How far does a 50nW (legal!) FM transmitter actually reach

[paulsherwin]

Mine also has relatively low deviation unless the mp3 files have been normalised to 0dB, but it's usable and the quality is otherwise good. I use 87.5 and do get swamped by adjacent cars occasionally.

[Karen O]

I once bought a mono device from a certain UK low cost retail chain and noticed the very low deviation. It turned out that it was a simple crystal oscillator being pulled by a varicap.

50nW is probably about what would leak from an unscreened oscillator without an aerial!

[G6Tanuki]

Originally Posted by HamishBoxer

I used to think but never tried putting an aerial on the o/put of an RF modulator VCR.Not sure how far around or if the house it would travel.

I'm reminded of the early-days of VCRs when someone in a block of flats mis-wired things - feeding the RF-Out of their VCR into the communal-aerial outlet in their flat, rather than into their TV.

Apparently the other residents in the block of flats were treated to some interestingly-pornographic breakthrough for several evenings until the problem was tracked-down.

[arjoll]

Originally Posted by paulsherwin

I use 87.5 and do get swamped by adjacent cars occasionally.

Here, in most cities that'd get swamped by at least one unlicensed LPFM station running their legal 1 watt
on 87.6. It can be really tricky finding an unused FM frequency in many areas - LPFM in the guardbands, and a commercial station every 800 kHz in the licensed part of the band.

[crackle]

When I tested the range of my Cygnett FM sender in the house, my son drove about 200 yards down the road before he lost the signal completely.
On his return though he did not pick it up again until he was back in the drive.

Mike

[paulsherwin]

Originally Posted by arjoll

a commercial station every 800 kHz in the licensed part of the band.

I'm really surprised to hear this works commercially. Here the FM band is only really 'full' in parts of London. Elsewhere it varies, but here in Oxford (150,000 people) there are only 5 clearly audible stations above 100MHz, and one of those is a low powered community station which only covers part of the city (their coverage map is extremely optimistic, presumably to encourage advertising ). Partly this derives from historically conservative licensing by the regulator, but it's mostly just economics - you need a certain number of listeners to interest advertisers.

[Otari5050]

Originally Posted by arjoll

Here, in most cities that'd get swamped by at least one unlicensed LPFM station running their legal 1 watt
on 87.6. It can be really tricky finding an unused FM frequency in many areas - LPFM in the guardbands, and a commercial station every 800 kHz in the licensed part of the band.

I was just about to ask whether the UK has what we Kiwis know as LPFM or the equivalent of when I saw your post, but then realized you're here in the land of the long white crowd as well!
I won't de-rail this thread with a discussion on LPFM in NZ, but if anyone can tell me about it in the UK I'd be most grateful.

['LIVEWIRE?']

As Paul Sherwin has said, we have Low Power Community stations in the larger towns & Cities, plus RSLs (Restricted Service Licences) These are either issued for temporary broadcasts from events such as Air Shows, etc., or to colleges, hopitals, BFBS, and other organisations who operate low power stations serving a limited area. AFAIK 87.6 or similar is used for temporary stations

[paulsherwin]

There is no equivalent of LPFM or FCC Part 15 in Britain, where broadcasting has always been tightly regulated. All legal FM broadcasting is individually licensed and all unlicensed FM broadcasting is illegal. The only legal unlicensed transmitters are below 50nW and must have gone through the EU approvals process, though the EU marks are widely faked.

In practice, Ofcom enforcement activity is concentrated on commercial pirate stations in large cities, who often operate substantial rigs and have criminal connections. If you keep a low profile and don't make a nuisance of yourself, a knock on the door is unlikely, and initial enforcement action is likely to be a sternly worded letter ordering you to desist.

[MrBungle]

Incidentally my little transmitter has not arrived yet. I'm going to connect it to my power meter and do some experiments when it does arrive and see what the deal is. I can't measure ERP easily but I can measure the power delivered to the antenna at least which should be in the order of 50nW but probably isn't

[David G4EBT]

This debate resurfaces periodically and provokes much speculation as to what is or isn't legal.

