Monday, November 16, 2009

Roll your own!

This is about my newest addition to the spectrum grabber installation. The regular reader will know, that I was mainly using my rockloop (see webpage) for the 30m suburban subharmonic grabber. My rockloop is, however, a multiband (15m to 40m) aerial, which provided me with enjoyable QSOs in its' entire bandwidth. OK, I could build another one, but than again, multiband?

Years ago, I learned about the DCTL (Distributed Capacitance Twisted Loop) antenna. Actually shortly after its' design has been published. To that time, I cut myself a version for 40m from 300Ohm window-line. This loop actually never worked... well, at least not to that point in time.
Just recently I found the bag in which the DCTL was rolled up for storage. That brought the thought that I may possibly made a mistake when making the loop. And yes, in fact, I made a mistake, I forgot the "twist" in it.
Some months ago, I thus fixed it by soldering the leads together which belong together... and... voila, a working 40m DCTL. So far, so good, rolled it up again a was busy doing other stuff.

And now, just recently, I remembered it again (actually I just wanted something to print, in order to test my print-server setup). Only God know why I was hacking "DCTL antenna" into the average search engine and printed just the first thing that popped up:
Now, that would form a nice and cheap receive loop for the grabber.... And yes, it does!

Here come the dimensions of my 30m DCTL (please refer to the link above to understand what I am writing about)
  • Ll = 347cm
  • Lz = 46cm
  • Lc = none
The 30m version is made from TV twin lead, which is much lighter and easier to roll up for transport as the window-line is.
The lazy dawg I am, I could not be bothered yet to include a balun in the design, I am thus sipping the signals off the loop by means of ordinary RG58 coax. Yes, I do consider using TV twin lead as feedline, however, the stuff is rare nowadays, and I'd therefore probably rather wind a balun.... We'll see....

My 40m version is good for TX, I guess, the 30m version will be as well. I will try to tune (trim/cut) it accordingly and give it a try during my next journey.

Roll it up, roll your own!