K5YAC – Cubex MK IV – 4 Element 5 Band Quad
Mark – K5YAC has just completed the installation of a new Cubex MK IV 4 Element 5 Band Quad. The boom length is 24 feet and the antenna weighs 114 pounds. Wow, I bet that antenna will be blowing some smoke! Below are some pictures and Mark’s install story. Congrats Mark, looks great, and thanks for the write-up!
K5YAC’s 4L/5B Cubical Quad
Cubical quads go back a long way with interesting origins, and I’ve always been fascinated with these large wire antennas. When I lived in Dallas as a kid in the 1970s, the first antenna I remember was a 4-element tri-bander that belonged to my Dad, Jerry (K5YAA). He installed it in 1968 and it stood prominent in our neighborhood until a tornado took it down. That tower never went back up as we would move to Missouri a couple of years later, but I always remembered how cool that antenna looked and Dad would talk to stations all over the world on his Heathkit set.
Fast forward to 1995, I was in the Army and about to be sent overseas for a 3-year hitch in north Italy. Dad said, “Get your ticket and maybe we can chat on the air!” So I did, and while I had several compromised antennas to play with, I built my first quad in 1996, a 3-element 10m monobander. It was a futile effort as there was no way I would be allowed to install it on our government quarters, but the practice was fun. Several years later while attending school, each of us in my Wireless Communications class were required to build an antenna for 144MHz, which would be tested on the school’s range. Most chose simple designs like J-poles, but I went with a hi-Q 5-element quad. Needless to say, no one came close.
Several years later in 2008 I was sketching out station upgrades (dreaming). The plan included a 50′ tower and a Cubex MkIV 4-element 5-band quad up top. I didn’t have the budget for such a setup, but I sure wished that I did! I’ve always operated on verticals and wires. Nothing wrong with that, but life’s obligations often got in the way as well, causing me to get into and out of the hobby at the worst times. I was active during the lows of cycles 23 and 24, but busy with other things during the peaks.
One more jump forward, to 2019. My wife and I built a new home with enough property to put up whatever I want, or at least, what I could afford. I stood up a 55′ tower in late 2020 with the intention of calling Cubex in early 2021. In the meantime, a DXEngineering Hexx-Beam would scratch the itch. Many calls and emails to Cubex went unanswered. I was getting discouraged at the thought that I would have to homebrew such a large antenna, but I wanted the robust and proven Cubex design. One day I discovered that the owner was no longer interested in building large antennas and was looking to sell Cubex, and another reputable brand, Tennadyne Log Periodics. For the first time in my adult life, I was about to be unemployed as the company I worked for was moving to Houston. Not me, no way! So I made an offer to buy Cubex and Tennadyne, which I did in October of 2021. Now I’m SURE to have my quad… maybe.
After bringing the companies home to Collinsville, OK I got BUSY! I didn’t have time to do anything. All my hobbies got pushed aside for many months and the last thing I wanted to do after long days in the shop was work on another antenna. Honestly, I was having fun working on shop processes, supply chain and other manufacturing challenges. Those efforts paid off in the long run as we are much more efficient now, and I actually find a little time to play. Finally, after 2 years of owning the business I’ve built my own antenna, and since I now manufacture these kits, I DID end up scratch building after all!
For 16 years I’ve wanted to try this thing out. Here we go!
Assembling the 24′ boom.
Assembling the spreaders and stringing the wires. This took two days.
Elements on the boom. It’s getting BIG!
The antenna sat on the scaffold for a few weeks while I kept up with work and waited for good weather. Finally, I had all the cables built and we were ready to schedule a lift.
Bye-bye Hexx-Beam… see you on Field Day! Thank goodness my tower cranks down to 25 feet. I really don’t like being up there!
The reflector and director 2 elements were removed to make the assembly a bit more stable.
I was exhausted from being up on the lift for two days, so my brother came up to stab the parasitic elements (he lives next door). See that mess of cables? Most choose to terminate into a remote switch up on the mast. I decided to run seperate feeds down to my ground mounted switch for easier maintenance. A little extra cost, but I can get to the relay box without a lift if I smoke one.
Looming Large over Cubex HQ.
Looking good against the Oklahoma sunset.
I wasn’t exactly sure what to expect from a muilti-band quad, and while the preliminary sweeps with my RigExpert looked ok, the real test would be at the radio. I tested several points up and down each band, but haven’t taken the time to create charts with my data points, so I’ll summarize here.
20m – 1.3:1 or less from 14.000-14.070 and 1:1 from 14.070-14.350
17m – 1:1 across the band
15m – 1.3:1 or less across the band
12m – 1:1 across the band
10m – 1.5:1 or less from 28.000-29.500, approaching 3:1 at the very top of the band
I couldn’t be more pleased with these readings. For whatever it’s worth, I used the RigExpert AA230 and AA650 on my initial tests and while the plots were similar, the analyzers read a bit higher than my radio. The R,X function must work ok on these because my match cables on 10, 12 and 15m are apparently working well!
So how does it perform? I jumped on the air around 10pm local to find many signals on 20m. In between those stations was a soft white noise, literally nil on the S-meter. Noise levels are typically low here, but I can tell a difference from the Hexx-Beam and vertical. The quad is quiet. Turned the beam NE and immediately heard a UJ7 station in Uzbekistan. I was fumbling around with my software and didn’t catch him in time. He would have been a new one for me. A spin of the dial and I found TJ9MD. Worked him for a new entity, on 100W. Turned the beam up north and worked several Russians over the pole, then out west to work three Australian stations that gave me good signal reports. One of them was in Tasmania running a 3-element Cubex quad. We had a nice chat.
So there you have it! It’s working good, now I just need to work on my operating skills. 🙂
73, and CU on the bands!
Mark – K5YAC
14Nov2023