These cans are recent vintage and have top mounted loops.
On Wed, Apr 21, 2010 at 8:24 PM, hfarrenkopf <[email protected]> wrote: > > > 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]<Repeater-Builder%40yahoogroups.com>, > 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> > <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! > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
