Well, there it is. My halo antenna -- assembled and tuned to
frequency: Spot on 50.200 Mcs.
Not clear yet? Here is a close up:
Not clear yet? Here is a close up:
Just having a little fun with you here...
As we all know, a halo antenna has to have a pair of ugly pie pans mounted at the ends of the halo -- at the gap. Right?
I didn't really want the 'traditional' 2-disk tuning capacitor at the gap for my antenna. For one thing, it just adds extra cross section and exacerbates wind load problems. Too, it was Just One More Thing for rain, snow, sleet, & dead bugs to mess with and screw up the tuning when mobile.
It's just a #$&@&$# capacitor! There's no law that says it has to be on the outside.
So... I designed a halo tuning capacitor to go on the inside.
The 'traditional' tuning device is a single, 2-plate capacitor across the two ends of the gap.
My internal 'solution' turns out to be two capacitors in series across the gap.
I can't really believe that this idea is original to me.
But, I can not think of any place that I've ever seen this scheme before.
(Gee! Maybe I've had an Original Thought . Do you suppose?)
I forgot to photograph this piece of the action.
So, you're stuck with a drawing I made:
As we all know, a halo antenna has to have a pair of ugly pie pans mounted at the ends of the halo -- at the gap. Right?
Some men see a thing and say "Well, OK?"
I see a thing and ask "HUH? ... There's gotta be a better way!"
I see a thing and ask "HUH? ... There's gotta be a better way!"
I didn't really want the 'traditional' 2-disk tuning capacitor at the gap for my antenna. For one thing, it just adds extra cross section and exacerbates wind load problems. Too, it was Just One More Thing for rain, snow, sleet, & dead bugs to mess with and screw up the tuning when mobile.
It's just a #$&@&$# capacitor! There's no law that says it has to be on the outside.
So... I designed a halo tuning capacitor to go on the inside.
The 'traditional' tuning device is a single, 2-plate capacitor across the two ends of the gap.
My internal 'solution' turns out to be two capacitors in series across the gap.
I can't really believe that this idea is original to me.
But, I can not think of any place that I've ever seen this scheme before.
(Gee! Maybe I've had an Original Thought . Do you suppose?)
I forgot to photograph this piece of the action.
So, you're stuck with a drawing I made:
I got the Teflon cylinder from my dad's Collection(s)-of-Stuff.
He had 3 of them: 2" long, 1 3/8" O.D., and with a 1/2" hole through
the center. I had one of them turned down as you see in the drawing
above. The outside shoulders were turned on a lathe such that it was
A Very Snug Fit into the halo end(s). The 3/4" center section
guaranteed that the (re)assembly of the gap was always consistent.
A 1/2" diameter, 5" long aluminum tube was slipped into, and centered in, the Teflon cylinder and the gap was assembled.
There was enough 'spring' out at the end of the halo to permit one end to pull off the Teflon cylinder and over the 1/2" tube without undo stress or strain. Then I would let it swing back in -- either over or under the Teflon cylinder -- while I futzed with the 1/2" aluminum tube.
This 1/2"-tube-to-1/2"-hole fit was Good And Tight -- something I wanted in order to defeat movement by road vibration. The first measurement showed the resonant frequency to be in the mid-40 Mcs. Using a pipe cutter, I whacked off about 1/2" of the aluminum tube -- re-inserted and re-centered it -- and re-assembled the gap. The resonant freq. was now around 47 Mcs. I used this to calculate the number of 1/16"-per-Mcs to do additional cuts on the tube -- and then I cut even less than the amount that was 'calculated'. I continued this up to about 49.9 Mcs. Then, I stopped cutting. Instead, I started sliding the tube to one side of the Teflon cylinder, and zeroed in on my target freq. of 50.200 Mcs. The MFJ-259 and the IC-706 both claim the 2:1 SWR is over 400 Kcs.
One other item: As you can see from the pictures up above, I installed heat shrink tubing over the gap. This affected the resonant frequency by about 170 Kcs. -- down. What I did was slide the (un-shrunk!) heat shrink tubing over one of the halo ends and off to the side while fiddling with the Teflon cylinder and the small aluminum tube. After I re-assembled the gap, I slipped the heat shrink tube over the gap. Then I did my measurements (with the MFJ-259.) The heat shrink tubing I used was the stuff you can find in the electrical department of your hardware store that is 1" un-shrunk and 4" long -- comes 2-to-a-package. The stuff is probably a skoosh over 1", and my lawn chair tubing measured 31/32".
