Tucson TAPR Assembly And Operation Manual

RF Power Limiter for SDR Receivers
Assembly and Operation Manual
Revision B
Revised: 7 February 2025
©2025 Tucson Amateur Packet Radio Corporation
The TAPR RF Limiter provides protection from strong RF signals to a receiver or other sensitive RF input.
It starts limiting signals at about -6 dBm input and is effectively "hard limiting" by +10 dBm. In other
words, very strong signals that might damage a receiver are limited to a power level that will (hopefully)
prevent damage. It is intended for operation at 54 MHz and below, but can be used at 144 MHZ if additional
attenuation is acceptable.
Operation is simple – just install it directly ahead of the device (preamplifier or receiver) that you want to
protect. If possible, any lowpass or bandpass filter should be installed ahead of the limiter. This minimizes
the likelihood of generating spurious signals (see note 3 below).
IMPORTANT NOTES:
1. The RF Limiter is rated for a maximum continuous power dissipation of 200 mW. Power input
above one watt will cause the fuse resistor to fail, which should cut off the output. However, we can't
guarantee that this will work, so please use care not to exceed safe input levels!
2. Some sensitive preamplifiers or other equipment might not be able to withstand even the reduced
power output by the RF Limiter. Review the information in this manual to make sure it is suitable for
use with your equipment.
3. The diode in the limiter is a non-linear device. That means that when it is limiting it will generate
harmonics of the input signal and possibly other intermodulation products. In other words, it could
create interference to nearby receivers on other frequencies. That's why putting it behind a filter may
be helpful.
Introduction