Thursday, July 16, 2009

Update on the new repeater and controller for 147.360+ PL 100 at Bellin Hospital

The Bellin repeater is now up to specs and fully functional as of 9:30PM July 10th thanks to KB9UAE and KB9MWR. Steve and Nick put in 12+ hours testing, re-programming and checking out every aspect of the installation including making up new cables for the duplexer which was still perfectly tuned after many years at the college! They also installed a common grounding strap between the power supply, duplexer and repeater. The controller is now indentifying with the proper ID. The power is approximately 40 watts ERP at the antenna.

Next, venting holes need to be drilled in the cabinets for the repeater to improve dissipation of heat. We can begin to develop a 360 degree range pattern for this site over time.

Saturday, July 11, 2009


Regarding the 147.360 squelch... It has been re-calibrated. But here is a little nugget for those curious:

Most FM squelch circuits incorporate a feature called hysteresis, which is a deliberate change in sensitivity between squelch-closed state and squelch-open state. If you design the circuit so that it is more sensitive after opening than before it functions much better in the real world. Without hysteresis, the squelch may drop out while someone is talking. If there is too much hysteresis, squelch threshold becomes hard to adjust properly.

Motorola coined this dynamic relation as "smart squelch", which I think sticks with people. The gist of it is as you get noisy due to mobile flutter or what have you, the squelch loosens, to help cut down on picket fencing.

A good example of a radio with no hysteresis is the Icom 706. If you have ever use this for FM mobile you know how annoying a lack of hysteresis is.

Hysteresis actually helps the weak signal performance, because it decreases threshold once the squelch pops open. Imagine how choppy every mobile users would sound if a repeater had no hysteresis. You want the carrier to reach a point that the noise level is driven below the critical point and hold the repeater COS open.

Steve, KB9MWR