Crystal ladder filter software

Beside the obvious uses in homebrew receivers and transmitters, crystal bandpass filters can be used with other test equipment to make measurements that are beyond the capabilities of the test equipment.

See the page on Phase Noise and Overload Testing for an example or click here. Filters having passbands within the amateur radio bands are more useful for testing receivers and transmitters but common crystal frequencies must be used in order for the crystals to be inexpensive.

Assuming that you are not trying to design a crystal filter for an exact frequency, the procedure is actually quite easy to do. Crystals not crystal oscillators are used with the resulting filter frequency usually a few kHz different than the number stamped on the crystal case. Frequencies such as 1. Also consider some of the special crystal runs by the QRP clubs for crystals in the 7.

I have built about a dozen filters and can design, construct and test one in a few hours. Here are the basic steps: 1. Pick a frequency which is a common crystal frequency but near to the frequency you want. The crystals cut to be used in a parallel resonant circuit will have series resonances below Buy a group of crystals to measure so that you can pick ones with similar parameters.

I usually buy about 25 crystals and can easily make 2 filters. Measure and sort the crystals. Simulate the resulting filter and adjust slightly if needed. Match the filter to the desired input and output impedances using transformers or L-networks. Construct the filter using good RF construction techniques.

Filter will work as expected! What can Crystal Filters be used for? What has Changed? Share this: Twitter Facebook. Like this: Like Loading Leave a Reply Cancel reply Enter your comment here Fill in your details below or click an icon to log in:. Email required Address never made public. Name required. Follow Following. Sign me up. Already have a WordPress. Log in now. Loading Comments Email Required Name Required Website. A low-quality crystal filter in even a high-priced commercial transceiver can degrade its selectivity and dynamic range.

On the other hand, a good crystal filter can significantly enhance receiver performance, whether in a simple "weekend" project or in a competition-grade station. Commercially available crystal filters are usually expensive and often discourage construction-minded amateurs from pursuing projects that include crystal filters.

In addition, studies conducted in recent years conclude that in a high-performance receiver, a crystal filter may become the "bottleneck" restricting the receiver's dynamic range. So, the goal of this article is to provide design and building methods that can be used to construct crystal filters that rival or exceed the quality of commercially available filters. I will describe a simple, practical step-by-step procedure to design, construct and align crystal filters using equipment available to most construction-minded amateurs.

The resulting filters achieve top-quality performance at a fraction of the cost of commercially available crystal filters. Most of the crystal filters described in amateur projects and those being sold commercially are lattice, half-lattice or cascaded half- lattice filters like those shown in Fig 1.

A two- or four-crystal filter of this type can provide a symmetrical response with reasonably steep skirts.

But the bandwidth of such filters is a function of the frequency separation of the crystals. If a steeper response is desired, designing a half-lattice filter with more than four crystals becomes more complex, requiring matched pairs of crystals and several adjustments. While it is reasonably easy to obtain matched crystal pairs for CW filters, it becomes considerably more problematic to obtain pairs of crystals separated by a couple of thousand hertz for use in SSB filters.

In addition, the coils used for lattice filter alignment often use small cores, which can result in the degradation of dynamic range because of core saturation at high signal levels. Another form of filter—which is the subject of this article—is the ladder filter shown in Fig 2.

It typically has an asymmetrical response and is sometimes called the "lower-sideband ladder" configuration.