Design of manual double stub tuner

[ooiben]

Hi all,
I have been trying to look for materials on designing a simple manual double stub tuner (as shown in picture). Seems like there are not many materials available on this. Could anybody help advise? Thanks.

Regards,
Ben

[/img]

 

[vfone]

https://www.agsrhichome.bnl.gov/AP/ap_notes/ap_note_106.pdf

 

[benooi]

SOrry, I should have mentioned I am a hobbyist looking to build a low cost version of this. My interest is in the mechanical construction. Thanks

 

[vfone]

The basic mechanical design is simple, but you need at least a model to copy it.
Basically is a horizontally 50 ohms coaxial cavity transmission line (with air dielectric), having a cut slot along its length.
A shunt-connected vertical stub (which is shorted at one end) is moving alongside the initial horizontal transmission line, and also having adjustable length (using a micrometer in your picture for accurate reading).
You can use only one stub, but double-stub tuners can get a PI configuration providing wider range of impedance matching.

Brand new devices like this are very expensive (up to $4000) but second hand you can find for $100, plus shipping. I think is worth to buy instead making one.

 

[ooiben]

Hi vfone,
Thanks for the reply. DO you know where i can buy a cheap one?

 

[biff44]

The picture appears to be a double slug tuner, not a double stub tuner. There is a coaxial line running from left to right, but the top of the ground plane cylinder is milled away for access. The two micrometers lower metal blocks that come close to, but do not actually touch the center conductor of the coax line.

Since these type of devices, although often very old, are still useable for load pull impedance measurements, they usually fetch a good price, like $500 to $2000 on ebay used.

If I needed to gin one up crudely, I would use a microstrip line and move either non-contacting metal blocks, or contacting plastic blocks, along the top side of the microstrip.

Making up a precision one from scratch is going to require a machine shop!

Double stub tuners look like this, and have trombone sections that are also hard to make: