70cmQuadiDesign
Note: This page is a reconstruction to a now defuct Univeristy of Idaho nearspace balloon wiki article I posted in 2008
70cm Quagi
Project Status
V1 Flight Tested on F08L01, two built : status unknown
V2 One built, no longer in service
V3 Preconstruction
Problem Statement
Ginger is a bidirectional data routing system equipt with 70cm j-pole antennas. These antennas have a gain of around 2.5dBi and using quarter wave whips the link range is around 37 miles at full power (250kbps) at 10 Watts of output power. To extend the range of operations which might be due to a run away balloon, damaged transmitters, or geographical obstructions, we have built two directional quagi antennas.
The quagi antenna consists of a quad driver (a driven element and a reflector) which already has a higher gain than a dipole fed yagi and reflector. This means that by feeding the same number of directors, a quagi will outperform a yagi at the cost of not being a completely flat design (which is merely a transport concern anyway). The 8 element quagis we have built should have a gain between 12 and 13 dBi and should increase the working distance to 80 miles at 250kbps.
Also, this makes a really good satellite antenna. While I no longer am involved with UIVAST, I still want to be able to use these for sat usage. These are linearly polarized antennas, but they have a lot of gain and are easy to do.
Photos
V1
V2
V3
Dimensions
V1
The dimensions, in a 1977 article by K6YNB in QST April 1977
| Element Lengths | 144.5 MHz | 147 MHz | 222 MHz | 432 MHz | 446 MHz |
|---|---|---|---|---|---|
| Reflector (all No 12 TW wire, closed) | 2200 mm loop | 2159 mm | 1432 mm | 711 mm | 689 mm |
| Driven Element (No 12 TW, fed at bottom) | 2083 mm loop | 2032 mm | 1359 mm | 676 mm | 657 mm |
| Directors | 913 mm to 889 mm in 5 mm steps | 897 mm to 873 mm in 5 mm steps | 594 mm to 568 mm in 3 mm steps | 298 mm to 291 mm in 1.5 mm steps | 289 mm to 280 mm in 1.5 mm steps |
| Spacing | |||||
| R - DE | 533 mm | 521 mm | 346 mm | 178 mm | 173 mm |
| DE - D1 | 400 mm | 391 mm | 260 mm | 133 mm | 130 mm |
| D1 - D2 | 838 mm | 826 mm | 546 mm | 279 mm | 272 mm |
| D2 - D3 | 445 mm | 435 mm | 289 mm | 149 mm | 144 mm |
| D3 - D4 | 663 mm | 651 mm | 432 mm | 222 mm | 215 mm |
| D4 - D5 | 663 mm | 651 mm | 432 mm | 222 mm | 215 mm |
| D5 - D6 | 663 mm | 651 mm | 432 mm | 222 mm | 215 mm |
V2
The deisgn has been optimized for 437MHz using NEC2. The dimensions are as follows:
RWIRE = .00258826 wire for quads diameter RROD = .003175 yagi director rod diameter RE = 0.755962 Total Length of Reflector Element DE = 0.718693 Total Length of Driven Element D1 = 0.280124 Total length of Director element D2 = 0.28434 Total length of Director element D3 = 0.283594 Total length of Director element D4 = 0.276571 Total length of Director element D5 = 0.244994 Total length of Director element D6 = 0.283213 Total length of Director element RE2DE = 0.177867 Distance from RE to DE DE2D1 = 0.138696 Distance from DE to Director DE2D2 = 0.383653 Distance from DE to Director DE2D3 = 0.547346 Distance from DE to Director DE2D4 = 0.851997 Distance from DE to Director DE2D5 = 0.984569 Distance from DE to Director DE2D6 = 1.092358 Distance from DE to Director
V3
I wanted to model it with tubing of a different diameter, and maybe even model a tuning stub. I changed all diameters to 1/8" and added a tuning stub.
