Unregulated frequencies

[anon]

Hi,

Hi,

I wonder if anyone can point me in the right direction.

I'm a hobbyist building a timing system for use in amateur bicycle
races in the UK. Commercially available systems use RFID tags and cost
many thousands of pounds. We don't need something that gives
world-record levels of accuracy so I decided to design a cheaper
system.

The way it works is this: each competitor carries a small circuit with
a microcontroller and passive receiver. On each lap, they pass over an
induction loop. This triggers the microcontroller, that has a crystal
controlled oscillator. It saves the lap time, and at the end of the
race they are all uploaded to a computer. It's a lot simpler than an
RFID system that would need to read multiple tags simultaneously. And
at the end of the race everyone has to return their expensive tags or
else they don't get their times.

I've managed to get prototypes working at both 8khz and 125khz (RFID
frequency).

My understanding is that frequencies below 9khz are unregulated in the
UK, though presumably there may be other restrictions on emitting
magnetic / electromagnetic radiation below these frequencies (EMC
considerations?)

I would prefer to use 125khz as this would be less likely to interfere
with hearing aids, pacemakers or heart-rate monitors. The power I need
is far less than the power that an active RFID tag requires. So I feel
my system would be unlikely to interfere with anything that a legal
RFID transmitter would not interfere with. But I can't find anything
that confirms this frequency is unregulated and believe me I've looked
hard. My tags aren't technically RFID tags as they only receive, and
don't transmit.

So which frequencies might be legal for me to use? And are there any
other restrictions on power output?

Thanks.

 

[Luhan]

My understanding is that frequencies below 9khz are unregulated in the
UK, though presumably there may be other restrictions on emitting
magnetic / electromagnetic radiation below these frequencies (EMC
considerations?)

There are some principles of US law that may apply here. One is that
you can really use any frequency you want if it does not radiate past
your property line. Another is that infringements are mostly based on
interference with 'other services'.

If you are making something for sale, of course, its a whole different
picture. You need to jump thru lots of hoops.

Making 'one off' projects seldom gets you in trouble unless you really
piss off somebody. I have personally 'witnessed' several over the
years.

Note: this is not legal advice; I am not an attorny.

Luhan

 

[John - KD5YI]

anon wrote:




There are some principles of US law that may apply here. One is that
you can really use any frequency you want if it does not radiate past
your property line. Another is that infringements are mostly based on
interference with 'other services'.

Hi, Luhan -

Can you please cite a reference regarding radiation within the confines of
one's property line? In many passes through Title 47 of the Code of Federal
Regulations, I have never seen any such property line statement. Most of the
regulations of which I am aware concern not exceeding specified volts/meter
at a specified distance (3 meters, 30 meters, etc). One exception is the
100mW final stage input power with antenna/lead-in/ground of not more than 3
meters on the AM broadcast band.

If I am wrong, I would appreciate the correction.

Thanks.
John

 

[Luhan]

John - KD5YI wrote:

Hi, Luhan -

Can you please cite a reference regarding radiation within the confines of
one's property line? In many passes through Title 47 of the Code of Federal
Regulations, I have never seen any such property line statement. Most of the
regulations of which I am aware concern not exceeding specified volts/meter
at a specified distance (3 meters, 30 meters, etc). One exception is the
100mW final stage input power with antenna/lead-in/ground of not more than 3
meters on the AM broadcast band.

If I am wrong, I would appreciate the correction.

This is not taken from FCC regs, it has more to do with property law.
I do not remember the reference. It may not in fact exist.

Much of my comments are simply common sense. What is legal is one
matter, what is practially enforcable is another. I've seen many
projects on the internet using 'illegal' transmiiting devices,
including the guy who use the innerds of his microwave oven to light up
flourescent lamps accross his basement.

I try to be pragmatic in my designs for clients. Many of 'one of a
kind' industrial production and test devices have no certification with
regard to spurious radiation, or meet with UL approval. This is true
for companies I've worked for accross the country.

