VHF-Band High Pass Filter – Learning the Basics of both VHF-Band Frequency and High Pass Filters

The VHF-band frequency (Very High Frequency Band) is any frequency range on the electromagnetic spectrum that ranges from 30MHz to 300MHz and its corresponding wavelengths range from one to ten meters. The most known uses for this frequency band are for FM radio broadcasting, television broadcasting and long range data communications that can reach up to several tens of kilometers with radio modems, amateur radio and marine communications.

In RF filters, the use of the VHF-band frequency in a high pass filter, usually referred to as the VHF-band high pass filter, has propagation traits that are ideal for short-distance communications, which are usually somewhat farther than line-of-sight from the transmitter. With the added feature of the high pass filter allowing high frequency signals to pass through and impeding every low frequency signals, bass sounds are then filtered out and audio transmissions become clearer.

In addition, VHF is the least to be affected by the atmospheric noise and interference from other electrical equipment than with other frequency bands. On the other hand, it’s easily impeded by land obstacles (hills and trees are some) than HF and other lower frequency bands; however, VHF-Band is less likely to be affected by tall buildings and other less substantial obstacles than UHF frequencies.

The Propagation Characteristics of the VHF-Band Frequency

As mentioned above, the VHF-band propagation traits are compatible for communication in short-distances. Below are some of the other propagation traits of the VHF-frequency band:

VHF-band frequencies are limited to only that local radio horizon that’s 100 miles or less.
Comparing the VHF-band with the HF-band (High Frequency), the ionosphere doesn’t usually refract the VHF-band frequency.
VHF-band frequency waves can be further strengthened by the tropospheric ducting.

The Basics of High Pass Filters

Aside from learning some of the fundamentals of VHF-band frequency signals, the high pass filter needs to be understood to better understand the relationship between the two of them. Basically, a high pass filter, as mentioned above, allows the entry of high frequency signals and blocks the entry of the low frequency signals. Designing a high pass filter can be possible by altering the design circuit of the low pass filter.

A low pass filter functions exactly the opposite from high pass filters. Thus, when altering the circuit design of the low pass to high pass, the capacitor is then replaced with an inductor and the inductor with a capacitor. The capacitor’s value is then the same with the inductor’s reciprocal and it’s the same the other way around.

The Universal Uses of the VHF-Band Frequency

Specific sub-components of the VHF-band frequency have the same utilization all over the world. Some of the national uses of the frequency band are detailed below:

• 108-118MHz: Air navigation beacons VOR and instrument landing systems
• 118-137MHz: Serves as an air band for controlling traffic in the air
• 144-146MHz: Used for amateur radios; however, there are countries that use a frequency range from 144-148MHz.

Overall, the VHF-band high pass filter has functions of eliminating every low frequency signals from entering the circuit for a better audio transmission minus the bass noises and interferences. While the VHF-band frequency better uses these transmissions for short-distance communications making reception clearer without being blocked by buildings.