75 Meter Inverted "L"

    The 75 meter inverted "L" started out to be a gamma matched antenna like the 40 meter. All did not go as planned. My son in-law Mike WY8F worked with me through the construction phase of the of the 66 foot gamma feed vertical, all went well and as planned. I had all the right tools and hands to get the job done, (a note to those who have son in-laws who help with antenna projects, don't let them use the good titanium oxide drill bits as you may have to replace a couple). We got it all constructed and perched on ladders across the back yard and started to push it into place when the aluminum tube below the top mounting bracket stress fracturced and the top 62 foot came back down rather quickly. It also bent the tubing used for the gamma match. Disconcerting to say the least, we disassembled the remaining tubing, put it in a neat pile, and sat on the deck, smoked a good cigar, and pondered over the rather expensive pile of a great idea gone bad. I think had I lined that bottom tube with the next size down and welded it top and bottom we would have got it in the air and all would have been well, like all projects that don't go as planned hind sight is always 20/20. If you looked at the 160 meter antenna on my web site, I have it configured as an inverted "L" and it works quite well. So I got the sawes-all out and cut the tube at the break and removed the gamma match. I had the guy point for the antenna at the 46 foot point on the antenna so that left me with 42 foot of good straight tube from 2.250" and tappered up from there. I added another eye bolt to the top and duplicated what I had done with the 160 antenna.(see photo). I took what was missing in tubing and replaced it with copper clad steel wire. I ran the antenna analyzer against ground, a 10 foot rod driven in at the base, and found it resonant at 3.756 Mhz. Like the other vertical antennas at my site this one was also located in the swamp (I mean natural ground plane) behind the house. I added a DX Engineering Balun - 1:1 5 KW / 10 KW For Use With Antenna Tuner ( DXE-BAL050-H10-AT)  that I had just picked up at the Dayton Hamvention,  tuned 3 ground radials, ran the RG-213 coax to the antenna relay  switching box and ran the antenna anayzer from the shack. The SWR at 3.750 Mhz. was 1.2:1, this is good but how much bandwidth did I get. Well that was the big shocker, at 3.52 Mhz I had 1.5:1 and at the top 3.995 Mhz 1.85:1. I didn't think that this was correct so I ran the inductive and capacitance readings from my Autek VA-1 antenna amayzer, and did the long hand math. At 3.75 it was 51 ohm, at 3.52 it was 56 ohms and at the 3.995 Mhz 32 ohms, these matched the readings from the anayzer. I was very pleased to have a vertical antenna that could run the whole band without using a tuner, this makes it much easier for the wife W8AMA to use also as she is more of an appliance user then I am. I like twisting all the knobs and stuff, she just wants to turn it on and use it. I added a 10 Meg Ohm 30 watt non-inductive resistor across the balun to bleed off static.
  If you have any questions feel free to e-mail me at w8ct@arrl.net.

75 M Mast

75 M Top

75 M Balun