Hi Bob, I was pretty curious about it as well, especially in the 'early days' of this project. Nobody seemed to know much about the stubs.
If you are looking at the spec. analyzer & trk gen, you see the notch. The left side goes down deep, then comes up on the right side of the notch. But, without the stubs, the right side doesn't come up as fast as the left side went down, hence more insertion loss. With the stubs, they got pulled right up. As far as your earlier question, the notches come up to the 0dB point well before the other frequency. They seem to be pretty tight. I guess I'm still looking for an answer to the original question. Do the notch cavities work @600khz spacing? I've always had the BpBr duplexers for ham stuff, & I guess I've gotten a bit spoiled working with 4 & 5mHz splits! Thanks, Tim W5FN --- In [email protected], n...@... wrote: > > At 8/10/2009 10:21, you wrote: > >Hi Dcflu7x, > > > >It's a DB products SP-1894. Can't get any info on it from > >anywhere. > > > >Each of the 8 cans have the approx dimensions of 5" x 21". > >A single screw-type shaft in the center, and one SO-239 > >sticking out of the top of the can. No variable caps, or > >anything else on the cans. Each can has an RG-9 jumper > >between each 'T'. The male portion of the 'T' screws down > >into the can. > > > >The 4 cans on the 147.7 side are strictly 4 cans in series. > >The 4 cans on the 147.1 side also have an additional 'T' > >between cans, and from that dangles a short stub. > > This sounds like a modified DB-4050. I don't understand why one side of > the duplexer would have additional Ts. > > The specs on the DB-4050 are: notches -95 dB, passes -2.2 dB. Sounds close > to what you're getting. > > > >The stubs actually pull up the high side of the notch. Without > >them, the cans exhibit high loss at 600khz above the notch. > >With them, the total loss is about 2 - 2.5dB. > > Bob NO6B >
