Bob, I think you got it right on. Placing in random lengths of cables (out of the junk drawer) between the band pass and the duplexer got different results.
Re-reading the VE2AZX duplexer theory paper on the Repeater-Builder web site verified that the cable should be shorter than a 1/4 wavelength. It seems it's pretty random on what the proper length should be depending on the can used. The PD-1173 can used a shorter jumper than a DB-4001 can. This is probably where the right angle connector trick would come into play. Thanks for you input, that really helped track it down. Dwayne Kincaid WD8OYG > > I think the length of coax you use between that BP > filter and the rest of the duplexer is critical. > > I have a 900 MHz duplexer that has a BP filter and a > BP/BR filter on each side. The BP filter gives me 25dB > attenuation 25 MHz away, and the BP/BR gives me about > 45dB. But when connected together with what seems to > be a 1/2 wavelength coax, I get 90dB attenuation. The > whole is greater than the sum of its parts, somehow. > > I'd suggest trying a piece of coax that's the same > length as what's being used now, which might be 1/4 or > 1/2 wavelength, to couple your BP filter to the > duplexer. > > Bob M. > ====== > --- ldgelectronics <[EMAIL PROTECTED]> > wrote: > > > This seems like a perplexing problem. Maybe someone > > can point me in > > the right direction. > > > > I have a TPD 1554, 4-can VHF duplexer. It provides > > about 77 db of > > isolation with 1.4 db of loss. This is just about > > what the spec says, > > so that all looks good. > > > > I happen to have some extra PD-1173 VHF band pass > > cans, so I'm > > thinking of adding a can on each side to get the > > rejection up to 85 > > db or so for use on a VHF repeater (Exec II base > > station at 25 > > watts). > > > > The bandpass can by its self shows about 0.5 db loss > > and 8 db of > > rejection at 600 KHz. The curve on the spectrum > > analyzer looks good > > and the return loss is very good (-40). > > > > Here is where it gets messed up. I added a can on > > the duplexer on the > > radio side (let's just say the RX side). The loss > > goes up to 1.9 db > > as expected and the return loss is still good. But > > when I go to > > measure the rejection, it now shows only 73 db. How > > can this be? > > > > Everything uses double sheilded cable and attenuator > > pads are used on > > the input and output to the analyzer. > > > > It seems like the rejection should be additive, but > > for some reason > > it's not showing up that way. Anyone know why? > > > > Dwayne Kincaid > > WD8OYG > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
