[CQ-Contest] Bandpass filters for M/S or M/M environment

[W0UN -- John Brosnahan <shr@swtexas.net>]

I have been asked for a few of the details on the filter testing so here is
a brief additional note for those who are interested.

Time flies when you are having fun.  Didn't realize it has been this
many years since Ed's article came out in QST which means that my
original testing was done in 1997.

Clean Up Your Signals with Band-Pass Filters  part 1 and part 2
Ed Wetherhold, W3NQN    QST May and June 1998

In addition to the W3NQN filters I had a few ICE filters that were used
as benchmarks for the testing.  My specific notes are still at my Colorado
place--so I can't provide any additional information to what was published
in QST.  But the QST article has extensive information on the performance
of the filters.

Filter Performance Tests were measured with my HP-4195A Network/Spectrum
Analyzer after a full calibration procedure using a pair of HP-41952A
Transmission/Reflection Test Sets.

Power Handling was done with an IC-781 driving an Alpha 87A amp to
the 200 W level on a Bird 43 watt meter, into a Bird 50 ohm load.   All 
filters
were mounted in their cases and periodically checked with an "old style"
contact instrument thermometer.   (This was done prior to my purchase
of an IR (non-contact) thermometer.)

Each filter was tested with 200 watts of carrier for 30 minutes.   The testing
uncovered a couple of instances where the cores were overheating and
W3NQN re-designed the inductors until each filter could pass this
30 minute continuous power test without overheating.

Each filter was designed to provide optimum rejection of the immediately
adjacent ham bands.  Performance remained quite good through low
VHF but there were some series resonances (low rejection) in the mid- to
upper-VHF range as there will be with all filters using real-world components.

73--John   W0UN
---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.675 / Virus Database: 437 - Release Date: 5/2/2004

_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest