L2 - NAR & TRATRF Supporter
- Nov 6, 2019
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I'd love to start a dedicated thread on rocket antennas, but not tonight. I've done a lot of testing with different antenna configurations in the rocket and on the ground. Most of my testing has been with higher powered radios, but the principles apply to most commercial products as well. Out at FAR on most weekends about half the student groups lose signal after the rocket takes off and many of them do not recover. It breaks my heart. It is a different class of challenge with large or high altitude rockets, but most of the time it comes down to the antennas. In the rocket I've tried five or six configurations. I've tried 1/4 wave (too bulky), inverted V (works well, but sticks out), whip (ok, but poor ground plane), helical (exotic, hard to get right), patch (too directional), PCB antennas (hard to get right), and my favorite the straight dipole. In my testing the dipole has been the most reliable. I've made them from stiff 14awg wire, but lately I've been printing them on PCBs for about $1 each and trimming them to frequency with a VNA. The only downside is they are long -- at 430mhz they are 12", but at 900 MHz they are only six inches. The dipole has a great radiation pattern for most orientations and is always balanced, although not necessarily the case with commercial products that already incorporate a ground plane.
On the ground, using a high quality yagi or an elevated antenna on a mast makes a huge difference. As others stated above, that is your likely your best investment to improve commercial trackers.
My other suggestion is to aggressively test your radios at home. I've got a lot of hills around me, so I have marked out line of sight locations that are 1km, 2km, 4km, and 10km away. For smaller rockets you could divide by 10. I put the transmitter inside the airframe or avBay and then drive to the different markers (usually 400-500 feet lower in elevation) to test reception. Real field tests will tell you the most about the performance of a receiver or a transmitter. If you can receive 1km away at 500 feet of elevation at home then there is a good chance you will have a solid "last report" up to 2km away.
Getting back to the OP... I recently tested an EggFinder Mini out of the box and found I couldn't even get 1km away with my reception test. I connected the LCD receiver to a ten foot mast and a 10dbi 900mhz antenna and got consistent reception at 1km. Link to antenna here: https://a.co/d/cJjMdAx -- also in my testing it was clear that bending the stock LCD antenna on the 90 degree hinge degrades reception. It doesn't always show up on the VNA, but antennas don't like to have their coax bent at 90 degrees, especially transmitters.
Example dipole printed antennas ("long" 433mhz)
View attachment 544545 View attachment 544544
In my part of Ohio I can go a 1/2 mile one way from my home and get rolling rises with corn & soybean fields. I go 1/2 a mile the
other way and I get hills and hollers. I do the same distance testing like you whenever I build a new rocket that uses a tracker.
Some of our launch sites in southern Ohio have very different topography from site to site.