Wacom WP-639 tuning from 160MHz to 146MHz - need new cables?

[CARC383]

A local ham club is looking at a used Wacom WP-639 duplexer factory ordered at 160MHz with a narrow split. Does anyone know if this model will tune down to 146Mhz with factory cables? Many other brands and models will not and I see no mention anywhere of the cable harness being different to cover 144 to 174MHz.

Thanks!

 

[MotoBill]

I don't think the cables will be so much of an issue with the design of the WP-639 so much as the notch subs will likely be too short to facilitate retuning down into the 2M ham band. However, there was an article published on the repeater-builder site that outlined modifications that you should be able to find quickly when searching for the WACOM WP-639.

 

[com501]

Anything more than 5% you should change the cables for best resonance, however, as stated, the notches will need work. Get out your calculator and Rl sheets for that unit. Not difficult, but care and finesse are your friends for best results.

 

[CARC383]

Thanks for all the info so far. I see mods for units ordered for wide split to make the notches work at 600KHz but no mention of changes to the interconnect cables. I'm used to making longer cables taking a duplexer this far from its original freq but the factory specs, instructions and other comments on Repeater Builder don't seem to be concerned with it. When we get it the return loss should reveal the answer but I'm hoping not to go through the cable hassles on this one.

 

[MotoBill]

No doubt that it will take some work to bring it down into the ham band. It's been a longtime since I've tuned a Wacom but don't think this particular design is quite so critical on cable lengths so much as a more typical design where the notch tuning is comprised of lumped constants that definitely are critical of harness cable lengths.

Going in, you at least know the 160 MHz model will need modifications that will have to be considered in making any decisions as to cost verses assured performance. One thing that stands out in my memory from hammy projects is that some of these duplexers tended to have electro-mechanical issues with the plunger tuning assembly causing noise desense making me tend to shy away from using them to begin with.