Why would it need to be a full wave length at pass frequency (or would that be reject) with a capacitor in series? Shouldn't that be a half with cap splitting the middle? Thanks! 73 de N5NPO Norm
----- Original Message ----- From: Repeater-Builder@yahoogroups.com <Repeater-Builder@yahoogroups.com> To: Repeater-Builder@yahoogroups.com <Repeater-Builder@yahoogroups.com> Sent: Mon Feb 01 10:20:59 2010 Subject: Re: [Repeater-Builder] Re: Building a notch duplexer with notch cans. Gentlemen: For those wishing to convert a BP cavity to operate as both a BP and notch cavity there exists a simple and convenient way to do so with out having to do surgery on the innards of the cavity. One only needs two 1/2 WL of coax (must be double shielded, can be RG-214 but I prefer an equivalent Teflon type) with connectors on one end to mate with two Tee connectors, one on each of the input and output of the BP cavity, and a high quality variable capacitor of 1-15pF, preferably quartz. The center conductors of the two open coax ends are connected in series with the variable capacitor. The shields of the coax must be securely connected together. I used a small 1" square of PCB material to solder the two shields together and to support the capacitor. Using Teflon coax makes this much easier. The 1/2 WL of each coax is measured from the center of one Tee adapter to the jct of the variable cap taking into account the VP of the coax. The variable cap series resonates with the inductance of the two loop assemblies and can provide a notch on either side of the center of the BP cavity tuning, depending on the inductance of the loops. If you find the cap adjustment not enough then a higher value cap may be required. The BP tuning is very broad and should be adjusted first for best return loss. Then the notch can be adjusted. Appropriate shielding should be provided around the variable cap and the open coax before using in the final configuration. If you have any problems or questions I will be willing to help. Just ask. Allan Crites WA9ZZU --- On Mon, 2/1/10, NORM KNAPP <nkn...@twowayradio.net <mailto:nknapp%40twowayradio.net> > wrote: > From: NORM KNAPP <nkn...@twowayradio.net <mailto:nknapp%40twowayradio.net> > > Subject: Re: [Repeater-Builder] Re: Building a notch duplexer with notch cans. > To: Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder%40yahoogroups.com> > Date: Monday, February 1, 2010, 8:53 AM > > > > > > > > > > > > > > > > > > > > > > > > > > I am also experimenting with some 8" DB > Products band-pass cans from a combiner network. I took a > coupling loop assembly from a Telewave TPRD series duplexer > and tried in one. It works great! I would imagine the TPRD > harness would be correct because of the loops. I sent an > e-mail to telewave about buying some loop assemblies, but > haven't heard back yet. I may try building some to try. > > > Keep us posted on your findings. > > > 73 de N5NPO > > > Norm > > > > > > ----- Original Message ----- > > > From: Repeater-Builder@ > yahoogroups.com <Repeater-Builder@ > yahoogroups.com> > > > To: Repeater-Builder@ > yahoogroups.com <Repeater-Builder@ > yahoogroups.com> > > > Sent: Mon Feb 01 07:46:16 2010 > > > Subject: [Repeater-Builder] Re: Building a notch duplexer > with notch cans. > > > > > > > > > > > > > > > > > > --- In Repeater-Builder@ > yahoogroups.com <mailto:Repeater- Builder%40yahoog > roups.com> , "skipp025" <skipp...@.. .> > wrote: > > > > > > > > Re: Building a notch duplexer with notch cans. > > > > > > > > You would not be restricted to using DB/Andrew/DB- > Spectra loops > > > > if the proper type and size were available from > another source. > > > > Regardless, the price is probably going to be over > $200 minimum > > > > for a 4 cavity probe kit and matching coax harness. I > would actually > > > > expect more... > > > > > > I am curious if andrew still support the DB line of filter > (next thing on my list of things to inquire about) > > > > > > > > > > > > we have 4 pass cans at the site in a cabinet that > are just > > > > > waiting to have some vari caps installed to make > them into > > > > > pass/reject cans. > > > > > > > > The free lunch you think you're going to get by > simply installing > > > > the small piston caps in series with the cavity loops > is in > > > > my opinion fairly optimistic. > > > > > > I dont think it would be a free lunch, even 10 to 15 db > notch on a pass can it still workable, but i am open for > your thoughts on the subject. > > > > > > > > > > > > as far as making these into pass/reject, i am not > sure how > > > > > you modify the loops. Unless you can add a vari > cap on the > > > > > ground side of the loop. > > > > > > > > That's the trick a lot of people are saying will > work. It's not > > > > the type of loop/probe I use or make (mine are > constructed more > > > > like the Telewave TPRD type) but they may work. The > Repeater Builder > > > > Web Site has information about how Hams have modified > cavity > > > > probes from Band-Pass to Band-Pass, Band-Reject with > reportedly > > > > decent performance and cost savings. > > > > > > > > If you're going to be constructing BpBr Probes, I > would suggest > > > > you make new cavity port probes rather than modifying > the > > > > originals. > > > > > > > > The materials and parts shouldn't be that exotic > or hard to find > > > > unless you live well away from a decent size city... > or lose > > > > access to the web/internet and the Post Office. > > > > > > > > s. > > > > > > > Ok i will look through the website and see what i can find. > I have an old FM/repeater manual from several years ago, and > the arrl antenna book, both provide construction articles > and i will look at the loops that they recommend building > also. > > > > > > I believe the 2 ways i have seen the loops modified are: > > > > > > 1) vari cap between the loops of a pass can. > > > > > > 2) veri cap inserted in the ground end of the loops of a > pass can. > > > > > > are there any others? > > > > > > By the way, i appreciate all the suggestions. thank you to > all that have responded. > > > > > > de kd4wov Tom > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
