There's a 8 metre pole at one end with a 19dBi grid, in to CA400 then in to an Edimax 100mW AP. The loss being about 3dB for the 10 metre cable and connectors excluding antenna loss. So around 3 to 3.5 Watts E.I.R.P. The overall result is 15-20dB S/N 3KM away non-line of sight.
The S/N is more than enough for a good connection, until something nearby wipes it out, which I suspect is an analogue video sender or something equivalent. I tried changing channels and channel 13 was a winner for quite some time, but that's being crowded on channel 11 to much now too and causing problems also. So DSL is winning at the moment and that's fine. But there's no real backup link if 3G fails also.
At my end, similar setup, except I swapped the AP for an older series Ubiquiti NanoStation2 with an external RP-SMA on it. However same result. The antenna's are good, I've ran a 10mW analogue video sender over them and then attenuated it slightly to align them as accurately as possible. The picture was to be expected given the low input power, but high gain of the antenna's. However the analogue audio is no good since analogue modulation is restricted to 1Watt E.I.R.P and on a video sender the audio doesn't get a decent amount of output power compared to the video.
Soon though a higher 12 metre aluminium pole gets pulled down and new 5.8GHz air-bridges from Ubiquiti go up. The freq shift should solve the problem, except introduce more path loss hopefully countered by the 4 metre increase. But I'm not holding my breathe. So I started thinking about how reliable the old Smarti codecs were at 32K over POTS (they never dropped at 32Kbps). With TCP/IP that takes us to 26-28Kbps AAC mono, which is good enough for a temporary mono feed of audio around 12-14KHz in bandwidth, better than narrowband 3-4KHz voice. Setting that up is a piece of the proverbial. The exsisting TCP/IP encoder for the out of town links does 64K AAC mono and can output a second feed of whatever needed bitrate. Low enough to just squeeze out of a dial-in link like the Smarti's. Terrible audio quality compared to an expensive $,$$$ DDS circuit with 128K musicam codecs on the end, but a pennies in cost comparison for a group of LPFM stations on a shoe string in an emergency.
I will see how the Air-Bridges go once they are up, or more importantly when the pole comes down for maintenance and they get added.
RE: call times, I would hope not to be using such a low bitrate codec for anywhere near 10 hours at a time, but it's possible more than 10 hours in a cumulative month or longer in a plan c situation. Plan D would be ring on anything and talk at whatever quality patched in to wherever possible. Plan E would be relay National Radio off satellite and don't let the door hit you bolting through it on the way out.
A Client of my old Job ran a satellite feed to pull in a radio station from overseas. They had 2 satellite feeds (Optus and AsiaSat) Their backup was a 128K ISDN BR that called the host country and pulled the audio that way This was not prefered as it was an expensive toll call, but worked very well.
I don't think you will be able to get a tie line from Telecom... But some of the smaller players may be able to jiggle something similar. I've had some friends across the country where you essentially just pay for two UCLFS services and they just tie the two lines together.
More about who you know.... and I'm sorry I won't be able to help you out pointing you to someone that could help.
I work for Spark, but as always my views are my own.