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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Wilksey on August 29, 2014, 10:55:06 am

Title: Radio Duty Cycle Question
Post by: Wilksey on August 29, 2014, 10:55:06 am

Hi,

Can someone please clear something up that I have been wondering for a while?

I have several 869MHz transceiver modules, 500mW which is capable of around 1km with a decent directional antenna, I have 4 of these working as a control system for home automation experiments.

Setting aside the fact I could use a lower power module, the higher powered ones were cheaper in this case as a bulk buy from Ebay, I have read several specs that state that we have to abide in the UK (and Europe) by a 10% duty cycle, it doesn't make it clear if this is per device or per system.

For example, the controller sends a "heartbeat" message every 250ms and the transmission burst lasts for 11ms, the sensors (switches, lamps etc) send their response on a random radio "slot" within 200ms of receiving the message from the controller which lasts for 6ms.

I have calculated that 11ms every 250ms is roughly 4.5%, and 6ms every 250ms is roughly 2.5%

Now, does this mean that the 10% limit is on the entire combined calculated percentage of the system (for ex, 2.5% * 3 + 4.5% = 12%), or does it mean that as long as each device is below 10% it will be OK to use?

Thanks!

Title: Re: Radio Duty Cycle Question
Post by: fcb on August 29, 2014, 11:09:42 am

From what I understand it's per device.

Title: Re: Radio Duty Cycle Question
Post by: PA0PBZ on August 29, 2014, 11:20:48 am

It is per device, but please have a look at the following:

(https://www.eevblog.com/forum/projects/duty-cycle-requirements-for-ism-band-radio/?action=dlattach;attach=60333;image)


(from https://www.eevblog.com/forum/projects/duty-cycle-requirements-for-ism-band-radio/ (https://www.eevblog.com/forum/projects/duty-cycle-requirements-for-ism-band-radio/)  where we discussed this also.

Title: Re: Radio Duty Cycle Question
Post by: Wilksey on August 29, 2014, 11:38:42 am

Hi,

Thanks for the responses.

PA0PBZ,

I have the TI app note, what does it define as "on" though? The device being powered on?
If so, then it will be on constantly but after 11ms of transmit time, the remaining time of the 250ms is in listening mode (even longer in listening mode for the sensor end).
Does that mean then, that for a period of 1 hour I can only power the radio module for 6 minutes or I can transmit for 6 minutes (not continuously)?

I thought that it only applied to transmit as when something is listening it isn't really doing any harm, but maybe I am wrong?

Thanks

Title: Re: Radio Duty Cycle Question
Post by: PA0PBZ on August 29, 2014, 12:03:22 pm

'ON' is the transmitter being on, so you're good.

Title: Re: Radio Duty Cycle Question
Post by: Wilksey on August 29, 2014, 12:36:49 pm

Thank you for the clarification!

Much appreciated.