Sunday, February 3, 2019

Low Band DX - The Idea Bites!

Tuning around the 80m band a couple mornings ago I hear some big signals out of California on 80m - 3.796MHz - chasing DX stations around, that - unsurprisingly - I could not hear at all with my OCFD at around 40ft.

The guys in Cali, one 800 miles south, the other 400 miles south, then started talking between them selves about ZL contacts, and someone I have known for a long time from ZL was mentioned, who has a nice 80m DX station setup. Something I have admired - a 4-square, which is pretty much the gold standard for 80m DX - nice if you have the space! I fired off an email to Nick to say hello, and that I heard these guys talking. Nick replied and said it would be great to chat on 80 some time. Right, challenge accepted!

What I have:
  • 1/4 acre lot with a 70ft Pine tree in the north west corner. 
  • A high noise floor on 80m, S5 to S9 on a horizontal wire antenna.
  • A general class license that limits me to 3.8-4MHz on SSB/AM voice modes, the DX seems to lurk in the upper end of 3.7MHz.

I researched the inverted L, with plenty of long radials these seem to work well on the low bands for DX.

Using a Delta loop came to mind, each side is about 80ft, I have 80ft between the trees at the back and a shorter tree at the front, but lack of height is a problem, I need about 70ft of height at the top of the triangle. Research also suggested that Delta Loops don't work that well for DX compared to other things.

I then remembered an article by W6NBC - High-Efficiency 40m Vertical Without Radials. These are essentially a 1/2 wave vertical dipole, one side is full length, the other leg is shortened, overall the vertical is around 2/3 of full length. In the hope of avoiding running miles of radials I discussed scaling this to 80m with a couple people who have experience with DX verticals, and none of them seemed very keen on it. However, I'm very interested in trying one of these out to compare.

1/4 wave verticals with a good radial system keep coming up as the best option. Some searching turned up a series of articles published in QEX by N6LF - Series of QEX articles on ground system experiments, I found this very informative and cleared up misconceptions I had about radials and ground planes. I have disliked antenna systems that require dozens of radials, its safe to say my thinking has been changed!

Tricky part, how to get something up into the top of that tree? While discussing my insane idea a couple nights ago on a local repeater, one of the guys suggested they know someone with a drone that can carry 25lb loads, and could get something up there no problem! I'm thinking of putting my 43ft vertical from Zero-Five to use. Attaching a ~20ft wire to the top, and pulling that up into the top of the tree to make it up-to a 1/4 wave on 80m.

How it might look from the street. 43 ft vertical will be phase 1. Phase 2 will be to add the 20 ft extension wire and support line from the top of the tree. Not sure of the effect of a "bent" top, but given the tree locations, and where I can fit the vertical in with reasonably symmetrical radials, choices are limited. Approximate but not to perfect scale. 

The proposed radial layout. Radials shown in yellow. Chainlink fence (galvanized) shown in cyan, this extends for some distance east/west down the street. Green is a wooden fence.

The noise floor is the next problem, noise will be much worse on a vertical!

Things to think about:

The last issue, getting full privileges on 80m so I can transmit in the 3.7MHz segment is solved by getting my extra class license.