How to Buy Ham Radio Oscillators and Filters

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How to Buy Ham Radio Oscillators and Filters

Ham radio oscillators are electronic circuits that produce frequency signals. Oscillators are a very basic radio transmitter used for sending signals such as Morse Code. If the circuit has amplification, a frequency control device, and positive feedback, it begins to oscillate automatically. In fact, an amplifier becomes an oscillator if it is provided with too much positive feedback. They are not designed to oscillate but can easily start doing it when there is too much feedback. Oscillators are a building block  in ham radio equipment and essential for anyone who wants to send coded signals.

The filters for ham radios are used to filter high and low frequencies through the circuit and reject the ones that are not needed. The devices can allow or stop frequencies depending on the type of filter. Essentially, they stop unwanted signals and reduce feedback. For example, RF filters reject noise from objects in the room such as a hair dryer.

Since both oscillators and filters are highly technical, they can be frustrating to shop for. Many people do not even know where to begin, but with just a little knowledge about how they work and what their specifications mean, the search for the right oscillators and filters becomes much easier.

History of Ham Radios

Ham radio, also called amateur radio, is enjoyed by hobbyists as well as emergency service workers. It is a short-range, non-commercial radio transmission system. The development of ham radio is contributed mostly to several amateur experimenters. It started with the invention of Morse Code and continued to advance until sounds other than just signals could be transmitted through the air. In 1895, Nikola Tesla was able to transmit Morse Code up to six kilometres. Then in 1896, Guglielmo Marconi sent messages over the English Channel.

By 1908 many people were experimenting with radio transmissions and the first radio club was formed in Australian by 1910. It did not take long for clubs to start forming around the world and the popularity of ham radio to skyrocket. Today, there are regulations on how far people can transmit and operators much obtain a ham radio licence before they can start the hobby.

Ham Radio Oscillators

Oscillators are used to create repetitive signals. They produce radio frequency (RF) signals through feedback and amplification. An oscillator is basically an amplifier with a tuned circuit. The type of oscillator is determined by its circuit and the circuit is either a crystal or an LC circuit. Crystals are the ideal choice for radio because LC circuits have a tendency to drift badly due to temperature and aging. Crystals are more resistant to drifting which is a change in frequency caused by instability.

Ham Radio Crystal Oscillators

Crystal oscillators have been in use since 1880 when inventors discovered that hard substances, such as crystals, produce energy when they vibrate. These oscillators are electric and use the resonance of vibrating crystals to create the signals at a specified frequency. Environmental factors such as temperature and humidity can affect the vibration of the crystals. However, most radio oscillators have design specifications that reduce the inconsistency.

Ham Radio LC Oscillators

LC oscillators have an inductor and capacitor that produce an electrical charge. The concept is similar to that of a tuning fork that stores energy and oscillates. A capacitor stores the energy and when connected to an inductor, the charge flows and builds up a magnetic field. When all the charge is dissipated, it begins to build up again. The biggest benefit of LC oscillators is that there is no dissipation of energy because of resistance.

Ham Radio Oscillator Specifications

When shopping, buyers learn that each oscillator has certain specifications. After choosing the type of oscillator to get, selecting the specifications is the next step.

Ham Radio Oscillator Specification



The frequency is the number of cycles per second and it is measured in Hertz. For example, 10 kHz is 10,000 cycles. The frequency capabilities should match that of the ham radio. Those operating on high frequency systems need an oscillator that can handle that

Number of Pins

Oscillators are connected by pins. The number of pins has to match that of the ham radio's port

Phase Noise

Phase noises are short fluctuations caused by waveform instabilities. It is measured in dBc/Hz. The lower the rating, the less phase noise there is


The oscillators are given temperature ratings that indicate how much the temperature fluctuation they can withstand before there is any loss in performance


This indicates how much power the oscillator uses

Warm-Up Time

This is the measurement of how long it takes for the oscillator to become operable after a cold start

Buyers should have a good understanding of what the specifications mean and what they need before shopping.

Radio Frequency Filters

Radio frequency filters, or RF filters, play a fundamental role in maintaining a clear signal. They filter out the bad signals which cause interference and feedback. Each filter allows a certain range of frequencies to pass through, called the pass band. The stop band is the range of frequencies that the filter rejects. The range of frequencies allowed determines the type of filter.

Types of Ham Radio Frequency Filters

There are four types of RF filters to consider: high pass, low pass, band pass, and band reject filters. They are each classified by their frequency ranges. Hobbyists need to choose the one that works with their radio transmissions. If they are using a high frequency (HF) or a very high frequency (VHF) radio, then they need a filter that operates in higher frequency ranges.

High Pass Filters

High pass filters have a low cutoff frequency so they allow high frequency transmissions while blocking out the low frequencies.

Low Pass Filters

Low pass filters are the opposite in that they have a high cutoff point. They operate clearly in low frequency transmissions ranges but reject any high frequency transmissions.

Band Pass Filters

Band pass filters have two cut off points within the desired band of frequencies. These are most common in crystal oscillators. They block any transmissions above or below the limits.

Band Reject Filter

Band reject filters block out a specified range of frequencies while allowing all others to pass. For example, it could only block out the range of 59 Hz to 61 Hz.

Classifications of Radio Frequency Filters

There are also four main classifications of RF filters. Each is specifically designed to meet certain requirements. Each classification is are optimised for higher performance in a specific area.

Bessel Filters

The bessel filter has the cleared in-band response, meaning that the signals that are within the allowed frequency range are high quality. However, the transition from the pass band to the stop band is slower than most other filters make it not idea for radio.

Butterworth Filters

Butterworth filters are frequently used in radio because it is known for having no ripples within the pass band. Ripples are unwanted variations in the signal current. It accomplishes this by completely rejecting frequencies outside of the allowed range but also by being sensitive to the desired frequencies. Overall, the butterworth filter is the most commonly used in radio.

Chebyshev Filters

Chebyshev filters are known for having a fast cut off of blocked frequency ranges. However, the fast cutoff causes more ripple problems. Because of the ripple, these are not ideal for ham radio applications.


Elliptic filters have some of the best rejection capabilities due to a quick transition from pass band to stop band frequencies. However, like the chebyshev filters, the elliptic does this by allowing higher amounts of ripple.

Find Ham Radio Oscillators and Filters on eBay

eBay is the ultimate place to shop for electronics, especially less common ones, because they have thousands of common and rare products in one place. Ham radio supplies are not often found in shops so eBay provides the solution that that hobbyists need when it comes to finding specific parts.

To begin, all shoppers have to do is type the name of what they want into the eBay search bar and then begin browsing through the list of products. For example, if you type "butterworth filter&" or "crystal oscillator&", eBay then compiles a list of all the butterworth filters or crystal oscillators for sale. Be sure to read all of the specifications before ordering and make sure that they are compatible with your ham radio. Some sellers also sell multiple oscillators and filters for a discounted price. Since oscillators usually wear out after a certain amount of time, getting several of them is a good idea.


Ham radios can provide hours of entertainment for hobbyists who like to chat with other enthusiasts. Communicating through Morse Code in particular is a lost art that many people are starting to enjoy again. Ham radios also have practical applications such as providing a means of communication during an emergency or power failure.

Regardless of their intended use, adding oscillators and filters to the radio provides another way to communicating in addition to the regular voice chatting. As long as people understand what to look for and where to look for it, anyone can find an oscillator and filter for their ham radio. In basic form, shoppers only need to know which frequency ranges to look for and what kind of port their radio takes. The recommendation is that shoppers get the crystal oscillator and a simple filter within their frequency transmission range.

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