After successful EME contacts on 2 Mtrs with a yagi array in 1976 a dish antenna for 432 Mhz seemed a good idea. Dish was 23ft dia, F/D 0.5.
Picture on the left shows completed antenna, manually steerable in all directions. It was nicely balanced with the weight of the two old rotary hoe wheels cantilevered out to the rear.
It took nearly a year to design and build. Sun noise figures were excellent, gain was very good, but I did little with it. Hours were spent up the pole with headphones on trying to tune the masthead preamp for best sig/noise. A U310 seemed a good low noise device at the time and the feed cable was Heliax. Performance slowly went down. It took some time to find that condensation on the cold metal of the N connector inside the Heliax was shorting out the signal path. The humid climate here is destructive.
Circumstances, time, and other interests ruled the day. The dish was sold for $500 to a chap in Whakatane. He came up with friends and cut it in half with a disc grinder to put on a trailer.!! Pity really, satellites were just beginning to proliferate. I still had my UK101 computer, built from a kit, to enable aiming calculations for the earlier yagi array. It would have been useful.
Picture on the left shows completed antenna, manually steerable in all directions. It was nicely balanced with the weight of the two old rotary hoe wheels cantilevered out to the rear.
It took nearly a year to design and build. Sun noise figures were excellent, gain was very good, but I did little with it. Hours were spent up the pole with headphones on trying to tune the masthead preamp for best sig/noise. A U310 seemed a good low noise device at the time and the feed cable was Heliax. Performance slowly went down. It took some time to find that condensation on the cold metal of the N connector inside the Heliax was shorting out the signal path. The humid climate here is destructive.
Circumstances, time, and other interests ruled the day. The dish was sold for $500 to a chap in Whakatane. He came up with friends and cut it in half with a disc grinder to put on a trailer.!! Pity really, satellites were just beginning to proliferate. I still had my UK101 computer, built from a kit, to enable aiming calculations for the earlier yagi array. It would have been useful.
Construction. (Click pics to enlarge)
Two sizes of T section aluminium were used for the radials. L section for the rim, rod/thick wire for mesh support encircled the structure at a number of radii. The central hub was ali' plate with 16 "petals" cut into it.
Picture above shows the antenna as it looked mounted on a wheel bearing. It was spun around to ensure symmetry and so the X and Y co-ordinates could be exact before riveting at the hub. Without such accuracy the dish would be of far less value.
Below shows method of radials assembly on a strong wooden jig.
Mesh was half inch chicken wire. One tenth of a wavelength 'rule' was ok and losses at 432 Mhz would be minor.
Two sizes of T section aluminium were used for the radials. L section for the rim, rod/thick wire for mesh support encircled the structure at a number of radii. The central hub was ali' plate with 16 "petals" cut into it.
Picture above shows the antenna as it looked mounted on a wheel bearing. It was spun around to ensure symmetry and so the X and Y co-ordinates could be exact before riveting at the hub. Without such accuracy the dish would be of far less value.
Below shows method of radials assembly on a strong wooden jig.
Mesh was half inch chicken wire. One tenth of a wavelength 'rule' was ok and losses at 432 Mhz would be minor.
This antenna featured in the ARRL 15th edition Antenna Handbook ( and others)
Foundation pipe, cast iron sewer pipe and mounting flange. About a cubic meter of concrete was used here, with angle iron stakes.
Pointing upwards, no feed horn yet.
Fitting the wire mesh after several coats of yellow chromate to the frame.
I can't remember the numbers but I weighed the dish using a long lever/plank and fulcrum and worked out the required length for the hoe wheels support arms to balance the dish. I felt very good when it turned out to be almost perfect.
To minimize windage the dish was parked pointing upwards and tied down.
To aim the dish at the sun for noise tests I arranged a long ali tube with a light dependent resistor at the bottom end. A meter reading peaked when aiming was best. This optical alignment was a help in avoiding eye damage.
A SETI organisation were sent details of this dish on request. Whether they ever built one like it, I have no idea. Letters are below and I was not a little surprised but somewhat flattered, at being considered helpful with dish building. I am certainly no expert, but I did build one like many others.
To minimize windage the dish was parked pointing upwards and tied down.
To aim the dish at the sun for noise tests I arranged a long ali tube with a light dependent resistor at the bottom end. A meter reading peaked when aiming was best. This optical alignment was a help in avoiding eye damage.
A SETI organisation were sent details of this dish on request. Whether they ever built one like it, I have no idea. Letters are below and I was not a little surprised but somewhat flattered, at being considered helpful with dish building. I am certainly no expert, but I did build one like many others.
Above, crane assistance required to place on pole.
Below, picture from house roof during assembly.
Below, picture from house roof during assembly.
Request and reply
after delivery.
Somewhere here is a copy of all the
info sent, perhaps it will turn up one day.
after delivery.
Somewhere here is a copy of all the
info sent, perhaps it will turn up one day.
