Primarily for general aviation discussion, but other aviation topics are also welcome.
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By PeteSpencer
FLYER Club Member  FLYER Club Member
#1833704
johnm wrote:Having done a bit more reading, as far as I can tell the only kit in a light aircraft that might have a power output and duty cycle that could be relevant is a Mode S ES transponder.


So back to the lead-lined Y fronts after all? :wink:
By johnm
FLYER Club Member  FLYER Club Member
#1833706
PeteSpencer wrote:
johnm wrote:Having done a bit more reading, as far as I can tell the only kit in a light aircraft that might have a power output and duty cycle that could be relevant is a Mode S ES transponder.


So back to the lead-lined Y fronts after all? :wink:



Not really, it's the only item worth doing the sums for and the answer is probably the depth of your seat :D
By Forfoxake
FLYER Club Member  FLYER Club Member
#1853433
Marvin wrote:OFcom have now published their updated, and simplified guidance, for all users including aeronautical bands.

Guidance on EMF compliance and enforcement

This looks a lot more sensible.

Looks like I will only need to bother if my Transponder does not have ground plane (does being earthed to a steel tube fuselage count?) and is less than 10.5 inches from my passenger seat!
#1853436
LAA Statement on this just issued:

Ofcom Issues Revised Guidance on EMF Compliance, Prepared in Conjunction With LAA

Communications regulator Ofcom has issued revised guidance on electromagnetic field (EMF) license conditions that will apply to radio equipment in light aircraft.

Following receipt of communications from Ofcom in April, the LAA made representations that the proposed requirements, while well intentioned, were overly onerous and hard to interpret. As a result LAA engineers Jon Viner and Joe Hadley worked with the regulator to better define the risks from aircraft equipage. Their work, carried out on behalf of other member organisations within the GA Alliance, has resulted in the revised guidance.

The simplified guidance for aeronautical radio users can be downloaded from https://www.ofcom.org.uk/__data/assets/ ... -radio.pdf

In summary:
• If you only use handheld radio equipment, you do not need to comply and do not need to take any further action in relation to your VHF radio.

• If you use fixed equipment with an external antenna and a radiated power of 25 Watts, and you transmit for less than 25% of the time in any six minute period (i.e. less than 1 minute and 30 seconds), you do not need to comply and do not need to take any further action in relation to your VHF radio. (There should be very few situations where operators would need to transmit for more than 25% of the time).

• Aircraft transponders generally have a nominal output power of up to 260 Watts, with a typical antenna gain of 3dB. However, they transmit very short pulsed signals for 0.55% of the time. This means that the average radiated power of this equipment is in the region of 4-5 Watts.

Ofcom has calculated that, in the absence of a ground plane, the compliance distance for this equipment would be in the region of 26cm. However, the presence of an antenna ground plane will mean that compliance distances will be very small (typically much less than 10 cm).

In most cases therefore, no further action will be required, unless an antenna ground plane is not installed AND the transponder antenna is located less than 26cm from a passenger who is a member of the general public. In such cases a compliance check will be required as outlined in the Ofcom advice.
T67M, Paul_Sengupta, kanga liked this
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By T67M
FLYER Club Member  FLYER Club Member
#1853437
Thanks to the LAA for making some sort of sense out of this mess. It is a shame that they did not do the calculation for a DME as this is the other transmitter fitted to many light aircraft. I suspect the answer falls into the same category as a VHF radio, but I haven't done the calculation yet.
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By Ian Melville
#1853439
Steve,
Should that 2nd bullet point be less than 25W?

Secondly not clear if the ground plane should be separate from a metal airframe (tube or skin). The later is often used as the ground plane, but could be touched by a pilot or passenger.
User avatar
By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1853440
My post from page 2...

Paul_Sengupta wrote:Our com transmitters are all a maximum of10W I believe, and transponders are no more than 250W? At least in our puddle jumpers. All the antennas are 1/4 wave ground plane antennas. Thus there should be one standard for all puddle jumpers, and a general statement of "no more/further than x" can be made for all aircraft in the fleet. We shouldn't have to work it all out individually.


Good outcome, thanks LAA people!

I do, however, have to work all this out for my amateur radio station(s)...
Dave W liked this
#1853445
T67M wrote:Thanks to the LAA for making some sort of sense out of this mess. It is a shame that they did not do the calculation for a DME as this is the other transmitter fitted to many light aircraft. I suspect the answer falls into the same category as a VHF radio, but I haven't done the calculation yet.


Ofcom statement says "Please note: you do not need to carry out a compliance check for Distance Measuring Equipment (DME). This is because this equipment only transmits at a very low duty cycle and its average power will mean that compliance distances will be very small (typically 5 cm or less)...."
Last edited by Stephen Slater on Thu Jun 17, 2021 1:44 pm, edited 1 time in total.
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By Marvin
#1853450
Dodo wrote:Can someone explain how a sky echo 2 fits into all this?


Its referenced in the documentation for the SkyEcho.

The power output is too low given the duty cycle.
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By gaznav
#1853466
Dodo wrote:Can someone explain how a sky echo 2 fits into all this?


Here you go, it’s already been done:

Important Pilot Advisory Note Regarding Safety of Radio Frequency Energy
Safe use of this device requires care as to the placement of the antenna. Place the antenna at least 4cm away from any part of your body or that of other cabin occupants. To stop all RF emissions, remove power from the equipment or configure the equipment for receive mode only. Retain these instructions with your maintenance logs/files and for future reference.
Dodo liked this
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