What is listening 10-up?

What use is an F-call? In passing a few weeks ago I mentioned listening 10-up. It's also a slogan I have on a t-shirt, it says: "I'm not ignoring you, I'm listening 10 up." So what does that mean and what do you do when a station tells you that they are listening "up", or "down"? If you're a DX station and you've got a desirable call, it's likely that you'll generate a pile-up, that is, lots of different stations all calling at the same time, trying to get the attention of the single DX station. As more and more stations join in the fray, the remote station will get drowned out by eager hunters who try to call early, or try to call late in an attempt to get the attention of the DX station. The impact of this is cumulative. Over time, the DX station will get buried entirely in spurious transmissions, so making a contact becomes harder and harder, sometimes impossible. I've talked about the rhythm of a contact. If it's all working as expected, the rhythm will help you synchronise your call with that of the remote DX, similarly, all the other stations on frequency will march to the same drum beat. Sometimes this just becomes too hard and a DX station might solve the problem by "operating split". In essence, the station operates two frequencies, their calling frequency, which is where you can hear the station, and their listening frequency, which is where everyone else is calling and the DX station is listening. This makes it possible for the drum beat to continue and for the DX station to not be drowned out. So, how do you do this? On many modern radios you'll have access to two VFOs, you tune one, VFO A, to the DX calling frequency, the other, VFO B, to the DX listening frequency. You'll push the "split operation" button and when you listen, you're listening to VFO A frequency and when you're transmitting you're doing that on the VFO B frequency. A station will announce this by saying something like "listening 10 up", or "2 up", what ever they pick. During contests this is generally frowned on, since it ties up two frequencies, but during normal day-to-day operations it's another tool to make HF contacts possible. I'm not Ignoring you, I'm listening 10-up. I'm Onno VK6FLAB