[RFI] DSL Filter Update

Roger Parsons ve3zi at yahoo.com
Sat Mar 7 12:01:26 PST 2009

I know that Nick used an N2PK VNA - .png attached - but no more than that. I did do a few sums on the filter design a few weeks ago and was surprised to find that the design impedance is close to 50 Ohms rather than the 600 Ohms that I had been expecting - or that I had been expecting until I thought about the likely characteristic impedance of two closely spaced small insulated wires. But even if the wrong source/load impedance is used the shape of the passband/stopband will not change - only the overall attenuation.

73 Roger

--- On Sat, 7/3/09, Jim Brown <jim at audiosystemsgroup.com> wrote:

> From: Jim Brown <jim at audiosystemsgroup.com>
> Subject: Re: [RFI] DSL Filter Update
> To: "rfi at contesting.com" <rfi at contesting.com>, "Roger Parsons" <ve3zi at yahoo.com>, "ve3zi at rac.ca" <ve3zi at rac.ca>
> Date: Saturday, 7 March, 2009, 2:42 PM
> On Sat, 7 Mar 2009 11:29:05 -0800
> (PST), Roger Parsons wrote:
> >Just to advise the group that a couple of other
> stations have had 
> >success with this filter. Nick, VE3FJ, also checked out
> its 
> >frequency response with the following results:
> >1.85MHz   -26dB
> >3.65MHz   -46dB
> >7.24MHz   -68dB
> >14.13MHz  -60dB
> >21.0MHz   -56dB
> >28.5MHz   -54dB
> >Of course in theory the stop band attenuation should
> continue to 
> >increase with frequency, but in practice there will be
> strays 
> >across the filter that will cause a performance drop at
> higher 
> >frequencies.
> Roger,
> Exactly how was the response measured?  What source
> and load 
> impedances?
> 73,
> Jim K9YC


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