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/
