I have been building 3 homebrew 8 director single dipole yagis to replace the Chinese ones supposedly for the 800-900 GSM. Gain on the previous ones was less than expected.
The Chinese GSM yagis only obtained about 1/3 of the signal strength of a simple omni in the main lobe and didn't even come close on maximum range.
While appearing to be well made of the proper durable materials the Chinese antennas had no taper to the director lengths and the spacing was entirely wrong for 1090 mhz.
Unless you are a AARL handbook geek, download a program that will help you design your "Perfect" yagi. I thank John Drew for making this calculator available. http://www.vk5dj.com/yagi.html
Scrounging for materials:
First off, you have to see what is available in your area for boom material and material to make the elements out of.
It will be handy to have a tubing cutter for thick wall aluminum tubing if found or if solid stainless rod is found a cutoff wheel with a thin thickness to attach to your bench grinder. You also need a micrometer to measure the tube lengths in fractions of a millimeter. Your tape measure has a centimeter scale but that is just a guesstimate when it comes to decimal millimeters.
I found my 1" boom material in an aluminum window shop. I found stainless steel rod in a hardware. I found antenna standoffs in an electronic store along with RG59 cable and connectors. You will have to decide whether to use pop rivets or bolts to hold things together.
Since 5/16" stainless steel rod was all that was available locally that was close to 8 MM which the design program used.
uses millimeter dimensions.
Single or double dipole
John Drew's program gives the dimensions for both but if you decide on the double dipole that will entail bending tubing precisely with a tubing bender. I chose the single dipole for simplicity sake and I didn't want to buy a tool for a one time project.
Oxidation
Water and weather cause aluminum to oxidize and if you are relying on rivets or bolts for grounding you need to seal them at the contact points. I will use marine epoxy and hopefully what is, will be what is for years to come.
Does a Verticle Polarized Yagi have an UP & Down?
From information I have gathered the answer is yes. The UP element is the one connected to the feedline center conductor. Accordingly, if the mounting is UP the wave pattern will be from the boom UP. Conversely, if the yagi is mounted with the feedline center conductor connected to the bottom half of the dipole the wave pattern will be from the boom DOWN. As you can see from my disclaimer I don't know this is FACT.
The yagis are built and I'll do rudimentary testing today from the ground. Stay tuned!
John
T-RPVD1
The Chinese GSM yagis only obtained about 1/3 of the signal strength of a simple omni in the main lobe and didn't even come close on maximum range.
While appearing to be well made of the proper durable materials the Chinese antennas had no taper to the director lengths and the spacing was entirely wrong for 1090 mhz.
Unless you are a AARL handbook geek, download a program that will help you design your "Perfect" yagi. I thank John Drew for making this calculator available. http://www.vk5dj.com/yagi.html
Scrounging for materials:
First off, you have to see what is available in your area for boom material and material to make the elements out of.
It will be handy to have a tubing cutter for thick wall aluminum tubing if found or if solid stainless rod is found a cutoff wheel with a thin thickness to attach to your bench grinder. You also need a micrometer to measure the tube lengths in fractions of a millimeter. Your tape measure has a centimeter scale but that is just a guesstimate when it comes to decimal millimeters.
I found my 1" boom material in an aluminum window shop. I found stainless steel rod in a hardware. I found antenna standoffs in an electronic store along with RG59 cable and connectors. You will have to decide whether to use pop rivets or bolts to hold things together.
Since 5/16" stainless steel rod was all that was available locally that was close to 8 MM which the design program used.
uses millimeter dimensions.
Single or double dipole
John Drew's program gives the dimensions for both but if you decide on the double dipole that will entail bending tubing precisely with a tubing bender. I chose the single dipole for simplicity sake and I didn't want to buy a tool for a one time project.
Oxidation
Water and weather cause aluminum to oxidize and if you are relying on rivets or bolts for grounding you need to seal them at the contact points. I will use marine epoxy and hopefully what is, will be what is for years to come.
Does a Verticle Polarized Yagi have an UP & Down?
From information I have gathered the answer is yes. The UP element is the one connected to the feedline center conductor. Accordingly, if the mounting is UP the wave pattern will be from the boom UP. Conversely, if the yagi is mounted with the feedline center conductor connected to the bottom half of the dipole the wave pattern will be from the boom DOWN. As you can see from my disclaimer I don't know this is FACT.
The yagis are built and I'll do rudimentary testing today from the ground. Stay tuned!
John
T-RPVD1
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