[Elecraft] Chinese Filters on eBay

[Walter Underwood]

One of the fun things I got to help with at a summer job was an acceptance test of a filter for aircraft use. We bolted that poor little filter to a huge shake table, then checked the group delay under vibration. It did not pass.

There were some serious vacuum tubes powering the shake table “voice coil”.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Nov 2, 2016, at 12:22 PM, Wayne Burdick <n6kr at elecraft.com> wrote:
> 
> FYI: You can't screen crystals just with a VNA. And it isn't just about Q. 
> 
> Crystals have physical IMD properties that are highly dependent on signal injection level. We have to screen the crystals over a range of signal levels individually, first, then again when they're assembled into a filter. The crystals also have to be burned in, or they can rapidly age when installed in the radio and develop undesirable properties down the road. There can be issues with electrodes, dust, etc., unless the crystal manufacturer is held to a high standard.
> 
> 73,
> Wayne
> N6KR
> 
> 
> On Nov 2, 2016, at 10:43 AM, Michael Walker <va3mw at portcredit.net> wrote:
> 
>> If are willing to invest $50, then go ahead.  He does have a return policy.
>> 
>> Next, I would buy, beg, borrow a VNA and sweep them.  That is the only way
>> to be sure.   It is hard to read his scans/sweeps.  They Q factor looks a
>> little soft, but usable.
>> 
>> If the soldering is poor, that is an easy fix.  Just redo them.
>> 
>> I'm sure they will work ok.  They won't do any damage to your radio.  But,
>> you normally do get what you pay for.
>> 
>> Mike va3mw
> 
> 
> 
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