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Monday, February 16, 2015

SolderSmoke Podcast #172: Pete's New Rig, Bill's BITX 2040,Crystals, MMM, SNA jr.,Portable SDR, KX3!, W7ZOI at a 'fest, BANDSWEEP!

Pete and Ben's LBS Receiver 

SolderSmoke Podcast #172 is available

16 February 2015

Bench Reports: 
Pete under the gun to finish SSB transceiver project. NEW VIDEO: 
Bill fixes his BITX 2040 Oscillator (Bandsweep!) 
Next: LP filter for 120 watt amp.
Bill's 13 dollar Chinese freq counter (Blue! With anti-wobble tape!)  
Bill's next rig:  Chipped to the Max, DDS, SBL-1s, plug in filters! 
Radio Shack going under and JAN no longer making crystals.
Mighty Mite Project:  Let's get them DONE! 
An easy way to get Q or ESR measurements on crystals? 
SI5351 as a crystal substitute. 
DuWayne's Scalar Network Analyzer lights up the internet!
The Portable SDR rig -- Pete almost goes to the dumpster! 
Report from the cutting edge:  Pete's new Elecraft KX3. 
MAILBAG:  Meeting W7ZOI and WA7MLH at a hamfest.
Instant Messaging with Farhan 

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  1. Hi Bill --- and thanks for Soldersmoke #172.

    RE: about using datasheet Q in addition to an L-C meter measure of Cp + calculating equivalent circuit values Lm + Cm with a W7ZOI oscillator + the G3UUR method to make “good enough crystal ladder filters”.

    I agree – you can make good xtal filters without knowing xtal Q. I did this in my early days before adopting a measurement means much mantra. However, I’ll respectfully argue that measuring xtal Q makes sense; is easy to do; and may reduce frustration from unexpectedly high filter insertion loss --- especially in narrow filters such as CW IF filters.

    As you know, insertion loss increases as filter bandwidth and xtal Q decrease.

    Relying on datasheet Q assumes that the xtals on hand match the datasheet values obtained when some product samples were last tested. My experiments, at least, show that 20-50% variance may occur ‘tween datasheet and my lab tests. Further, many of us get our xtals on eBay, from friends, or perhaps from some yellowed envelope for which no datasheet measures exist.

    It sounds like you manually sweep your filter with a DDS signal generator and some kind of 50 Ω terminated detector like a ‘scope. By placing a series xtal with a 1 nF capacitor shunt to ground on either side sandwiched between 2 homebrew attenuator pads in your 50 Ω measurement system – you need only make 1 additional measure to get IL. You may then infer Qu with the software that ships with EMRFD. This Simplified Measurement of Crystal Q was developed by Wes, W7ZOI and I show it on the QRP HomeBuilder archive Topics 2010-2011 | Crystal Parameter Checker.

    Further, many builders now run hobbyist-grade VNAs, or low-cost/high fun factor scalar network analyzers such as the PHSNA. While allowing for skill and device variations --- not only can they crunch xtal equivalent circuit values and Q, you might locate xtals with excessive spurious responses and toss ‘em out.

    When I examine a batch of new xals, I first measure their Q and decide if they’re suitable for my intended application. For example, if I wanted to make a 500 Hz CW filter and my bag of 4.92 MHz xtals show a Qu of 30K – those xtals go right into the garbage. If they measured 90K or greater, then its game on!

    Good enough may work well enough, but sometimes we should go deep?

    Best and keep up the good work!

    Todd, VE seven BPO (not VE3)

  2. Hello,

    Been enjoying both of you on the Soldersmoke podcasts. Did have one question though. Does Pete use some sort of new wormhole technology that allows him to know the future? I see that the note on the "Let's Build Something" web page, about when it was updated always seems to be couple of days in the future. Keep up the good work!

    Ken N0HRL


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