The KA1RCI Repeater Network
Established 1984

JAGY-146-7-EM "KA1RCI Thunder Boomer"

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The JAGY-146-7-EM aka "The KA1RCI Thunder Boomer" yagi antenna has been developed to meet the needs of amateur radio operators who require a high gain, broadband, premium quality directional antenna providing 9.5 - 10 dBd of gain with a low VSWR across the entire 144-148 MHz frequency band.

Up until 2010, JAG Electromagnetics only made VHF yagis with up to 6-elements. However, in late 2010, KA1RCI required a rugged yagi with 7-elements in order to squeeze out as much forward gain as possible; hence, the "Thunder Boomer", which KA1RCI affectionately named.

The JAGY-146-7-EM antenna consists of a seven-element yagi of exceptional durability and performance. All elements including the driven folded dipole element are maintained at DC Ground potential for lightning protection.

The JAGY-146-7-EM antenna is suitable for mounting on the top or side of a tower or pole. No mounting hardware is supplied with this antenna as site specific mounting hardware is necessary with the Thunder Boomer to assure optimum performance. This Yagi can be installed in either a vertically or horizontally polarized orientation. A special JAG HMK kit is required when mounting for horizontal polarization.

Building the Boomer

While Dad was raking up the last of the ground cover I was unpacking and building my new custom JAG 144-148 MHz seven element end mounts Yagi antenna. This antenna is very impressive and much bigger than I expected. It did not look so large in the example photo that Jag had send me several weeks ago small but I am very pleased.

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Here are the detailed, hand written, instructions that Jag sent me to assemble my new antenna.

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  It took me a few hours to unpack and assemble the antenna and it wasn’t until after I was finished (felling a great sense of accomplishment) that I realized that I had just assembled a 13 foot long by 3 foot wide antenna on the floor of a 10 X 15 foot room!

How the hell was I going to get this thing out of the house???

After a few minutes of beating myself up for being so blonde I was able to jockey the antenna out into the hallway, up the stairs to the double front doors and get outside that way…

I wonder if the Chief will be able to hear me now?

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Tomorrow I hope to get started by mounting my new JAG 144-148 "Thunder Boomer" on the tower, cranking up the four sections we have assembled and performing the fine tuning adjustments for the best VSWR.  Jag is on "stand-bye" waiting for Dad and I to call if we have any issues getting the new end mounted Yagi dialed in on my tower.


Monday Morning October 11th

Tuning the JAG 144-148 "Thunder Boomer"

Monday morning the weather was perfect and Dad & I got an early start.  We mounted the new JAG 144-148 MHz seven element end mounted Yagi on the tower and cranked the tower up so we could fine tune the new "Thunder Boomer".

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We only four sections (half the tower) we are able to crank the tower up and down very easily which allowed us to work on the new JAG antenna down on the ground but crank it up for the VSWR sweeps. In the test location the antenna was only 12 feet off the ground so Dad was also able to stand on the repeater shed and make small adjustments to the various elements as well.

(click on images to enlarge)


Working with Jag via email, we got the initial rough tuning by adjusting the spacing between Element No. 1 and Element No. 2 at the end of the boom and then dialed in the fine tuning matching the "Thunder Boomer" to my tower by adjusting the spacing between the Driven Element and the Reflector. In this series of VSWR Plots you can see the antenna moving towards the desired frequency as we made the adjustments.

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This is the last VSWR Sweep of the antenna in the test position; I will post the results of VSWR measurements when the antenna in mounted in the final position and the whole tower has been cranked back up.

FREQ Watts Fwd Watts Rev VSWR
143.50 40 4.4 1.99
144.00 50 4.8 1.90
144.50 70 5 1.73
145.00 80 4 1.58
145.50 82 2.6 1.43
146.00 86 1.2 1.27
146.50 86 0.5 1.17
147.00 84 0.6 1.18
147.50 82 1.5 1.31
148.00 80 3 1.48
148.50 80 5 1.67


In the first three plots above the boomer was mounted on the tower at approximately 12 feet above the ground so Dad could stand on the repeater shed roof and move the various elements. In the final configuration (third adjustment) we had the end element out 24 inches and the back reflector 21 inches off the face of the tower. That plot look real good to me and I knew that when we mounted it on the tower in the final location I could move that back spacing out from 21 inched to 24 inches.

Sunday Evening October 21st

Testing the JAG 144-148 "Thunder Boomer" on the tower

These next two plots below are with the Thunder Boomer in the final mounting position on the tower at 33 feet above the ground with the back reflector 24 inched off the face of the tower and the front element also spaced at 24 inches. The difference in these last two plots is the 220 MHz dipole array that was directly in front of the boomer about 21 inches away.

You can see the temporary 220 MHz dipole array for the 224.040 repeater in these photos. It was directly in the path of the new JAG yagi and very close to it as well. The 220 dipoles were obviously affecting the new yagi as the VSWR plots below show...

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The VSWR sweep with the temporary 220 MHz dipole array still mounted in front of the yagi

FREQ Watts Fwd Watts Rev VSWR
144.00 50 8.6 2.42
144.50 52 7 2.16
145.00 48 5 1.95
145.50 42 3 1.73
146.00 38 1.6 1.52
146.50 38 0.72 1.32
147.00 40 0.4 1.22
147.50 42 0.7 1.30
148.00 44 1.6 1.47


Once we had the 224.040 repeater moved over to the new antenna at the very top of the tower we were able to remove the temporary 220 MHz dipole array that was directly in front of the new JAG "KA1RCI Thunder Boomer"

In these two photos below you can see the new JAG yagi has a nice clear path once the temporary 220 MHz dipole array for the 224.040 repeater had been taken down...

The VSWR sweep once Dad & I removed the the temporary 220 MHz dipole array.

The final VSWR sweep on my desired frequency of 147.000 MHz

 44w FWD / 0.18w REF / VSWR = 1.14 

FREQ Watts Fwd Watts Rev VSWR
144.00 36 2.6 1.74
144.50 38 2.1 1.61
145.00 40 1.6 1.50
145.50 44 1 1.36
146.00 44 0.48 1.23
146.50 44 0.22 1.15
147.00 44 0.18 1.14
147.50 45 0.32 1.18
148.00 46 0.82 1.31



You can order your own JAG Thunder Boomer from JAG Electromagnetics


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