Overhaul and Conversion of DB Products 4-Cavity Duplexers to 6-Cavity “B” Models

We’ve recently converted a couple of sets of Decibel Products (a/k/a/ dbProducts and dbSpectra) 4-Cavity 4060-WOC-C duplexers to 4062-WOC-B models. Translation:

4062-WOC-B Duplexer built by converting a new set of 4060-WOC-C cavities to “B” models, and overhauling and converting two additional “C” cavities from a failed set, resulting in a great working 6-cavity “B” model with over 100 dB of isolation in each branch.

we’ve converted 4-cavity sets which were built for operation at higher, public safety and commercial frequencies to 6-cavity sets which are optimized for operation in the 2-Meter Amateur Radio / ham frequency bands.

Doing so involves a fair amount of time and work, including total overhaul of each cavity, custom manufacturing of the correct length loops, capacitor replacements, and the building of a new frame for the expanded 6-cavity set, not to mention final tuning and performance testing.

Tuning Plunger Removal, Inspection, and Polishing

After disassembly of the old cavities, one of the many steps in the overhaul and conversion process involves getting the tuning plungers back in good

Aged, oxidized tuning plungers BEFORE cleaning and polishing.
The same two tuning plungers after careful cleaning and polishing.

shape. As can be seen in these photos showing the plungers before and after the application of some TLC, the difference is more than visible. So is the resulting performance and ability to be accurately tuned (and for that tuning to remain stable.)

Custom Copper Loop Fabrication and Loop Enclosure/Cavity Conversion

In order to obtain the best cavity SWR (lowest insertion loss) along with the maximum branch notching/isolation performance, the copper loops in one

Original capacitor with signs of excessive heating, old flux residue which had not been cleaned off after soldering, etc. This capacitor had failed, causing the set set to be taken out of service.
New capacitor and custom made loop installed. The enclosure has been relabeled from the original “003” part number to its new, proper “005” designation.

branch of the duplexer assembly have to be replaced with loops of the correct length. At DuplexerRepair.com, we handcraft the replacement copper loops. We start with high quality, 30-mil copper and carefully cut, shape, drill, and polish the replacement loops.

During the installation of the new, replacement loops of proper dimensions for 2-Meter operation, we also replace the trimmer capacitors. This is actually a delicate process, as these capacitors do not tolerate excessive heat. It is quite common for us to discover signs of overheating from the combination of the original capacitor installation, soldering, and RF heating over time (mistuning, high SWR, and lightning will destroy these capacitors pretty easily.)

Frame and Mounting Rail Fabrication / Conversion

The original 4-cavity frame and mounting rails for assembling the cavities into a set have to be replaced in order to accommodate six cavities. We

Custom machined mounting and frame bars for conversion to 6-cavity set.
New custom made rails with cavity braces and clamps installed.

 

custom machine these from square aluminum tubing.

Reassembly, Cable Harness Inspection and Service, and Final Testing

With all the components overhauled and reassembled using the new frame and mounting rails, each cable, Tee-connector, etc. is inspected and cleaned

Another 6-cavity 4062-WOC-B set we recently converted, overhauled, and built, reassembled and ready for final tuning and testing.
Duplexer assembly being put through final tuning and performance testing and verification. The client gets a complete report of the testing, including the network analyzer graphs showing proof of performance.

or replaced as necessary.

Each cavity is then individually performance tested, followed by connecting each branch as a set and testing it, and finally the entire harness is secured and the entire set undergoes its final tuning and performance testing.

The End Results

A complete conversion, expansion, and overhaul job such as the ones described here, commonly involves between 15 to 20 hours of labor, plus

With 113.37 dB of isolation (factory spec is 100 dB or higher) with only 1.45 dB of IL (Insertion Loss (factory spec is 2.2 dB or less), this set is working considerably better than factory specifications. Well worth the investment of time, money, and energy.

materials. It’s not exactly cheap, but the results are worth it. What usually starts out as a 4-cavity 4060 “C” model (not built for factory spec operation in the 2-meter Amateur radio band, and often a set which has failed and been pulled from service) becomes a great working 4062 “B” model — as though it left the factory as a set intended to work to specs in the 2-Meter band. The 4-cavity 4060 models are rated at 80 dB or more of branch isolation; whereas the 4062 6-cavity sets are rated for 100 dB or higher isolation. At the typical 600 KHz “split” used in 2-Meter band, this extra isolation makes a world of difference, especially at transmitter power levels above 40 watts or so, and can be a game-changer when trying to get better performance out of certain repeaters, such as the Yaesu Fusion DR-1/DR-1X series, which tend to have lower receiver selectivity compared to most of the commercial grade repeaters with highly selective physical filtering on the front-end. Very often we deal with duplexers sent to the DuplexerRepair.com labs with complaints of “They worked great for years with our old Mastr II repeater running 40 Watts, but when we bought and installed a new Fusion repeater (or D-Star repeater, DMR¬† machine, etc.) everything went to crap.”

We deal with such all the time. And we’re here to help. Call or contact us if you’re experiencing similar problems. We’ll be delighted to help you get things working the way they should. As they say, “A chain is only as strong as its weakest link.” Duplexers which aren’t up to the task will result in a poor or totally useless repeater setup. It doesn’t have to be that way. We’re here to remedy that.

 

 

 

 

 

 

Do Your Duplexer Cavities Look Like This Internally?

This short video shows what years of oxidation can do to the internal workings of a set of duplexers. This is the inside of one of the tuning cylinders in a set of EMR 65544 UHF cavities. These cavities are known for

great performance; however, time takes its toll on anything metal and RF duplexers are no exception. These duplexers would not tune for proper pass or notch frequencies. This is what an endoscopic inspection revealed — lots of corrosion and contamination. Along with damaged trimmer capacitors, these sort of problems often lead to duplexers being replaced with new ones at tremendous expense. A replacement set of these duplexers lists for $1,710. At DuplexerRepair.com this refurbishing job would run somewhere in the range of $250-$400… less than 1/4 the cost of buying replacements, and the duplexers will be ready for many more years of service when the job is done.

If your duplexers no longer perform correctly, contact us about having them repaired and refurbished. Call (334) 787-9005 or send an email to service@duplexerrepair.com to arrange repairs, overhaul, or retuning services.