[CQ-Contest] Bandpass filter

Jeff Blaine jeff at ac0c.com
Sun Jul 8 17:58:24 PDT 2012

Actually both are right - the current and the heat are the problem - but 
they are tied together through the ESR  (if specified).

The cap has a finite electrical resistance at any given frequency.  And just 
like a resistor, it causes the cap to dissipate heat.  The heat leads to the 
caps' eventual failure.

SM have very low ESR at RF.  So they are a great pick.  And the idea of 
building the same value through a parallel combo works with caps just as it 
does with resistors - something you often see in paralleled plate blocking 
caps in an amp, for example (and used in parallel for the same reason - 
current splitting).


-----Original Message----- 
From: Keith Dutson
Sent: Sunday, July 08, 2012 4:01 PM
To: 'Dave Hachadorian' ; 'cq-contest reflector'
Subject: Re: [CQ-Contest] Bandpass filter

Hot dog!  Never thought of that.

Thanks for the tip.  I will be ordering a batch of these for both bands.

73, Keith NM5G

-----Original Message-----
From: David Hachadorian [mailto:k6ll.dave at gmail.com] On Behalf Of Dave
Sent: Sunday, July 08, 2012 3:08 PM
To: Keith Dutson; cq-contest reflector
Subject: Re: [CQ-Contest] Bandpass filter

> I use the ICE 419 banpass filters... Ten meters is by far the most
>vulnerable section.  I have a large supply of 270pf 500v silver mica
>caps on hand to make repairs.  Two of these caps are wired in parallel
>to get 540pf for the tank circuit.  If I could find caps rated at
>1000v, I would use them.

It's the current, not the voltage that causes capacitors in the ICE filters
to heat up and change value.  The ones that fail are the caps that go to
ground on the radio side (not the antenna
side) of the pi-net.  I helped a friend service his unit, and we replaced
the 10 meter caps with THREE of these:

We also replaced the 15 meter caps with THREE of these:

Dave Hachadorian, K6LL
Big Bear Lake, California


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