Modifying the DB-4048
Notch Cavity Duplexer

By Ralph Hogan W4XE

The DB-4048 factory stock duplexer came as a six can set of notch cavities.   Ratings are about 70 dB of isolation.   The TX leg notches the RX freq and the RX side notches the TX freq.   This just isn't enough for current solid state PAs which need at least 80-85 dB.   Evidently these cans were brought out around 1975 because the ARRL did a product review of them in QST June 1975 (I'm looking for a copy of this BTW).   I imagine with a tube PA back then, these were more usable specs.

Recently there has been interest on the repeater reflectors in the DB-4048 VHF notch duplexer for amateur radio repeater applications.

Here are the original DB-4048 data sheets.

Evidently the modifications below change the harness lengths for 1/4 wavelength ham frequencies and also add on some notch stubs for additional rejection.   I personally just got these conversion documents and haven't had time to look them over closely or implement any of the changes to my stock set of DB-4048.

The DB 4044/4046 base duplexer bandpass factory specs

Here are the data sheets on the factory stock individual band pass cavities (DB-4001 / 4011 / 4015 / 4018):
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Here are the specs on the factory stock individual notch cavities (DB-4104 / 4140):
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Thanks to Gary Katona K2UQ, I now have some old documents from DB Products on conversion of these cans to ham application suitable for 600 kHz splits.   Evidently some hams were modifying the less desirable six can bandpass 'base duplexer' (3 MHz split) DB-4046 by removing one pickup loop on each cavity, changing loops on the TX side for longer ones and constructing a new harness.
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Thanks to all!
Ralph Hogan W4XE
w4xe //at// qsl //dot// net

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Page created 11-Jan-2004 by Mike Morris WA6ILQ
Article text © Copyright 2004 by Ralph Hogan W4XE
Hand-coded HTML © Copyright 2004 and date of last update by Mike Morris WA6ILQ

This page last updated February 17, 2010 KKC

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.