W5GM Converts his Analog Repeater to NarrowBand FM

by Jay Urish - 11/07/2011

Recently in North Texas an issue arose where several Narrowband digital repeater systems lost their interim coordination. This caused a conundrum. The vhf spectrum in the metroplex is congested and the waiting list is lengthy. The idea was put forth to begin the process of converting several pairs to narrowband 2.5kc max deviation channels.

This process intrigued me as I am of the mindset that Amateur Radio should be leading the way in radio communications. I firmly believe hams should be efficient users of the spectrum they are allowed to use. With this in mind I decided to convert my 145.230 repeater to narrowband.

This change was really simple. My VHF system is composed of a Kenwood TKR-750 repeater. Moving to narrowband was as simple as plugging in a programming cable, reading the repeater using the KPG-96 software and clicking on the radio button to move from 5khz deviation to 2.5khz and clicking on write to radio. Done! The hard part was setting the audio levels on the Arcom RC-210 repeater controller.

With the help of Mike Chittenden AE5IV and his service monitor, I was able to have him generate a signal on the repeater input at the proper level, while I measured the levels with my DVM in the controller. Once the input level was set, I could watch the output on my service monitor and set the output level to be right at 2.5kc.

All the radios I use are narrowband ready, such as my Yaesu FT-60, Icom IC-2820 and Icom ID-92AD. 98 percent of my users also have newer equipment that is compliant. Results have been favorable with few complaints. Most users have no problem changing the mode for the channel they have 145.230 programmed in.

The TKR-750 is pretty tolerant of wideband signals on the input and will usually pass them unless they are really wide, over 6.5kc or so. If somebody is running wide, usually they sound distorted and raspy on the output. They can sometimes still work the machine by just backing off the microphone or talking softer.

All in all, I would have to say the experiment has been a raging success! I am planning on staying narrow on vhf and would encourage all new repeater builders to go in that direction as well. If you are ever in Denton County, feel free to drop by and give it a try, 145.230 PL 110.9.