EMRFD Message Archive 1312

Message Date From Subject
1312 2008-01-12 12:30:36 Dimitri Aguero Calculating a Butterworth filter
Good evening to all.

I am building an SP-1 transmitter, published in SPRAT number 129.
The transmitter does not have any output filter. To meet quality emission required by French law, I
want to add a passband Butterworth filter. I found a table of normalised filter values in the 2004
ARRL Antenna Book.

Now, the problem arises when trying to know the output impedance of the output stage (a couple of
hundred miliwatts on the collector of a PNP transistor) in order to calculate filter values. Is
there any way to calculate or measure this impedance ?

Please forgive such a stupid question, I am just a beginner.

73 Dimitri F4DYT

Dimitri Aguero - dagueroATfree.fr / f4dytATfree.fr
F4DYT - Locator JN18av G-QRP 11905
Saint-Germain-en-Laye, France
1313 2008-01-12 13:32:09 Ed Almos Re: Calculating a Butterworth filter
For quick filter designs I always use the web page at

Edward Almos HA6SST