Just I elaborated a 868,5 MHz antenna with high gain, may tell how to do it and give a sizes. Just use it for free.
1) obtain the electricians cable-channel plastic pipe 25 mm Dout, white. Colored may have a diminished resistance due the carbon consistuent. Cut it in the 710 mm pieces.
2) put the 12 mm thick plate on the table and draw along it to this pipe the line. As accurately as can, it will serve the center-line. Measure identical line in the other side of pipe, small mistake +/- 0.5 mm there is okay, but anyway the position must be marked very exact. All other methods to mark the centerline are wrong. Any trial to drill the holes with very exact drill-machine in one single pass gives a deadly mistakes.
3) mark the 13 mm from the rear the D7 place, then D6, D5.... and end with Ra and Re. Positions must be: Re=30, Ra=99, D1=125, D2=187, D3=261; D4=348, D5=444, D6=548, D7=656.5 mm.Use the one piece metallic lineal, all other methods will not gain the aim plus minus the half mm. Then drill it separately from both sides with tiny drill, for example 1 mm. Later re-drill it to 1.5 or 2 mm and only then apply the needed diameter of 3.5 for all except Ra 2.5 mm. All trials to drill it in one pass will lead to giant mistakes by slip-away due the drill-center never is exact in center.
4) Then use the old stock of aluminium (or copper) monolite wire with heavy, thick pvc isolation. My wire is 3.5 and with isolation 6 mm. Cut it by lengths as sharp as can or alter the cut place by sliffing. Lengths are Re=159, Ra see below, D1=139, D2=137.5; 135.5; 133.5; 132.5; 131; 130 mm tip to tip. Cut the insulation in pieces of lengths 67, 57, 56, 55, 54, 54, 53, 53 mm. Push the rods in their holes and fix with original insulation pieces giving the grip keeping it at the position and giving the good atmosphere resistance. By the way, the heaviest was to measure how strong is the shortening factor of insulation. Those thick white for alu had Vf=0.940, but copper thinner had 0.9565. So, as soon as one use another wire type, the vibrators lengths must be corrected, and that is true nightmare.
5) The Ra is separate thing, cut the 2.5 mm diameter electric copper single wire into two pieces of 73 mm. Pull the 63mm of it original insulation over it, end 10 mm is nude. Buy the electrician terminal blocks (picture is only for understanding what like it looks https://vuec.co.uk/amazon-ebay/upload/images/sem-tme-441801.jpg-33599.jpg), You need a size H3 (measure 15 mm in width and wire-hole size 2.8 mm. Cut the two in one block. Screw both missing keepers out and re-arrange it both in one of tunnels, other tunnel let stay empty. Between both put the 5 mm washer of good dielectric, preferably teflon, 2.5 to max max 3 mm thick. Both keeper ends will look outside for some 3 mm nude now, use it for soldering the coaxial, but inner screw places use for gripping the dipole vibrators (Ra) and keeping a keepers in the place.
6) take the 50 Ohm RG58 and solder central wire to one side keeper nude end and shirt to the other keeper end. Cut the 11 mm diam (Do) glass pipe 6 cm long and spiralize the coaxial on it some 5 turns. Fix with the tape a cable ends be kept stable. All other methods of baluns are too impractical for insulator traverse case - I checked the many constructions but or they are damn non-technologic, or demands a grounding what is non-existant here, etc etc. Mark the place where will happen the central screws position and drill there 5 mm holes in the traverse downside. Push the block into traverse pipe, push into keepers the dipoles and fix it by screws via those both holes. Fill into screwdriver holes a bit of silicone mastic to hermetize. From both ends hermetize the traverse with 10 mm thick cut-off from the champain or wine cork. Cable is lead out via this cork (drill the 5,5 mm for 6,5 mm cable). End the cable with BNC.
7) Check-up - Apply the cross-plug from RF vector analyser N1201SA, passing BNC to much smaller in size original analyser plug. I tried to solder similar by myself, but.... it gave a plenty of resonant peaks, so I ordered, waited, and factory job was brilliant. So resistance may happen as well the 50 as well the 65 Ohms, but slightly (for 5 degrees bending back the Ra toward Re the resistance may be set for perfect 50 Ohms and SWR between 1.1 to 1,2 between 855 and 885 MHz, yet in very side SWR jumps to 1.5 and then to Cosmos. In very middle the range is slight "camel spine" peak SWR=1.2, but at about 860 and 870 are 1.1. Gain 13.2 dBi=11.0 dBd. Width of mainlobe about 40-45 degrees at 0.707 level.
8) Mounting: The traverse is 73 mm longer as needed, use this length for mounting - drill the 4 mm holes horizontally at position 12 mm from tube end and next 30 mm from it. Put there a bow-shaped M4 thread-rod gripping the 70 mm long cut-off material of rest the traverse pipe. Fix the piece vertically. Make the identical holes in this menber too, and bow, and push in the grip another piece about 150 mm long. Upper bow permits to adjust antenna by vertical axis and rotate a plane. Next grip is for vertical alt-az adjusting. Between each two pipes apply the crossed channel plate of mld plastic, it will stabilize the grip. Plates may be encarved by ordinary stationary drill machine using it like grinding freeze. One line longitudinally, other 90 degree to it. And then cut into pieces.
For a while I am rather happy with a job, however I made only twenty such antennas until now. After year I shall know exact how good or bad them are in high winds and winter ices.
