[CQ-Contest] Bandpass filter

[Keith Dutson]

Tom,

Thanks for the SPICE model.

73, Keith NM5G

-----Original Message-----
From: cq-contest-bounces at contesting.com
[mailto:cq-contest-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Monday, July 09, 2012 7:10 AM
To: Keith Dutson; cq-contest at contesting.com
Subject: Re: [CQ-Contest] Bandpass filter

> I can relate to the problem of capacitors with lower than sufficient 
> voltage rating.  I use the ICE 419 banpass filters while on 
> DXpeditions.  I have two A models and two B models.  Both models do a 
> good job rejecting out-of-band crosstalk.  However, the caps in the 20 
> meter and up tuned circuits have heated up, resulting in high VSWR.  
> This usually happenes when the operator switches the transmitter to a 
> different band but does not remember to change the filter until AFTER 
> transmitting and seeing high VSWR.  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.

Keith,

I added a SPICE model of two low pass 3.6 MHz filters to my webpage. You'll
see the stress on parts there for a 100 volt peak source through a 50 ohm
resistor, which is about like a 50 watt transmitter when matched.
[snip]