From 878c30bbbb31c011004bcdb263d822977913a0a0 Mon Sep 17 00:00:00 2001 From: Bdale Garbee Date: Mon, 21 May 2012 23:30:37 -0600 Subject: [PATCH] document the fintenna design --- rockets/airframes/YikStik3/index.mdwn | 38 +++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/rockets/airframes/YikStik3/index.mdwn b/rockets/airframes/YikStik3/index.mdwn index 4d696e4..63c124a 100644 --- a/rockets/airframes/YikStik3/index.mdwn +++ b/rockets/airframes/YikStik3/index.mdwn @@ -67,6 +67,44 @@ with other capabilities. Installing the electronics in the fin can bay is a *huge* challenge due to the restricted space between the MMT and airframe. +### Fintenna ### + +On 2YikStik, one of the big disappointments was a very poor signal from the +UHF transmitter on the TeleMetrum board mounted in the fin can. This isn't +surprising, since the antenna was just a wire whip running in parallel with +and very close to the motor casing. For this build, I decided to try +something completely different. + +The quick summary is that I'm loading the two fins that don't have thermistors +in them as an antenna. And it works brilliantly! + +Before bagging the fins with the CF and glass lamination, I put 1 inch wide +copper foil tape on two of the fin substrates, running from near the tip +down to the root. Then the fins were bagged with 2 layers of 5.7 oz 2x2 +twill carbon fiber and a 6 oz glass sanding veil layer on both sides, all in +one bagging operation to ensure all the layers formed a strong chemical epoxy +bond. + +After unbagging, while the epoxy was still somewhat leathery, I carefully +cut the CF back at the root edge of each fin exposing the copper foil. The +fins were then allowed to cure and get sanded normally. When installing them +in the airframe, I oriented them so that the thermistor fin is on the anti-rail +side of the airframe, and the two copper-foil-equipped fins bracket the rail +side, with the copper foil sides facing each other across the rail-side valley. + +After applying fin to fin glass across the motor mount, additional copper foil +tape was used to join the two fins, soldering the new foil to the foil embedded +in the fins. I then cut a "gap" in the center of the space between the two +fins, and installed a 1.5-20pF piston trimmer capacitor with the screw aimed +aft, and a piece of small diameter teflon coax with two ferrite beads on the +forward side of the gap. The coax was run through a hole near the root of +the fin separating this valley from the ebay and terminated with an SMC +connector to mate with the TeleMetrum board. + +I'm pleasantly surprised at how well this seems to work. With a Pro75 6xl +case installed, the variable cap allows the antenna to be tuned to about 1.3:1 +SWR, and the resulting transmitted signal seems strong... + ## Build Parts gathered during late 2011 and early 2012. Built underway in early -- 2.30.2