Anyone familiar with Blaw-Knox Antennas?

berkeman

I hadn't heard of those. Do you have a link to more information?

berkeman

Hmm, I did some reading on the web, and am still a bit confused. The articles did stress the need for a good counterpoise to help manage common-mode reflections at the feedpoint.

I'd be interested in reading a comparison of a center-fed dipole versis the end-fed dipole+counterpoise, if anybody finds one.

the_emi_guy

I have attached photo of feedline to a typical series fed tower. Feedline comes out of tuning shack to the right and attaches to antenna just above insulator. This particular tower is not a "Blaw Knox" type, but idea is same.

Fence surrounds it because there are thousands of volts on the feedline and the entire bottom of the antenna.

I also attached technical documentation for 314 meter high Blaw-Knox which includes schematic of tuning shack, impedance data, Smith charts etc.

Note that the antenna height is half wavelength at 540KHz. Also note that the antenna feedpoint impedance is about 300 ohms magnitude. If it were a quarter wave monopole the feed would be more like 36 ohms, and the required current an order of magnitude higher.

Driving this dipole at its midpoint (in textbook fashion) would be really impractical. You would have to install multiple fragile insulators halfway up the structure and relocate the tuning shack way up there.

Attached Thumbnails

 

Attached Files

1E-8920-810-DO_documentation diplexer Lakihegy.pdf (595.5 KB, 5 views)

userdnl

I've been busy the last couple weeks and forgot to come back here and write a reply. emi_guy, I'm literally drooling over the documentation that you posted. It's interesting how they are simultaneously broadcasting two different frequencies. I guess that the tower acts as a 1/8 wavelength monopole for the 135.6kHz signal and a 1/2 wavelength for the 540kHz signal?

I was also wondering if you could confirm my conclusions in posts #8 and #13 of this thread? Thanks again for all of the information!