Are they for top mounted loops or side mounted. The side mounted loops had different loop lengths for the different insertion losses and hence the cable lengths were different. Unless the top loops were extra large for making a wider pass window, they should be very close in lengths (within an inch or so) for a given frequency.
See my previous post for the correct notch depths. --- In [email protected], Larry Horlick <llhorl...@...> wrote: > > 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 <hfarrenk...@...> 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 <llhorlick@> 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 <hfarrenkopf@> 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! > > > > > > > > > > > > > > > > > > > > > >
