HF-Band Bandstop Filter
16MHz HF-Band Bandstop Filter: ABSF-16M05BW400K-01
A HF-Band Bandstop filter can have a stopband rejection anywhere within 3-30MHz. It has two passbands, a lower passband and an upper passband. This is best illustrated by looking at the frequency response of ABSF-16M05BW400K-01.
The filter has a lower passband frequency from dc – 13.5MHz with an insertion loss of less than 1 dB and an upper passband frequency from 19.4MHz to 31MHz with an insertion loss of 1 dB.
The stopband lies in between 13.5 to 19.4 MHz. The 40-dB stopband frequency is 15.85 to 16.25 MHz.
Application of HF-Band Bandstop filter
An HF-Band bandstop filter is used in an HF-band receiver or in the IF section to remove some spurious which may lie within a narrow band of frequencies. Whilst it may be possible to use high pass or low pass filters, band reject filters typically give the best rejection for a given real estate.
As can be seen from the frequency response plot of ABSF-16M05BW400K-01, the stopband is very steep and rejection above 40 dB can easily be achieved using just a 5 section band stop filter.
| Part Number | Passband | Insertion Loss | Rejection | Description |
|---|---|---|---|---|
| ABSF-5MBW1M-01 | dc – 3.5MHz, 7 – 30 MHz | 1 dB typ | > 40 dB @4.5 – 5.5 MHz | 5MHz HF-Band Bandstop filter |
| ABSF-10MBW2M-01 | dc – 7 MHz, 14 – 30 MHz | 1 dB typ | >40 dB @ 9 – 11 MHz | 10MHz HF-Band Bandstop filter |
| ABSF-15MBW1M-01 | dc – 12 MHz, 19 – 30 MHz | 1 dB typ | >40 dB @ 14.5 – 15.5 MHz | 15MHz HF-Band Bandstop filter |
| ABSF-20MBW2M-01 | dc – 16 MHz, 26 – 50 MHz | 1 dB typ | >40 dB @ 19 – 21 MHz | 20MHz HF-Band Bandstop filter |
| ABSF-25MBW4M-01 | dc – 19 MHz, 33 – 50 MHz | 2 dB max | >35 dB @ 23 – 27 MHz | 25MHz HF-Band Bandstop filter |
The Challenging, Yet Fun World Of HF-Band BandStop Filters
Of the wide assortment of bands in the IEEE (Institute of Electronics & Electrical Engineers) radio frequency spectrum, the high frequency (HF) band is one of the most crowded (but most lucrative). The HF band is the ITU (International Telecommunication Union) designation for the range of radiofrequency electromagnetic waves between 3 and 30 megahertz (MHz), and is also called the decameter band or decameter wave. The frequencies below it are called MF, or “medium frequency” while the next band of higher frequencies is called VHF (very high frequency). But what keeps other out-of-range frequencies from messing with the HF field? It’s done by devices called “filters”. Let’s look at how this electronic filter type does its job.
The HF Band Is Also Part Of The Short Wave Band
Here’s why the HF band is a very busy one – it’s actually part of the shortwave frequency band that’s truly suitable for long-distance communication across vast distances (or even continents). This frequency range is utilized by international shortwave broadcast services, government time stations, weather stations, amateur radio stations and citizen band services goes from 2.31 to 25.820 MHz. And this is where HF-band band stop filters effectively do their jobs.
What Are Band Stop Filters?
Of the different types of electronic filters, “band-stop” filters are a unique bunch. Well, it’s not because they function in exactly the opposite way as band-pass filters, but they’re also called “band reject” filters, because they allow certain frequencies to pass, and block those that are within a specific stop band, which are heavily attenuated.
But like band-pass filters, a band-stop filter is described as a second-order or two-pole filter, which has two cut-off frequencies, and its function is to pass all those frequencies from zero (DC) up to its first frequency point cutoff. It allows all frequencies above its second (or upper) cut-off frequency to pass, but it blocks or halts all those frequencies in-between.
What Makes An Ideal HF-Band Band Stop Filter?
So what makes an ideal band-stop filter for the ever-busy HF band? The “ideal” band stop filter should have infinite attenuation in its stop band, and in either pass bands will apply zero attenuation. The transition, or access, between the two pass bands (as well as the stop band) is vertical too.
While a band-pass filter is created through the combination of low pass and high pass filters, band-stop filters are made by combining together the low pass and high pass filters in a parallel configuration or set-up.
The ideal, or nearly-perfect band-stop filter (especially for the high frequency band) also has a frequency response which is the inverse of the band-pass filter, and should effectively block or reject frequencies that lie between its cut off frequency points, yet it passes all those frequencies on either side of this range.
Lastly, HF-band band-stop filters also accomplish their tasks by adding up, or summing up, all the outputs of a high pass with that of a low pass filter, with the filter’s output being the difference. Band-stop filters that are created or designed with a wide stop band are called band reject filters, while band-stop filters with a narrow stop band are called “notch” filters.