Martin,
Yes, at least the 20m W3NQN filter changed from the original QST article
to what was shipped from Array Solutions about 6 months ago. I have a
plot that I can send you of the measured differences but unfortunately I
don't have both units to compare the schematics. I only have the ones
from the QST article. The original filter with the 20m passband was
down ~40dB in the 40m band and ~43dB in the 15m band. The new filter
has a notch in the 40m band so the attenuation on 40m is >50db while the
15m attenuation is reduced to only about 32dB.
73,
Larry, W0QE
On 11/27/2010 9:39 PM, Martin Sole wrote:
> Wonder if someone here might be able to help with some info on the W3NQN
> bandpass filters. Our club station has some we are using between the rig and
> amplifier (phew, worked the amp reference in nicely there.) Somebody put the
> 20 metre one on the amp output where 200 watt filters don't live long. So
> one toasted filter. I thought this would be no problem. I have the 2 QST
> articles by W3NQN that describes these filters. BTW these are the ones sold
> by Array Solutions. Popping the cover shows they don't match the circuit of
> the QST article though so now I'm confused.
>
> Here are the differences:
>
> 1. C2 is not in series with L2, rather it is across the L2A and L2B pair.
> 2. C1 and C3 are shown in the QST article connected between ground and one
> end of L1, L3 but in the filter I have here C1 and C3 are between the ends
> of L2 and ground.
> 3. The shorter of the three windings is from the connector to ground and the
> longer pair appear in series.
>
> The values for C1 and C3 are the same, the L1, L2 and L3 have the right
> number of turns and what appears to be the right cores.
> No idea about the value of C2 as that is what smoked and is now a charred
> black lump.
>
> Hopefully the drawing below shows up okay. This is how the filter is
> configured.
>
>
> Input-------L1a-------L2a--------L2b--------L3a--------output
> | | |
> |
> | |---------C2----------| |
> L1b C1 C3
> L3b
> | | |
> |
> ---------------------------------------------------------------------
>
> L1b, L3b 5 turns
> L1a, L3a 10 turns
> L2a, L2b 18 turns
> C1, C3 90pF
> C2 ?
>
>
> Martin, HS0ZED
>
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>
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