Compact Moxon Module

You may recall reading about my Yagi Module,” used for VHF/UHF contesting and exhibitions. It’s quite large, heavy, and impractical for routine use. So, I built a “compact tower” after being asked to bring a VHF setup to a group “Parks on the Air” (POTA) activation near Baltimore, MD. I wanted better reach than what my “Loop Module” provides, but not the commitment of mounting and traveling with my 75-lb (34 kg) micro-tower with 11’6″ (3.5 m) of road clearance. My new compact tower is half the height of the micro-tower and has just two Moxons, one for 6m and another for 2m, which are my most commonly used 50+ MHz bands.

For 50 MHz, I use a SM-50 Stressed Moxon by Par Electronics, referred to as the cheese slicer by my wife. It’s the same antenna from my contest tower. I use an SE-2MC Moxon by SAL Electronics for 144 MHz. Moxons have about 3 dBd of gain and can travel sideways down the road for compact width (tree avoidance). So far, the setup is a great compromise between my contest setup and the loops. The SE-2MC has a secondary benefit of being easy to switch to vertical polarization and tuning the entire 2m band. That is very useful when providing remote communications support for sporting events. My support position is on the edge of my club’s repeater coverage. Having even a modest beam is a huge benefit, especially since I can place it much higher than my roof-mounted vertical antennas.

Being shorter and lighter than my contesting setup, the 3-foot mast does not require the same support that’s provided by my 22-inch micro-tower. Plus, 2m Moxon would sit too closely to the tower shelf if it was present. Instead, I added an inline thrust bearing by Yaesu and then guyed it with my existing Seasucker setup. That was my quick solution since I already have synthetic lines cut and spliced for the Seasuckers. I will eventually prepare dedicated lines that allow me to guy this mast directly to the roof rack, eliminating the need for the Seasuckers altogether. This mast and antennas weigh half as much as the 6-ft mast with larger Yagis. So, I don’t think the extra anchor points directly on the car are needed.

Compared to my micro-tower setup, the “compact” is 55% lighter, more aerodynamic, and safer to drive down roads with tree cover. I can even fit it through my favorite drive-thrus! Much to my surprise, the lower wind load improved fuel economy to an impressive point: 28 mpg! Fuel economy with the Yagi module is usually around 23-24 mpg. For comparison, I can achieve 32 mpg or better with a naked roof and some self control. See this article on my other website for details.

I must admit that I didn’t have any success on VHF for the group POTA event. I think that have been because VHF SSB operation is a niche activity that’s often done with a schedule in mind. For example, there are local groups that get on 2m, 6m, and 10m SSB nets each week. Everyone knows the time and frequency; so, calling the NCS is an easy task. For the POTA event, I entered an online spot for us and then called CQ. I might have had better results if I had advertised in advance and coordinated with SSB clubs in the area. I KNOW there are SSB nuts in MD, NJ, and PA. So, making contact is possible unless they just don’t favor POTA. Maybe I’ll be able to schedule something next time.

Despite the setup’s shortcomings at the POTA event, I have seen an improvement during local SSB nets on 6m and 2m. This setup may replace my Loop Module. I’ll have to try it for a while and see what I think about the extra steps of using it instead.

Compact, but Still an Odd Station!



About Scott

I grew up near Houston, TX and served in the U. S. Coast Guard ordnance and electronics communities for over 35 years. I became involved with ham radio and computers in 1995. The explosion of technology made my jobs and hobbies quite interesting. My hobbies include Volkswagens, bicycling, photography/videography, electronics, ham radio, and web management.
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