CB, Ham & Communications etc

[DEANO3528]

Yes indeed people, your caring and sharing Labour(ious) government has excelled once again.

As they obviously never made any money from taxing CB'ers they dropped that and have maoved on to VHF instead.

Problem is, that a lot of voluntary not to mention charity funded organisations such as Mountain Rescue and Lowland SAR, not forgetting the 4x4 Response groups rely on VHF for their comms.

If you feel able, then please sign the petition

http://petitions.number10.gov.uk/LSAR-RF-LICENSES/

TIA

[western]

VHF is already licenced on VHF low & high band you have to hold a UK General licence IIRC about 60quid for 3 years. & I believe Mountain Rescue frequncies fall under that licence requirement. also they recently made the ham licence a lifetime duration.

[Ryan]

There was something on my local news a couple of weeks ago regarding the effect on the RNLI. Apparently they get one licence free for one radio (at their base), but any additional radios either at the base or on boats etc, have to be paid for. I found this on the BBC:

Peter Bradley, RNLI's UK operations manager, said the charity pays a 50% discounted fee of £38,000-a-year for its VHF licence.

Radio use on all vessels is free of charge, however, the costs apply onshore and include lifeboat stations and volunteers' pagers.

Mr Bradley said the new proposed fee would be £260,000 - £130,000 if a reduction was agreed.

He said: "In the current economic climate it is going to be asking a lot of volunteer fund-raisers and the public to find that extra £100,000."

Mr Bradley hoped volunteers and the public would respond to Ofcom's consultation, which finishes on 30 October.

[western]

I've signed it as the RNLI & MR teams do a fine job without needing to find massive amounts of extra cash that could be put to better use on kit/vehicles.

[discojmz]

do land based VHF operators require licensing also? I only ask because I have a MCA marine VHF licence that I had to do a course for.

VHF on board a boat from what I remember has almost never been free, and as it gains more and more features such as DSC, (which is used for distress and specific calling, for which every vessel is assigned an identifying number), I can understand it getting more and more expensive.

BUT... Ive a real problem with emergency services being charged to use it, particularly voluntary organisations that should by rights be funded by the govt in the first place!

[western]

http://www.ofcom.org.uk/radiocomms/ifi/licensing/classes/ more info on those pages

[TJ101]

VHF on board a boat from what I remember has almost never been free, and as it gains more and more features such as DSC, (which is used for distress and specific calling, for which every vessel is assigned an identifying number), I can understand it getting more and more expensive.

You have to have a ship Licence,, but the fee for it was scrapped about 18 months ago

[Projectblue]

Mods: if this should be somewhere else please shift it

please chaps; whats the lightest, easiest to errect (fnarr), tallest and (naturally) cheapest way of getting a decent length of telescopic radio mast?

Cheers

Jez

I know someone who has the odd BT towable mast from time to time. Beast of a thing though, s'about 18 ft long folded down

[ThreeSheds]

Hi,

I was looking at a SAMLEX Mod. DX27 CB Radio / Car Radio Splitter which apparently allows you to receive FM/LW/MW radio stations via your CB Radio Antenna and I wondered if anyone has any opinions on them?

They look like this:

and, although the above is an eBay image, Thunderpole are very much cheaper

Cheers,

Roger

[pux]

Yes i had one fitted to my old 110 and found it to be a good bit of kit.

[TheRecklessEngineer]

I'm slightly skeptical.

As far as I remember from my electromagnetics* the amplitude of a signal in an aerial is dependent on it's length and the wavelength of the signal.

The long 'whip' type CB aerials are 1/2 a wavelength long at 27MHz. At about 100MHz, they would be a shade over 4 x the wavelength. This would result in a very poor signal.

Shorter CB aerials may work better. It is too early in the morning to crunch the maths.

Personally, I'd separate the two systems. CB aerial for the CB, FM aerial for FM.

*I nearly failed that module, so I may be talking out of my arse here...

[western]

Samlex is usually good kit, but seperate antenna would be much better for both units.

[SacredDog]

I'm slightly skeptical.

As far as I remember from my electromagnetics* the amplitude of a signal in an aerial is dependent on it's length and the wavelength of the signal.

The long 'whip' type CB aerials are 1/2 a wavelength long at 27MHz. At about 100MHz, they would be a shade over 4 x the wavelength. This would result in a very poor signal.

Shorter CB aerials may work better. It is too early in the morning to crunch the maths.

Personally, I'd separate the two systems. CB aerial for the CB, FM aerial for FM.

*I nearly failed that module, so I may be talking out of my arse here...

I use these, they work extremely well certainly as well as the 'standard' car aerials I have replaced. I've had a quick look inside and they seem to simply filter out about 27MHz for the CB signal and block 27MHz for FM.

I wouldn't be concerned about the length of mobile CB aerials even a full length 1/4 wave at 27MHz is about 9Ft long and most are only about half that and Base loaded, so the active part of the aerial is almost ideal for 100MHz.

The filters also tune the aerial a bit so it can improve the SWR slightly for a badly tuned CB aerial.

Colin.

[TheRecklessEngineer]

I use these, they work extremely well certainly as well as the 'standard' car aerials I have replaced. I've had a quick look inside and they seem to simply filter out about 27MHz for the CB signal and block 27MHz for FM.

I wouldn't be concerned about the length of mobile CB aerials even a full length 1/4 wave at 27MHz is about 9Ft long and most are only about half that and Base loaded, so the active part of the aerial is almost ideal for 100MHz.

Colin.

I stand corrected!

[TSD]

The filters also tune the aerial a bit so it can improve the SWR slightly for a badly tuned CB aerial.

