Re: The Broadband Butterfly ... an HOA-friendly all-HF antenna for your attic


Jim Jenkins
 

By the way, If you don’t quite have the 235 ft, you can let each end hang vertically for 10 to 20 feet and have almost no affect on performance.

 

From: TLARC@groups.io <TLARC@groups.io> On Behalf Of George N2APB
Sent: Thursday, January 31, 2019 10:04 PM
To: TLARC@groups.io
Subject: Re: [TLARC] The Broadband Butterfly ... an HOA-friendly all-HF antenna for your attic

 

Hi Jim,

 

That was my first thought too. As they say, even a dummy load will radiate and have flat SWR across such a wide frequency range. 

 

In a more conventional terminated folded dipole, the terminating resistor will lower the overall gain of the antenna at the expense of getting a better SWR across the bands, with much of the power being dissipated as heat in the resistor. As you said, the efficiency stinks but you get broadband coverage. 

 

FYI, there’s a good article on the Terminated Folded Dipole in QST for Sept 2010. 

 

Anyway, Juan suggested it might be worthy of doing some experimentation ... It’s usually fun trying new approaches to antennas, modeling and measuring them, etc.  Learn something every time. 

 

Personally, I’m going the diametrically opposite direction with my experimentation:  I’m constructing a 160m “Small” Transmitting Loop using two turns of 7/8” Heliax with 10’ diameter.  With a vacuum variable capacitor, the loop (inductor) will resonate with SWR of 1.2:1 ... with a 6 KHz bandwidth! 

 

Fun stuff, antenna experimentation!

 

73, George N2APB

 


On Jan 31, 2019, at 8:33 PM, Jim Jenkins <jim@...> wrote:

I would question the efficiency of this antenna as a 16:1 balun wired to a 1200 ohm resister would convert the 1200 ohms to 75 ohms and be low vswr as he measured, but the power would almost all be dissipated in the resister rather radiated. Since the connections are lengths of wire there may be some radiation, but since the currents are very low in the wire due to the 1200 ohm impedance I expect this antenna may measure well, but not work well.

Regards,

Jim

AA1J

 

From: TLARC@groups.io <TLARC@groups.io> On Behalf Of George N2APB
Sent: Thursday, January 31, 2019 7:23 PM
To: TLARC@groups.io
Subject: [TLARC] The Broadband Butterfly ... an HOA-friendly all-HF antenna for your attic

 

Build a simple "terminated dipole antenna" for your attic that will operate across the entire HF band ... without an antenna tuner!  

Visit the TLARC home page to learn all about it!

73, George N2APB
www.tlarc.org 

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