As far as I know, the FCC does not much snoop around looking for
problems, they simply process compaints from 'other services'. Maybe
you can tell me if this is not so.

Thanks for your unusually polite comments.

Luhan

 

[[email protected]]

The way it works is this: each competitor carries a small circuit with
a microcontroller and passive receiver. On each lap, they pass over an
induction loop. This triggers the microcontroller, that has a crystal
controlled oscillator. It saves the lap time, and at the end of the
race they are all uploaded to a computer. It's a lot simpler than an
RFID system that would need to read multiple tags simultaneously. And
at the end of the race everyone has to return their expensive tags or
else they don't get their times.

I've managed to get prototypes working at both 8khz and 125khz (RFID
frequency).

Run it at the horizontal scanning frequency of local TV's (would be
around 15.75 KHz in the US).

Then the only interference you might have to worry about would be
TV-tax vans

(which in the unlikely even they have actual receivers are probably
looking for the colorburst clock ot the receiver LO, not the horizontal
output)

 

[Luhan]

Run it at the horizontal scanning frequency of local TV's (would be
around 15.75 KHz in the US).

Mental Note: Use 15,750 Khz for clandestine transmissions.

Luhan (Spooky) Monat

 

[[email protected]]

Mental Note: Use 15,750 Khz for clandestine transmissions.

Mental Note:

Cover spy as sprinkler piping installer for golf course. You're going
to need a big antenna to get much range (miles and miles and miles if
the Navy's ELF submarine links are any hint)

 

[Luhan]

Cover spy as sprinkler piping installer for golf course. You're going
to need a big antenna to get much range (miles and miles and miles if
the Navy's ELF submarine links are any hint)

For RF transmission, yes. Not for induction coupling.

Luhan

 

[John - KD5YI]

John - KD5YI wrote:





This is not taken from FCC regs, it has more to do with property law.
I do not remember the reference. It may not in fact exist.

Much of my comments are simply common sense. What is legal is one
matter, what is practially enforcable is another. I've seen many
projects on the internet using 'illegal' transmiiting devices,
including the guy who use the innerds of his microwave oven to light up
flourescent lamps accross his basement.

I try to be pragmatic in my designs for clients. Many of 'one of a
kind' industrial production and test devices have no certification with
regard to spurious radiation, or meet with UL approval. This is true
for companies I've worked for accross the country.

As far as I know, the FCC does not much snoop around looking for
problems, they simply process compaints from 'other services'. Maybe
you can tell me if this is not so.

Thanks for your unusually polite comments.

Luhan

Like you, I suspect that the FCC does not actively look for low-power
unlicensed emissions unless they receive a complaint. However, I cannot tell
you if that is their policy.

Cheers,
John

 

[[email protected]]

For RF transmission, yes. Not for induction coupling.

Yes, but your proposed "clandestine transmission" isn't going to go
very far inductively coupled. Perhaps it's a digital dead drop that
you simply bicycle over each day?

 

[Michael A. Terrell]

Mental Note: Use 15,750 Khz for clandestine transmissions.

Luhan (Spooky) Monat

Why? The horizontal sweep rate is 15.734.34 hz. Do you really think
you can pick up a clean signal less than 16 Hz away from all the TV sets
radiating noise for miles?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Christopher]

I wonder if anyone can point me in the right direction.

I'm a hobbyist building a timing system for use in amateur bicycle
races in the UK. Commercially available systems use RFID tags and cost
many thousands of pounds. We don't need something that gives
world-record levels of accuracy so I decided to design a cheaper
system.

The way it works is this: each competitor carries a small circuit with
a microcontroller and passive receiver. On each lap, they pass over an
induction loop. This triggers the microcontroller, that has a crystal
controlled oscillator. It saves the lap time, and at the end of the
race they are all uploaded to a computer. It's a lot simpler than an
RFID system that would need to read multiple tags simultaneously. And
at the end of the race everyone has to return their expensive tags or
else they don't get their times.

