What is Long Path and Short Path in Amateur Radio?

I have been hearing about Long Path and Short Path ever since I started amateur radio operations in 1985. This was mentioned in discussions over the air by hams having directional beam antennas at that time. As I was active only on 40 and 80 m in those days, I did not hear anyone calling CQ on Short Path and Long Path in those days. We did not have anyone in my region having beam antennas for lower bands. The only HF Yagi antenna which I had seen in those days was a 20 m beam antenna at my Elmer’s location. I also had the opportunity to see a two element 20 m cubical quad at another location. Now we have hams with 4 element 40 m Yagi in my district as well.

For the past few days I have been hearing one VU ham calling CQ Long Path United States and CQ Short Path VK simultaneously. So I could gather that if he beams Short Path to VK, meaning Australia, it would take Long Path to United States as well. The call was heard on 20 m in the evening. So I presumed that he would be looking for grey line propagation to the United States, just as I used work US stations on 40 m CW long back during dawn and dusk for a short period. If you look at the ‘Detail’ tab of any callsign, it will show the distance from your location for both Long Path and Short Path. As an example, I checked my friend N8LI. Bearing was shown as 332.5 degrees NNW, Distance as 13265.2 km, which would be Short Path and Long Path as 26738.0 km. 

Importance of mentioning Long Path and Short Path during the CQ call is that hams hearing the call can direct their beam antennas accordingly if they have one. If they do not have a beam antenna, they could also presume that calls sent to the station on a different direction may not be received well. Even dipole antennas have some directional beaming to both the broad sides and a  null at the ends. So if the broad side of the dipole antenna is not oriented towards the beam of the calling station, reception will be poor and you may not get a reply. This is inspite of the fact that you may be hearing the other station loud and clear, simply because  you may be running lower power and the other station may be using high power with a linear amplifier! HF antennas will have lesser number of elements and  hence lower front to back ratio compared to VHF/UHF antennas with much higher number of elements. So a higher power HF station may be heard fairly well in the reverse direction as well.

Usually good Long Path and Short Path propagations do not co-exist, only one will be dominant at any given time. A path along the Grey Line or Twilight Zone is usually associated with a good Long Path propagation. A circle including both Long Path and Short Path from a station is known as a Great Circle which goes around the globe. A special situation is in which two stations are equidistant on the Great Circle for both Long Path and Short Path. In that situation, the point of the other station is known as Antipode. Long path from your station to a DX station will pass through your Antipode and is more than 20,000 km, which is half the circumference of the Earth. Long Path propagations are better appreciated on 20 m to 10 m HF bands for DX. A look at the approximate Long and Short Paths from my region to the location of N8LI in my way of representing it on the world map will explains why I heard a VU station calling Short Path for VK and Long Path for US. He would have directed his antenna towards Australia.