1 Reply Latest reply on Feb 28, 2013 4:02 PM by jasonrc
      • 1. Re: Why do WICED modules only transmit at around 17dBm?
        Some of the reasons WICED modules are configured to use an internal transmit power amplifier (PA) include :

         

           

        • minimise cost
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        • minimise peak power consumption
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        • high power designs require +5V bias on the PA, which many embedded products do not have
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        • external power amplifiers (ePA) or front-end modules (FEMs) make the module physically larger
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        • higher transmit power translates to increased difficultly meeting FCC requirements at band edges and with harmonics
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        The majority of designs in the embedded & mobility markets use an internal power amplifier (iPA).

         

         

        While the FCC limit is 30dBm, the EU limit is 20dBm EIRP. From that perspective, WICED modules transmit near the upper limit.

         

        The chips themselves usually output up to 18.5dBm (at lower data rates) and the firmware uses a backoff due to tolerance of components and to compensate for differences in mean and peak power.

         

         

        Another thing to keep in mind is the power characteristics at higher-order modulation & data rate. Max power is what you get at 11b rates. For performance clients like PCs or tablets, they will connect at 11n (and soon 11ac) MCS rates much easier. The Tx power at those rates is backed off several dBm just to pass regulatory.

         

         

        So a low bandwidth connection (1Mbps-11b or 6Mbps-11g) from a low throughput deeply embedded device at 17dBm is not as bad as it seems.

         

        It is in fact likely higher Tx power output than you