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03-07-2017 11:24 PM
I'm trying to read the ETSI standard regarding my 868MHz transmitter design.
I would like to transmit in one of the channelized bands ex. (868.600 to 868.700), which has a demand on 25KHz channel spacing.
This sets a huge demand on the frequency error of the system. See table 5 of EN300 220-1. In table 5 it is also stated that the whole frequency band may be used as 1 wideband channel for high speed data, but I cannot find a definition of high speed data. We use 2400bps FSK, is that high speed ?
A crystal of +/-10ppm would result in frequency error of +/- 8680Hz at 868MHz. So this does not leave much space in the channel for modulation of the carrier, and sets high demands on the modulation not spreading into the adjacent channels.
So, I was looking into high precision crystals, like +/-5ppm but these seems expensive, around 3USD which is more than my transmitter IC.
Does there exist any low cost, but high precision 10-12MHz oscillators that can be used for this purpose ?
Solved! Go to Solution.
03-08-2017 03:02 AM
Note that the standard you are referencing is harmonized according to R&TTE which is replaced with the RED. As of now the updated EN 300 220 is not harmonized but it is approved and awaiting publication in the OJ. All product being placed on the market after 12:th of June 2017 has to comply with RED.
The band you are planning on using is a high reliability narrow band intended for wireless alarms. If your product has trouble meeting these standards within budget I would recommend that you move to a different band with wider channels.
03-08-2017 03:59 AM
First of all, thank you for your answer. :-)
If I read the EN 300 220-3-2 Table B.1 correctly, I'm allowed to use the 868.600Mhz - 868.700Mhz band, with an OCW of 100KHz.
This would make the design more easy and low cost, since we could place our transmitter at 868.650Mhz, and use the a 2-FSK modulation with relative high deviation. Also the demand on the frequency error, would be easier to meet.
Or is that not allowed ?
03-08-2017 04:04 AM
I would assume you only need one channel and in that case there shouldn't be any issues with using the whole band as one broad band channel. I interpret the standard the same as you so I would say you are correct.
03-08-2017 04:19 AM
The frequency error is not defined in the new standard as ppm, and seems that it should only be measured and recorded, but there is no limit set on it. And Adjacent channel power only complies to OCW up to 25Khz.
So, if I'm correct, I "just" need to comply to the EN 300 220-1 5.8 Tx Out Of Band Emissions, when using the 100KHz channel ?
(And of course all the other restrictions, about spurious, transient, ect.).
03-08-2017 01:23 PM
Once again I would say you are correct Table A.1 of EN 300 220-3-2 gives a good overview. There are additional requirements that could be affected such as 5.6 Occupied Bandwidth but you should be fine.