Modifying the DB-4060 and DB-4062 Commercial Band Cavity Duplexer to 2M

Modifying the DB-4060 and DB-4062
Commercial Band Cavity Duplexer
to 2M
By Kevin Custer W3KKC

General Information:
The DB-4060 and DB-4062 factory stock commercial band duplexer came as either a four cavity (4060) or a six cavity (4062) pass / notch duplexer. Recently there has been interest on the repeater groups to convert these duplexers when originally built for the US commercial bands for amateur radio repeater applications. While this is not a complete step-by-step guide, the information provided here will give you all of the detail you need to fabricate new coupling loops to allow these duplexers to properly function on a 600kHz or 1MHz split in the 2M Amateur Ham Band.

You basically want to use (or make) the loops called out as "DASH NO" 004 and 005 in the loop document below. The 004 will be (or become) your Low-Pass - High Reject (LPHR) and 005 is your High-Pass - Low Reject (HPLR) loops. You may want to consider clicking on all of the hyperlinked articles referenced on this page - as a more complete understanding and other visual references (like VNA sweeps @ 0.600 kHz spacing) are shown. The stock for the loops is ¼” wide, 32 mils thick (20 gauge). We prefer using 40 mil (18 gauge), it holds its shape better. The loops are simple to form using hand tools. Suggest using a 1/8” Whitney punch for the holes; drilling such thin/narrow stock often results in a lot of four-letter words being uttered.

Factory Datasheet and Tuning Instructions:
Here is the original DB-4060 / 4062 data sheet.
The DB-4060 / DB-4062 base duplexer tuning instructions.

Factory drawings for the coupling loops, assemblies (boxes) and overall duplexer drawings:
The DB-4060 / DB-4062 base duplexer loop drawings document.
The DB-4060 / DB-4062 base duplexer loop assembly drawings.
The DB-4060 / DB-4062 base duplexer overall drawing.
Jeff WN3A's Notes Document on these duplexers.

Photo Tour of a real "005" coupling loop:
DB-4060 / DB4062 "005" Loop Photo Tour by Jeff DePolo.

Additional Notes:
As seen in Jeff WN3A's "Notes" document, sometimes these duplexers have compromised performance. This can happen if the conductivity between the loop assembly (box) and the top of the cavity is corroded or otherwise electrically compromised.

One problem W3KKC personally found was paint overspray from the factory:
DB-4060 Cavity Overspray

Another issue is inferior RG214 cables. Like another duplexer manufacturer, the cables may not be real silver plated RG214. Any cables that include the word "type" should be suspect.
This WN3A PDF document shows this cable and it's recommended that it be changed to real silver plated coaxial cable. See below for an optimized example.

Intercavity and Bridging Cable Optimization for the 2M Ham Band - by Jeff DePolo WN3A:
I’ve seen a lot of variation in cable lengths and quality for the DB4060/4062 series over the years, some of which I commented on in my "Notes" document above. Because of that, in recent years I’ve taken the approached that it’s better for my sanity to simply assume that the harness should be replaced. I use RG-400 cable lengths that I have optimized in the past: 12.5” tip-to-tip between cavities, 13.0 tip-to-tip” to the common port for the 2M band.

DB-4060 Tuning Capacitor Replacement Article
Johanson 5602 30pF trimmer capacitor article.

Thanks to Jeff DePolo WN3A for supplying the factory drawings and most of these conversion notes!

Kevin W3KKC

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This page last updated September 20th 2026 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.