V-Dipole Antenna for Weather Satellites

[Pavel]

Short answer: For common 137 MHz low-Earth-orbit weather-satellite reception, a simple horizontal V-dipole uses two elements about 53 to 55 cm long with an included angle near 120 degrees. Mount it in the clear and orient the V consistently; geometry and a low-noise location matter more than high gain.

Before you start​

• Define the target frequency and polarization before choosing an antenna, LNA or filter. A wide tuning range on the SDR does not make one antenna efficient across that range.
• Sketch the RF path from antenna to receiver and include connector adapters, coax length, DC bias and every active component.

Step-by-step method​

1. Step 1: Choose a center around 137.5 MHz. The ideal quarter-wave is about 54.5 cm, so start each element near that length and keep the two sides symmetrical.
2. Step 2: Mount the elements in a horizontal V with roughly 120 degrees between them. Feed the center with coax and add a common-mode choke or several coax turns near the feed if cable pickup is a problem.
3. Step 3: Place the antenna outdoors or near an unobstructed opening, away from computers, LED supplies and metal roofs. Record the V direction and height so later changes are comparable.
4. Step 4: Test on passes of similar maximum elevation. Record baseband and compare signal-to-noise ratio, lock duration and decoded image lines, not only the strongest moment.

Concrete example​

A practical first build uses two 54 cm conductors at about 120 degrees, mounted horizontally around one metre above a non-metallic support. Exact preferred orientation varies with convention and site; document it, test several passes and rotate only as a controlled comparison.

How to judge the result​

Success is a continuous pass with fewer deep fades and enough signal for the chosen decoder to maintain lock. If noise rises when the coax is touched or moved, address common-mode pickup before changing element length.

What to record​

• Compare the same signal at the same time, receiver gain and bandwidth; record signal level and noise floor separately.
• For a receive antenna, decoded message count or usable signal-to-noise ratio is usually more meaningful than waterfall brightness.
• An accessory helps only when the wanted signal improves more than interference, noise or overload products.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Mounting the V-dipole directly against a metal balcony, roof or window frame can detune it and create deep directional nulls that the calculated element length cannot fix.

Final check​

Return the RF chain to its original state and repeat the comparison. Keep the antenna or accessory change only when the wanted-signal result repeats without overload, unsafe DC or an unexplained noise increase.