[MAMS] 24 GHz waveguide filter

[Lloyd Ellsworth]

Dave, 

Every now and then, you run into one for sale. 

Charles Suckling, G3WDG, has a good construction article on HB one using WR42 waveguide. About 4 inches long as I recall. Alignment is a bit of work. But it works. I may have a copy of his construction article somewhere. Likely, you can substitute some K&S hobby brass rectangular tubing and make it work. Early experiments ran with WW8M, showed it to work. Nearest K&S Brass size works out to WR34. But the spacing is the same on the holes and iris. Mounting brass screws is tricky because the brass is thin. Does not take much heat. Warps easy. We made a pile of Home brew waveguide transitions. I wrote up an article on that for MUD some years ago. Still using them. Still making them. Takes me about 4 hours. W2PED has/had some very nice transitions available. 

I had some WR42 for sale, and standard 4 hole flanges, but don't know if I have any waveguide left. I might have a couple extra flanges. WR42 is not as common as WR90, and it is more expensive. Then the effects of the price of scrap copper these days. 

Dayton, and MUD, I have found some extra home brew wave guide filter units FS. Usually, extra made, then keep the best one. 

Germany, Henrik the Machineist, and Pale OZ8AFC in Denmark, make some really nice professional ones. Silver plated. About $100. Adjustment is pretty straight forward. Cavity design. Also 47 GHz. That is what I eventually graduated to. I use them now. Low insertion loss, and performs well. 

Testing is a bit of a trick. All about the available test equipment. 

P.S. Plenty of SMA relays, work on 24 GHz. However, you have to test them first. Find out if they do, and if the losses and performance are acceptable. Same with SMA connectors. K type SMA are what you want for 24 GHz. But they are a bit scarce and pricey. UT.085 is rated to 65 GHz. I would compare using a SMA on 24 GHz, about like using a PL259 on 2M. Not the best, but it will work. Get you on and going. Later as the proper surplus, or parts become available, or affordable then upgrade. 

Also the Dish Network Dishes. Work just fine. So do the DH dishes. Also wrote up an article for MUD, for a HB affordable dish feed for 24 GHz. Used a .310 empty brass casing, and solder up a bit of UT.085. Called it the "Detroit" special. 

Big problem you learn about 24 GHz and up. Lead solder absorbs RF. It becomes a problem. Minimize use. 

Good luck. 

73, Lloyd NE8I/r
EN74 etc