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
VE3ZI
--- On Sat, 7/3/09, Jim Brown <jim@audiosystemsgroup.com> wrote:
> From: Jim Brown <jim@audiosystemsgroup.com>
> Subject: Re: [RFI] DSL Filter Update
> To: "rfi@contesting.com" <rfi@contesting.com>, "Roger Parsons"
> <ve3zi@yahoo.com>, "ve3zi@rac.ca" <ve3zi@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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