Tuesday, May 7, 2019

Cloudy, Rainy, Dreary Day in Northern Colorado

And I have a cold on top of it, so that means no outside antenna work today.

Raising the center support from ~15' up to ~25' had very little effect, so my Wire Antenna Guru first thought I needed a "Common Mode Choke" on the feedline. These can be as simple as a number of turns of the coax feedline coiled up, or you can use a ferrite toroid core, and wrap the coax through that. Sine I already have a Balun Designs "Line Isolator", I went ahead and tried that. It made a slight improvement at the low end of the frequency range, but wasn't a Magic Bullet, so I took it back out.

The company that makes this antenna claims it will work without a counterpoise, but the coax needs to be at least 25' long. This is a huge red flag to me, because it means they're using the feedline as part of the antenna, and I've always read and been taught that you don't do that. It's a Kludge, and generally leads to poorly reproducible results. As in change the orientation of the coax, and your antenna no longer "works".

And they're pretty cagey in describing the use of a counterpoise:

"It could work without counterpoise (Coaxial cable has to be at least 25feet long) but grounding at wingnut next to connector is recommended."

And:

"Due to possible common mode currents on your feeder, we recommend using CMC-Common Mode Choke/Line isolator such as CMC-154-3K to keep RF away from you and your equipment. It will also help you on receive by filtering induced noise from various sources."

Hence my Guru's recommendation to try the choke.

Hmmmm.....On to "Grounding"? How? Run a #10 wire down to a good old "8' Ground Rod"?

Anywhoo.....It's an antenna, and it requires some kind of ground to work against. If not a properly engineered Ground System", which is basically as direct a connection as possible to Mother Earth, than it needs an "Artificial Ground", generally referred to as a Counterpoise. I've used the term many times before, and it's important to understand that pretty much any antenna other than a dipole must have a ground. In a dipole, one half of the antenna serves as the "ground" for the other half. It's "self contained" in a way, and doesn't require a separate ground.

Anywhoo (reprise)......Since the manufacturer is so vague, it looks like I'll have to explore playing with the counterpoise wires I have. My Guru now thinks they're too long, and I might only need a single one. After it dries out some and I'm feeling better, I'll get out there and start modifying what I installed. It's very easy to temporarily shorten them by coiling them up, so that's where I'll start.

At this point, since I now have the center point at 25', I'm musing about just putting up a 40 Meter (66' long) dipole......

4 comments:

  1. Replies
    1. Welcome back to the Front Range in Spring!

      Delete
  2. Get better! THEN screw with the antenna... LOL

    ReplyDelete
    Replies
    1. Yeah, my nose is running like a leaky faucet, I'm burst sneezing every 20 minutes, and don't feel 100%.

      Delete

Keep it civil, please....