OK. That makes sense. How did you arrive at 9dB for .9 IL? And about the cable lengths between the pass cavites, I have found 3 different documents from Sinclair that gives me 3 different lengths for the same frequency. One document shows only 2 different cable lengths for the entire VHF band. If these are all correct it tells me that the lengths are not that critical.
lh On Wed, Apr 21, 2010 at 7:32 PM, hfarrenkopf <[email protected]> wrote: > > > No, using a T connector on the loop, you have a notch cavity although it is > a non symmetrical notch - doesn't matter. You adjust the loop for a notch > depth of say 9dB using the T one loop at a time and that balances the > impedances of the loops in and out so that they are the same. The notch > depths will vary on the frequency of the cavity for a given insertion loss. > This is how the cavities are set up at Sinclair. They know what depth of > notch to set the loop at to give a particular pass response. Quick, > repeatable and reliable. > > --- In [email protected]<Repeater-Builder%40yahoogroups.com>, > Larry Horlick <llhorl...@...> wrote: > > > > So you actually come up with an RL value and equate to an IL value? > > > > lh > > > > On Wed, Apr 21, 2010 at 9:08 AM, hfarrenkopf <hfarrenk...@...> wrote: > > > > > > > > > > > Here is how you do it...... > > > Take a T connector and put it on one of the pass loops. Leave the other > > > loop unterminated. Adjust the loop position so that the notch depth is > about > > > 9dB for 0.9dB IL through if I remember correctly - this is done like > > > measuring a notch cavity with the spectrum analyzer and tracking > generator > > > on the T. Adjust the other loop the same way but ensure that the loops > are > > > rotated the same way from the maximum coupling position as observed by > the > > > weld mark on the loop (rotated clockwise or counterclockwise). Recheck > the > > > first loop's depth and adjust so it is the same. This process makes the > in > > > and out loops symmetrically tuned. Measure the pass insertion loss to > ensure > > > you have the desired insertion loss. If not, readjust the loop's notch > again > > > to a slightly different depth - more for less pass loss and less depth > for > > > more insertion loss. > > > > > > Once both cavities are tuned to frequency, the cable length between > them is > > > somewhat critical in length. With the correct length, the individual > pass > > > curves add without the need to retune the frequency and the return loss > > > curve will show 2 dips approximately equal and above and below the pass > > > frequency. If you don't get 2.0dB IL with the 2 cans at 0.9dB, then the > > > cable is incorrect. > > > > > > Enjoy! > > > > > > > > > > > > > >
