[CQ-Contest] Bandpass filtering

VK4TI vk4ti at yahoo.com
Thu Dec 30 18:07:24 PST 2010


Don't ICE make a receiver overload unbuilt into a lightning detection device?

Trent Sampson 
0408 497550


On 31/12/2010, at 10:31 AM, "S56A" <s56a at bit.si> wrote:

> N4ZR wrote: From what W3LPL has told me, I am pretty confident that I can 
> simply parallel the output of the 6 filters, but can I also parallel the 
> inputs?
> 
> I very much doubt that W3LPL told you that!  His BPF are triple tuned 
> circuits with top capacitor coupling.  They exhibit low impedance on the 
> frequencies above bandpass.  10 m filter is coupled to 50 Ohms with 33 pF 
> while 160 m has 719 pF.   That gives 475 (square) power ratio or -27 dB 
> loss.
> 
> Only serial tuned circuits can be paralleled at 50 Ohms and even that 
> becomes difficult beyond triplexer.  Check http://www.nuhertz.tv/
> 
> You don't need any BPF for QS1R, just band STOP filters to prevent input 
> frying from nearby TX.  ICE filters might be easily converted to band-stop 
> with change of both inputs to serial notch and adding just one more small 
> coil for parallel resonance (de)coupling.
> 
> HNY & 73 de Mario, M/S56A from London
> 
> 
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