DW1000 Transmit Power

Hi,

We need to configure the DW1000 output power to a very minimal level for regulatory purposes. We need to set the radiated power below -53.3dBm/MHz.

Considering the peak antenna gain is 2.5dBi, the conducted output power should be less than -55.8dBm/MHz. But the output power is -54.7dBm/MHz when the minimum power setting is set to 0dB (Coarse setting = 0dB, Fine setting = 0dB).

In other words, we can’t set the power below -54.7 dBm/MHz. Is it the minimum power value that we can set?

What will be the behavior if we set the setting as Coarse setting = OFF, Fine setting = 0dB. The transmitter will be switched off?

Regards,
Shijo Thomas

What country requires this level of power? It is unusual being 12 dB below typical limits of -41.3 dBm/MHz. I wonder if the regulations have been misinterpreted and you would be fine at a higher power.

Generally, the minimum useful power is when TX_POWER is set to 0 dB.

One way to reduce transmit power is to reduce voltage. The DW1000 can run at 2.8 volts, 0.5 volts less than the typical 3.3 volts. That lowers transmit power by about 1.5 dB. That’s just within what you need.

Another option is to build a circuit where there is a fixed attenuator between the DW1000 and antenna. This will hurt reception sensitivity, too.

Yet another way is to put in some sort of attenuator that only affects the transmit direction. This can be done with an RF switch.

Lastly, the spectral power limits are specified averaged over 1 ms of time. If your packet is short, say under 250 us, and you don’t transmit more often than once in any 1 ms window, then you have a 6 dB power excess you can use. That is, you can transmit at -47.3 dBm/MHz for 250 us and that is -53.3 dBm/MHz averaged over 1 ms.

“Off” is not fully off, there is still some radiation, but it is very weak, so you drop off a cliff in power. My software guys use “off” on their desk when developing code so they don’t transmit a strong signal and mess up our lab experiments. Range is very short, say under 1 meter.

Mike Ciholas, President, Ciholas, Inc
3700 Bell Road, Newburgh, IN 47630 USA
mikec@ciholas.com
+1 812 962 9408

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Hi Shijo,
Just to add that PRF also impacts transmit power. You might be using PRF64, in which case changing to PRF16 should give about 6 dB lower power, as 4 times fewer pulses are transmitted.