I've managed to get prototypes working at both 8khz and 125khz (RFID
frequency).

My understanding is that frequencies below 9khz are unregulated in the
UK, though presumably there may be other restrictions on emitting
magnetic / electromagnetic radiation below these frequencies (EMC
considerations?)

I would prefer to use 125khz as this would be less likely to interfere
with hearing aids, pacemakers or heart-rate monitors. The power I need
is far less than the power that an active RFID tag requires. So I feel
my system would be unlikely to interfere with anything that a legal
RFID transmitter would not interfere with. But I can't find anything
that confirms this frequency is unregulated and believe me I've looked
hard. My tags aren't technically RFID tags as they only receive, and
don't transmit.

So which frequencies might be legal for me to use? And are there any
other restrictions on power output?

Hello,

You might also consider detection of an "overhead" continuous 40khz
ultra-sonic blast from a tweeter speaker or two.

Then have the listening device on each bicycle for detection and
tripping your micro-controller.

http://www.uashem.com/pageid-65.html

If you can make home brewed circuit boards for the receivers, assembly
would be quick for each unit required.



* * *
Christopher

Temecula CA.USA
http://www.oldtemecula.com

 

[anon]

Hello,

You might also consider detection of an "overhead" continuous 40khz
ultra-sonic blast from a tweeter speaker or two.

Then have the listening device on each bicycle for detection and
tripping your micro-controller.

http://www.uashem.com/pageid-65.html

If you can make home brewed circuit boards for the receivers, assembly
would be quick for each unit required.

It's a nice idea, but my circuit is cheaper and more energy efficient.
It will run for over a hundred days on a CR2032 battery and has a
quiescent power consumption that will let it stay in standby for
several years. It has 11 components overall and fits 35x50mm.

 

[anon]

Run it at the horizontal scanning frequency of local TV's (would be
around 15.75 KHz in the US).

Then the only interference you might have to worry about would be
TV-tax vans

(which in the unlikely even they have actual receivers are probably
looking for the colorburst clock ot the receiver LO, not the horizontal
output)

I didn't know you had tv tax vans in the US. Actually that's a concern
because I don't have a TV and the UK TV tax people are scary.

I think I managed to answer my own question in the end. OFCOM classes
inductively coupled equipment as 'class 1' and you don't need a
license, or approval, or anything. There are just some power
restrictions that one mustn't exceed.

I buy all your comments about 'if it doesn't cause interference don't
worry' but I'm spending other people's time, effort and money on this
system and I want to get it right. If OFCOM stopped me from using it
my name would be mud and I don't want to risk this happening.

The other concern is stopping pacemakers. Whilst unlikely, this
doesn't bear thinking about which is why I wanted to do my due
diligence.

Thanks for all your help

 

[YD]

Hi, Luhan -

Can you please cite a reference regarding radiation within the confines of
one's property line? In many passes through Title 47 of the Code of Federal
Regulations, I have never seen any such property line statement. Most of the
regulations of which I am aware concern not exceeding specified volts/meter
at a specified distance (3 meters, 30 meters, etc). One exception is the
100mW final stage input power with antenna/lead-in/ground of not more than 3
meters on the AM broadcast band.

If you're low powered enough to not be "heard" beyond a few meters, at
any frequency, who's to complain?

- YD.

 

[[email protected]]

I didn't know you had tv tax vans in the US. Actually that's a concern
because I don't have a TV and the UK TV tax people are scary.

No, we don't have TV tax, and even you probably would not get their
attention with a horizontal output inductive transmitter.

But not having a TV - I hear that does confuse them.

 

[Luhan]

Yes, but your proposed "clandestine transmission" isn't going to go
very far inductively coupled. Perhaps it's a digital dead drop that
you simply bicycle over each day?

Yes of course. I was refering back to the original post where you
would ride over it with a bicycle.

Luhan