Complex Ionospheric Propagation Modes
I found this image on a wonderful site regarding the many facets of ionospheric propagation:
There is also a very interesting PDF available for download here:
This paper confirms something that I have experienced on 160M, which is “ducted mode” propagation. In the diagram above, this is the blue line, and basically, rather than having your signal bounce between the ground (or water) and the ionosphere, it gets “tunneled” within a channel in the ionosphere, resulting in very low signal loss – as opposed to your signal buncing off the ground. This is where a station very far away comes in amazingly strong. I have experienced this with VK0EK, FT5ZM and a V51 station. Here is what the author of what this paper says:
“You may not realize it, but a considerable number of DX openings on Topband over distances
greater than 4,000 kilometers may owe their occurrence to a phenomenon known as signal
Its impossible to really know if I experienced this form of propagation, but I do remember having a hand held 2 meter radio standing in my back yard on Mt. Davidson in San Francisco, and talking to someone on a simplex frequency in San Juan Bautista – where he sounded like a local. Sure – it wasn’t HF – but it was a form of ducting – due to an inversion.
Since 160M is just above the AM radio band, and because when I was a kid I had built a crystal receiver to listen to the local AM radio station – I’ve always had a romance with this part of the radio spectrum. In fact, before I became a ham I was an SWL and did a lot of BCB DX-ing. I recently bought a used Palstar R30CC:
and Wellbrook ALA1530LNP loop receiving antenna:
and this combination makes it fun to see what I can hear at night. Its a “place holder” while I wait for DX to pop up on Top Band.
So – now you know the reason why I started new blog with the name that I am using – these complex propagation modes that enable very long distance DX-ing on 160M are simply magic – and something that while you can’t count on, when it does happen – its way more memorable than simply pointing your yagi and throwing full steam (on 20M and above) at the DX and almost taking it for granted. Like shooting fish in a barrel?
Top Band DX-ing is easily the most challenging and rewarding band – and the one place in this wonderful hobby where I don’t see an end to the fun. Its my new “chapter” – my new pursuit.
I also plan on concentrating on all bands from 160 – 30M, and my station has become an (almost) 100% dedicated low band station. This happens to fit where I am at with my goals and also where the sunspot cycle is heading (we’re already there me thinks). As you remember, 40M is my favorite “every day” band. It offers great DX year round and sunspot cycle round . . .
My NEW DXE 40M phased vertical array will be featured soon. Stay tuned.