The Pedersen Ray and Chordal Ducting

The ARRL Extra Class License Book contains the best explanation of why my DX Engineering DV-40-P 40M phased vertical array out performs the low Cushcraft D40 rotatable dipole up only 40′ to ZS on the Short Path at night (the lower angle goes farther and its launched in the dark at my end).

The “magic” that I experience during the morning greyline to ZS on the Long Path and with a higher angle ray – is called The Pedersen Ray. It is best documented in the ARRL Extra Class Manual, and also an explanation I received from Tom, N6BT of Force-12 fame:

“Propagation on low bands with a high angle radiator – the probable method is the Pedersen Wave. This is from a high angle launch and then is ducted across the path (long path) and then dumped out at the termonal end. Had this happen for many years when I was using a 42′ high 3el 40, comparing to N6RO’s at 140′ (which I put up). We were usually equal on LP, but short path was a different story. His antenna always opened earlier than mine and closed later.”

The ON4UN Lowband DX-ing Book (starting on page 1-17) and the Ian Poole, G3YWX RSGB Radio Propagation book (page 49) both describe this, but curiously do not call it The Pedersen Ray, but “Chordal Hopping” or “Chordal Ducting”.

A fun way to find your Antipode –

The ON4UN Book does cover this quite well, but one diagram would have really helped. Some take aways:

  1. Higher take off angles penetrate the E Layer which gets the ray into the duct
  2. The antipode from your QTH is where this ducting is most likely to occur, and year round – because when its your sunrise, its their sunset, and vice versa
  3. Ducting seems to work better at low sunspot times because either excessive ionization or auroral disturbances can wipe out these ducts. Furthermore, there are other forms of ionization that happen during a low SSN part of the cycle – galactic and cosmic rays

When Kat and I visited the Museum of the Rockies in Bozeman, we visited a great show on deep space telescopes and the new research that is being done to measure deep space rays and their influence. What is exciting is that there is still much to discover and learn, and so this is a main reason why I am still a DXer – even after “earning” my DXCC Awards.


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