There is no approvals process as such for commercially manufactured equipment - just a requirement that the equipment complies with the 'R&TTE Regulations' (The Radio Equipment and Telecommunications Terminal Equipment Regulations 2000, SI 2000/730 (as amended). It's down to the manufacturer to ensure that the equipment does comply.

The regulations apply not just in the EU, but throughout the European Economic Area (EEA), which includes EU countries and also Iceland, Liechtenstein and Norway. It allows them to be part of the EU’s single market. (Switzerland is neither an EU nor EEA member but is part of the single market).

(Brexit won't change anything with regard to the UK legislative/regulatory process on matters such as this).

Quite simply, if any transmitting equipment - however minute the power - doesn't comply with the R&TTE regulations, it's illegal.

The best place to gain a better understanding of the R&TTE regulations is from the FAQs at Ofcom's Website:

Frequently Asked Questions on the Radio and Telecommunications Terminal Equipment (R&TTE) Directive 1999/5/EC

FAQ:

8-<

Are there rules for selling radio equipment in the UK?

Yes. Before radio equipment can be placed on the market or put into service it must comply with UK regulations known as the 'R&TTE Regulations'.
(The Radio Equipment and Telecommunications Terminal Equipment Regulations 2000, SI 2000/730 (as amended)).

8-<

So, 'placed on the market' imposes a legal duty on the seller, and 'put into service' places a legal duty on the user.

https://www.ofcom.org.uk/spectrum/information/rtte_faq

Hence, it is illegal for example, to use widely popular items such as the SSTRAN anywhere in the EEA, or to sell or put into use products such as the 'Spitfire' (AM MW) micro-transmitter, as it does not, and cannot, comply with the regulations. Certain UK firms seek to get round that with a disclaimer by saying it may not be used for its intended purpose. Nice try, but such disclaimers are meaningless. If it looks like a duck, walks like a duck, swims like a duck, squawks like a duck - it's a duck. The seller cannot transfer responsibility for compliance to the buyer. I don't think this is keeping anyone awake at night, but if Ofcom did want to make an issue of it, a prosecution could ensue, as this OFCOM FAQ makes clear:

FAQ:

Can't I just put a disclaimer on my website or on the radio equipment itself?
No . This would not alter your legal responsibilities.

8-<

Ofcom does not have the power to make its own rules and it's an enforcement body - not an approval body:

FAQ:

8-<

Can Ofcom approve radio equipment as compliant or give advice?
No - Ofcom is an enforcement authority

8-<

But who cares? Not Ofcom. Who's complaining? No-one.

The reality is that micro-transmitters just aren't of Ofcom's radar and unless or until they do cause a problem, that will remain so. They cause no problems to other spectrum users and it's such a trivial matter compared with Ofcom's huge problem which Paul has alluded to, with illegal and unregulated FM transmitters in every large town, linked to organised crime. Ofcom have minimal enforcement resources and their overriding concern is that interference is not caused to essential services such as air traffic control and the emergency services, which could have a bearing on safety.

There is of course a wide range of legal applications for low power RF devices such as wireless intruder alarms, baby monitors, central heating controllers, intercoms and the like. Then there's the PMR446 licence-free service introduced in the UK in April 1999 which permits commercially produced two-way communications equipment ('walkie talkies') using up to 500mW.

In 2003, PMR446 replaced the former short-range business radio (SRBR) service, often used on construction sites and at sporting events. PMR446 compliant equipment may be used anywhere throughout Europe (except in Montenegro). However, PMR446 radios use frequencies that in the U.S. and Canada are allocated to amateur radio operators, so PMR446 radios can only be used in North America by licensed amateur radio operators.

The range of remote RF key fobs for cars never fails to amaze me. Mine has a range of about 250 Metres.

Have fun - a good motto is lyrics of 'The Beautiful South' - 'Carry on Regardless'!