From a recent post on the AREDN website (www.arednmesh.org), Joe AE6XE calls our attention to a new question in the General class license examination question pool which refers to Amateur Radio Emergency Data Network (AREDN) mesh network transmissions. There may be a problem with correctly answering this question.
Here is what Joe has to say:
G1E08 (B) [97.313(j)]
When using modified commercial Wi-Fi equipment to construct an Amateur Radio Emergency Data Network (AREDN), what is the maximum allowed PEP transmitter output power?
A. 100 milliwatts
B. 10 watts
C. 100 watts
D. 1500 watts
Part 97.313(j): No station may transmit with a transmitter output exceeding 10 W PEP when the station is transmitting a SS emission type.
Ah’o… AREDN devices or commercial Wi-Fi equipment predominately do not transmit spread spectrum signals.
The following standards are in use:
802.11b: Direct Sequence Spread Spectrum in 22MHz BW
802.11a: OFDM — 64 modulated carrier waves in 20MHz BW
802.11g: OFDM — 64 modulated carrier waves in 20MHz BW
802.11n: OFDM — 64 modulated carrier waves in 20MHz BW
802.11ac: OFDM (future use by AREDN)
What is the part97 power limit of a Spread Spectrum signal in these bands = 10 watts
What is the part97 power limit of OFDM or modulated carrier waves in these bands = 1500 watts
What is used on these devices?
A) on 2GHz and 900MHz devices, 802.11b, 802.11g, and 802.11n are used.
B) on 5GHz and 3GHz device, 802.11a and 802.11n are used.
What does this mean? Predominately, AREDN devices do not use Spread Spectrum (SS) modulation (802.11b). AREDN 3GHz and 5GHz devices only use 802.11a and 802.11n or OFDM with 1500 watt limit. On 2GHz and 900MHz SS is generally only used for beacons, broadcast packets, and management frames. All the data ends up using the higher rates in 802.11n. Any given transmitted frame could be using a different modulation scheme, rate, and error correction code than the prior transmitted frame.
While there are 2 answers to this question, the more correct, or more prominently in use, would be ‘D’. But this misses the intention of a question for 97.313(j)…