New repeater is on the air

The new mixed-mode Hytera repeater went live at 15:00 on 2/1/20. As discussed previously, it is a DMR repeater on the Brandmeister network, and an AllStar analog FM repeater on ASL. Our club callsign K7EVR is assigned to the station with a -DR suffix for “digital repeater”. It should be an interesting experimental platform.

Through some generous and gracious friends, and some help with frequency coordination, an excellent site for the repeater has been provided. The antenna is about 1200 feet above the average terrain of the metro Phoenix East Valley. Although the repeater output power is limited to about 40 watts, the anticipated coverage should be excellent except straight South of the location, where a somewhat higher peak blocks propagation.

The site has many other commercial and Amateur repeaters, but the receiver is well protected by a pair of large bandpass cavity filters in addition to the duplexer. The 2 dB loss of the filters plus about 1.6 dB in the feedline is compensated by a low noise preamp based on a SPF5189 MMIC. A dual stage isolator on the TX, and PD526 six cavity duplexer complete the RF setup. All interconnects are done with FSJ1 Superflex, with the exception of the new duplexer harness. There, the old original single shielded RG8 coax was replaced with Belden RG142u and high quality silver plated N connectors.

I was very fortunate to be allowed to use an abandoned DB408 antenna fed by LDF5 Heliax that was present at the site. Adding all losses, about 20W of RF is feeding the antenna.

DC power for the repeater is provided by a home brew N+1 redundant power supply using two 15V 25A Meanwell switchers and Schottky diode isolation. It’s a bit of a overkill; the repeater only draws about 8.5A on TX, but the supplies are PFC corrected and are efficient even at light loads. An external diode isolated DC input with a 5V 5A buck regulator module for the Pi is also provided, but not used in the present configuration. The RasPi used as the AllStar controller is presently powered by another 5V 3A Meanwell supply with a separate AC input, so both the repeater and Pi can be switched on and off independently by an 8 port APC IP power switch. Doing this with external DC power applied would require another way (relay or MOSFET switch) to interrupt the DC power to the repeater for remote reset. An additional DC filter board with an inductive/capacitive Pi configuration provides very clean 12V power to the preamp. A 5V linear regulator and more capacitive filtering is present in the shielded preamp case for 5V Vcc supply to the SPF5189Z.

The site has an emergency generator for AC backup which is augmented with a 600W Magnum Energy inverter-charger unit with it’s internal transfer relay, plus a deep cycle battery that together act as a UPS. This should hold things up until the generator comes on line. The overall system is very efficient compared to many repeater setups. Only about 130W of AC power is consumed during TX and about 30W on RX standby.

The gear is housed in an 18U freestanding fully enclosed steel rack cabinet with front and rear doors. This should provide a degree of additional shielding. Fans in the repeater, power supply, inverter-charger and cabinet will keep things at a reasonable temperature.

Some items that need to be fine-tuned are hang times for both the DMR and analog sides of the system, and auto-disconnect intervals for ASL connections. The RasPi that controls the AllStar functions can be SSHed into on a custom port for editing settings remotely. Additionally, Hytera RDAC is in place as needed to monitor forward power and VSWR, as well as change some, (but not all) codeplug parameters. Required out of band control is provided by Zoiper, a phone app that connects via IAX to the Asterisk AllStar controller. As a last ditch, the APC IP switch can be accessed to turn off and/or reset the Pi, or kill power to the repeater.

Dave K7DMK

K7EVR Digital Amateur Radio