The Parasitic Vertical – Part 2
who know me realize that I am not often tempted to leave well enough alone.
parasitic beam project is no different. I have been playing with
the 40M director
version ( MK1) for a few nights and it is indeed a neat DX antenna. I like this vertical for Euro,
Performance of the vertical is good !
Now…. I am dreaming away while playing with the rig last night on 40M and I think “…. Geeez… I should have the same sort of advantage with this antenna to the NE on 30M too “ . Yeah, hmmmmmm, how would I do that ? EZNEC to the rescue again !
1) Drop the 40M director and figure out a 30M director.
2) Use the same director but make it work on two bands with a trap.
3) Add another director inside the first one
4) Add a 30M reflector on the other side of the antenna.
The trap idea isn’t too bad but I start with 1) as it is a “Clean slate”. (Model wise.) What I quickly realize is that I can’t make the antenna develop the same nice beam pattern as I did on 40, no matter what I do with the geometry of the director. Why ? Well, this antenna is no longer a simple ¼ wave element on 30M. It is too long and has a different current distribution on it. The parasite element isn’t going to be the same as the case with a true ¼ wave element, it seems. It will work though, but has very different dimensions than the 40M unit. There goes any hope of using a trapped element, so 2) is out. I don’t want to keep going in and out to the antenna to change elements while operating ( Waaaay to lazy for that) so 1) is out. Can I put the two elements in the same plane ? Let’s try it on the model… kind of works but danged cranky. I don ‘t like it.
Were down to 4) How about an element on the other side of the antenna as a reflector ? Ah hah… that works OK it turn out. And real easy to put up as you can still haul it up with one halyard at a fixed point on the top support line ( top fish line, in this case).
Here is the model:
Here is the same model with 30M currents:
You can see that the right hand 40M director elements aren’t doing much in the pattern. That’s good !
Here is the 40M currents:
Looks good ! I strung this one up in a jiffy and sampled the impedance at the base. Sure enough, looks like my 4:1 UNUN is going to carry on and make a nice match to the coax for me, on both bands. I had to tweak the series capacitor in the 30M matching circuit, but that is all. I also found my new 40M bottom leg was about 9” too short. That was easy to fix as well.
I probably should do another one of sketches, and I will get to it. Thing is though, if you are going to apply this technique to your antenna.. you really should model the thing first and play with the elements. What I have shown here very likely WON’T work on your antenna, unless you have a similar simple 32 foot , 1” diameter, aluminum monopole over the same kind of crappy ground.
Operating: This evening I am listening to the DX on 30
and 40 and whaddya know ?
This thing is my best listening antenna now for signals to the NE. (
Now for some operating to see how it compares.
There will be a part 3 to include a sketch and some performance reports. Stay tuned !