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 http://www.wa4dsy.net/filter/hp_lp_filter.html Edward Almos HA6SST

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

--
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Dimitri Aguero - dagueroATfree.fr / f4dytATfree.fr
F4DYT - Locator JN18av G-QRP 11905
Saint-Germain-en-Laye, France
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