1) obtain the electricians cable-channel plastic pipe 25 mm Dout, white. Colored may have a diminished resistance due the carbon consistuent. Cut it in the 710 mm pieces.
2) put the 12 mm thick plate on the table and draw along it to this pipe the line. As accurately as can, it will serve the center-line. Measure identical line in the other side of pipe, small mistake +/- 0.5 mm there is okay, but anyway the position must be marked very exact. All other methods to mark the centerline are wrong. Any trial to drill the holes with very exact drill-machine in one single pass gives a deadly mistakes.
3) mark the 13 mm from the rear the D7 place, then D6, D5.... and end with Ra and Re. Positions must be: Re=30, Ra=99, D1=125, D2=187, D3=261; D4=348, D5=444, D6=548, D7=656.5 mm.Use the one piece metallic lineal, all other methods will not gain the aim plus minus the half mm. Then drill it separately from both sides with tiny drill, for example 1 mm. Later re-drill it to 1.5 or 2 mm and only then apply the needed diameter of 3.5 for all except Ra 2.5 mm. All trials to drill it in one pass will lead to giant mistakes by slip-away due the drill-center never is exact in center.
4) Then use the old stock of aluminium (or copper) monolite wire with heavy, thick pvc isolation. My wire is 3.5 and with isolation 6 mm. Cut it by lengths as sharp as can or alter the cut place by sliffing. Lengths are Re=159, Ra see below, D1=139, D2=137.5; 135.5; 133.5; 132.5; 131; 130 mm tip to tip. Cut the insulation in pieces of lengths 67, 57, 56, 55, 54, 54, 53, 53 mm. Push the rods in their holes and fix with original insulation pieces giving the grip keeping it at the position and giving the good atmosphere resistance. By the way, the heaviest was to measure how strong is the shortening factor of insulation. Those thick white for alu had Vf=0.940, but copper thinner had 0.9565. So, as soon as one use another wire type, the vibrators lengths must be corrected, and that is true nightmare.
5) The Ra is separate thing, cut the 2.5 mm diameter electric copper single wire into two pieces of 73 mm. Pull the 63mm of it original insulation over it, end 10 mm is nude. Buy the electrician terminal blocks (picture is only for understanding what like it looks https://vuec.co.uk/amazon-ebay/upload/images/sem-tme-441801.jpg-33599.jpg), You need a size H3 (measure 15 mm in width and wire-hole size 2.8 mm. Cut the two in one block. Screw both missing keepers out and re-arrange it both in one of tunnels, other tunnel let stay empty. Between both put the 5 mm washer of good dielectric, preferably teflon, 2.5 to max max 3 mm thick. Both keeper ends will look outside for some 3 mm nude now, use it for soldering the coaxial, but inner screw places use for gripping the dipole vibrators (Ra) and keeping a keepers in the place.
6) take the 50 Ohm RG58 and solder central wire to one side keeper nude end and shirt to the other keeper end. Cut the 11 mm diam (Do) glass pipe 6 cm long and spiralize the coaxial on it some 5 turns. Fix with the tape a cable ends be kept stable. All other methods of baluns are too impractical for insulator traverse case - I checked the many constructions but or they are damn non-technologic, or demands a grounding what is non-existant here, etc etc. Mark the place where will happen the central screws position and drill there 5 mm holes in the traverse downside. Push the block into traverse pipe, push into keepers the dipoles and fix it by screws via those both holes. Fill into screwdriver holes a bit of silicone mastic to hermetize. From both ends hermetize the traverse with 10 mm thick cut-off from the champain or wine cork. Cable is lead out via this cork (drill the 5,5 mm for 6,5 mm cable). End the cable with BNC.
7) Check-up - Apply the cross-plug from RF vector analyser N1201SA, passing BNC to much smaller in size original analyser plug. I tried to solder similar by myself, but.... it gave a plenty of resonant peaks, so I ordered, waited, and factory job was brilliant. So resistance may happen as well the 50 as well the 65 Ohms, but slightly (for 5 degrees bending back the Ra toward Re the resistance may be set for perfect 50 Ohms and SWR between 1.1 to 1,2 between 855 and 885 MHz, yet in very side SWR jumps to 1.5 and then to Cosmos. In very middle the range is slight "camel spine" peak SWR=1.2, but at about 860 and 870 are 1.1. Gain 13.2 dBi=11.0 dBd. Width of mainlobe about 40-45 degrees at 0.707 level.
8) Mounting: The traverse is 73 mm longer as needed, use this length for mounting - drill the 4 mm holes horizontally at position 12 mm from tube end and next 30 mm from it. Put there a bow-shaped M4 thread-rod gripping the 70 mm long cut-off material of rest the traverse pipe. Fix the piece vertically. Make the identical holes in this menber too, and bow, and push in the grip another piece about 150 mm long. Upper bow permits to adjust antenna by vertical axis and rotate a plane. Next grip is for vertical alt-az adjusting. Between each two pipes apply the crossed channel plate of mld plastic, it will stabilize the grip. Plates may be encarved by ordinary stationary drill machine using it like grinding freeze. One line longitudinally, other 90 degree to it. And then cut into pieces.
For a while I am rather happy with a job, however I made only twenty such antennas until now. After year I shall know exact how good or bad them are in high winds and winter ices.
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