[Lowfer] high Q caps for lowfer and VLF?

[Bill Ashlock]

Hello Art,

 

You didn't mention dipped silver mica caps which are still available from most suppliers at reasonable prices. Also take a look at various forms of COG ceramic dipped caps. I was surprised some years back to find out they typically had a higher Q and often more temperature stable than silver mica - and are much lower in cost. I had been going on the assumption from way back that ceramic caps had necessarily low Q and high tempco but was confused when I saw TV tuner designs using them in the LCs of the oscillator section.

 

Bill Ashlock
 
> Date: Mon, 16 Mar 2009 13:45:08 -0400
> To: lowfer at mailman.qth.net
> From: KY1K at myfairpoint.net
> Subject: [Lowfer] high Q caps for lowfer and VLF?
> 
> Hi everyone.
> 
> It seems mylar and polystyrene caps are going away at an alarming 
> rate, which make building high Q circuits for LF and VLF more problematic.
> 
> Disk ceramic and especially ceramic SMT caps are small and compact, 
> but the electrodes are less than .001 inch thick, hence they have 
> horrible ESR ratings at LF and VLF. And, the ceramic caps have 
> horrible temperature stability, as anyone who ever tried to use on in 
> a timing circuit already knows.
> 
> I need low voltage caps that do not need to carry large ac currents 
> (for receiver front end tuned circuits).
> 
> Are there any good to medium LF/VLF optimized caps on the market 
> today, or is that I'm just not looking in the right places?
> 
> Thanks any and all suggestions.
> 
> Regards,
> 
> Art
> 
> 
> 
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