Why Use RF Dummy Load on VTX, Radio, and Antenna

by Oscar

In this post we will talk about the use of RF dummy loads for VTX, radio transmitters and Triple Feed Patch antennas. These are self termination circuit with 50ohm impedance and SMA interface, which is used to dissipate RF energy, AKA “RF terminations”.

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Where to Buy?

You can get RF dummy load from these vendors.

For Radio and Video Transmitters

Sometimes it’s easier to have the antennas removed from the quad and radio when you pack them in the bag, but you could be in trouble if you forget to re-attach the antennas when you power them up!

Further Reading: TX16S Removable Antenna Mod

When there is no antenna, all that power generated by the transmitter gets reflected back into the output circuitry. Heat will build up really quickly and it could damage the transmitter (output transistor). Some radio transmitters may have internal protection and gives you a warning if the antenna is absent, but it’s better safe than sorry.

Image credit: SnowLeopardFPV (https://intofpv.com/t-homer-simpson-moment)

RF terminations, or dummy loads, are excellent for protecting our transmitters whenever you want to remove the antenna, be it a 5.8GHz VTX or 2.4GHz/900MHz RC transmitter. They are tiny and inexpensive, and protects your gear if you forget to put your antennas on.

They also keep your SMA connector dust-free! (And debris can’t get in.)

Some people even use dummy loads for changing VTX channels in the field. Because it radiates very little signal compared to a proper antenna, it doesn’t affect other pilots in the air.

For Triple Feed Patch Antennas

Dummy loads are commonly used on Triple Feed Patch antennas (product page: https://oscarliang.com/product-fxgz). These antennas have two outputs, RHCP and LHCP, and usually we only use one of them. By putting a dummy load on the unused output keeps the signal from leaking. This avoids signal loss and improves performance and efficiency of the antenna.

Triple feed patch antenna with dummy load on one output

Check Before Use

You may want to test with a multimeter and see if your dummy load actually have the correct impedance (measure the middle pin and the outside). Your meter should read around 50ohms if they are working properly.

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