Date   : Tue, 10 Aug 2010 20:10:45 +0200
From   : rick@... (Rick Murray)
Subject: Free Stuff Tranche III [Results]

On 10/08/2010 19:07, Rick Murray wrote:

> changes in SWR. Never used a burner, but did use a half-wave. Thank God
> the UK took its own set of freqs, for the CEPT channels were often full
 > of Latinos (sounded Italian to me, but I may have been wrong). 27MHz,
 > in Somerset. Either ~'93 was a damned good year for skip, or they were

Upon rereading, it occurs to me that this might read like gibberish, so:


SWR:
Standing wave ratio, I think. Little meter like a satellite finder that 
hooks between your CB and the antenna and measures, I think, 
reflections. Because too many reflections back, or maybe reflections too 
strong?, could damage the CB's output transistors. Annoyingly, the SWR 
depends upon frequency, so you need to tune either for best results on 
your favourite channel, or best results across all of the channels. 
Don't forget for GB/CEPT use, this means two sets of frequencies!


Burner:
Legal CBs output a miserly 4W. In open land, this might get you 5-10 
miles. In a town setting, it'll get a mile and a half across Bridgwater, 
but drops off quickly the further you go. Depends on the weather, the 
phase of the moon...
If you want to blast your signal to the moon, you'll need a "burner" 
properly known as a "linear amplifier", which can accept your CB's sucky 
4W and spit a couple of hundred watts. It might have some application in 
places like Texas where you'd need a burner to communicate from one end 
of your farm to the other, but in a place like the UK... [they're 
illegal, too, in case it wasn't obvious!]


Half-wave:
The length of a CB emission from peak to peak is something like 11 
metres. In order to "not cause interference to aircraft communications 
and radar", the legal limit to a CB antenna was a little over a metre. 
This being a big chunk of government balls as it was later found that a 
?10 ratio is about the dumbest length they could have chosen, but hey, 
it was in the Maggie Era when everybody hated everything except 
themselves... This goes into harmonics and such and big heavy books have 
been written on the subject. Anyway, a half-wave is a big metal tube 
about five metres in length.

I heard the restrictions were going to be eased to permit half-waves 
(omnidirectionals up to ~6m). Did this happen?


Freqs:
27MHz. 40 channels, FM (AM and upper/lower sideband not legal).

CEPT ("PR 27 GB") freqs are:
   26.965 MHz - 27.405 MHz split into 40 bands. Same as USA.

Older UK-specific ("27/81 UK") freqs are:
   27.600 MHz - 27.990 MHz split into 40 bands, 10kHz spacing.


Chernobyl:
As for my comment about pumping out the RF, if 4W gets you around 4-10 
miles, how much power is necessary to get a fairly clear signal in 
Somerset from a transmitter in Rome (or pick any other Italian city, it 
makes little difference). Remember, radio decay is logarithmic.

Oh, and if the wildfires reach the Chernobyl exclusion zone, all that 
lovely radioactive crap will fly high into the air, pollute us all over 
again, and...
   http://www.heyrick.co.uk/blog/index.php?diary 100606
   [second heading, you'll know which]



For what it is worth, those little PMR walkie-talkies provide CB-like 
behaviour ( < a mile in a town to 4-5 miles in open ground) using 500mW 
of power, operating 446.00625 MHz to 446.09375 MHz (eight channels with 
12.5kHz steps) and they don't need a licence. The end of CB? But, then, 
some could argue that CB died a nasty death after "Smokey And The 
Bandit" was released. ;-)


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...