VHF ranges

Depends a lot on how far VHF is heard.
When we fly over North Shore we can hear near the entire north island on the open channel. But we do have the advantage of height.

To hear Picton from the H Gulf water level would almost certainly have to be repeated somehow.

I can be over Whangarei and chat to Christchurch Information via VHF but it does use repeaters.

Yeah, but not that far.

HF waves propagate because they bounce off the ionosphere.

VHF radio waves can be refracted by humidity and can curve with the earth but not from Picton.

I doubt a 25W transmitter would even have the range to reach Auckland from Picton even if they had line of sight because the atmosphere would break up the signal.

TROPOSPHERIC DUCTING:

Tropospheric Ducting is the phenomenon responsible for those happy occasions when VHF radios communicate over hundreds (or even a thousand) miles. The “Tropo” effect can occur at any time in any season, but late spring and early fall sunrise and sunsets are the most likely times.

Tropo’ Ducting occurs when humidity and temperature combine to create a wall of ionized particles in the troposphere, typically during a wide-spread temperature inversion. At sunrise, the air aloft is warmed more rapidly than the air below. As the sun begins to set, later in the day, the upper air is kept warm, while the ground cools. This creates a duct, or channel, between the ionized layer. Because sunspot activity increases ionization, certain times within the 11 year sunspot cycle are more likely to produce ducting. The current cycle is increasing through 2004, then will subside until 2009, when the cycle begins increasing again. The next 2 - 3 years should produce some interesting opportunities for VHF’ers to communicate over long distances.

The radio signal is bounced back & forth between these ionized layers, until they find a path back to earth. The result is that your signal may seem stronger 300 - 500 miles away, than it does a mere 15 miles away. As long as both stations are within the duct zone, extremely long range may be experience. The phenomenon is more likely at frequencies above 144 MHz (VHF is 156-157MHz), and most likely between 432MHz & 1296MHz.

So, watch the weather for temperature inversions - you may get the opportunity to do some “Ducting” in the next few years.

There is an on-line “Tropospheric Ducting Forecast” available at:
<http://www.iprimus.ca/~!hepburn/tropo/_nwe/html>

“Basic VHF Radio Wave Propagation” First Draft Copy - June 17/03
Copyright 2003 by Gordon A. May - All Rights Reserved

I think there’s a chance he pressed the wrong button.

But I have heard “Plenty Radio” or “Taupo Radio” frequently enough when I’m in the Gulf that I’m confident that isn’t always operator error but extended propagation.