Go Sporadic This Summer

A large number of professional broadcast engineers share a background of both listening to distant stations or playing disk jockey, or both. I certainly have.

When I got off work from playing background music at KRCO in Prineville, Oregon in 1973, I tuned across the FM dial to hear multiple signals where none normally existed. A baseball game between Spokane and Phoenix turned out to be originating from Arizona. I put up rabbit ears at home and experienced a massive influx of low-band VHF TV stations from Texas to Alberta on what I learned was the sporadic-E mode of propagation. It turns out that E-layer propagation takes place mostly in May and June, with smaller openings at other times of the year. Due to the angle of reflection, reception of a single E-layer bounce tends to take a signal somewhere in the range of 700 to 1700 miles. Multiple bounces are more rare, but can double or triple that range.

Every May and June now, I tend to log a couple dozen ham stations on the 50 MHz 6 meter band. A casual operator only, I’ve logged multi-hop contacts to Georgia, Hawaii, and a couple in Japan using my rooftop Create log-periodic and 100 watts.

A Limited Opportunity

Starting June 13, the number of full-power TV stations occupying the low-band VHF band will dwindle to a handful, and if you count only those in the E-skip zone, the number of DTV stations most likely received in San Diego will be down to 14. Obviously, these channels will eventually fill with either low-power DTV signals, or the FCC will reassign the band to other uses like the commonly discussed audio services. So I consider this a limited opportunity to enjoy relatively interference-free DXing.

Actually, the transition isn’t that simple. A number of analog stations will remain on the air for up to one month broadcasting “nightlight” service to help uninformed over-the-air viewers get the information required to transition to DTV. Many of those stations will be on low-band VHF.

Then there are the remaining TV stations in the skip zone from western Canada, central and northeastern Mexico, and low-power channels that may add enough noise to make 8VSB reception impossible during certain E-skip events. And did I mention low-band VHF analog channels 3 and 6 from Tijuana remaining on-the-air?

A listing of the 14 candidate DTV stations is below. I did not count low-power analog broadcasters, nor one 270 watt Jackson, Wyoming station with a null to the southwest. I did not list double-hop stations, but if you monitor long enough, you are likely to catch one or more. The best way to learn of sporadic-E clouds is to monitor the VHF-DX.net real-time map that accumulates the “spots” of operating hams. The MUF, or Maximum Usable Frequency, tends to rise to a peak that may never approach channel 2 VHF, but can, on occasion, extend above the FM band. I have occasionally been made aware of big openings by having our channel 6 viewers complain of big black lines and heterodyne audio tones.

If you don’t care about high definition, you can use one of the new, inexpensive DTV converters. The Zenith and Insignia (Best Buy house brand apparently also manufactured by LG Electronics) get high marks for sensitivity and allow manual channel entry. The Magnavox TB100MW9 is able to scan a single channel at a time and can freeze a frame for photographing. The Accurian HDTV receiver box can meter signal strength of a single channel even when it is below decoding threshold, which makes it very useful for DX’ing. The RCA brand is consistently criticized for its lack of sensitivity. Actually you can check the list of converters reviewed by MSTV for one with extra dBs of sensitivity, quick scanning, and easy channel ADD.

If you have a directional VHF antenna, rotator, and DTV, you should be good to go. Computer capture software or a digital camera set at 1/15 second exposure will allow record keeping.

45° 645 Grand Junction, CO 2 KREX CBS
53° 1080 N Platte, NE 2 KNOP NBC
40° 1085 Rapid City, SD 2 KOTA ABC
328° 685 Eureka, CA 3 KIEM NBC
29° 1118 Miles City, MT 3 KYUS NBC
49° 1360 Florence, SD 3 KDLO CBS
60° 1584 Rock Island, IL 4 WHBF CBS
13° 946 Butte, MT 5 KXLF CBS
57° 1172 Hastings, NE 5 KHAS NBC
337° 717 Medford, OR 5 KOBI NBC
39° 1080 Lead, SD 5 KIVV FOX
93° 1090 Fredericksburg, TX 5 KCWX CW
65° 1030 Ensign, KS 6 KBSD CBS
13° 946 Butte, MT 6 KTVM NBC

Data for this table came from the latest FCC Table of Allocations and Hammett and Edison coverage maps. Email me with any changes.