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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|