3D print your subsequent antenna

The construction of antennas is a time-honored amateur radio tradition. Shortwave antennas are usually bulky, but antenna sizes are fairly manageable at FM frequencies. [Fjkaan’s] The 2 meter quadrifilar helicoid antenna is a good example, and the structure for it can be created using 3D printing combined with an electrical line.

Lots of people including [G4ILO] Use PVC pipes for the structure, and this design inspires [Fjkaan]. Although the line is a little less extensive, it seems to work well and is easy to cut. The helical design is common for satellite work because of its circular polarization and omnidirectional pattern.

A quad helicoid antenna is actually two antennas in one with a 90 degree phase difference between the two. There are several ways to achieve this, but in practice most of these antennas use different loop sizes for the two antennas. A loop is slightly larger than the frequency of interest and therefore inductive. The other loop is slightly smaller and therefore shows capacitive reactance at the center frequency.

Although both antennas are reactive, the reactances cancel each other out in parallel, leaving behind a nice ohmic load that suits the radio. However, the lining above needs to be balanced by some form of balun or choke.

We have seen these antennas do great things. If you need a satellite receiving primer, we saw a good one last year.

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