[CQ-Contest] Filters

Mario, S56A s56a at bit.si
Tue Jun 13 17:31:37 EDT 2006

I am well aware of W3NQN long time involvement with filters design.  I also 
studied K4VX and W3LPL solutions.  I know top DL7AV HP BPF design.

I remember opening ICE filter for the first time and admiring KISS design 
with 500 V mica caps.
Knowing filter theory, it was obvious that improvements can be made by 
simply taping the coil (Dunestar).
The price you pay is higher voltage on caps.  Same occurs in W3NQN design 
with additional stress on serial coupling circuit with high L/C ratio.

My engineering optimal solution would be Dunestar configuration tested at 
YT6A.  When the money is no limit, I'd go for W3NQN.  I rarely blew-up 

Disclaimer: I am discussing this subject from purely tech viewpoint although 
I am aware that this might influence some marketing decissions.

73 de Mario, S56A, N1YU

----- Original Message ----- 
From: "Tim Duffy K3LR" <k3lr at k3lr.com>
To: "Mario, S56A" <s56a at bit.si>
Cc: <cq-contest at contesting.com>
Sent: 13. junij 2006 21:54
Subject: Re: [CQ-Contest] Filters

> Mario:
> Just for the record; I used ICE band pass filters when I started multi 
> multi in 1992.
> I noticed several things:
> I was surprised how much in band loss they had. Measured on a HP 8752A
> The near band rejection wasn't very good. Measured on a HP 8752A and 
> verified with
> station tests.
> The components inside got very hot on 10 and 15 meters when running 85 
> watts into them
> for multi multi service (I need 50 watts (that is what is left after the 
> filter loss)
> to drive my amplifier to 1500 watts).
> After a blow up or two during a contest with the ICE filters, I called 
> W3NQN on the
> phone and asked him to design a better set of filters.
> That is what we have today.
> I have used W3NQN filters (built by W3NQN with the same parts he described 
> in his
> article) in full bore K3LR multi multi efforts on all bands for 8+ years 
> with no
> failures or heating what so ever. Perfect operation.
> I also used W3NQN filters on Field Days and at the WRTC events running in 
> the low
> power category with the exact same results. No problems, low through loss 
> and the best
> near band rejection of any LP BP filter.
> BTW, I don't consider myself "lucky". These filters are the result of 
> sound
> engineering, which is one component of a successful contest station.
> 73!
> Tim K3LR
> "Mario, S56A" wrote:
>> W0UN: And at no time did any capacitors fail the 200 watt test -- or even
>> get very warm.
>> I guess you were lucky!  I made W3NQN filters with a big VU mica caps for 
>> 2
>> kV and they all failed on 7 MHz and above.
>> Manufacturer sent us new batch for free but they are not tested yet. 
>> specifies VAR power ratings required.
>> Simple ICE filter configuration should survive most abuses but 21/28 MHz
>> isolation is not good enough for SO2R.
>> Please note that BPF info is available in ON4UN book on low bands.
>> 73 de Mario, S56A
>>   --------------------------------------------------------------------------------
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