CaHRTenna Poseidon is the Coffee and Ham Radio’s take on the popular Rybakov vertical non resonant antenna. Today we’ll talk about Poseidon, show you how to build your own, and put the Greek god of the sea on the air.

CaHRTenna Poseidon Vertical Antenna:

The Rybakov Antenna:

Coffee and Ham Radio’s Poseidon is based on an antenna called the Rybakov. That antenna, created by Italian ham IV3SBE about 20 years ago is a non resonant ground ground mounted vertical antenna with a radiating element of 25 feet. At the feed point is a 4:1 unun or transformer to match the 200 ohm impedance the antenna presents. Radials of about a similar length provide the ground network for the antenna. With a tuner, the antenna will operate on the 80 through 6 meter bands, although it gets pretty inefficient on 40 meters and below. Your best performance will be on the higher bands and this style of antenna really excels on 10, 12, and 15 meters. As you get higher in frequency, the RF radiation angle gets lower and lower, making it an excellent DX antenna.

But why the name Rybakov? When IV3SBE designed the antenna, he envisioned it being supported by an 8 meter fishing pole. The antenna’s 25 foot length makes it perfect to deploy with a lightweight mast or fishing pole. Rybakov is Russian for fisherman, so it makes sense to give the fishing pole antenna that name.

Coffee and Ham Radios did send me a Poseidon vertical antenna kit to build and put on the air in exchange for a video. But my opinions are my own and there is no outside influence. So let’s head inside, build this antenna, and then put it on the air.


So what makes Poseidon different? I believe the key difference lies in the transformer. If you look at most 4:1 unun designs, they use a red T200 style toroid. The red toroids work well and offer very good overall efficiency, but a key design element of this antenna was to make is tunable with a transceiver’s internal tuner. That means you will need an SWR that’s 3:1 or less over the entire frequency range the antenna is designed for. Unfortunately the T200 isn’t up to that and you will get higher impedances at the lower frequencies. This green colored iron powder core that’s used in Poseidon offers an overall better impedance matching at a wider range of frequencies, with a slight tradeoff of efficiency. Is the tradeoff worth it? It is if you don’t want to bring an extra piece of gear out into the field. Also consider, lower impedance coming out of the antenna means less losses in your feed line. So overall, its a valid choice to make.

The second consideration with this antenna is that 4:1 transformers can pass along common mode currents, causing the outer shield of your feed line to radiate. This will affect your antenna’s radiation pattern. Proper 4:1 windings will also include a second toroid would as a 1:1 choke. In order to make this antenna easier to build, Poseidon does not use the double toroid winding, instead you will need a choke of some sort on your coaxial cable. Today I’ll be using an integrated choke on my feed line for this antenna.


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