From: Bdale Garbee Date: Mon, 10 Feb 2020 16:45:21 +0000 (-0700) Subject: add docs on making a TeleLCO antenna X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=de210077dd75d2bb697518d7f86185bc24f78b82;p=web%2Faltusmetrum add docs on making a TeleLCO antenna --- diff --git a/Documents/SlimJimAntenna/index.mdwn b/Documents/SlimJimAntenna/index.mdwn new file mode 100644 index 0000000..e259b2a --- /dev/null +++ b/Documents/SlimJimAntenna/index.mdwn @@ -0,0 +1,95 @@ +[[!meta title="Antenna"]] + +# The TeleLCO "Slim Jim" Antenna + +Several people have asked what's inside the PVC radome of the "Slim Jim" style +antennas we deliver with the TeleLCO component of our [TeleLaunch](/TeleLaunch) +wireless launch control system. The kind of antenna we provide is called a +"Slim Jim" in the amateur radio world, it's a variation on a class of antennas +often referred to as "J-Pole" antennas. + +Because there are a number of issues involved in antenna design that come into +play with this antenna, including a significant de-tuning effect from putting +antenna elements inside a radome made from a material with the dielectric +coefficient seen in small-diameter PVC pile, we decided to explain exactly +what we build in case our customers have reason to want to just make another +antenna for use with a TeleFireEight or to replace the one shipped with their +TeleLCO. + +If the materials and dimensions we use are copied exactly, the antenna should +"just work". Note, however, that the real world being what it is, each +antenna built is likely to have slightly different performance characteristics, +and so if you or a friend have access to suitable test equipment, feel free +to go completely nuts optimizing an antenna using your specific materials and +techniques based on this design! + +Even if you don't have access to a fully-equipped RF test bench, each of our +TeleLaunch products has built-in [RF debug]( https://altusmetrum.org/AltOS/doc/telelaunch.html#_radio_signal_strength) +tools that you can use to verify the performance of your system, compare the +performance of different antennas, etc. + +Like many documents we provide, +Creative Commons License
this work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. + +## Basic Design + +Bdale started with [this calculator](https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/), +adjusting dimensions to achieve a reasonable match and good operating +efficiency at 434.5 Mhz in a PVC radome. The result is a relatively +inexpensive, reliable antenna that is robust enough to survive typical +launch site handling. + +## Required Materials + +For the PVC pipe, we use 1/2" thin-wall pipe rated for "315psi" found on +the shelf at our local Lowes home improvement store, not the thicker-wall +schedule 40 pipe. This is because the ferrite chokes fit better in this +pipe (you don't have to remove the plastic holder around the ferrites). If +you change this material, all dimensions may need to be adjusted due to a +difference in dielectric coefficient. + +- 15" length 1/2" PVC +- 1" length 1/2" PVC +- 1/2 PVC tee +- 2 pieces 1/2 PVC cap +- 10'+ RG-58 coax with BNC, cut [25' BNC cable assembly](https://www.amazon.com/gp/product/B009GUN32W) in half +- 16-1/2" 300 ohm TV twin lead +- [ferrite choke assembly](https://www.amazon.com/gp/product/B015RDVGDE) +- electrical tape +- nylon zip tie +- PVC cement + +## Prepare PVC Sub-Assemblies + +- drill 7/32" hole in the middle of one end cap +- glue this cap to one end of 1" PVC pipe +- glue the other cap to one end of 15" PVC pipe +- glue one side of tee to the other end of 15" pipe + +## Prepare Twin-Lead Sub-Assembly + +- cut 420mm of twin lead +- cut approximately 6mm insulation away from one end +- bend conductors and solder together +- repeat at the other end, such that end to end, the loop is 407mm +- mark 14.5mm from one end for coax attachment point, cut away enough + insulation to be able to solder to conductors +- mark 133mm from the same end, and 263 mm from the other end, + leaving two marks approximately 11mm apart +- cut one wire only at these two marks, trim insulation to get + the 11'ish mm piece of wire to go away + +## Final Assembly + +- slide drilled end cap + 1" PVC sub-assembly over wire +- strip and trim coax end for attachment to twin lead +- solder center conductor to long wire on twin lead, shield + to the short wire, at the marked feed point 14.5mm up from the bottom +- put ferrite around coax close to feed point +- put a zip tie around coax to act as a strain relief against + drilled PVC cap +- insert twin lead assembly into radome via side port of tee +- dry fit PVC assemblies +- quick performance check, tweak if absolutely necessary +- glue PVC assemblies together + diff --git a/Documents/index.mdwn b/Documents/index.mdwn index 0c32c5e..889cf89 100644 --- a/Documents/index.mdwn +++ b/Documents/index.mdwn @@ -14,6 +14,7 @@ think before you act! * [Remove the protection circuit board from a LiPo battery](./FixBattery) * [Use a separate pyro battery](./SeparatePyroBattery) * [Use a Featherweight magnetic switch](./MattsActiveSwitch.pdf) + * [Build a TeleLCO-sytel "Slim Jim" antenna](./SlimJimAntenna) ## Product Outlines and Drill Patterns ##