Transcom GBX4000 CB27/81 UK FM CB radio - service & alignment

[@hancecrawford]

good job richard well done

[@paulchapman1175]

hi 👋 richard good luck servicing &alignment the transcom gbx 4000 cb 27/81 uk fm cb radio from paul chapman at east sheen 73's also it is 9:45 at night

[@JamesHowe-ci5vt]

A Mustang in disguise but a nice radio, now it's ready for the airwaves again will look forward to the scratchy corner test.

[@godhandneo505]

Nice job, 5 min to spare !

[@ukfmcbradioservicingTango21]

well that's the video length edited down! Richard

[@TheOptimod]

You should do an actual repair video for the Marconi test set to get the deviation measurement circuit working properly.

[@ukfmcbradioservicingTango21]

Not likely, I'm too near retirement age. We have three of the Marconi test sets, a Schlumberger, two Farnell ones & the Quartzlock test set on the bench behind me that we use for deviation.

[@sciencefollower]

Have frequencies of citizen band changed. What is 27/81, 27/91, 27/95 ..... etc. etc. what all this shit is about. Are the frequencies for fm cb different from a.m. cb. Why it is only 4 watts. Which has longer range, fm or am. Do the frequencies vary in different countries. Can we use 100 watts in cb band. Do we require a license for cb radio. Do we have call sign to operate cb radio. Why we are unable to hear cb signals on short wave radios. What is the precise length of antenna for cb band. Thanks and regards.

[@ukfmcbradioservicingTango21]

The frequencies haven't changed. UK CB introduced in November 1981 4W FM 40ch. unique channels of 27.60125Mhz to 27.99125Mhz. MPT1320 type approval shown by front panel CB27/81 logo. In 1985 UK citizens were allowed to buy a different CB radio covering the CEPT 40channels 4W FM from 26.965Mhz to 27.405Mhz. Type approval was MPT1333 shown by the printed front panel logo PR27GB. The EU were stopping us in the UK from having 80 channel combined UK/EU Cb radios because our original specification was slightly lower...mainly because we didn't have a minimum receive quality spec. We affredded this in the UK by introducing PR27/94....this is just the same as CB27/81 UK frequencies, but a hiher spec. Because we did that, the EU then said we could have 80 channel 4W FM EU/UK combined radios. This 1997 specification is shown as PR27/97. This was soon superceeded in 2000 with CE type approval for multiNorm FM oly 80 channel radios. In 2014, CE approved new radios could be bought & used in the UK covering CEPT 40 channels in AM, FM & SSB...4W for AM & FM & 12W PEP for SSB, in adition to covering the UK FM original 40 channels channels at 4W. So that brings us up to date.... UK 40 channels 4W FM CEPT 40 channels 4W AM or FM, SSB 12W PEP Different countries have CB systems on different frequencies. I think Russia can have 8W, but I haven't asked Mr Putin. Japan are on UHF 8W with government issued selective calling numbers. UK licencing for CB. From 1981 to 2000 you needed to buy a CB licence. In later years they did come with a callsign which wasn't mandatory to use. Around 2000 both CB radio & Dog licence requirement was removed...you no longer have to pay. However, you still have to stick by the rules set out by offcom. If you're naughty, you can be banned from having/using CB radio.....same with dogs...you can be banned from having a dog. Regarding licenced amateur radio, the requirement to pay for a licence was also removed. These days you have to renew it online every five years & of course stick by the rules. I've been a licenced radio amateur since 1979, but my interest is soley in UHF FM. I have what used to be called a class A licence (with morse code exam). This is now called a 'full' licence CB radio is a short range non-technical 2-way radio service with official range quoted by the government of up to 16Km. Yes, power greater than 4W AM.Fm or 12W SSB is illegal. So is using non type approved radio sets, such as amateur radio equipment on Cb frequencies. You can of course hear CB on a short wave radio that is capable of receiving 27Mhz. Most cheap shortwave radios don't cover 5-21Mhz AM only. AM is less range than FM.....about 7/8th of FM range. It takes more electrical power to produce AM because for a 4W RF output you also require 4W of audio to modulate it. AM transmitters produce much more interference than FM transmitters. When I did my training around 1979 it was quoted as 12 times more interference from an AM teansmitter compared to an FM one. I spent years in commercial business radio back when many business sytems like taxis & plumbers etc were on AM VHF systems. The range & clarity improvement as these firms swapped to FM systems was staggering. You can look up aerials very easily. Richard, G0OJF, UK