A recent thread here got me thinking about the performance of my previously installed Sportcraft Antenna. In my installation, I didn't follow the directions exactly; I sort of threw the antenna into the left wing tip of my RV-7 and layed a couple of strips of fiberglass on it to hold it in place.
During a typical flight (6500-8500ft), I could receive VOR's that were within 30NM.
I decided to rip out/re-do the installation. Carl F. clued me into a design (very similar to Sportcraft SA-001) in the AeroElectric Book -- attached for reference.
I made a couple of modifications to it:
1. Extended the "arm" from 11.7" to almost 16",
2. Cut down the "leg" from 16.5 to 14",
3. Used .063" LEXAN sheet for the insulator under the gamma match and lengthen the gamma match element to 3.75"
4. The "base" leg is attached to the wing tip rib with 2 #8-32 screws, and the aft tip of the "leg" has a little gaffers (gorilla) tape on it to prevent chafing inside the wingtip.
Testing the whole affair with an MFJ-259D yielded an SWR of 1.2:1 at 112.75MHz, a Gamma Match efficiency of 99%, and impedance of 45 Ohms.
I test flew with the new setup and was able to receive VOR stations up to 100NM at 6500FT. I also flew an ILS approach fully coupled with the aircraft displaced to the right of the centerline by about 12 feet (The antenna in left wing tip, so this makes sense.)
I'm pretty happy with this, and as Carl F. mentioned in other thread, the whole setup was about $2.00 in scrap aluminum, screws, nuts...
Cheers!
During a typical flight (6500-8500ft), I could receive VOR's that were within 30NM.
I decided to rip out/re-do the installation. Carl F. clued me into a design (very similar to Sportcraft SA-001) in the AeroElectric Book -- attached for reference.
I made a couple of modifications to it:
1. Extended the "arm" from 11.7" to almost 16",
2. Cut down the "leg" from 16.5 to 14",
3. Used .063" LEXAN sheet for the insulator under the gamma match and lengthen the gamma match element to 3.75"
4. The "base" leg is attached to the wing tip rib with 2 #8-32 screws, and the aft tip of the "leg" has a little gaffers (gorilla) tape on it to prevent chafing inside the wingtip.
Testing the whole affair with an MFJ-259D yielded an SWR of 1.2:1 at 112.75MHz, a Gamma Match efficiency of 99%, and impedance of 45 Ohms.
I test flew with the new setup and was able to receive VOR stations up to 100NM at 6500FT. I also flew an ILS approach fully coupled with the aircraft displaced to the right of the centerline by about 12 feet (The antenna in left wing tip, so this makes sense.)
I'm pretty happy with this, and as Carl F. mentioned in other thread, the whole setup was about $2.00 in scrap aluminum, screws, nuts...
Cheers!
