Ofcom made their decision

[trevbouy]

Be careful with your calcs when you use 3dBi the i is isotropic, an antenna in free space with no other limiting factors. As to an antenna with 3dBi that has zero gain in real life, it's put on by the advertising guys to help sell them.
The 25W output is just that, into a nominal 50 ohm load. Use the EIRP calculater for that 3dBi

 

[gandy]

25W electrical output with 3dBi antenna gives an EIRP just under 50W. Treating 3dB as multiplying by two is a pretty good rule of thumb.

 

[Ademist]

Has anybody done the calculation for an icom 801e SSB radio? I hope my radio handset is far enough away from the antenna!

 

[wiggy]

Life is too short, I probably use the VHF for a total of 10 minutes a year, the aerial is 12m above my head and if they check every time they check you licence it’ll never get checked. CBA.

 

[FulmarJeddo]

The RYA have simplified this. It’s not as straight forward as our radios transmit at 25W. That somehow converts to 41 Watts EIRP. A mast head antenna pushes the danger well out of the way. If you use your radio for less than 10% of the time it also cuts the separation distance considerably. Basically we need to assess our own boat and keep a record of it with our license. I copied the RYA info to my club website the other day.

EMF Compliance and Enforcement – Lower Halstow Yacht Club

 

[prv]

I copied the RYA info to my club website the other day.

EMF Compliance and Enforcement – Lower Halstow Yacht Club

Just a heads-up that your link to the Ofcom draft guidance note doesn't work - possibly they've moved it from under you?

Pete

 

[prv]

Also, while searching (unsuccessfully) for the above note, I found a statement from Raymarine. This includes the very useful snippet that:

For current and legacy Raymarine Radars, the compliance distance is within the rotating diameter of the antenna on radar arrays, and within the product casing for Radome products.

Pete

 

[TwoHooter]

I would normally write a spreadsheet for something like this but I simply don't have the time.
Is anyone thinking of doing one and sharing it?
We have 2 fixed VHF transceivers, 1 hand-held, an open-array radar, and SSB.
I believe the twin SSB antennae are potentially a genuine hazard and I have already mitigated that but for the others all I need is something to fill my numbers in and spit out an answer.

 

[mattonthesea]

I would normally write a spreadsheet for something like this but I simply don't have the time.
Is anyone thinking of doing one and sharing it?
We have 2 fixed VHF transceivers, 1 hand-held, an open-array radar, and SSB.
I believe the twin SSB antennae are potentially a genuine hazard and I have already mitigated that but for the others all I need is something to fill my numbers in and spit out an answer.

Ship's Radio I think is this

Ship’s VHF: 25W x 156MHz = 41W EIRP (x10% Use) => 0.65m Compliance Distance

Correct me if I'm wrong

Portable VH>F is not high enough EIRP to be included (fails at first stage on the flowchart )

 

[prv]

Is anyone thinking of doing one and sharing it?

I'm not doing anything till the marine "guidance note" comes out, as I hope it may simplify things.

Pete

 

[FulmarJeddo]

Just a heads-up that your link to the Ofcom draft guidance note doesn't work - possibly they've moved it from under you?

Pete

Yes, thanks, I did notice that after posting it, but I read something in the Ofcom stuff that they were publishing more guidance information soon and assumed the RYA had linked to the page in advance.

 

[TwoHooter]

Ship's Radio I think is this
Ship’s VHF: 25W x 156MHz = 41W EIRP (x10% Use) => 0.65m Compliance Distance
Correct me if I'm wrong
Portable VH>F is not high enough EIRP to be included (fails at first stage on the flowchart )

I hope you are right.
Copy and paste - wait to be told it's wrong!

Seriously - is the 'Compliance Distance' the distance from the VHF set (the actual transceiver box) or the antenna?
I assume it is the antenna.

 

[Buck Turgidson]

Ship's Radio I think is this

Ship’s VHF: 25W x 156MHz = 41W EIRP (x10% Use) => 0.65m Compliance Distance

Correct me if I'm wrong

Portable VH>F is not high enough EIRP to be included (fails at first stage on the flowchart )

10% use would be 876 hours per year.

I would estimate I transmit voice for a cumulative 1 hour per year maximum.

AIS on the other hand........ but it's only 2w at the box.

 

[Daverw]

10% use would be 876 hours per year.

I would estimate I transmit voice for a cumulative 1 hour per year maximum.

AIS on the other hand........ but it's only 2w at the box.

I’ve also just been looking at transmit time, on a typical day sail, 30 seconds to call VTS and then 2x 30 seconds to call lock / Marina so less then 2minutes in 4 hours, do I base the calculations on this?

 

[awol]

So by now we all know the answer - do we really have to show our workings? And anyway, what is this licence thing - are we meant to have one?

 

[JumbleDuck]

I’ve also just been looking at transmit time, on a typical day sail, 30 seconds to call VTS and then 2x 30 seconds to call lock / Marina so less then 2minutes in 4 hours, do I base the calculations on this?

I think their "average" was intended to cover continual but intermittent transmission, like radar or AIS. When this first came out I tried but failed to find out how it was to be applied to occasional transmission, like VHF.

 

[nigel1]

From the notes on the OFCOM calculation spreadsheet. I guess time in use is within any 6 minute period.
So if you spend 1 minute on a VHF transmission, that would be equel to roughly 17%

"However, spectrum users may also choose to enter an average power (e.g. over the six-minute averaging period specified in the ICNIRP Guidelines) which takes account of the duty cycle (or factor) of the equipment and/or the maximum percentage of time that a transmitter will be operating during the averaging period."

 

[Daverw]

Looking at the calc difference for mast head antenna for 17% or 8% not much difference, going to print off spreadsheet for each vhf, radar and AIS and keep these with licence. Job done then. May get a sticky label to put on stern arch to remind all. Still easier than when I put the long wire up and operate my Ham gear with 200watts and sat underneath. Note to myself need to review this.

 

[TwoHooter]

From the notes on the OFCOM calculation spreadsheet. I guess time in use is within any 6 minute period.
So if you spend 1 minute on a VHF transmission, that would be equel to roughly 17%
"However, spectrum users may also choose to enter an average power (e.g. over the six-minute averaging period specified in the ICNIRP Guidelines) which takes account of the duty cycle (or factor) of the equipment and/or the maximum percentage of time that a transmitter will be operating during the averaging period."

The wording does NOT say 'the maximum percentage of time that a transmitter will be operating during the averaging period, such averaging period being when the transmission time is greatest' (my emphasis). It just says 'the averaging period'.

Which averaging period?

Is the averaging period the 6 minutes when I am approaching and entering a lock and making perhaps 2 transmissions of 8 seconds ("Sutton Lock, Sutton Lock, this is Coracle, Coracle, passing Fishers Nose inbound, request lock, over", and 5 seconds ("Sutton Lock, Coracle, understand wait for 3 greens, listening channel 12")? That would be a percentage of 13 seconds / 360 seconds = 3.61%

Or do I take any random 6 minutes during a typical passage during which I make no transmissions at all? Hours on end with not a peep out of me.

Still easier than when I put the long wire up and operate my Ham gear with 200watts and sat underneath. Note to myself need to review this.

Get a tinfoil hat?

 

[Daverw]

Do I need the hair as well? ?