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Technical Topics => The RF Workbench => Topic started by: redhat on September 27, 2016, 2139 UTC

Title: The death of DIY receiver building (the loss of discrete baseband components)
Post by: redhat on September 27, 2016, 2139 UTC
Several years ago I had the idea to build a small stereo HF receiver based around some then available parts.  I was working on the design for this a week or so ago and when I went to my part vendors, I noticed that most of the 455 KHz IF filters made by Murata and others have been either slated for, or outright discontinued.  Whatever vendor stock is out there appears to be all that will ever be, as even a sweep through ebay reveals very little in the way of options.

What is an RF hobbyist to do?  The world has gone to DSP, and most of the development kits for these thing exceed the mean income of most of the residents of Detroit (Sorry, had to do it).  Nevermind that most of these solutions draw too much power for battery applications.

Anyone have any leads on these things?

+-RH
Title: Re: The death of DIY receiver building (the loss of discrete baseband components)
Post by: ChrisSmolinski on September 27, 2016, 2220 UTC
https://www.aliexpress.com/ still has 455 kHz ceramic filters. I see some as cheap as $5.98.  No, not each, but for a lot of 100 of them. With free shipping.
Title: Re: The death of DIY receiver building (the loss of discrete baseband components)
Post by: Pigmeat on September 27, 2016, 2316 UTC
Do you know how they're set for knobs, Chris? A friend of mine wants to know.
Title: Re: The death of DIY receiver building (the loss of discrete baseband components)
Post by: ChrisSmolinski on September 28, 2016, 0006 UTC
Quote from: Pigmeat on September 27, 2016, 2316 UTC
Do you know how they're set for knobs, Chris? A friend of mine wants to know.

50 knobs, assorted colors, for $3.33, with free shipping! 

https://www.aliexpress.com/item/WH148-knob-knob-plastic-knob-AG2-15X17mm-type-potentiometer-power-amplifier-knob/32529541531.html (https://www.aliexpress.com/item/WH148-knob-knob-plastic-knob-AG2-15X17mm-type-potentiometer-power-amplifier-knob/32529541531.html)

(https://ae01.alicdn.com/kf/HTB1fincKpXXXXbnXpXXq6xXFXXXz/WH148-knob-knob-plastic-knob-AG2-15X17mm-type-potentiometer-power-amplifier-knob.jpg_220x220.jpg)
Title: Re: The death of DIY receiver building (the loss of discrete baseband components)
Post by: redhat on September 28, 2016, 2131 UTC
There appears to be a similar problem with this option as well.  The Token datasheets lists parts I could use, but there are no distributors listed, and the ones I can find are not in usable bandwidths.  I am looking for +/- 3, 5, 10, and 15 KHz.  The 15 KHz filters are actually 30 KHz wide and will be used as a roofing filter at the front of the IF chain, with smaller filters used in front of the demodulator.

*edit* after some searching on Token's website, it looks like they will sell in small quantities to individuals.  Might be worth a try.

+-RH
Title: Re: The death of DIY receiver building (the loss of discrete baseband components)
Post by: Josh on September 29, 2016, 0002 UTC
Surplus Sales of Nebraska has a few ceramics in that freq range. I also see them for sale on qth often.
Title: Re: The death of DIY receiver building (the loss of discrete baseband components)
Post by: redhat on September 29, 2016, 0649 UTC
In this particular application group delay is important because it can screw up the crosstalk between I and Q in the stereo quadrature demodulation process so filters with optimized GDT are nice.  Fortunately most digital modulation methods also get cranky over group delay, so a lot of the filter designs over the last 20 years or so were designed with this in mind.

+-RH