Tuesday, October 26, 2010

The 2.4 GHz saga (South African edition)

I have been observing the 2.4GHz radio debacle with interest and amusement. I hoped that SAMAA would keep its nose well clear of this hornets nest aspect of ICASA rules and regulations and would stay focused on the interests of their members, even if it meant ignoring certain irrelevant, unpractical, and in its present form, unimplementable regulations that has no benefit for members, their safety or protecting the radio spectrum. After reading Allen Fraser’s report I have a few comments.

First let’s make a correction. The term used by Allen:

“100 milliwatt and 20-dBm gain (radiated power)”

Do not make sense. I don’t know if this is the way that it was defined in ICASA’s regulations but if that is the case the regulation is null and void to begin with.

I presume that it should have read:

“20dBm (100 milliwatt) effective radiated Power”

ICASA rates transmitter output in terms of dBm (dB milliwatt) this means that the output is compared to a transmitter with an output of 1 milliwatt (1/1000 of a watt) and the difference is expressed in dB. 1 milliwatt is 0 dBm and 20 dBm is 100 times one milliwatt thus 100 milliwatt. The decibel is typically used to indicate the gain of an antenna but in this case I don’t know why the “gain” was added. Effective Radiated Power or ERP is a term used to indicate the power of a transmitter after the gain (effectiveness) of its antenna has been taken into account. For example : if an transmitter has a output of 20 dBm and connected to a 1/4 wave antenna that has 0 dB gain the effective radiated power would be 20dBm + 0dB =20dBm or 100 milliwatt. If a 20dBm transmitter has an antenna with a 3dB gain its ERP will be 20dBm + 3dB=23dBm or 200 milliwatt

If you could double the power of your model plane’s engine the effect would be dramatic but not so when it comes to radio transmitters and thus it is referred to as a gain of only 3dB and has little effect in practice. But in this case it could mean the difference of being a criminal or not, suffering significant financial loss or not.

Measuring the power output of transmitters operating above 1000 MHz (1GHz) accurately are very difficult but measuring the ERP of any handheld transmitters accurately are imposable. At best it would be a calculated guess, not something that would stand up in court. But ERP is not only determent by power output but also by antenna efficiency. A 1\4-wavelength antenna is considered to have 0-db gain, for 2.4 GHz this would be a whip type antenna that’s only about 3 cm long. All type approved 2.4 GHz transmitters have antennas longer than this and are probably 3\4 or 5\4 wavelength long with a calculated gain of more than 3dB and thus a calculated ERP of more than 200 milliwatt!(23 dBm).This makes the regulation a contradiction in terms.

The American 200 milliwatt radio’s that is being referred to, in the report, all carry a FCC certification which is much more stringent than any regulation that ICASA can think of or maintain. I would not agree with the use of any equipment that operates outside our allocated frequencies like for instance 75 MHz FCC certified equipment but in the case of 2.4 GHz it poses no danger and there is no reason that it should affect the SAMAA insurance.

ICASA’s main purpose is to serve the people and protect their communications interests. But like other parastatals (they should really drop the “I”) they have become top-heavy and incompetent. The 2.4 GHz spectrum is under great threat from wireless networks. But they never seem to have the situation under control. In this regard they absolutely will not act against government departments and seems reluctant to tackle big business especially if it involves BEE, instead they go after soft targets like RC pilots. I recently attended a SSE (Specialist System Engineering) road show. This company supply, among other things, telemetry networks that can work without a licence on the 2.4 GHz band. The radios that they supply with these systems have been “type approved” by ICASA and have a power output of 200 milliwatt. The output can be decreased or increased, via a computer interface, if the client requests it. So far only one client has insisted that the output should be decreased to 100 milliwatt ERP. When I asked about possible action from ICASA I was told that ICASA does not care about this band and will not take any action, especially if it involves government or semi-government departments. ICASA must self generate a certain amount of their funds and some of this must have been obtained via the thousands of type approvals that they sell for R4000 every month. I suppose if SAMAA were prepared to pay enough, ICASA would also “type approve” the American 2012 Glider team’s 2.4 GHz radios. This would also solve any insurance problems with FCC type 2.4 GHz radios that were sold by some “recognized dealers” in the past and the ones that were imported by individuals

Best regards,
Piet le Roux

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