ARROW Communications Association

by Corwin Moore (WB8UPM)

This originally appeared on the ARROW mailing list, but I thought it deserved a little wider publication, so Corwin has given me permission to put it here.......Dan KB6NU

The repeater antenna is on my tower on Scio Church Road, near the geographic center of Washtenaw County. The base of the anternna is at the 152 foot height above ground, or at 1182 feet HAMSL. The antenna is 21 feet tall. The boom is mounted on the west tower face, and the antenna points toward the south.

The antenna is similar to a Phelps-Dodge Super Stationmaster, nominally 6 dBd gain. It is mounted a quarterwave off the tower, which produces no additional gain, but results in a null from just east of True North counterclockwise around to about the ENE. The null depth, according to the manufacturer's data, is about 10 dB at its greatest.

The antenna is constrcted with a center tuned frequency of about 155 MHz, an obvious mismatch for its current use. The VSWR at the shack is 2:1. Estimating cable and connector loss, I believe this system to be delivering about 12 watts to the antenna feedpoint, but getting 8 watts back. Truly ugly!

Because of the frequency mismatch, I have no idea of the angle of maximum radiation above/below the horizon.

This mounting location is intended to provide primary coverage from about east counterclockwise around to the north northwest. Within this zone, and excepting for the terrain-shielded area along the Huron River in Ann Arbor, the station appears to operate reciprocally with a 10- to 15-watt mobile transmitter.

The RX sensitivity is 0.14 uW (-124 dbW). There is less than 1 dB of desensitization by the transmitter through the duplexer.

The basic duplexer is a 4-cavity pass/reject model, supplemented by a single pass cavity on the TX side to provide a buffer for a PA that is notoriously unstable in a high VSWR environment. VSWR between the TX and that BP cavity is down to 1:1.2, acceptable for the modest power being run (about 25 W TPO).

The squelch is gated to near critical, to benefit low-power users. HTs with a little less than 100 mWatt ERP can satisfactorily access this station from Signal Hill, from downtown Chelsea (Public Library), from Willow Run Airport, from Bridgewater Township, and from well south of Milan. Considering the antenna frequency mismatch, this more than meets my current design objective.

I have left the squech gate at near critical adjustment, even though this results in FM sideband noise from transmitters on nearby frequencies during band openings. The "noise" heard in the past few days has come from users of repeaters on the 146.355/.955 MHz and 146.370/.970 MHz pairs more than 100 miles away. I have left the near-critical setting so that our users can realize when their (especially low-power) input signals may be suffering from others' "FM sideband wash."

(By contrast, the ARROW two-meter repeater atop Tower Plaza has employed a much more aggresively [closed] squelch in recent years, which has prematurely truncated low-level but still fully intelligible signals. This aggressive setting has also effectively but unfortunately disabled the TP machine's squelch hysterisis.)

I set the "courtesy beep" to a value somewhat greater than some ARROW users may be accustomed. Some users have had a problem adopting their operating practices to this longer setting. Others have also become somewhat lazy in following FCC requirements regarding periodic station callsign ID (at max 10 minute intervals).

I do ask that users identify themselves by FCC callsign within their first 2 or 3 transmissions. This is the common operating standard on many repeaters, and there's really no reason not to ask that users follow this protocol.

If you have other complaints or recommendations, please feel free to voice them. The deviation level of the repeater IDer is one thing that I can't really do anything about without making major hardware modifications, although I would if I could.