CM QUagi 437Mhz Sattelites fiddled with and optimized by KE7PHI from ARRL handbook model CM RP 0 181 1 1000 -90 0 1 1 CM RP 0 1 361 1000 90 0 1 1 CE SY RWIRE = 0.0015875 'wire for quads diameter SY RROD = 0.0015875 'yagi director rod diameter SY RE=0.74 'Total Length of Reflector Element SY DE=0.702517 'Total Length of Driven Element SY D1=0.290414 'Total length of Director element SY D2=0.29013 'Total length of Director element SY D3=0.285381 'Total length of Director element SY D4=0.276766 'Total length of Director element SY D5=0.245045 'Total length of Director element SY D6=0.287901 'Total length of Director element SY RE2DE=0.177909 'Distance from RE to DE SY DE2D1=0.138761 'Distance from DE to Director SY DE2D2=0.380606 'Distance from DE to Director SY DE2D3=0.554942 'Distance from DE to Director SY DE2D4=0.851939 'Distance from DE to Director SY DE2D5=0.982862 'Distance from DE to Director SY DE2D6=1.096131 'Distance from DE to Director SY STUBLEN=.0635 SY STUBPOS=0.030165 SY GAP=.01 GW 1 6 -RE2DE -RE/8 -RE/8 -RE2DE RE/8 -RE/8 RWIRE GW 2 6 -RE2DE -RE/8 -RE/8 -RE2DE -RE/8 RE/8 RWIRE GW 3 6 -RE2DE RE/8 RE/8 -RE2DE RE/8 -RE/8 RWIRE GW 4 6 -RE2DE RE/8 RE/8 -RE2DE -RE/8 RE/8 RWIRE GW 20 7 0 -DE/8 -DE/8 0 -GAP -DE/8 RWIRE GW 21 7 0 GAP -DE/8 0 DE/8 -DE/8 RWIRE GW 6 6 0 -DE/8 -DE/8 0 -DE/8 DE/8 RWIRE GW 7 6 0 DE/8 DE/8 0 DE/8 -DE/8 RWIRE GW 8 6 0 DE/8 DE/8 0 -DE/8 DE/8 RWIRE GW 9 6 DE2D1 -D1/2 0 DE2D1 D1/2 0 RROD GW 10 6 DE2D2 -D2/2 0 DE2D2 D2/2 0 RROD GW 11 6 DE2D3 -D3/2 0 DE2D3 D3/2 0 RROD GW 12 6 DE2D4 -D4/2 0 DE2D4 D4/2 0 RROD GW 13 6 DE2D5 -D5/2 0 DE2D5 D5/2 0 RROD GW 14 6 DE2D6 -D6/2 0 DE2D6 D6/2 0 RROD GW 22 3 0 GAP -DE/8 0 GAP -DE/8-STUBPOS RROD GW 23 3 0 -GAP -DE/8 0 -GAP -DE/8-STUBPOS RROD GW 22 3 0 GAP -DE/8-STUBPOS 0 GAP -DE/8-STUBLEN RROD GW 23 3 0 -GAP -DE/8-STUBPOS 0 -GAP -DE/8-STUBLEN RROD GW 24 1 0 -GAP -DE/8-STUBPOS 0 GAP -DE/8-STUBPOS RROD GE 0 LD 5 0 0 0 37700000 'Copper wire GN -1 EK EX 0 24 1 0 100.00 0 0 0 FR 0 0 0 0 437 0 EN
Performance
V1
- At 437MHz the SWR is measured at 1.0 for Quagi Orange and 1.2 for Quagi Green (due to coax losses from crappier cable)
- Raw data showing rough measurements of directionality Excel XLS file
V2
- At 437MHz the gain should be 13.43 DBi best theoretical. SWR S/B 1.07
Insights
- Wind is a real problem and keeping both aimed at the same location is not a trivial task. Mount both on a single crossbar and have a lockable central pivot.
- It would be pretty neat to read the GPS data from the CNDH board (already scheduled) and have a QT module to decode them and steer the antennas in the right direction.
- I don't trust ARRL - always simulate those "best anntenna ever" designs first before building!
