Build your own satellite antenna: V-dipole, QFH and a handheld Yagi
The antenna matters more than the radio. Three home-made antennas that cover almost every beginner satellite target, what each one is good at, and the mistakes that cost the most signal.
Why the antenna comes first
A $40 receiver with a good antenna hears more than a $400 receiver with the whip from the box. Satellite signals are weak (a few watts from hundreds of kilometres away), so every decibel the antenna collects, or loses in cable, decides whether a pass becomes a clean picture or noise.
The good news is that the best antennas for satellites are cheap to make. You need metal rods or wire, a piece of plastic pipe, coax and an afternoon. Here are three designs, from the simplest to the most capable.
1. The V-dipole: 137 MHz weather satellites in ten minutes
Two straight rods, each about 53 cm long, joined at the centre in a V with 120° between them. The centre conductor of the coax goes to one rod, the shield to the other. Lay the V flat (horizontal) about a metre above the ground, with the open side of the V pointing north or south.
It works because weather satellites in polar orbit pass from north to south or south to north, and a flat V hears the sky above it fairly evenly. It costs almost nothing, and it is how most people get their first Meteor-M image. Its weakness is low passes: below about 20° elevation the signal fades.
2. The QFH: the best all-sky antenna for weather satellites
The quadrifilar helix (QFH) is two loops of wire or copper tube twisted half a turn around a vertical pipe. For 137 MHz it looks like a twisted cage about 70 cm tall and 30 cm wide. It hears circular polarisation, which is what the satellites send, and keeps nearly the same strength from the horizon to straight up.
Don't guess the dimensions: use a QFH calculator (search for the KF8EEZ or jcoppens calculator) with your exact frequency, conductor thickness and the usual width-to-height ratio of about 0.44. The two loops are slightly different sizes on purpose. Symmetry and clean, solid joints matter more than millimetre accuracy. Mount it vertically, as high and as far from the house as you can.
A QFH takes a weekend, and in return it gives longer, cleaner passes than a V-dipole, especially when the satellite is low over the horizon.
3. The handheld Yagi: for the ISS and amateur satellites
A Yagi is a row of rods on a boom: a reflector at the back, a driven element connected to the coax, and one or more directors in front. It is directional: it hears strongly where you point it and little elsewhere. That is what you want on the 145 and 435 MHz amateur bands, where signals are weaker.
The classic home build for 2 m is the tape-measure Yagi: three elements cut from a steel tape measure on a PVC pipe boom, each element around a metre long. Use a published plan (search for the WB2HOL tape-measure beam) rather than calculating your own, because the tape's width changes the ideal lengths. Dual-band handheld Yagis that cover both 145 and 435 MHz can also be bought, and they are the standard for working FM satellites by hand.
Hold it like a flashlight: aim at where the satellite rises, follow it across the sky, and twist your wrist slowly. Twisting matches the polarisation, which changes during the pass, and often turns a faint signal into a clear one.
Which one should you build?
- Weather pictures only: start with the V-dipole tonight, and build a QFH when you want better images.
- ISS voice, SSTV and amateur FM satellites: a handheld Yagi. A V-dipole will catch the ISS on a high pass, but a Yagi makes it easy.
- Unattended recording (a station that receives while you sleep): a QFH or a turnstile, because nobody has to aim them.
- Tracking with a rotator: a Yagi on a rotator gives the strongest signals of all (see our rotator guide).
The mistakes that cost the most signal
- Long, thin coax. At 435 MHz, 10 m of RG-58 throws away about half the signal. Keep runs short, or put the receiver at the antenna and run USB or network back to the computer.
- Mounting next to noise: walls with wiring, LED lamps, solar inverters and computers. A few metres away from the house can matter more than a better design.
- Unsealed connections. Water gets into coax and slowly ruins it. Seal outdoor joints with self-amalgamating tape.
- Skipping a check. If you can, measure SWR with a cheap antenna analyser such as a NanoVNA. If not, compare two passes before and after any change.