[CQ-Contest] How to hook up 4O3A Series S bandpass filters??

[Jim Brown]

On 11/23/2017 11:22 AM, Pavel Perchine wrote:
> John,Such filters should be symmetrical inside.

In general, yes. Note also that BPFs are designed to work into a MATCHED 
load, so if there is an antenna tuner, High Power BPFs should be between 
the power amp and the antenna tuner. A mismatched load on the BPF can 
degrade performance AND increase dissipation. Lower power BPFs 
(100-200w), of course, MUST be between the rig and the power amp.

Another point. BPF specs describe performance for a 50 ohm source and a 
50 ohm load, and measurements of filters are made under those 
conditions. The signal generator and detector (or Vector Network 
Analyzer) have 50 ohm output and input impedances at all frequencies.

But the real world where we USE these BPFs is quite different. The 
output Z of most power amps is rarely 50 ohms resistive at the TX 
frequency, and FAR from 50 ohms resistive at harmonic frequencies. 
Multiband antennas ARE likely to be close to 50 ohms resistive on bands 
where they are designed to operate, but most single-band antennas are 
not even close. A dipole or monoband Yagi, for example, have a VERY high 
impedance at even harmonics.

73, Jim K9YC