Repeater Details

(updated 1-16-2017)

This section describes the club repeater systems, and the equipment that runs them.

SARA operates two repeater systems that run under the W8WKY club callsign:

  • VHF 2 meter repeater on 147.390 MHz (+600KHz offset), PL (CTCSS) 114.8Hz. Transmit power is about 90 watts into the duplexer. This repeater is also connected to the AllStar network as node 43211, and the Echolink network as W8WKY-R node number 580387
  • UHF 70 cm repeater on 442.275 MHz (+5 MHz offset), PL (CTCSS) 110.9Hz. Transmit power is about 80 watts into the duplexer. This repeater is connected to the AllStar network as node 43078

Both repeaters require the PL tone (also known as CTCSS) to be sent by your radio, and both also transmit the same PL tone back to you. This means you can set your radio to use Tone Squelch or CTCSS Decode if you wish.

More details on the AllStar and Echolink connectivity can be found here.

Both VHF and UHF repeaters are available for use by any licensed amateur radio operator.

Repeaters are really just a separate transmitter and receiver, that are connected together with a repeater controller. Whatever is received on the receiver is re-transmitted on the transmitter.  A great guide to how repeaters work by N4UJW can be found here.

Both of SARA’s repeaters are at the same physical location, which is a commercial tower and building owned by N8XPK. The two repeaters share a cabinet, power systems, feed line, and parts of the antenna system. The VHF and UHF systems operate as independent repeaters most of the time. Both the UHF repeater and VHF repeaters are controlled by Raspberry Pi 2 boards, with both running the HamVoip.org Allstar image v1.02 Beta. The Raspberry Pi boards do all of the repeater control duties including identifiers, courtesy beeps, timers, etc, as well as connections to other repeaters via Allstar and Echolink. No “traditional” repeater controllers are in use in the system.

The diagram below shows the high level of how the systems are interconnected, and which components are shared. There are obviously more components than what is shown on this diagram, but the main components are represented.

Since both the VHF and UHF repeaters are at the same site, and share a cabinet, it is relatively easy to link the VHF and UHF repeaters together using the AllStar system. Although this type of linking uses a Voice Over IP (VoIP) system, the traffic never goes to the Internet between these two repeaters. When they are linked, the controller simply sends whatever it hears on either repeater to the transmit side of both VHF and UHF systems. Since both repeaters share a site and an antenna, there is generally not much difference between the coverage of the two, other than some variations in how VHF and UHF signals propagate and behave.

The VHF repeater’s output power is around 90 watts from the Henry amplifier, but losses in the duplexers, feed lines, and other equipment mean that more like 55 watts actually makes it to the base of the antenna. The UHF repeater output is about goes into a Mirage repeater amplifier with about 80 watts output, but losses in the components mean about 50 watts make it to the antenna. While this doesn’t sound like a lot of power, location is everything on VHF and UHF. These repeaters have a great location.

All of the repeater equipment is contained in a single 19″ rack at the repeater site. Below are pictures of the front and back of the repeater cabinet showing the various components. Some of the components such as the power supply and UHF RF amplifier and pre-amp have been updated since these pictures were taken. Click the pictures to get a bigger version.

repeater-cabinet-front  repeater-cabinet-rear

DSCF4082

 

Both systems feed into coaxial cable that is much larger and much lower loss than most people use at home. The coaxial cable is known as Hard Line, and more closely resembles copper tubing than it does traditional RG8 coax. This 7/8″ cable is difficult to work with and bend where it is needed, so it has a short length (about 8 feet) of smaller diameter hardline at the repeater end to connect to the equipment, and another short length at the antenna end to reach to the antenna.  The smaller diameter cable is shown below being prepared for connectors.

IMG_0227

 

 

 

 

 

Finally, all the equipment connects through the hardline to a “crossband coupler”, which is an industrial version of the diplexer or splitter you might use on a dual band radio. This crossband coupler connects the VHF and UHF antennas into a single feedline. The picture below shows the location of the repeater antennas at the end of the yellow arrow. The VHF repeater uses a Commscope DB224 4-pole folded dipole antenna, and the UHF repeater uses a Commscope DB-411 4-pole folded dipole antenna. Also shown below the repeater antenna is the Ubiquiti PBE-M5-400 5.8GHz dish/radio combo used to provide data linking into the system.

Tower showing VHF/UHF repeater antennas and the 5.8 GHz dish used for linking

The result of all the above hardware and work is a coverage map for the VHF system that looks like the picture below (click the picture for a larger version). Note this propagation model is an average based on a mobile radio running about 10 watts and a 1/4 wave antenna. Coverage will likely be significantly better for base or improved mobile installations. The green color is solid coverage, and the blue coloring shows more marginal areas. Coverage for the UHF repeater is slightly less than the VHF model, but is almost exactly the same pattern.

39-coverage-map

 

Compared to most ham’s home stations, there are some big differences in what repeaters experience:

  • They are powered on 24x7x365
  • They often are transmitting for several hours at a time without a break
  • The antennas cannot be disconnected when storms approach, so they are exposed to lighting and other hazards
  • The extreme height of the antenna exposes the antenna to more wind, ice, snow, and other conditions than most home systems
  • The antenna height also exposes the repeater to more RF noise from other near and distant radio systems, repeaters, cell towers, lightning static, and electrical noise than most home systems experience.
  • Repeaters must be operated under the coordination of the Ohio Area Repeater Council

Over the 35+ years that the 147.390 VHF repeater has been on the air, it has evolved from re-purposed commercial equipment controlled with home brew controllers based on discrete TTL chips and transistors to the more modern, purpose built commercial radio systems they are today.

Enjoy the SARA repeater systems!