January 21, 1976
W6PO - Robert I. Sutherland, San Mateo, CA
The second three months of operation with up to 2500 watts of output power on 144MHz moonbounce have been just as rewarding as the first three months even though my fellow experimenter Lester Whitaker, W7CNK, lost his antenna.
The W7CNK antenna array consisted of eight-sixteen element log periodic yagis. The antenna was well constructed and braced for everything except a swirling wind coming up from the ground. The wind lifted both ends of the main boom and then very abruptly dropped them. The result was a fracture in the center of the boom. The loss of the antenna aborted my plans for tests with half of W7CNK's antenna. He plans on having the array operational again in March 1976.
The loss of W7CNK's antenna is indicative of the problems a moonbounce operator has with large VHF antennas. WA7BJU, a moonbouncer in Oregon, lost his antenna in the same storm. A smaller array with a higher power transmitter can provide the same effective radiated power with considerably less trouble.
The four-fourteen elements antennas which were ordered for W6PO during the first 90 day test period, have arrived. I have enlisted the aid of Brian Palumbo, WB6LAM, to help modify a U.S. Navy surplus large TV Camera "pan mount" to use with the small 144 MHz EME (earth-moon-earth) array mentioned in my first 90 day report to the FCC. In addition to the azimuth and elevation drive provided by the camera mount, a system is being devised to change polarity of the antenna array. It is hoped that a smaller array with variable polarity can be adjusted for optimum signal strength. A larger array having only azimuth and elevation adjustments is very seldom operating optimumly.
While using the 2500 watts power output, there have been no complaints from neighbors concerning TVI, BCI or interference to high-fidelity systems. I have had past troubles in one azimuth direction when I use my 40 element collinear and on kilowatt input. Normally during prime TV time I do not point the large antenna in that direction. If I must, I drop the power down to 200 watts which seems to stop the problem. My 160 element collinear antenna will not go below 25 degrees above the horizon, so at no time does the main lobe ever point at a neighbor. This is probably why the 2500 watts does not cause a problem.
I am almost certain a quarter-wave open stub on the neighbor's TV set would allow me to run a kilowatt input when using my horizon antenna. However, the only time I need the kilowatt input is when I am running meteorscatter schedules early in the morning. The neighbor isn't watching TV at this time so no problem exists.
An unexpected problem did arise with the 2500 watt output power permit. When the transmitter is keyed, the power line voltage at the service drop fluctuates three volts. I contacted the local power company and found that the California Public Utilities Commission allows a six volt fluctuation. That is to say, the power company will do nothing to reduce the voltage drop if it is under six volts. It is surprising but three volts of flicker can be seen in an incandescent lamp and can be annoying to someone reading. To solve this problem, I designed and constructed a special power supply ballast system. I have two ballast tubes in parralel across the power supply that dissipate the same power on the key-up that the transmitter draws key-down. This is a rather expensive and inefficient way to do things, but does eliminate power line fluctuation.
A review of the station log for the second 90 day period reveals a number of "almost" contacts. I could hear a moonbounce station calling me, but I could not copy it adequately for a contact. The increased power at my end probably accounted for most of this problem. They could hear me, but I could not hear them. However, even when stations have identical power the EME path is not always reciprocal.
I have received many requests during this second 90 day period for schedules from potential moonbouncers. Most of them felt that my increased power would allow them to test their antenna and receiving capability even though they did not have sufficient power, or antenna, to make a two way contact. Several well equipped European meteoscatter stations have been attempting moonbounce using the setting moon at their end. HB9QQ (Switzerland) and OZ6OL (Denmark) are two of the successful stations.
There has been much discussion among the moonbounce amateurs as to the reason for the non-reciprocity of the EME path. My personal conversations with Dr. Taylor Howard, of the Stanford University Radio Propagation Department, indicate the path should be reciprocal. Amateurs are attempting to correlate this non-reciprocity with the relationship of the amateurs longitude and latitude with the magnetic north pole. It has been observed, for example, that a station in Tacoma, Washington, will hear a different group of EME stations than a station in San Mateo, California, in the same time period.
Amateurs also have noted a complete inability to work moonbounce during the auroral display. Don Falle, VE2DFO, in Montreal, Canada, reports all EME echoes stopped as if a switch had been thrown at the start of an Aurora. At the very same time, I was able to successfully complete a two-way contact with a station in Missouri. Apparently the Aurora attenuates the signal sufficiently to remove any excess gain in the path loss resulting in a loss of echoes.
The W6PO station log pages showing the EME operation during the period November 16, 1975 - December 21, 1975, are included in the Appendix.