What kind of filter is this? FM?

[tomhouston]

I found this device (I think it's some sort of FM filter?) while cleaning out my fathers basement but have no idea what it is. I'm 100% sure it's his design/build but would like to know what it's actually used for if anyone knows.

 

[merlin]

This is a converter, Has a filter centered at 21.4 MHz. the small can is a diode ring mixer.
Bottom BNC is likely filtered IF output. Top left, from the protection circuit likely RF input(ant ?)
Top right, oscilator input.
So, the heart of this is the MD-108 mixer. with datasheet, you canuse this as some up or down converter.

 

[tomhouston]

merlin - Thank you for the response! I have no idea the application for such a device but thank you none the less for the info.