You can do as you so choose. I tried building them and they were a joke. There is a Very Good reason why manufactures use zero coefficient of expansion metal in their commercial duplexers. I have talked to Wacom people in the past about my experiences and they told me none of my experiences surprised them. Locking the internal pipes down doesn't solve anything. The rods the adjustable part of the 1/4 wave section are attached to, change length if made of the wrong material. I am sorry but copper does not reflect zero coefficient of expansion characteristics. Physics is physics. Copper expands and contracts with temp changes. But, it's really the rods that change length that are the biggest problem. I guess if you have an environment with no change in temp, you could get by with run of the mill metals but I have not had any repeater located in such an environment myself. If building cavities were as easy to build as you describe, there would be a lot more home made jobs in service. Manufacturers are not getting the big bucks for something that could be built easily at home for $49.95 for nothing. Lee w0vt
----- Original Message ----- From: skipp025 To: [email protected] Sent: 12/25/2006 8:23:30 PM Subject: [Repeater-Builder] Re: 6M cans made from other metals > "" <[EMAIL PROTECTED]> wrote: > I have built cans in the past and would NEVER do it again. It > is a waste of time. Some people don't have great results... > As the metals expand and contract, so does the tuning. The > main tuning rod shafts are the biggest problem. The metal > needs to have ZERO coefficient of expansion properties. Unless > you have access to such material, DON'T GO THERE! I went there with pretty good results... if you build the plungers right you don't have a big problem with drift once they're locked down. Telewave's plungers are just copper pipe with quality fingerstock. You don't have to use metal threaded rod... > I had to tune the cavities I made around 7 times a day in > a relatively stable but not totally stable temperature > atmosphere. Something you did in your project was not as well done as it probably could have been. > Yes, it is a very good learning experience so you can > appreciate how good a commercial set really are. Probably true in your example. > The can changes can be minimized by making use of a VERY LARGE > diameter can, such as a metal garbage can, so its change has > little effect on the center section. Not the way to go about things... more like material thickness and rigidity are the big players in the game you mention above. These stove pipe cavities I have here include steel angle iron bracing on the cavity hot end. Decades of stable operation so far... > ZERO coefficient of expansion metal is vital. I can assure > you, you will never be happy with a home made duplexer. opps... now I've got to go pull the 5 or 6 home brew duplexers we use out of service. cheers, s.
