Operation on 88-108mhz FM band

[VK2AAH]

Hi Richard,

Thanks for the reply and explanation- I'm not having a dig at people like yourself. The technology is great and the price is even better- but as you suggest only the upside is found in the sales blurbs, not the technical limitations or risks. Nothing new in that!

Cheers

Richard

[VK3MIX]

It is no different to those companies (and some country councils are shockers...) who use license free 2.4GHzish spread spectrum links designed for short hop office to office links on broadcast sites to give them a very cheap microwave link.

Hi Richard

As someone who has worked in this industry for about 13 years I can perhaps explain why there are so many class licenced point to point links around. To get 100 Mbps in a licenced link in Sydney used to need a 28 MHz wide channel at about $5000 a year. Newer technology means we can squeeze that to half the bandwidth and cost these days. Smaller companies with a couple of offices, or councils with many sites needing low bandwidth to things like community centres can't afford/justify that. Plus line of sight restrictions mean that often a telescopic mast on the roof is needed, feasible for an antenna but not a licenced microwave dish.

It's been a while since I installed a 2.4 GHz link due to bandwidth limitations as well as interference, though we still have some we service. Most these days are 5.4 or 5.8 GHz, where we can give the customer around 70 Mbps over a few kilometres even off a crowded site like Horsley Park Tower. There are rules as to eirp (4 watts at 2.4 or 5.8 GHz, 1 watt at 5.4 GHz). I know there are cowboys out there who ignore those limits, and I knew of one operator in Adelaide a few years ago running about 200 watts eirp to get a high bandwidth link over about 40km.

These links are designed for long hops though, reading the marketing blurb that comes with them they often talk about 70 or even further kilometres (though of course they fail to mention you won't get the full bandwidth at those distances).

As for causing interference - I am not sure what licenced services there would be in these bands to interfere with. But ACMA I doubt would have the capability to track it down anyway - we had interference on an 18 GHz licenced link near Sydney CBD and they didn't have the equipment to work out where the interference was coming from, despite us paying $10k per year for the frequency.

Note I do also work with licenced microwaves, millimeter wave (70 & 80 GHz) as well as laser comms.

Cheers

Richard

Speaking of 5.8Ghz licensed services. In my area the CFA have a couple right in the middle of the 5.8Ghz band where under the LIPD we are limited to 4 watts without DFS required. Makes you wonder how critical that link is and what it is used for. Under their license it also states..

Special Conditions No interference shall be caused to any Radiocommunication station or service and no protection from interference by such stations or services shall be afforded.

http://web.acma.gov.au/pls/radcom/assig ... ID=2256121