We built a duplexer back in the late '70s using sections cut from the refueling boom from a KC-135 tanker. After cutting the six sections to length, the inside of the top end had to be machined to be able to insert a cap with the center tube and coupling loops inside with a tight fit. The other end of the tubing had a square piece welded to the bottom to close out the tube.
The tubing was about six inches in diameter and about a quarter inch thick, as I recall. We used the design in the repeater section of the VHF manual and used two connectors with a cap between the connectors on one side and an inductor between the connectors on the other side. The thing worked as long as the temp was constant, but with varying temperature, it was all over the place in tuning. When we finally got the money together we bought a 4 can 8 inch DB duplexer and it is still in service. 73 - Jim W5ZIT --- On Sun, 4/26/09, cruizzer77 <[email protected]> wrote: From: cruizzer77 <[email protected]> Subject: [Repeater-Builder] Re: W1GAN and square duplexers aka homebrew duplexer To: [email protected] Date: Sunday, April 26, 2009, 3:03 PM Since your post I've been googling like hell and found one Dutch design of a copper clad duplexer by PA0NHC, but this also has two loops per cavity and uses 8 cavities. However it answers the question about square enclosures and could be a reference design. Furthermore I found a design by WB3AYW which uses 16 gallon transmission fluid barrels as cavities in BPBR configuration using 4 cavities. This one looks easy to build and is somewhat similar to the beer keg duplexer which has been made professionally in the seventies afaik. The problem with these is that a 4 cavity duplexer gets pretty big and will hardly fit into a 19" cabinet. Does anyone know of any other particular homebrew design, especially one which uses some kind of available enclosure similar to the barrels but more space-saving? I also found some notice that the heliax duplexer, which is well-known for 6 meters, could also be built for 2 meters, but no detailed info was given. If anyone knows more about this, please tell... --- In Repeater-Builder@ yahoogroups. com, DCFluX <dcf...@...> wrote: > > There were a couple of designs that used copper circuit boards to form > square boxes for the outer jacket of the duplexer. > > Size maters as the inner to outer diameter ratio effects the impedance > of the cavity. It is my understanding that the optimum impedance for > a cavity is approx 70 ohms. Not sure if this is true for cavities, but > with helical resonators square shields have higher Q than round ones. > > You would also probably be better off using a BpBr style design, as I > remember W1GANs was for pass cavities which would require 6, BpBr can > get away with use 4, they would be similar but only have 1 coupling > loop that has a high quality trimmer capacitor such as a johansen or a > coaxial gimmic in the ground leg of the loop to set the notch > frequency. > > On Fri, Apr 24, 2009 at 4:19 AM, cruizzer77 <atlant...@. ..> wrote: > > Hi > > > > Most of you who are into duplexers will know W1GAN's old QST-article "A > > Homemade Duplexer for 2-Meter Repeaters". > > > > His design uses 4" copper tubes, but today many duplexer manufacturers use > > square aluminium profile as duplexer bodies, i.e. Sinclair but others as > > well. Now I wondered if W1GAN's design could be used for building such an > > aluminium square tube duplexer as well and if it would work equally well. > > Does anybody know? > > > > Instead of the 4" round tube, would a 4" square tube be used, or does the > > circumference matter? > > > > Kind regards > > > > Martin > > > > > > > > ------------ --------- --------- ------ > > > > > > > > Yahoo! Groups Links > > > > > > > > > __
