Saturday, 25 May 2019

Custom drive on mast base finally finished!

For many years I have been using a drive on base to foot the antenna mast when out portable. It was made by GW5NF using two pieces of wood and a gate hinge, allowing a KR400 rotator to be mounted. It has survived many outings but recently the hinge had been showing signs of stress. Time for a new one, a possibility thought about a few years ago but never executed.

I had previously bought a drive on mast from Moonraker, made from welded steel angle with a piece of 2" tube mounted vertically at one end. This had no tilt mechanism and with an 18" long base it was also a bit short for the width of landrover tyres, 20" was optimum.

The other design consideration was that the new base should allow the mast to be raised parallel or perpendicular to the car, allowing antenna erection on narrow tracks.

The new hinge assembly consisted of two 178 x 178 x 12mm aluminium plates and a 4" ball bearing grade 13 steel hinge. The plates were drilled and tapped to assure vertical alignment by using G4BVY's pillar drill. Care was taken when positioning the holes for the rotator that the terminal block was in a suitable position, especially the edge nearest the tyre.

Next a welded base was needed to mount the hinge on. Having no welding facilities I searched for a local welder/fabricator. Driving back from Worcester one day I saw a sign for Melvs welding at Powick. I took along my moonraker base, the hinge and a dimension sketch, he was very helpful  and between us we came up with an executeable design. By using M8 tapped holes in the base on a square pattern, the hinge could be rotated easily to drop the antenna in any direction. Two units were ordered.

One week later the units were collected and he had done a great job, including spraying them with cold galv paint to preserve them. £96 for the pair was a good price.  The hinge and rotator were added quickly and all worked fine. The only slight issue was that due to the sloping gap between the top and bottom plate the mast, when near vertical stressed the hinge. This was cured by adding nuts to the two rear bolts securing the plate to the frame which meant the top plate and bottom plate were parallel at the resting position.

Note the two levelling nuts at the right of the plate.

Monday, 13 May 2019

24GHz DATV World Record

The day after the Wirral mini tv convention, 12 May 2019, it was planned to try to extend the 24GHz DATV distance record with a path from Brown Clee IO82QL and Winter hill IO83SO. M0MHO, G7ACD, G4FRE, G8AQA, Dave G8VZT. and G8GTZ were at Brown clee and the Wirral club G3NWR with G4CBW were at Horrockswood IO83SO.

I had recently upgraded my DB6NT 24048/432 Transverter to use a DB6NT local oscillator. Checking out the system it was seen to produce 2W of DATV when measured on an HP432C power meter. Searching in the loft I found my Practical wireless 18" dish with its penny feed which was pressed into service

After setting up, G4CBW signal was easily seen on 24GHz with a MER of 17dB and both myself and G8GTZ exchanged 2 way signals for a new world record.

The Wirral could be seen to the left of the Wrekin which houses the GB3ZME 24GHz beacon

The PW 18" dish on its tripod

The signal received from G4CBW

The signal G4CBW received from G4FRE/P