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I want to build an ladder SSB filter using 8 MHz quartz resonators. I don't have frequency meter but I have NWT-70. How can I match crystals to build a good filter? What kind of parameters should I take into account?

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    $\begingroup$ I assume that NWT means "network tester"? It's not an abbreviation I'm used to, and my google-magic sems too weak to answer this. In what way does it differ from a network analyzer? You don't happen to have a link to a datasheet of that device? $\endgroup$ – Marcus Müller May 20 at 18:13
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    $\begingroup$ I found NWT-70 to be a USB interface, software-controlled, software-displayed sweep generator/frequency analyzer. Search for that exact text and you'll find the device. $\endgroup$ – Zeiss Ikon May 20 at 18:48
  • $\begingroup$ @MarcusMüller I don't have a datasheet but I found one of pages which have some information. It is some sort of network analyzer but not a professional grade. I am pretty green there so I might ask some bad/silly questions. $\endgroup$ – zoonman May 20 at 19:33
  • $\begingroup$ @zoonman if that's the case, simply have one rung of your ladder (i.e. a capacitor from center to outer conductor, the crystal, another capacitor from the other end of the crystal to ground) and attach that between the connectors of the NWT; should give you a frequency plot; save that. Replace the crystal (don't also replace the caps, they are non-ideal too, and would make measurement way to complicated), get the plot. Compare the plots on whether their passbands align. $\endgroup$ – Marcus Müller May 20 at 19:46
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    $\begingroup$ Charlie Morris (ZL2CTM) did a really nice series of videos on this some time back: (youtube.com/watch?v=Ur7Cze-X0zo & youtube.com/watch?v=xnUMzz0vo9U). He offers a couple of options to measure frequency as I remember. $\endgroup$ – Buck8pe May 22 at 15:46
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One good option here would be to buy and build a crystal tester and frequency counter kit. These are available on eBay for under $20, and take less than two hours to assemble. It's only a 4 digit counter, however, so if you need a closer match than 1 kHz you'll need one with more precision. Still available as a kit, though likely without the direct crystal testing function, and the kit will cost a bit more.

Alternately, if the control software lets you directly control the frequency on that sweep generator, you should be able to spot the amplitude peak when you hit the crystal's frequency; the peak will be a good bit wider than the 1 Hz resolution claimed for the NWT-70, but you if you can sweep a narrow range, you ought to be able to read the peak well enough to at least equal a 4-digit frequency counter, if not get down to a few tens of Hz.

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  • $\begingroup$ I think NWT gives me information about frequencies but I need to understand how can I use that information. $\endgroup$ – zoonman May 20 at 17:06

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