Notes on 6-Element Wide-Band 2-Meter Yagis
Antenna Circular Polarization
Yagi Uda Antenna Calculator
Coaxial Power Split Calculator
Calculate the extra length of coax feeding the other dipole for circular polarisation
In the final version, after few weeks of testing (satellite reception), I passed the two coaxial cables through the back of the plastic box, like this:
This allows the cables to run easier towards the back of the antenna along the central tube.
A thing that I liked to do differently is this: You see the connection of three cables for phasing and matching
Don’t connect the cables like this, all running in the same direction
because they create an ugly bulge, and can’t go nicely along the central tube.
Instead, try to connect them exactly as in the diagram, with the main coax going towards the back, and the other two towards the front. For the longer cable you simply make a loop, which looks nicer.
One thing I should have shown in the video is how to connect the shield of the three cables. The copper is easy to solder, but the 75Ω coax usually has an aluminum shield. I used a crimping pin like this
About the connections inside the plastic box, remember this: the longer cable goes to the Horizontal antenna. Horizontal antenna is the one towards the front.
So the blue antenna is for Horizontal and it’s more to the front. Also respect the side where to attach the core and the shield. Keep the central wire of the coaxial as short as possible. The shield can be prolonged as needed (the green wire in the photo)
Of course, the antenna can be rotated as you like, there’s no Up or Down, as long as you respect the schematic.
Another thing to pay attention to: The aluminum tube has a thin layer or aluminum oxide which is electrically insulating, so before attaching the cables, use a bit of sanding paper to clean the surface. Do this before you finish the job, because after it will be very hard. I know.
Now the main coaxial cable goes to the radio. Because the losses are big with such a thin cable over long distances, I used a very thick coax that I had laying around for years. To buy such a low loss performant cable is very demanding on the budget. This is how I did it (observe the difference in thickness).
I used an N-type connector at the bottom of this cable. Here you see attached both the VHF and the UHF cables to a coaxial relay for cross band satellite operation.
VHF antenna design, 6 elements, 2 meters long, 9dB gain
UHF antenna design, 2 meters long, 12 elements, 12dB gain
Be aware of the cable loss!!!
I used this Antenna (Vector-Network) Analyser to measure the cable loss…
Here you see the loss of a 15m long, RG58 (50Ω, Ø4mm, ordinary) cable.
The loss is considerable in VHF – 5dB, and enormous in UHF – more than 9dB.
-9dB means that only 10% of your power is passing thru.
Almost the entire antenna gain is lost over the cable.
So a high quality, thick, expensive cable is mandatory, especially in UHF. RG58 is to be used for short connections, of less than 3 meters.