Derek, Your suggestions are right on the money! My only disagreement is with the statement in the last paragraph; increasing the coupling will both sharpen the bandpass AND increase the insertion loss. Depending upon where the coupling loop is positioned, rotation in a given direction may increase or may decrease the insertion loss.
Adjusting a duplexer on a spectrum analyzer with a tracking generator will usually get the unit tuned to 90% or so of optimum, and this is adequate for most installations. The advantage of using a network analyzer, or a spectrum analyzer with a return loss bridge, is that you can optimize the duplexer for a correct match as well as an ideal pass/notch ratio. Very often, this separates an "average" installation from an "exceptional" one. It is instructive that real-life situations do not always exactly correspond to the theoretical rules. As Derek pointed out, it is entirely possible that the TPRD-1554 duplexer will perform admirably when the "rules" say it should not. I continue to be amazed when this happens, but that does not deter me and the many other purists from seeking to always use the appropriate part when the situation calls for it. Experiment! 73, Eric Lemmon WB6FLY "Derek B. McIntyre" wrote: > > I have several TPRD-1554's and 1556's that will certainly work well > in the ham band for 600 KC split. The 1556's (six cavity) will work > down to 400 KC I think. At 600 KC, the 6 cavities have about 2.2 dB > loss. The 4 cavities like you have will run around 1.8 dB typical. > > You may encounter a little more loss because the interconnect cables > are cut for 162 MHz for this model which is the geometric center at > the frequency ranges they are designed at. You may either do one of > two things. > > 1. Use it like it is. It will work well and you'll never notice the > half a dB of loss that you encounter at 146 MHz that you don't have > at 160 MHz... > > 2. Make some new interconnect cables about an inch longer than > what's on there at the moment. Telewave uses electrical 1/4 > wavelengths between cavities. With a velocity factor of 0.66 (which > is RG-214 they are using) their measurement for 162 MHz is 12.0 > inches from center pin to center pin. For 146 MHz, it would be > around 13.25 inches (2952/F * 0.66) In short, just make new cables > about an inch or so longer than the stocks, if you so desire this > mod.. > > If you are using a tracking generator, you will notice that if you do > not make new cables, the two bandpass curves may never quite match up > to make one nice curve at 146 MHz but will be perfect in the spec'd > range. > > Also, you may notice the piston capacitors may not drag the notch > close enough to make the 600 KC split. If you find you have run out > of range while trying to tune the notch, loosen the three screws > which hold the coupling loop down and rotate the loop counter > clockwise about 5 degrees at a time. This will decrease the > coupling, which increases the sharpness of the bandpass curve, and > allows the notch to drag closer. It takes a little trial and error > and a tracking gen to do this properly! > > 73, Derek KC4FWC > > --- In Repeater-Builder@yahoogroups.com, doug <[EMAIL PROTECTED]> wrote: > > > > just picked up a set of these VERY cheap. > > > > in nice shape, some scratches, etc. > > > > telewave is sending the tuning directions via FAX, > > > > has anyone used this in a 2m application? > > > > > > as usual, the factory listed split is 148+, but i'm sure > > it'll cover at least the top end of the ham band. > > > > > > anyone? > > > > > > > > > > doug > > > > 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/ 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/
