I have an array of towers that was installed in 2017. They run Sensorgnomes that only detect Lotek tags. I’m writing a project proposal to upgrade the system to dual mode. I like the setups I’ve seen with 4 antennas reading 166.380MHz and 4 antennas reading 4.34MHz placed higher on the mast. Each group of antennas are on a single plane.
I currently use 9-element Yagis. Is it possible to set them up in this configuration? All of the other photos I’ve seen use smaller Yagis. I want to make sure this isn’t a structural issue before I submit an equipment list for this proposal.
Hey Jamie,
I don’t see any issues with your plan. If you already have four 9-element Yagis (166HMz), adding four 434MHz antennas to pick up CTT tags shouldn’t be a problem as they’re substantially lighter and smaller than the 9-element antenna. Not sure what you have for a mast set up, you’ll just need some extra height for the 434 additions and make sure your sensorstation or sensorgnome has enough ports to support all of your antennas. I have helped set up 5 dual mode towers in the last year that have different mast setups and support three to four of each antennae.
You can end-mount the UHF antennas on the same plane because they’re small enough, but due to their size, the 9-element VHF yagis generally need to be center-mounted. If you can’t end-mount adjacent antennas (which makes them nearly invisible to one another, interference-wise), they need to be spaced a wavelength apart on the mast to reduce interference issues (~3’), so you’ll need enough mast real estate to do that. I have seen examples of people end-mounting larger antennas and then supporting the antennas themselves with additional guylines, so maybe someone can speak to that, but it looks complicated. For most of our dual-mode stations, we have 4 UHF antennas end-mounted on the same custom mounting plate or canopy mount (can share if you’re interested), and then the larger VHF antennas are center-mounted and spaced below them along the mast every 3’.
Another thing I thought of… Do the 434 yagis need to be higher than the 166 yagis? The yagis on half of my current stations are 20-30m off the ground. I’m curious about how much I will need to alter the current setup.
Correction on this- the 3’ spacing is about 1/2 a wavelength for the VHF (which should be adequate if the neighboring VHF antennas on the mast are at 90 degrees to one another; they would have bigger interference issues and need more spacing if you stacked them at 180 degrees).
Sharing this information here in case it’s helpful to others. There are a couple options for end-mounting the UHF’s that we’ve used on free-standing stations. A canopy mount was recommended to us by some Motus folks on the east coast and it’s a good off-the-shelf option if you have antennas that have coax cable attachment points that allow for this. We needed to shim the canopy mount with PVC to get everything snug, but then it worked well. The UHF antennas from Maple Leaf allow for this design.
Some of the other antennas we’re working with have coax that comes out the end, so we moved to using a custom aluminum plate. My coworker, Gavin, can share more information on his design for that in case it’s useful for anyone.
Attached are photos of one of our stations using a canopy mount and another using the custom plate.
Here is the updated design for our CAD top plate. We order from Xometry but most machine shops are capable of cutting custom plates like this.
We use 1/4" thick 5052 aluminum with a diameter of 22 inches. The cost is typically around $100 depending on the quantity ordered and I am happy to provide the .step file if anyone is interested.
