Elmer help/advice needed

Started by RFExplorer, September 30, 2019, 08:15:24 pm

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RFExplorer

Ok Gil, Guys and Gals. I know before I ask, the standard answer is: "Try it and see if it works." But allow me to ask some questions as you entertain visions of an old guy stumbling on the rooftop, swinging from the trees, and banging his head in a low ceiling attic, as he tries to erect an antenna.

So, hold on to your ladders and let me begin. I'm Hell bent on erecting an EFHW for 80 meters CW.

Why 80m? Who knows? Maybe it's because I cut my ham radio teeth on 80 meters many years ago.  Or, maybe it's because most of my home-brew seems to work on 80 meters. Or, maybe it's because I'm very old school. As I said, "Who knows."

Back to my quest:  the operative word might be "bent."  I have 110 ft clear and straight distance between the peak of my house to the peak my tool shed.  It's an East-West run  25 -35 ft above ground.

At 80m CW frequency, I'm short about 20 ft. for an EFHW.  So, I figures I can get the needed length  with a 120-degree bend into the attic. Think: [ 110 ft free space - 120 degree bend - 20 ft inside the attic - tuner  - 50 ft feed line - xmtr]

I see some immediate logistic advantages of this situation:
    • The weighted pulley system in the attic that keeps tension on the wire is out of the weather.
    • The tuner is inside the roof, high and dry.
    • Antenna measurements and trimming are done inside the confines of a roof.
    • And all electrical connection are protected from the elements.

As far as RF related disadvantages .... I'm all ears..... obviously, an inside-outside antenna must have some detractors. And, don't forget the "bent" part of hell-bent.   

The free space leg has to be important but is is worth stringing the wire to my neighbor's tree to gain a few feet?

BTW, the inside leg in the attic is also "free space" in so far that is within a 5 ft tall attic space. (The antenna wire is not attached to any framing but hanging in "free space" with the weighted rope and tuner.)

And, then there is the antenna coupler: 10:1 ... 9:1 ... 8:1 ? I assume an antenna analyzed will tell me what ratio, but what coupler design makes sense for my situation? Since I have the luxury of a protected environment, should I build the auto-transformer design, or match the wire with an independent primary-secondary transformer design? The www has lots of examples and plans for both, but little on which to use, when and where.

Obviously the simple answers go with my opening supposition:"try it and see if it works?"  but I'd like to save some attic crawling. After all, I'm getting old, or as my wife says, "You are old!"

BTW I'll have about  50 ft. coax run between the tuner and the xmtrs, QRP power levels never more than 10 watts. I WILL NOT be climbing up in the attic to disconnect antennas every time a thunder boomer comes by. We have lots of lightening here in Virginia, USA.

All comments, suggestions, and criticisms are welcome.

Ed    de KA4IBG (recently gave up his quest to be the "Last NOVICE")







bkmoore

Have you considered a 1/4-wave vertical? Here's a design that looks like it's easy to make:

http://www.dj0ip.de/vertical-antennas/80m-on-18m-pole/

73,

Brian

gil

Hello.

I think it will work just fine. I wouldn't worry about the bend or the inside part. However, the transformer you need is a 49:1. For 80m I suggest using an FT-240-43 toroid. Three turns primary and 21 turns total. You will also need a high voltage 100pf capacitor, like 5 to 10KV. There is a group on facebook explaining the details... Also see:

https://www.youtube.com/watch?v=MgZap6xWZLs
https://www.youtube.com/watch?v=G2x67h7-cwI
https://www.youtube.com/watch?v=G2x67h7-cwI
And especially:
https://www.youtube.com/watch?v=0zF7bDoqkG4

Gil.