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Title: If I had to dream Post by: KB2WIG on December 29, 2020, 03:50:18 PM Having some time to kill, I was thinking about how someone could install the "75M Local & DX Antenna " by the elusive k1jj. This is just a dream, but....... Asuming maybe 40 or 50 foot tower of used Rohn 25for the center mount, what would one use to seperate dipoles/inverted Ve ? And as usual, hamcheep would be helpfull. Put it on a pivot point and armstrong rotate from on the ground? Thanks and good luck in the corntest. KLC Title: Re: If I had to dream Post by: WBear2GCR on December 29, 2020, 03:58:25 PM Where's the documentation on K1JJ's design?
Never heard of it... _-_- Title: Re: If I had to dream Post by: KB2WIG on December 29, 2020, 04:07:04 PM East Coast Sound. On the left under "On AMfone". Title: Re: If I had to dream Post by: K1JJ on December 29, 2020, 05:03:35 PM I think you're referring to this antenna?
http://amfone.net/ECSound/K1JJ21.htm A pair of standard 75M 1/2 wave dipoles up as high as possible and flat - both fed with coax - dipoles spaced 40-60' apart broadside, equal length feedlines to the shack. Feed them together (0 degrees) for a cloud burner. Add a 1/4 wave length of coax to one side to make it a DX antenna to beam either direction. (unidirectional with a 25 dB f-b. Even at 60' high on 75M it is a killer antenna. At 120' high it is like a bad ass Yagi - can't be beat. With a single tower, hang an aluminum boom or well trussed PVC pipe at the top to support the centers. Inverted vees will work but flat elements have a better f-b. A wire cable boom in the proper direction between trees with pulleys to raise the elements works well too. I use a similar antenna on 75M using two delta loops at 190' high spaced 60' apart. Best antenna I have ever used on 75M. More details in the article. T The Huzman took this picture and added a little contrast to bring out the wires. It's been up for about 12 years now. Made with #10 wire. At the top the boom is 4" diameter 1/4" wall with overhead guy cable trussing. It just laughs at ice loads. This one I put up by myself using a car to tow - and tag lines hanging out the car windows. (20M 60' homebrew 20M beam mounted below it at 100'.) Title: Re: If I had to dream Post by: WBear2GCR on December 29, 2020, 06:06:06 PM Well, Mr. Vu... if we ever heard you on a semi-regular basis on 75m AM someone might possibly believe your tale! _-_-signed, long time listener Title: Re: If I had to dream Post by: K1JJ on December 29, 2020, 08:02:35 PM The urge comes and goes in cycles, Bear.
Some guys get on every day like it's a job. Some live their lives in virtual reality listening to web receivers. Others break up the time and build more than operate. Lately I've been getting the urge for some action. So stay tuned... ;) T Title: Re: If I had to dream Post by: KB2WIG on December 30, 2020, 09:46:28 PM T, The cycle has a flux of 83 today, so you should get on the air..... if there really is a 'you' or aliens are in control. Well, 60' height seems to be the point of strapishness. I'm imagining a 60' Rohn 25 tower on a fold over mount with a +40' boom? ( there is no way that I'm going to climb anything over 10'.) Maybe if it went up, a 6m yagi could fit on top. It seems with the 80m band going long for the next few years, the cloud warmer may help for the close in people. klc Title: Re: If I had to dream Post by: K1JJ on December 31, 2020, 12:07:25 AM KLC, AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
To eliminate any twisting torque on the tower, use overhead trussing cables on the boom and connect the apex point in the center of all the support cables to a sidearm eye-bolt. This way the boom hangs off the side of the tower and can swing 10-15 degrees or so in the wind - and the tower feels no torque. That is what brings many towers down - torque. The inverted vee legs pulled out on each end of the boom take all the stress, have big leverage and keep the boom straight. If left reasonably loose, the system can stay up for a long time. T |