HF-Band Low Pass Filter

The HF Band Low-Pass Filter – A Necessity in Short-wave Communication

Filters, whether for radio frequency (RF) or for microwave (MW) filters are both passive devices that are designed to operate with signals in a wide range of frequencies. Usually, such frequencies are applied to wireless communications like mobile phones, Wi-Fi, and so on.

Such filters typically find themselves more as building blocks for set-ups like duplexers, diplexers, or in components that separate or else combine multiple bands of different frequencies. One such component is the HF band low-pass filter.

HF-Band LC Low Pass Filter

Due to the low frequencies of the HF Band, HF low pass filters can only be realized using inductors and capacitors. With cut-off frequencies from 1 MHz to 30 MHz, our HF Low Pass filters can be made very compact.

Take for example, ALPF-10M-01, a 10MHz low pass filter. The filter measures only 40mm X 12mm x 10mm. This filter has a 0.5 dB cut-off frequency at 10MHz and is used primarily for rejecting harmonics of 10 MHz that arises from a 10MHz OCXO clock that is commonly used in many satellite modems. It has a rejection of more than 30dB from 20MHz to 100MHz.

The table below lists some of the common HF low pass filter in our HF-Band low pass filter product line-up. For more information send us an email at info@awgrf.com or fill in the enquiry form here.

Customized Low Pass Filter

Most of our filters are customized to our customers’ requirements. We can design the filter with different cut-off frequencies and stopband rejection at no extra cost to you. Contact us today to get a high quality custom designed low pass filter.

Part Number1dB cut-off frequencyInsertion LossRejection
ALPF-01M-011 MHz3 dB max> 85 dB at 2 MHz
ALPF-10M-0110 MHz3 dB max> 50 dB at 20MHz – 200MHz
ALPF-22M-0122 MHz3 dB max> 40 dB at 40 MHz
ALPF-30M-0130 MHz3 dB max>30 dB at 50MHz – 500MHz

What is the HF Band?

HF stands for ‘high frequency’, and it refers to the range of radio wave frequencies that lie between 3 and 30 MHz (megahertz). This makes it a large part of the frequencies used in shortwave radio – transmissions using frequencies from 1.6 to 30 MHz, often involving long distances.

Because the ionosphere can reflect the waves in these frequencies back to Earth, this band of frequencies are suitable for such applications as aviation communication and weather stations.

The Low-Pass Filter

Also sometimes called a treble cut filter or high-cut filter when used in audio applications, this is one of the four general functions of RF and MW filters. It’s designed to let signals lower than a cut-off frequency pass through, but attenuate signals higher than said frequency.

There are many ways low-pass filters can be used in communications, such as in anti-aliasing before converting audio from analogue to digital media, or digital filters for smoothing data sets.

Ideally, a low-pass filter would completely eliminate (that is, reject) the frequencies higher than the one it’s designed to use as the cut-off. However, it’s impossible to realize the ideal filter because of time constraints – the ideal filter needs signals in an infinite extent of time.

Designs for real filters, for real-time applications, do their best to come as close to the ideal as possible.

Applications of an HF-Band Low Pass Filter

Putting both of these together, you have a component that can be used in anything from amateur radio to transoceanic communications. By using a low-pass filter tuned to, say, 20 MHz, those using such systems can ensure only signals below that frequency, so there are less chances of miscommunication in some way.

Such a filter is also used to remove small amounts of high-frequency noise from a signal, resulting in a clearer, if not smoother transmission.

Using only a first-order filter, where the signal amplitude decreases by half each time the frequency doubles, may not bring about the desired results. AWG Tech recommend at least a fifth-order filter, which attenuates higher frequencies earlier than a first-order filter does. This is particularly important in applications related to, say, aviation.

Since this sort of filter is passive, it’s relatively simple to design – however, there are certain drawbacks. Low frequencies, for example, bring about high L and C values, leading to components that are quite large. Also, if the circuit requires gain, it can’t be added directly to the filter.

AWG Tech designs and manufactures a custom HF-band low pass filter for your application’s needs. Contact us by filling in the form here.

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