Jim,
You are absolutely right and there is nothing to add.
The BPF can perform at 100% from its specification only being connected to a
feed line with a good VSWR.
It is always recommended to decrease the output power if antenna's VSWR is high.
All efforts should be taken to improve VSWR of an antenna system to keep all
connected gears alive :)
Pavel
Va6am.com
----- Original Message -----
From: Jim Brown <k9yc@audiosystemsgroup.com>
To: cq-contest@contesting.com
Sent: Thu, 23 Nov 2017 13:38:34 -0700 (MST)
Subject: Re: [CQ-Contest] How to hook up 4O3A Series S bandpass filters??
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
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|