna. Full wave for FM broadcast equates to nearly 10ft!

Multiply 27 by 4 and you get 108... Which means a CB antenna will really only give you good reception at the top end of the FM broadcast spectrum - although for practical purposes, in a strong signal area, it should cope - but won't be anywhere near as good as a dedicated FM broadcast antenna of a similar size...

Bump · Oct 11, 2012

Stuballsed said:
Well, got the CB aerial up and running. Signal is pretty good, but not hit any of my old black spots yet.

Seem to have lost front speakers. Im's assuming I just pulled some wire plugging in the new aerial lead. Surely this has nothing to do with the new aerial and lead?????????

Yeh, sounds like you've just pulled a plug out for the speakers

Stuballsed · Oct 11, 2012

Bump said:
Yeh, sounds like you've just pulled a plug out for the speakers

Yep. Fixed it this morning.

Stuballsed · Oct 11, 2012

Clarky130 said:
The aerial length has to be a defined fraction of the wavelength you intend receiving. 1/4 wave is common, as are 1/2, 5/8, and 1/8. Full wave less so, as the antenna would be quite large for the FM broadcast wavelengths.

IIRC, the formula for antenna size is 984/frequency in MHz. Since The CB spectrum centres around 27MHz, this is what the antenna lengths are tuned to... It equates to about 36ft for a full-wave antenna. Full wave for FM broadcast equates to nearly 10ft!

Multiply 27 by 4 and you get 108... Which means a CB antenna will really only give you good reception at the top end of the FM broadcast spectrum - although for practical purposes, in a strong signal area, it should cope - but won't be anywhere near as good as a dedicated FM broadcast antenna of a similar size...

Blood hell

So, assuming I keep the short springer what would I have to chop off its lenght to improve signal??

As a contingency plan I have a 41cm FM antenna on the way and I'm going to make a thread adapter ( 1/8th to 5mm) to fit it into the CB mounting bracket. I will have to try and remember to remove this when out playing though as first low branch will probably kill it!

Repacement Roof Mounted Aerial Mast Whip Beesting 41cm 5mm Male fitting | eBay

Paulmitchell1984 · Oct 11, 2012

what connectors did you use for cb to aerial as my disco one is about as much use as a chokky fire guard.

Freelaner · Oct 11, 2012

pl259

Clarky130 · Oct 12, 2012

Stuballsed said:
Blood hell So, assuming I keep the short springer what would I have to chop off its lenght to improve signal??

As a contingency plan I have a 41cm FM antenna on the way and I'm going to make a thread adapter ( 1/8th to 5mm) to fit it into the CB mounting bracket. I will have to try and remember to remove this when out playing though as first low branch will probably kill it!

Repacement Roof Mounted Aerial Mast Whip Beesting 41cm 5mm Male fitting | eBay

FM spectrum is 88-108 (give or take), so aim for the mid-point - 98.

984 / 98 gives you 10.04 (it's in feet with that formula) - so 1/4 wave will give you 2.54 ft.

Bear in mind chopping it to that length will make it next to useless for CB, if you intend ever using it for that again...

Also, with a springer (or any "loaded" antenna) you have to take into account the length in the "spring" as well...

Stuballsed · Oct 12, 2012

Paulmitchell1984 said:
what connectors did you use for cb to aerial as my disco one is about as much use as a chokky fire guard.

Eh? What you on about? I'm using a CB springer aerial for my FM car radio. CB aerial mount at the back, normal car radio socket at the unit

Stuballsed · Oct 19, 2012

Piccie time.

Here's what I ended up doing. Got hold of a brass 3/8th plumming end cap, tapped a 5mm thread in the end for the car aerial then filled in the void with some plastic metal to give it some more strength.

Not used it in anger yet as I'm actually getting a pretty decent signal with the short springer CB aerial. Will check it out soon though.

CB Aerial for FM Radio

New Member

Well-Known Member

New Member

I'm not special I'm limited edition

New Member

Well-Known Member

New Member

soft and furry

Landy Driver

Well-Known Member

New Member

New Member

Well-Known Member

New Member

New Member

Well-Known Member

Landy Driver

New Member

New Member

New Member

Attachments

Similar threads