Honolulu AM Nondirectional Patterns

[trusty]

Was looking in Radio-Locator at Honolulu AM stations and noticed two things:
1. All AM's are non-directional with one tower.
2. All AM's have coverage patterns that look very directional.

??? why (gotta be simple) ???

 

[jd]

Was looking in Radio-Locator at Honolulu AM stations and noticed two things:
1. All AM's are non-directional with one tower.
2. All AM's have coverage patterns that look very directional.

??? why (gotta be simple) ???

There are a couple of exceptions to the rule, but first, regarding point number two: it's all about ground conductivity, or in this case water conductivity. Since virtually all AM's in Hawaii are located very close to the coastline, the patterns look directional because they spread out over the water. If a neighboring island gets in the way (so to speak) it results in a sharp null (or notch) in the shape of the pattern. Like this one: www.radio-locator.com/cgi-bin/pat?call=KHVH&service=AM&status=L&hours=U That pattern isn't too different from most of the others around Honolulu, and it's due to the vastly greater conductivity of the water versus the land around the transmitter. Take a look at the patterns for non-directionals in California like KFI or KNX and you'll see the same thing, where the pattern "fans out."

KHNR 870 Honolulu was using a 50,000 watt directional pattern from Kaunakakai on the neighboring island of Molokai until they received authorization to change frequency to 880, back on Oahu with 10,000 watts non-directional. (FCC records show that the station is currently silent while construction continues on the new 880 facilities.)

And over on the Big Island, KIPA 620 Hilo (5,000 watts ND) is authorized to operate two co-channel synchronous repeaters, one with 5,000 watts ND in Naalehu (on the southern tip of the island) and another one in Kalaoa (on the western side) with 10,000 watts and a directional pattern. Unfortunately I'm not able to retrieve a copy of the pattern, but I think it's in somewhat of a north-south configuration.

 

[trusty]

??? why (gotta be simple) ???

Tanks. (forgot about the coastline stations).

 

[BobOnTheJob]

A similar pattern distortion is shown on the non-DA New York City stations where much greater signal goes out in to the ocean than does back where people actually live. Sometimes life just ain't fair...