Changes to VHF licence

[JumbleDuck]

The 1.64 is the difference in gain between an ideal isotropic antenna (EIRP) and an ideal dipole antenna (ERP). Seems a bit OTT for Ofcom to be expecting people to do this.

It would seem easier to do it in the spreadsheet.

 

[Bilgediver]

It would seem easier to do it in the spreadsheet.

They did.

 

[JumbleDuck]

They did.

 

[longjohnsilver]

How many people have been reported as dropping dead by a vhf aerial when in transmit mode? I wondered why so many passengers on my flybridge when sitting close to my vhf aerial never made it home

 

[st599]

It would seem easier to do it in the spreadsheet.

It would be easy for them to add boxes asking for the antenna gain, the transmitter power, the cable used and the cable length rather than ask for EIRP.

 

[JumbleDuck]

It would be easy for them to add boxes asking for the antenna gain, the transmitter power, the cable used and the cable length rather than ask for EIRP.

Perhaps, but I think this is supposed to be an easy, typical-values calculator. One would do more detailed calculations if the spreadsheet suggested a possible problem.

 

[Achosenman]

I've watched this saga unfold. I'm trying to reduce the headache to what I need to do as a sailor and forget the empire-building.

I've done the calculations for my boat. I have AIS, VHF and Radar.
By my understanding, I enter 25W (VHF) + 5W (AIS) + 20W (radar) in the spreadsheet. For my installation, I use a splitter on the VHF aerial so you can't in reality use AIS and VHF simultaneously, but never mind. I then ran the calculation for the lowest frequency at(155Mhz)and highest at (9446Mhz) and took the worst-case scenario. The output was 2.26m in my case. Can anyone tell me if this is right, or am I off base?

 

[st599]

I've watched this saga unfold. I'm trying to reduce the headache to what I need to do as a sailor and forget the empire-building.

I've done the calculations for my boat. I have AIS, VHF and Radar.
By my understanding, I enter 25W (VHF) + 5W (AIS) + 20W (radar) in the spreadsheet. For my installation, I use a splitter on the VHF aerial so you can't in reality use AIS and VHF simultaneously, but never mind. I then ran the calculation for the lowest frequency at(155Mhz)and highest at (9446Mhz) and took the worst-case scenario. The output was 2.26m in my case. Can anyone tell me if this is right, or am I off base?

You need to take account of the antenna gain on each of those, so with a 3dB antenna the 25W transmitter output would give 50W EIRP.

 

[NealB]

Agree - very techy and not at all easy to get to the bottom of. Followed loads of links and finally found a helpful bit - I'll summarise my understanding:
- you will have to ensure that your radio antenna doesn't come within a certain distance of the "general public". This is not just anyone on your boat and does not include people working (doesn't say why).
- There's a spreadsheet so you can calculate the required distance for your radio
- the inputs are: the power you transmit at, and the frequency
- I input 25W and 162mhz - the answer (safe distance) was 1.6m
- As my antenna is mounted atop the mast - 20m in the air...I comply

Does that align with others' understanding?

Thank you!

 

[JumbleDuck]

You need to take account of the antenna gain on each of those, so with a 3dB antenna the 25W transmitter output would give 50W EIRP.

Why not use their factor of 1.64?

 

[Achosenman]

You need to take account of the antenna gain on each of those, so with a 3dB antenna the 25W transmitter output would give 50W EIRP.

Thank you for this.
The antenna bumpf I have states 0 dB gain, so am I right in thinking this makes the calculation more basic?

 

[JumbleDuck]

I've watched this saga unfold. I'm trying to reduce the headache to what I need to do as a sailor and forget the empire-building.

I've done the calculations for my boat. I have AIS, VHF and Radar.
By my understanding, I enter 25W (VHF) + 5W (AIS) + 20W (radar) in the spreadsheet. For my installation, I use a splitter on the VHF aerial so you can't in reality use AIS and VHF simultaneously, but never mind. I then ran the calculation for the lowest frequency at(155Mhz)and highest at (9446Mhz) and took the worst-case scenario. The output was 2.26m in my case. Can anyone tell me if this is right, or am I off base?

I think you need to do it for each system separately, which will give you a distance for each antenna. Remember to include the effect of duty cycles: AIS only transmits for 26.6ms in every 30s (slow boats) or 5s (faster ones) and radar only points in any given direction for a fraction of the time.

In due course manufacturers will give these figures as a matter of course, if they don't already.

 

[st599]

Thank you for this.
The antenna bumpf I have states 0 dB gain, so am I right in thinking this makes the calculation more basic?

Possibly.

Unfortunately antenna gain can be measured against 2 possible standards.

This is what the x1.64 figure is for on the spreadsheet - to convert from one standard to the other. The safe bet if the antenna spec doesn't say dBi would be to use 25x1.64.

 

[Achosenman]

Possibly.

Unfortunately antenna gain can be measured against 2 possible standards.

This is what the x1.64 figure is for on the spreadsheet - to convert from one standard to the other. The safe bet if the antenna spec doesn't say dBi would be to use 25x1.64.

Oh, it gets better and better. ? Thanks for the help. It's getting time to hand this headache to the installer.
In the meantime, I've run the calculation as you have suggested and assumed I have the perfect storm of everything pinging at once. Now it's 2.89m. Soon we'll all be banned from being allowed anywhere near the boat, let alone sail it. ?

 

[Achosenman]

I think you need to do it for each system separately, which will give you a distance for each antenna. Remember to include the effect of duty cycles: AIS only transmits for 26.6ms in every 30s (slow boats) or 5s (faster ones) and radar only points in any given direction for a fraction of the time.

In due course manufacturers will give these figures as a matter of course, if they don't already.

I suspect many will find out the data isn't available. It's a shame OFCOM don't have something more pressing to occupy themselves with.

 

[Never Grumble]

I think you need to do it for each system separately, which will give you a distance for each antenna. Remember to include the effect of duty cycles: AIS only transmits for 26.6ms in every 30s (slow boats) or 5s (faster ones) and radar only points in any given direction for a fraction of the time.

In due course manufacturers will give these figures as a matter of course, if they don't already.

So I have a 5W AIS with transmitter aerial mounted on my pushpit I'm a yacht so with a relatively infrequent transmit rate, how close can I sit to it? Can I still stand at the wheel or do I need to send everyone down below into the saloon?

 

[JumbleDuck]

So I have a 5W AIS with transmitter aerial mounted on my pushpit I'm a yacht so with a relatively infrequent transmit rate, how close can I sit to it? Can I still stand at the wheel or do I need to send everyone down below into the saloon?

Tin foil hats: not just for The Lounge any more.

 

[agurney]

Well I will start to worry about it WHEN I see reports of random checks by Ofcom demanding yotties demonstrate their compliance with this new regulation.

Until then I will just go sailing.

If you're compliant you won't need to worry at all.

• Do you only slow down when you know there's a speed camera nearby?
• Do you only get an MOT when you hear there are spot checks locally?
• What if you are not compliant but you're the first to be checked?

 

[madabouttheboat]

This is completely ridiculous. Not only is the statement from Ofcom complete gibberish to the average boat owner, it requires calculations that few will understand using figures that most won't have. What on earth were Ofcom thinking, or did they suspend thinking when putting this together?

 

[agurney]

This is completely ridiculous. Not only is the statement from Ofcom complete gibberish to the average boat owner ...

Average boat owners are not the primary audience for these measures; they are are for everyone who who is licensed to use the radio spectrum - so all the Telcos, broadcasters, taxi companies, anyone using RF to transfer data from remote sites, microwave communications, ham radio, and so on.