Well, I finally figured it out

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10-12-2010, 10:50 AM
KC2UGV

Well, I finally figured it out

So, the attic antenna I currently am using (Which is a "fan dipole", multiple tuned elements fed at a common feed point) is still running. No fire in the house yes, and my leads have not melted, even when putting out 100W or so via a tune.

But, since this "dipole" is not really lain out in "dipole fashion" (It's in the shape of a "V" almost), it's lain out as such:

Code:

| <---- Feed line | ^ <---- Feed point / \ | | | | | | |______| About 25ft separation between sides And, at ends, 10ft or better separation of each element

I've always wondered the directivity. Is it like a dipole? If so, end-fired of which "side"? One direction, or two?

Turns out, it's directional. It's fires off of one side. So, my challenge over the next few weeks or so is to model this thing in EZNEC, so I can play with some items.

PSKReporter is a really good tool when trying to figure out your lobes and what not :)
10-12-2010, 11:14 AM
KG4CGC

Do you have a device you can rig up to test field strength? Key up at the lowest power setting and test it on different bands to get an idea of the type of pattern you are getting.
I had an article somewhere that detailed how to attached a very simple home brewed device to a DMM for use as a FS meter.
10-12-2010, 11:23 AM
KC2UGV

Quote:

Originally Posted by KG4CGC

Do you have a device you can rig up to test field strength? Key up at the lowest power setting and test it on different bands to get an idea of the type of pattern you are getting.
I had an article somewhere that detailed how to attached a very simple home brewed device to a DMM for use as a FS meter.

Hm... I should give that a whirl. I'm sure a tuned coil attached to a DMM can suffice as a FS meter. I also have a radio shack 3-30MHz FS/SWR meter that says it can be used as a FS meter (I have my doubts).
10-12-2010, 11:27 AM
KG4CGC

I guess you already know, the lower the power setting the better. Attenuate the feedline maybe??? To keep the readings within walking distance LOL!
10-12-2010, 11:42 AM
W3MIV

Judging from your diagram, it is hard to see how it could work without significant interference of one element with the other. Just because an antenna "loads" does not mean it radiates well, or even much at all. A good deal of your power could be heating up the ground.

If you ever want to try a practical test, I will be available just about any evening you choose -- except tonight: On Tuesdays I hold a regular bullseye pistol match and tonight I also have a gun club meeting. Any other time, however, I will be happy to give it a shot. PM or email me as you like.
10-12-2010, 11:43 AM
W3MIV

BTW, if you want to attenuate the antenna, I have a pin you can borrow. :mrgreen:
10-12-2010, 12:09 PM
KC2UGV

Quote:

Originally Posted by KG4CGC

I guess you already know, the lower the power setting the better. Attenuate the feedline maybe??? To keep the readings within walking distance LOL!

Thinking maybe a series resistance in the feedline? I dunno. I may have to work it at 5 watts (Should be noticeable at that level).

Quote:

Originally Posted by W3MIV

Judging from your diagram, it is hard to see how it could work without significant interference of one element with the other. Just because an antenna "loads" does not mean it radiates well, or even much at all. A good deal of your power could be heating up the ground.

If you ever want to try a practical test, I will be available just about any evening you choose -- except tonight: On Tuesdays I hold a regular bullseye pistol match and tonight I also have a gun club meeting. Any other time, however, I will be happy to give it a shot. PM or email me as you like.

It get's out subjectivley well. PSK reporter routinely shows me hitting the entire US (Short of PA, NY, and OH, that's because I'm "shooting over" them). I heard KB6JSO a couple of days ago, and I at times, hit Europe.

But, you're point of heating up worms is most likely true. It's cut for 40-20-10 meters, and for 20 and up, it's nowhere near 1/2 wave above ground. I was interested in how this antenna worked, since I knew it was "sub par" in it's layout. I think the only saving grace is it's in the attic, and I have a near metal free environment up there.

Quote:

Originally Posted by W3MIV

BTW, if you want to attenuate the antenna, I have a pin you can borrow. :mrgreen:

:snicker:
10-14-2010, 08:18 PM
W5GA

Corey, have you ever thought about using an inverted L? Usually seen on the low bands due to space constraints, but no reason it won't work on the higher bands if you have space issues.
10-14-2010, 08:28 PM
KC2UGV

Quote:

Originally Posted by W5GA

Corey, have you ever thought about using an inverted L? Usually seen on the low bands due to space constraints, but no reason it won't work on the higher bands if you have space issues.

It's my next one :) I just have to figure out where to place it. My landlord/neighbor downstairs is also a ham, so I have to try and keep a bit of distance between antennas. And, he has an inverted V for 40M up too :)
10-14-2010, 10:48 PM
W5GA

Cool! Just remember that you want as much of it vertical as you can get.