23 Sep Tools for VHF propagation
Last Updated on May 14, 2021
Working VHF DX is a lot of fun, but it can be challenging. I’ll show you the tools for VHF propagation I use to work VHF from -20 to 40 over.
The 6 and 2 meter bands can be a lot of fun, after all, they don’t call 6 meters the magic band for nothing. These bands come to life as we come out of winter and head towards summer. In the southern states of Australia, 6 meter activity kicks of late October with big signals from one end of the country to the other, even New Zealand, JA and beyond.
There are two methods of VHF propagation, tropospheric ducting, and Sporadic E.
Tropospheric ducting, or tropo as it’s affectionately known to the locals, is the signal propagation along a temperature inversion. The tropospheric layer is from sea level to 10km above the surface of the planet and is where all of our weather happens.
Sporadic E is the second type of VHF propagation. This occurs at much higher altitudes as the name suggests, in the E layer, some 90 to 12km above the ground. Either way, both these methods of propagation ramp up as we come into summer.
There’s more activity in the early morning here in the southern states and it’s not uncommon to hear dozens of locals on the bottom end of 2m when the band is open.
As the bands come to life, signals will slowly come out of the noise, but you can still work distant stations digitally. WSPR stands for Weak Signal Propagation Reporting and operates on all bands.
WSPR sends and receives low-power data transmissions consisting of Callsign + 4 digit locator + dBm transmit power, a total of 50 Bits. The program can decode signals with a signal to noise ratio as low as −34 dB in a 2500 Hz bandwidth.
Even if you don’t have WSPR capabilities, you can see LIVE propagation on the band of your choice in your region on the WSPR website. You can see the band come to life with increased reporting between stations as well as the direction of propagation. This means you’ll know which way to point your antenna.
VK spotter is another interactive website for real-time monitoring of the amateur bands. As beacons are heard and contacts are made, registered users post ‘spots’ which draws a path on a map between stations. Again, this is a site for those who are interested in propagation. The site supports multiple bands and emissions, and a chat which is for those to try to establish a reliable contact.
As VK spotter is all user-generated data, it’s a great place to find current information on beacons around the country, like if it’s on air.
VK Spotter also has a PSK reporter viewer, a distance and bearing calculator and also a tropospheric propagation map which gives a visual indication of tropospheric conditions.
While on the subject of tropo ducting, William Hepburn’s DX Info Center is another reputable source of band conditions. The Hepburn charts, as they’re often know as, offer a 6 day tropospheric forecast of all the entire world, but the Australia and New Zealand region is what we’re interested in.
Here you can step through the forecast maps and plan ahead. The Hepburn Tropo Index is the degree of tropospheric bending forecast to occur over a particular area, which is an indication of the overall strength of tropospheric radio signal strengths on a linear scale from 0 to 10.
It’s worth noting, overland paths are usually the strongest at sunrise and weakest at mid-afternoon. Water paths are usually the strongest at mid-afternoon and weakest at sunrise and the combination of land and water paths may peak at various times depending on the local weather conditions.
Keep in mind that since tropospheric propagation occurs in the lowest part of the atmosphere, local terrain has a great impact. Significant variation in signal strengths/interference can be expected depending on local effects, often between locations only a few miles apart. This is especially true during elevated-ducting events, where elevation becomes increasingly important.
Unstable signal areas are shown by areas enclosed with dotted lines labelled “U” are areas that may have isolated or scattered heavy rain showers or thunderstorms which could occasionally disrupt paths and cause unusual and sometimes rapid variations in signal strengths. This usually occurs when the lower atmosphere is stable, but the middle & upper atmosphere is unstable. This is most pronounced at night and also ahead of warm fronts.
So now you have the tools, it’s time to get on the air.
The easiest way to get on the air digitally is by using a radio with a provision for USB audio. You’ll find this feature in most modern radios, else you might have to get the soldering iron out and make some cables.
There are many software options to choose from for digital radio, and my software of choice is WSJT X which is open-source software designed for weak-signal digital communication by amateur radio. It does WSPR, FT8 and a raft of other digital modes including MSK for meteor scatter enthusiasts.
When the bands seem dead, chances are you just can’t hear the activity… but chances are, your computer can! So in order of appearance, firstly check WSPR for activity, then FT8 or SSB or both depending on the state of the bands. On 6m, many start on FT8, and as the signals become stronger, QSY to voice. Once FT8 signals rise to -10 to 0dB, it’s time to go voice. Don’t forget the 6m and 10m beacons which are dotted all over Australia which are also great indicators of band conditions.
Between 6m and 2m is the FM broadcast band and this too can be monitored for band conditions.
So as we head into spring each year, it’s time to tune up antennas, dust off the radio and update your software. Working DX on these bands is very rewarding and it’s open to all classes of licence.
Catch you there!