RF Pre-selector: An overview of RF Pre-selector

There are many wireless systems co-existing in the same geographical location. In today’s environment involving radio receivers and the like, it’s important that you find ways to improve the performance of the devices you’re working with – or at least improve their components.

To improve the performance of your RF receiver, you need to remove any spurious signals from interfering and saturating your receiver. At the same time, you need to amplify the signals in the passband without degradation of the passband signal.

Radio scanners and other broadband front-ends – the devices usually on the receiving end of radio frequencies – tend to overload now and then, affecting their overall performance. Using an RF pre-selector, though, may help prevent the overload from happening, among other things.

RF Pre-selector: What do they do?

An RF (radio-frequency) pre-selector is a device that goes in between a radio receiver and the antenna, blocking certain frequencies and letting others pass through.

A pre-selector is usually tuned to have a narrow bandwidth, centred around the receiver’s operating frequency. This helps it prevent interference from other carrier signals. Some pre-selectors can also be further engineered so that it helps protect the receiver from voltage spikes and static input.

Without a pre-selector, sounds that are broadcast would be static-y and hardly intelligible. A pre-selector cannot, however, remove interference on the frequency it is tuned to. It’s also not the same as an antenna tuner, even if they’re placed in roughly the same place. A tuner transfers signal power from the transmitter to the feed cable as smoothly as possible.

Limitations of an RF pre-selector

Besides being unable to remove interference on the frequency it’s tuned to, a pre-selector can’t improve the ratio of the desired signal to noise picked up by the antenna.

No matter how well the signal is received, there will usually be noise accompanying the carrier signal, whether it’s atmospheric or generated within the pre-selector or the receiver themselves. Typically, what matters more is how much stronger the, say, radio station is compared to the noise level.

An RF pre-selector can only help a weak signal if its noise figure is better, or higher than that of the receiver; if their noise figures are the same, the signal isn’t improved. Therefore, it’s important to consider the noise figures of both pre-selector and receiver, so the right pre-selector can be chosen.

Good designs usually keep pre-selectors from overloading, save for when dealing with extremely high input levels based on the frequency the device is tuned to. However, high-gain pre-selectors – those that can considerably amplify a signal – can cause overloading even if the receiver is designed to be resistant to it.

With all pre-selectors, no matter the quality, there is some loss at the frequency it’s tuned to, usually in the inductor (the tuning coil), or the component made to resist changes in electric current. Unfortunately, tuning the pre-selector to a narrower bandwidth only increases this loss. Tuning it to a wider bandwidth can help increase the signal strength, but at the cost of more interference.

Despite these limitations, there’s still a place for a well-made RF pre-selector in telecommunications today; that’s why such establishments as AWG Tech PTE Ltd still offer them. Whatever you need a pre-selector for, you can always have one custom-engineered to better suit the project and to make the most out of it, without compromising the other components.