It's also interesting to investigate what happens to harmonics when
presented with a real multi-band antenna, say a multiband yagi on the other
side of various filter types.
David
G3UNA
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <Amps@contesting.com>
Sent: Monday, January 21, 2008 5:39 PM
Subject: Re: [Amps] tuning bandpass filters
> It's critical to understand that a filter is a passive network
> that interacts with the impedance of the source and the impedance
> of the load. When we design filters, we make the optimistic
> assumption that they will be terminated by a purely resistive
> impedance at all frequencies. That assumption ONLY is true on the
> test bench, when we drive the filter from 50 ohms and load it with
> a 50 ohm analyzer. It is a BIG LIE in the real world, so filters
> in the real world don't come anywhere close to test bench
> performance. W3LPL recently pointed this out in a post to a ham
> list -- maybe even this one!
>
> Example: Our transceiver may be a 50 ohm source and our power amp
> may be a 50 ohm load at the operating frequency (but probably
> not). If, by luck, it is, the response through the filter at the
> operating frequency will be as predicted. Most transceivers, amp
> inputs, and antennas are not anything close to 50 ohms at the
> frequency of harmonics, so the performance of the filter won't be
> anything close to what it measured on the test bench.
> >
> 73,
>
> Jim Brown K9YC
>
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|