The NWT-7 frequency response meter is deservedly popular among radio Amateurs and designers of various equipment. Now there are many varieties of this frequency response meter. They are United by one thing – the use of DDS as a computer-controlled sweep generator. The first publications of this DK3WX Amateur radio circuit appeared in the German Amateur radio magazine FUNKAMATEUR on 12/1997 and 1/1998 . Since then, the software and circuitry of the device have changed. The project is also supported by the German Amateur radio operator DL4JAL. There were also domestic developments using the same idea.
From the very beginning of the appearance of this device, radio Amateurs began to use bridges for measuring SWR, remote high-resistance and 50 Ohm heads, etc. There were further developments of the device up to 500 MHz NWT-502 (DL1ALT). However, their cost and often unavailability of the element base narrow the circle of users of such devices.
Sergey Belenetsky (US5MSQ) developed a scheme for a module box for NWT for setting up and testing different filters in the range from 100 kHz to 30 MHz. One of the simplest options is presented today. the chain of tuning resistances allows you to set the source/load resistances very quickly and accurately, which allows you to quickly check any quartz filters, piezo filters and EMF.