[R-390] Filters

[Bob Camp]

Hi

It's hard to see the coupling wire on both sides in the pictures, so there's no way to tell if it's broken. The wire is likely not magnetic in any way. It's purpose is acoustic coupling between the resonator disks. The material is chosen for it's acoustic properties (low loss at 455 KHz) and stability (temperature / time).  The other constrain on all the materials is weldability. 

When these filters were designed, the process for making the disks was fairly similar to crystal manufacture. The disks are taken to diameter first and then lapped to thickness. Adjusting the time in the lapping process is what gets you to roughly the right frequency. After lapping the resonators are sorted into bins by frequency. Different frequencies go into different locations on the various filters. 

Bob


On Feb 16, 2013, at 3:25 PM, Graham Baxter <graham at delphe.co.uk> wrote:

> I think we are speaking of the magnetostrictive wire which from the picture
> looks to be absent at one end.
> 
> On 16 February 2013 20:18, KA9EGW <ka9egw1 at britewerkz.com> wrote:
> 
>> Could one unravel a length of Litz wire to get the requisite wire, or is
>> it something like phosphor bronze?
>> 
>> 
>> On 2/16/2013 2:09 PM, Graham Baxter wrote:
>> 
>>> There does seem to be a lot of interest in the doughnuts at the expense of
>>> the intriguing physics of the filter!
>>> 
>>> It is my recollection that the filter was completely symmetrical. If you
>>> can't see the wire, it is probably broken. That is sad news, but hopefully
>>> someone will be able to supply a filter with bad coils but intact
>>> mechanics.
>>> 
>>> Graham
>>> G8OAD
>>> 
>>> On 16 February 2013 19:55, quartz55 <quartz55 at hughes.net> wrote:
>>> 
>>> I get the feeling like no one is really reading my posts so I may quit
>>>> dealing with it, too bad for someone that wants to rebuild filters.  But
>>>> I
>>>> will post pictues on my photobucket account for anyone that is
>>>> interested.
>>>> 
>>>> Here's a picture of what I think is the center wire attached to the
>>>> second
>>>> resonator disk on the top (output) end of the filter.  On the bottom end
>>>> (input), I don't see the wire like that, but I have not yet pulled out
>>>> the
>>>> coils on that end, the center wire may be coming off the end disk there
>>>> and
>>>> that's why I don't see it in the resonator disks.
>>>> 
>>>> 
>>>> http://s251.beta.photobucket.**com/user/DogTi/media/R390A/**
>>>> filtertopcenterwire_**zps1e973e91.jpg.html?sort=3&o=**0<http://s251.beta.photobucket.com/user/DogTi/media/R390A/filtertopcenterwire_zps1e973e91.jpg.html?sort=3&o=0>
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