How does it know if the antenna is too long or too short?

[Anderzander]

I presume it must be able to read the SWR? Where if the reading on Channel 1 is greater than the reading on Channel 40, your antenna is too short and you'll need to lengthen it. If the reading on Channel 1 is less than the reading on Channel 40, your antenna is too long and needs to be shortened.

[SacredDog]

How does it know if the antenna is too long or too short?

I presume it must be able to read the SWR? Where if the reading on Channel 1 is greater than the reading on Channel 40, your antenna is too short and you'll need to lengthen it. If the reading on Channel 1 is less than the reading on Channel 40, your antenna is too long and needs to be shortened.

No it does know if it's too long or too short or read any SWR. It's simply a filter.

I don't know exactly how it works I just noticed that with an antenna that was previously about 1.8:1 (at band edge) it came down to about 1.5:1 with the Splitter in line. That was on Channel 1 CEPT with an antenna previously tuned for UK band, UK band was a fairly flat 1.2:1 across the band with or without the Splitter.

Colin.

[TSD]

No it does know if it's too long or too short or read any SWR. It's simply a filter.

I don't know exactly how it works I just noticed that with an antenna that was previously about 1.8:1 (at band edge) it came down to about 1.5:1 with the Splitter in line. That was on Channel 1 CEPT with an antenna previously tuned for UK band, UK band was a fairly flat 1.2:1 across the band with or without the Splitter.

Colin.

It 'works' in one of two ways : either the mismatch added by the filter tuned out the mismatch of the antenna (in which case you were just lucky and it won't be the same for a different radio/antenna/install), or (far more likely) it's just lossy.

Putting a loss in the cable between meter and antenna improves the measured SWR. Your SWR numbers suggest a loss of around 30%. Sounds a lot but you won't really notice it in normal use.

The point is that while the measured SWR has improved, the real match of the antenna hasn't changed, and the transmit power has decreased slightly, so the radio performance is worse, not better.

[ThreeSheds]

I must get a decent SWR meter one day - I had a cheap one that showed about 1.3 across the range and I thought 'great - the antenna is good straight out of the box' and then one day I forgot to put the twig in place and guess what - still 1.3! The meter obviously needed to be "earled" - straight in the nearest bin!

On the splitter - I think that on balance, opinion (of those that have tried them) appears to be that they work well, so I think I'll get one.

Thanks for the help chaps!

Roger

p.s. Another related question has just occurred to me - on the RRC, there is a radio aerial amplifier (the black box next to the rear wiper motor) - could it be used between the splitter and the radio?

And more importantly - would it be worth it or would it be better to let the (brand new) radio do it's thing rather than submit the signal to a piece of 20 year old technology?

[western]

the amplifier uses the rear window heating element or side window has a antenna built into the glass

[SacredDog]

It 'works' in one of two ways : either the mismatch added by the filter tuned out the mismatch of the antenna (in which case you were just lucky and it won't be the same for a different radio/antenna/install), or (far more likely) it's just lossy.

Putting a loss in the cable between meter and antenna improves the measured SWR. Your SWR numbers suggest a loss of around 30%. Sounds a lot but you won't really notice it in normal use.

The point is that while the measured SWR has improved, the real match of the antenna hasn't changed, and the transmit power has decreased slightly, so the radio performance is worse, not better.

Yeah, I was wondering that, if it uses a band pass filter (thats what it would appear to be) for the CB it would have to be a bit lossy to cover the entire CEPT/UK bands. That would also make sense with me not seeing any change of SWR in the UK band (for which it was tuned).

Colin.

[mike4444244]

Hi

Bit OT sorry but I know there are a few radio wise people on here, I have a pair of motorola T5710 walkie talkies, they came from the US am I allowed to use them over here? My intended use is to talk to my pillion/other riders when on my bike, I'm not sure if its legal because the frequency range may be wrong? AFAIK the channels range from 462.56-462.72Mhz. Secondly, if I do use them am I likely to interfere with anyone/anything important? I think they are quite short range?

Can you tell I have no idea what I'm on about

Mike

[SacredDog]

Hi

Bit OT sorry but I know there are a few radio wise people on here, I have a pair of motorola T5710 walkie talkies, they came from the US am I allowed to use them over here? My intended use is to talk to my pillion/other riders when on my bike, I'm not sure if its legal because the frequency range may be wrong? AFAIK the channels range from 462.56-462.72Mhz. Secondly, if I do use them am I likely to interfere with anyone/anything important? I think they are quite short range?

Can you tell I have no idea what I'm on about

Mike

They are definitely illegal to use in the UK, I've got a feeling those frequencies are allocated to 'Licenced Operators' by which I think they mean Security people & the likes of Outside Broadcast comms. In which case they would be very upset if you interfered with them and OFCOM could be monitoring their use (since they pay a lot for their Licences apart from anything else). But I guess the chances of you actually interfering with anyone is fairly slim, getting caught transmitting by OFCOM would be slightly higher and actually getting physically caught even slimmer (depending on how fast your bike is ).

Colin.

[mike4444244]

Ok cool thanks for that! looks like I'll have to get some uk spec ones...

Mike

[nicksmelly]

461 Mhz up to 462.450 Mhz is used by the fire brigade for their personal radio's. But up until 2001 461.500 Mhz up to 462.950 Mhz was used for SRBR (Short Range Business Radio). Kenwood and Motorola released a couple of different radios that used this band. The Kenwood TK361 and the Motorola Handi-Com. They were restricted to 500 mW and you had to pay £15 a year for a licence. I've still got a few that I occasionally use, and have not had any problems with interference to or from anyone.