Spring 2003 Issue

Comments on VK7MO’s
“WSJT Meteor-Scatter Experiences
in Australia”

Following publication of the above-mentioned article by Rex Moncur, VK7MO in the last issue of CQ VHF, your editor asked Shelby Ennis, W8WN, to peer-review it. What follows is his critique.

By Shelby Ennis,* W8WN
 

The Winter 2003 edition of CQ VHF included an article by Rex Moncur, VK7MO, describing Australian experiences with WSJT’s FSK441 high-speed meteor-scatter (MS) mode, plus experiments they ran to determine how VK-style HSMS operation compared with information contained in the classic Meteor Science and Engineering by D.W.R. McKinley (McGraw-Hill, 1961).
Rex has done an excellent job of presenting FSK441 HSMS operation, and a number of the tests go beyond anything that has been attempted in North America. However, there are three things that should be noted:

1. The paper was written for a technical conference in Australia. Thus, several things are specific to the Aussies.

2. Australian equipment and procedures are somewhat different from what is used either in North America or Europe. Unless allowances are made for these variations, some invalid conclusions could be drawn.

3. There were several errors introduced when the artwork was redrawn for publication, which could lead to confusion if details were studied closely. Corrections are on the next page.
Please note that this article is in basic agreement with everything in Rex’s work. As noted above, the primary reason for this article is to show some of the differences between the operating practices and equipment, which could lead the typical North American or European VHF DX operator wondering if the reported results and conclusions are actually true. Also, several points will be expanded slightly.

The Differences

First, some differences between VK and W: In Australia, operators are limited to 120 watts on FSK441. Most run a 150-watt “brick” backed off to about 100 watts. In North America (and in Europe), there probably is no “standard” power. Many run the same 150-watt solid-state amplifiers that are used in Australia. However, a lot of serious VHF DX operators run more power—350 watts, 800 watts, or even a full 1500 watts. Because there is a 3 dB difference between a 150-watt and 300-watt station (and a 10 dB difference between 150 and 1500 watts), the power difference can become quite significant for weak-signal MS work.

A second difference is antenna size. According to Rex, most VK MS operators use single Yagis of around 10 elements (on a 3-wavelength boom). Again, there probably is no “standard” antenna in this part of the world. A single 10- to 16-element Yagi is perhaps the most widespread, but much larger arrays are just as popular. Four-Yagi arrays with antennas of anywhere from 9 to 20 elements are common, and much larger arrays have been used successfully for MS operation.

The size of the array used for MS operation (and thus the sharpness of the main lobe vs. its gain) has long been a major point of discussion for North American operators. This will be examined in more detail under the heading “Antenna Gain” below.

A third difference of some of the VK tests is that much of the Australian outback is flatter than the parts of North America where many of us live. While this should have a relatively minor effect on the results, it does introduce differences that may be noticeable to some.

Many of the Australian tests (and some of the examples from the equations) used shorter distances than the schedules typically run in North America. How much difference this makes depends upon a number of factors—primarily the local terrain and antenna height, but also the power level and antenna size.

Click here to return to this month's highlights
 

Click here to subscribe to CQ VHF and read more of
Comments on VK7MO’s  “WSJT Meteor-Scatter Experiences in Australia”

_________________

© Copyright 2003, CQ Communications, Inc. All rights reserved. This material may not be reproduced or republished, including posting to a website, in part or in whole, by any means, without the express written permission of the publisher, CQ Communications, Inc. Hyperlinks to this page are permitted.