• By Howard - edited: May 20, 2021

    I was looking through some Forum posts and noticed a common question - the power output and quality of radios inside of Access Points versus those in Client devices.   

    First of all, and based on economic reality, radio(s) in an AP stand a much better chance of being higher quality radios.   Yes, there are some comparatively  expensive clients, like very large card printers, but overall the manufacturers cost for a radio in any printer is peanuts.   In fact, the radio in that $8-k card printer, is most likely the exact same radio as is used in that $450  handheld printer - although it will likely be installed on a separate board in the larger product..

    Whereas the handheld printer sells 100-k copies a year, the big monsters may only reach 1,500 customers..   The  cost of the radio itself, is based on making a profit in the larger market and therefore its price needs to be as low as possible.   It doesn't matter from an 802.11 perspective, if the customer is charged $400 for that option on the bigger device, it still costs the manufacturer much less than $20 to produce in quantity.

    Less expensive radios use less expensive parts, and for client devices that usually means no additional Power Amplifier (PA) circuitry, smaller or no heat sink, and other reduced features, making for a lower cost product.

    Face it, a single client radio may only be transmitting in short bursts.   An AP on the other hand may be  transmitting long packets much of the day.   Its radios must be much more durable, and are  therefore more expensive.   Even the QA tests on the AP are more thorough and costly. 

    Just as an aside, I once worked with a (RF naive) senior EE who could not understand why an in-expensive client radio would literally burn up, if tested for hours, or even minutes, at a 90+% duty cycle.  These tests, generated by dedicated WLAN testers, can produce millions of complete packets, and hand-shakes, per hour.

    Speaking of burning up, more expensive radios like those used in AP's also (today) have RF power Fold-Back circuity in them, in case it is turned on without an antenna attached.   Many client devices have permanently installed antennas, and require no fold-back protection.  Without an antenna, radios can easily die in mere seconds due to the impedance mismatch.   Just ask a Compliance Engineer running FCC certification tests if you don't believe me.

    Quality manufactures, such as Cisco, have a reputation for publishing reliable specifications for its radios regarding power output, and sensitivity.   Many, if not most, client devices and home AP's however are notorious when it relates to the same measurements.   Just as an example, we can talk about power output claims.   You can safely assume that if Cisco says it put out 17 dBm, at a certain modulation rate, in the 2.4 GHz band, it does that reliably across every channel with probably better than 0.5 dB variation.   If a small AP claims that same power level, you "might " find the average power to be that high, but more likely that is the maximum power level on one of the channels.   Real power levels might actually range anywhere from 11 to 17 dBm.  Which channel is the highest ?   I am not exaggerating, and that 6 dB difference equates to twice the range between two of the channels. 

    Smaller and cheaper radios, in general, have poorer Error Vector Magnitude (EVM) readings and their signals have more Spectral Regrowth which increases Adjacent Channel Interference (ACI).   Either of these factors will reduce maximum range, and increase retry counts. 

    I am NOT saying that you will always expect to get more for your money, with more expensive radios, but it is likely.   One good indicator to a products radio quality, is to ask for the technical specifications on their radios.   

    Look at the technical specifications on a Cisco product, not so much for comparison, but for a list of things they know about the radios.   You'll probably be amazed.   Just don't expect your client devices to compare, especially in terms of sensitivity.

    Based upon personal experience including thousands of quantitative radio tests, and hundreds of indoor and outdoor range tests I can also tell you that when comparing output power, versus sensitivity, that sensitivity has a much more profound effect on range than does power.


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