It's interesting to hear about your projects! I would be interested in knowing which VHF manual you're referring to, Jim.
While the original barrels used by Aerial Facilities Ltd. are pretty big I had the idea to try the beer kegs that are common here in Switzerland. These are 20 litre kegs so less than half the capacity of the original 11 imperial gallons. The diameter is 23cm (about 9") and measured from the outside the height could be just about sufficient to mount the plunger. But the overall size of 4 cavities would still be ok. I'll see if I can get some scrap barrels of this kind... Regards Martin --- In [email protected], Jim Brown <w5...@...> wrote: > > 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 <atlant...@...> wrote: > From: cruizzer77 <atlant...@...> > 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 <dcflux@> 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 <atlantis7@ ..> 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 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > __ >
