[Elecraft] K0BRA Active Antennas AMRAD

[Don]

Why not be interested?  It is an interesting project.

I built the active antenna two years ago, not for use with VLF  but as an 
antenna to use with old broadcast AM radio receivers.  I had found that my 
old Philco, which was designed to use a random wire antenna, picked up more 
hum than than anything else and I needed to place an effective antenna well 
above the electric fields existing in my living room and then bring the 
signal down to the  radio through coax where I could then use a conventional 
step up transformer to match the antenna input of the receiver.  There are 
probably easier ways to make the old Philco perform but I was interested in 
the concept of using a short whip, remote amplifier, and coax to suck 
signals out of the air.   Anyway, it  worked well.  I found that it was 
effective up to about 7 MHz although performance fell off gradually about 4 
MHz.

The special power transformer (wound with very low capacitance between 
primary and secondary) may be a cost issue.  I made my own by stripping the 
secondary off a cheap RS transformer and adding a new secondary with a *lot* 
of insulation between the two windings to reduce the capacitance to very 
near that reported in the qst article for the purchased version of the 
transformer.

Don  K7FJ



> Well after all of the variations of URLs and browsers, I finally clicked 
> on the Active LF Antenna article and was told "You are forbidden access to 
> this page....I guess I'm not interested after all :-( ....K4TO