[CQ-Contest] Re: TopBand: Preamplifiers

Frank Donovan donovanf at sgate.com
Thu Sep 25 19:16:56 EDT 1997

Hi Carl!

ASCII graphics leave a bit to be desired...  In this version I've
used asterisks to show each electrical connection.  

You will find that these are terrific filters!  I often demonstrate the
20M filter by pointing my 40M 3 element beam at the loudest 40M broadcast
station at night, then inserting the 20M filter.  There is  A B S O L U T
E L Y  no trace of any 40M broadcast stations under such conditions!  Its
much easier to design very effective, yet simple and inexpensive, filters
when you do not need to to handle transmit power levels.

Good luck!
donovanf at sgate.com

50ohms -- C1 --*----*---- C3 ---*----*--- C5 ---*----*---- C7 -- 50ohms
               |    |           |    |          |    |
               |    |           |    |          |    |
               C2   L           C4   L          C6   L
               |    |           |    |          |    |
               |_*__|           |_*__|          |_*__|
                 |                |               |
                 |                |               |
               Ground           Ground          Ground
KM1H> Does C2/L go between C1/C3?

Yes, C1 is an input matching capacitor between the 50 ohm source and
the first parallel tuned circuit (C2/L).

C3 is a minimum value top-coupling capacitor between the first parallel
tuned circuit (C2/L) and the second parallel tuned circuit (C4/L)

KM1H> Then C4/L goes between C3 and C5?

Yes, C3 and C5 are top-coupling capacitors between the three parallel
tuned circuits.

KM1H> And C6/L goes between C5/C7 ?

Yes, C5 is a top-coupling capacitor between the last two parallel tuned
circuits.  C7 is a matching capacitor between the last tuned circuit and
the 50 ohm load

> Tnx   Carl   KM1H

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