I have been building my own cross-band couplers for years. Two meters and 440 work fine as long as you stay away from harmonically related frequencies.
My cross band coupler consists of a standard Tee section tuner for 440 with a series cap on the input, a shunt inductor, and a series cap on the output. The two caps are tuned for the best SWR on the input into the existing antenna system - even if there is some SWR. For two meters I use a series inductor, a shunt capacitor, and a series inductor. The two meter output inductor is connected in parallel with the 440 output cap, and again the two meter section is tuned for best SWR back to the two meter load. Tune the 440 section first, and you will find that the very small capacity on the output of the two meter section is no problem. Likewise, the inductor back to the two meter section poses no problem to the 440 output. Spreading or compressing the turns on the two meter coils will allow a good match when tuning the two meter capacitor. This system provides a two band to one band combiner, along with antenna matching for each band. The 440 section is hi pass while the two meter section is low pass, and each band is actually tuned to resonance Z matcher style. We operated a 440 repeater through one of these combiners to a GP-9 type antenna along with a two meter remote base. An MVP at 12 watts was the 440 repeater, and an Icom 22S was the remote base. It worked great with no interaction that we could tell. I added six meters to one of these couplers by simply putting a capacitor and inductor in series with no ground connection with the inductor connected to the output side of the combiner and had good operation on all three bands at the same time. The capacitor stator was connected to the six meter input. 73 - Jim W5ZIT -----Original Message----- From: [EMAIL PROTECTED] To: [email protected] Sent: Fri, 27 Apr 2007 8:58 AM Subject: RE: [Repeater-Builder] Re: Repeater Antenna Question I don't think any of them have cavities in them. I would suspect that the telewave is built very similar to the diamond etc. Mostly lumped circuit tuning (capacitor and coils) and maybe some 1/4 wave stub tuned coax rolled up inside. For a long time most commercial manufactures like telewave Sinclair etc. stayed away from cross band couplers between 150 and 450 bands but readily did it between 800 and 450 or 800 and 150. The problem with 150 and 450 is that they are harmonically related. A quarter wave length cavity on 150 is a three quarter wave length cavity on 450. A three quarter wave cavity resonates just as well at three quarter wave as it does at a quarter wave but of course has more selectivity as a three quarter wave. Most of the better transmitter combiners for 800 and 900 MHz used three quarter wave length cavities in them. Most of the cross band couplers use capacitors and inductors to form low and high pass filters to get around the 3rd resonance mode of cavities. Cross band couplers open the door for intermode problems as those 3rd harmonics are not attenuated all that much in the couplers. They do work but sometimes may cause problems. DUPLEXER / DIPLEXER A duplexer and diplexer are very similar. A diplexer is what it is usually called when two transmitters are combined together. If a transmitter and receiver are combined then it is called a duplexer. The cross band couplers I suppose could be called either as they do combine two transmitters but they also combine two receivers and allow duplex operation. You could have a 450 receiver working at the same time as a 150 transmitter so that would be a duplex situation. Maybe they should be called duo-duplexers. :>) 73 Gary K4FMX > -----Original Message----- > From: [email protected] [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of crackedofn0de > Sent: Friday, April 27, 2007 9:34 AM > To: [email protected] > Subject: [Repeater-Builder] Re: Repeater Antenna Question > > --- In [email protected], [EMAIL PROTECTED] wrote: > > > > In a message dated 4/26/2007 4:39:57 P.M. Eastern Daylight Time, > > [EMAIL PROTECTED] writes: > > > > cross band coupler > > > > > > Thanks that sounds like the ticket..... Seems like the way to go > > > > > > JA > > How about a diplexer from Comet or Diamond? I looked into this > recently for a similar application and couldn't tell the difference > between the expensive Telewave crossband couplers and the dime-a-dozen > amateur diplexers. The specs given for the diplexers even indicate > about twice the isolation compared to the crossband couplers. While > the designs appear to be different (tuned "cavity" vs. tuned circuit), > I can't find any information that would indicate any pros or cons > between the two in practice. Anybody? > > Both Comet and Diamond call their diplexers duplexers. I have no idea > why. They get it right when they call their triplexers triplexers. > > I was thinking about going with a Diamond product (they at least have > a metal housing) and swapping out any UHF connectors for N types. > > http://www.rfparts.com/diamond/Product_Catalog/plexers.html > > http://www.cometantenna.com/products.php?CatID=1&famID=6&childID=0 ________________________________________________________________________ Check Out the new free AIM(R) Mail -- 2 GB of storage and industry-leading spam and email virus protection.