Once I had the thing tuned to 50.200, I ran a thin bead of hot melt glue around each halo tube about 1" back from the tube end(s). Thin -- because the heat shrink tube has to slide over it! Then I shrunk the heat shrink tubing -- carefully using a propane torch in my case. I think you can see the 'bumps' of the hot melt glue under the heat shrink tubing up in picture number 2. I'm hoping this will be a Good Seal against water. If water were to wick-in, under the heat shrink tubing, it would wreak havoc with the halo's resonance until it dried out.
One Last Comment: Tune it on the high side of your target frequency as far a you can live with.
Everything hereafter will conspire to lower the resonant freq.: rain, dust, mud, bugs, bird poop.
Nothing will raise it. (Except, maybe, whacking a tree limb at 65 mph!)
Taa Daa! It's all done!!
Well, I do have some final comments and miscellaneous reflections,
... and some more pictures:
6M Halo - Comments - Reflections
W3DHJ 6M Halo - Front Page
W3DHJ Home Page
A 1/2" diameter, 5" long aluminum tube was slipped into, and centered in, the Teflon cylinder and the gap was assembled.
There was enough 'spring' out at the end of the halo to permit one end to pull off the Teflon cylinder and over the 1/2" tube without undo stress or strain. Then I would let it swing back in -- either over or under the Teflon cylinder -- while I futzed with the 1/2" aluminum tube.
This 1/2"-tube-to-1/2"-hole fit was Good And Tight -- something I wanted in order to defeat movement by road vibration. The first measurement showed the resonant frequency to be in the mid-40 Mcs. Using a pipe cutter, I whacked off about 1/2" of the aluminum tube -- re-inserted and re-centered it -- and re-assembled the gap. The resonant freq. was now around 47 Mcs. I used this to calculate the number of 1/16"-per-Mcs to do additional cuts on the tube -- and then I cut even less than the amount that was 'calculated'. I continued this up to about 49.9 Mcs. Then, I stopped cutting. Instead, I started sliding the tube to one side of the Teflon cylinder, and zeroed in on my target freq. of 50.200 Mcs. The MFJ-259 and the IC-706 both claim the 2:1 SWR is over 400 Kcs.
One other item: As you can see from the pictures up above, I installed heat shrink tubing over the gap. This affected the resonant frequency by about 170 Kcs. -- down. What I did was slide the (un-shrunk!) heat shrink tubing over one of the halo ends and off to the side while fiddling with the Teflon cylinder and the small aluminum tube. After I re-assembled the gap, I slipped the heat shrink tube over the gap. Then I did my measurements (with the MFJ-259.) The heat shrink tubing I used was the stuff you can find in the electrical department of your hardware store that is 1" un-shrunk and 4" long -- comes 2-to-a-package. The stuff is probably a skoosh over 1", and my lawn chair tubing measured 31/32".
Once I had the thing tuned to 50.200, I ran a thin bead of hot melt glue around each halo tube about 1" back from the tube end(s). Thin -- because the heat shrink tube has to slide over it! Then I shrunk the heat shrink tubing -- carefully using a propane torch in my case. I think you can see the 'bumps' of the hot melt glue under the heat shrink tubing up in picture number 2. I'm hoping this will be a Good Seal against water. If water were to wick-in, under the heat shrink tubing, it would wreak havoc with the halo's resonance until it dried out.
One Last Comment: Tune it on the high side of your target frequency as far a you can live with.
Everything hereafter will conspire to lower the resonant freq.: rain, dust, mud, bugs, bird poop.
Nothing will raise it. (Except, maybe, whacking a tree limb at 65 mph!)
Taa Daa! It's all done!!
Well, I do have some final comments and miscellaneous reflections,
... and some more pictures:
6M Halo - Comments - Reflections
W3DHJ 6M Halo - Front Page
W3DHJ Home Page
Constructive comments and/or discussions:
Last updated: 06-Sep-17 -- Now "Mobile Friendly"
Last updated: 06-Sep-17 -- Now "Mobile Friendly"