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2 Meter Slot-Cube Antenna (QST Jan 2019)

Jan 17th, 19:47

KJ7BVU

Joined: Nov 16th 2018, 19:58
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Total Posts: 0
I built one but I cannot get it to work very well. I cannot get it to raise the repeater and even my rubber ducky can do that. I am going to order a SWR meter. When building, I even made a jig to keep everything square and level. I have something wrong but I do not know what.

One question I have in on the feed. I did not see exactly how the feed is wired in the photos. Do I take the center (signal) line of the coax and connect to both? And then what do I do with the coax shield?
Jan 18th, 00:16

N7LT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Look at the picture W6NBC uploaded.
http://www.arrl.org/files/file/QST%20Binaries/Jan2019/Slot%20Cube%20Pipe%20Lengths%20in%20Inches.jpg

That should help you see the feed point better.

Lyndel, N7LT
Jan 18th, 06:37

N1ZIH

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I just finished mine. I have it leaning against a wall bringing up repeaters 25-30 miles away It is now permanently installed on the 2nd floor of my apartment and performing flawlessly 73 DE N1ZIH
Jan 18th, 17:28

KJ7BVU

Joined: Nov 16th 2018, 19:58
Total Topics: 0
Total Posts: 0
Quote by N7LT
Look at the picture W6NBC uploaded.
http://www.arrl.org/files/file/QST%20Binaries/Jan2019/Slot20Pipe20in%20Inches.jpg

That should help you see the feed point better.

Lyndel, N7LT


Thanks Lyndel, I can see the photo but the feed point is still not clear to me. I cannot see around the corner to see how the coax is connected. I did order a SWR meter so that should help me tune it.
Jan 19th, 16:34

K1TGF

Joined: Jun 29th 2016, 13:11
Total Topics: 0
Total Posts: 0
I built this antenna this past week and was able to get swr down to 1.0:1 at 146.50mhz. I lengthened the vertical pipes to 8.5" and adjusted the feed pipes to approx. 4.25" to keep the gap between them at about 1/8". I also did not use the CVPC connector but end caps instead to keep everything sealed. I just drilled through the pipes and attached the feed line directly to them with bolts and eyelets soldered to the coax.

https://www.dropbox.com/s/z3i3fo4nw9245sd/2M-Slot-Cube-Antenna.jpg?dl=0
K1TGF
Jan 20th, 20:33

jimvw57

Joined: Dec 16th 2017, 15:23
Total Topics: 0
Total Posts: 0
Working on assembly and soldering. Had to wait until after the grandson went home for the soldering part, he helped with what I figured he was safe to do. Update: I lengthened the loops to only use about 1/4 inch inside the elbow connectors and I ended up with SWR at 3.6 at 140 mhz time to start playing. open to suggestions. using the starting verticals at 7" maybe they need to be longer??
Jan 21st, 14:49

AC8QB

Joined: Mar 27th 2014, 10:48
Total Topics: 0
Total Posts: 0
Completed project last month.
Using a MFJ analyzer I got the antenna to tune @ 151.5 MHz.
Using HP Oscillator & 250 Mhz Tecktronix scope the antenna radiated pretty well at 146.5. Have not calibrated analyzer but suspect it may be off frequency.
Plan to visit DARA clubhouse and we will use a better analyzer and then we will know.
I will publish results of test.
Jan 22nd, 01:21

jimvw57

Joined: Dec 16th 2017, 15:23
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Total Posts: 0
This was driving me crazy so I did a little playing and found that by rotating the orientation of the cube, It would affect the readings..I then found the coax connection ground was touching one of the vertical uprights depending on how it was sitting on the bench. A little electrical tape (temporarily) and now it is reading 1.2 at 139.02 if I lay it on one side, flipping it 180, I get a 1.2 at 141.74..I think I need to take this outside away from everything and check it again. Of course it is only 10 degrees outside right now...
Jan 23rd, 10:44

N0FAZ

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
So I guess a picture (or drawing) is really worth a thousand words.
Jan 25th, 10:45

N0FAZ

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Is the spacing between the two vertical elements critical? What are other users finding this dimension comes out to?
Jan 25th, 20:28

WE2DX

Joined: Apr 13th 2015, 02:44
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Total Posts: 0
I built this antenna. A couple of times. The dimensions may not be correct. Built as described, it tuned at over 151 MHz. I re-build with the feed point as a sliding arrangement, as the author described, and it was a pain in the neck, but it allowed for some adjustment. Sliding the feed point away from the two vertical elements only made things worse and I realized that I needed to bring the feed point tubes closer in. I trimmed off one side of the T's to allow them to slide up as close as possible to the two 7" vertical tubes. Bingo! The antenna now tuned up at 147 MHz and was inside of 2:1 SWR from 145 to 148 MHz. Basic on-air evaluation had me getting into local repeaters well and even some more remote repeaters when I was parked at a higher elevation location. I have photos of my modifications if it would help anyone.
Jan 29th, 09:09

AD4PM

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I just built this antenna, and it resonates at 150 MHz with the impedance at about 32 ohms. At 145.0 MHz, SWR is about 2.3. I'm thinking I might need to lengthen the whole thing a bit. I also think I need to redesign the feed point so I can adjust it.
Jan 29th, 10:08

jimvw57

Joined: Dec 16th 2017, 15:23
Total Topics: 0
Total Posts: 0
I extended the antenna (all corners) by sliding the tube so it only is about 1/2 way into the corner elbows, and I got resonance at 137 MHZ with 1.4 SWR
Feb 3rd, 20:56

jimvw57

Joined: Dec 16th 2017, 15:23
Total Topics: 0
Total Posts: 0
UPDATE

I took this guy to the local club meeting, we were also participating in the Minnesota QSO party, and talked to some extremely knowledgeable hams. I learned a lot! I found that the construction i did was not as square as it needed to be and after a bit of tweaking, I am able to get SWR to 1.1 at 139Khz, and at 1.6 at 149Khz which is pretty darn good! Next will be mounting the antenna to stabilize dimensions and getting it above the ground. Right now it is sitting on a wooden desk with a bunch of tools and equipment nearby.
Feb 9th, 21:58

kmikemoo

Joined: Jun 15th 2018, 21:54
Total Topics: 0
Total Posts: 0
I built this as soon as it came out in QST but my SWR maxed out my little meter at my repeater frequency. When I finally got it on an antenna analyzer, my resonate frequency was 155! 1.2 SWR Since my cube was already too small, I cut 1/2" off each of the 8" legs to see how much "movement" I would get. 3MHz - in the wrong direction (of course). I rebuilt it today by lengthening the 8" pieces to 8.5" and lengthening the 8.5" pieces to 9.5". It resonated at 139-140, 1.1 SWR. I also honed out the T's so they could be adjusted (files and sandpaper). By moving the feed point T's to where there was a 1" gap between the edge of the T and the edge of the 90, my resonant frequency is 146.5 with a SWR of 1.0.
I hope this helps someone out there like the comments already posted helped me.

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