Low Pass Filter for UHF Transmitter: How are they used?

If you are building a UHF transmitter, there is a high chance that you will need a low pass filter for UHF transmitter.

A UHF transmitter transmits an RF signal in the UHF band, which could be anywhere in the frequency band from 300MHz to 1 GHz.

An example of a UHF transmitter is a GSM 900 transmitter. Such a transmitter typically operates at 890 to 915 MHz. The output power of a UHF transmitter could be +20dBm. ETSI or the European Telecommunications Standards Institute standard requires that all GSM transmission devices be able to conform the following spurious emissions:

• 9KHz~1GHz ≤ -36 dBm
• 1GHz~12.75GHz ≤ -30 dBm

Now, almost all UHF transmitters for GSM mobile devices operate in the saturated mode or near to saturation region for maximum efficiency. The drawback to operating near the non-linear region is that the second and higher order harmonics would be high. In such cases, it would be necessary to add a low pass filter for UHF transmitter after the power amplifier to block these spurious even before they can reach the antenna.

Wide Selection of UHF Band Low Pass Filter for UHF Transmitter

AWG Tech has a wide variety of UHF low pass filter with different cut-off frequencies and stopband rejection characteristics. You can choose from our standard product catalog or you could contact us with your detailed requirements. You can rest assured that we can provide the best filter that suits your needs.

Click here to see a list of our standard UHF low pass filters.

Looking at the Basics of Low Pass Filter and UHF Frequencies

Low pass filters are types of RF filters that only permit the entry of low frequencies in their circuitry and impede every high frequency signal attempting to enter the system. The passive low pass filter circuitry is made up of a fusion of capacitance, inductance or resistance with the intention of generating high attenuation above a certain frequency and little or zero attenuation below that certain frequency.

There are different types of low pass filters; one of them is a low pass filters for UHF transmitter. UHF, or Ultra-High Frequency, is one of the commonly used frequency band in daily applications. They help in the transmission of television signals and they are also used for mobile phones as well. Plus, UHF waves is made up of frequencies that fall between 300MHz and 1GHz, and is also called as the decimeter band or decimeter wave due to the wavelengths measuring up to one to ten decimeters.

Let’s tackle on the basics of both Low Pass Filters and the Ultra-High Frequencies below.

Low Pass Filters: The Basics

As mentioned above, low pass filters, as the name implies, only accepts low frequencies and blocks off every attempting high frequency entrance. These filters are utilized in a wide array of applications, particularly in radio frequency applications. The most basic low pass filters is manufactured out of a resistor and a capacitor; however, complicated low pass filters have a fusion of series inductors and parallel capacitors. Let’s skip the complicated low pass filters and focus on the simple form.

A simple low pass filter is made up of two components, the inductor and the capacitor.

The inductor’s blocking capabilities increases in line with the increase in frequency. This high blocking power in series oftentimes blocks high frequency signals from reaching the load. On the other hand, the capacitor’s blocking capabilities lowers in line with the increasing frequency. This low impedance in parallel with the load resistance oftentimes shorts out high frequency signals.

The Fundamentals of Ultra-High Frequencies

Adding up to the above mentioned information about UHF band frequencies, they multiply mainly by line-of-sight. These signals are being impeded by physical obstacles such as hills and mountains, although the transmission of UHF band is powerful enough to pass through and is strong enough for indoor reception.

One main benefit of UHF transmission is the shortened wavelength that is generated by the high frequencies. However, one main disadvantage of UHF is the limited range of broadcast. Plus, UHF transmission and reception is further enhanced, or degraded, by the tropospheric ducting as the atmosphere warms up and cools down throughout the entire day.

Overall Conclusion

Knowing the fundamentals of both low pass filters and UHF transmissions, it can be said that the main function of a low pass filter for UHF transmitter impedes the entrance of high frequency signals allowing the passage of only low frequency signals. Signals are permitted to pass through walls and the short wavelengths produced by the UHF transmission provides a clear communication between two-way radios and with mobile phones.