Eggfinder GPS Antenna Question

[Powderman]

I've got an Eggfinder Mini that's going in the nosecone of a 4" Punisher. Currently I have the 2dB "stubby" antenna that came with the unit.
Is there a larger antenna that I can use that will extend my range or maybe give me increased accuracy?

Thanks,
Powderman

 

[Crazyrocket]

I've had no issues with range or accuracy using the stubby antenna. Granted, my flights do not go that high (~5K), but never had any problems.

 

[cerving]

The MIni was designed for a permanent-mount screw-on antenna, it doesn't have the same RP-SMA pads that the other transmitters have for a different external antenna. Size was the deciding factor, any other antenna would have added at least 2" to the total length. Putting a larger antenna on it isn't going to increase the GPS accuracy... that's a function of the little brown square GPS antenna, not the transmitter antenna. I did a quick search on Mouser's site, and it looks like the one that ships with the Mini is the only screw-mount 900 MHz antenna they have. I've tracked rockets to over 14K with that antenna, and I know people who've gone twice that, so the Mini should be fine for just about any sport flight. I would recommend getting the external antenna for the LCD receiver, however... that makes a big difference, more than the antenna on the transmitter.

 

[Powderman]

The MIni was designed for a permanent-mount screw-on antenna, it doesn't have the same RP-SMA pads that the other transmitters have for a different external antenna. Size was the deciding factor, any other antenna would have added at least 2" to the total length. Putting a larger antenna on it isn't going to increase the GPS accuracy... that's a function of the little brown square GPS antenna, not the transmitter antenna. I did a quick search on Mouser's site, and it looks like the one that ships with the Mini is the only screw-mount 900 MHz antenna they have. I've tracked rockets to over 14K with that antenna, and I know people who've gone twice that, so the Mini should be fine for just about any sport flight. I would recommend getting the external antenna for the LCD receiver, however... that makes a big difference, more than the antenna on the transmitter.

Thank you for taking the time to answer...much appreciated.

Powderman

 

[SolarYellow]

Is there a lighter-weight antenna that will work, like a "just a wire" antenna that could be adapted?

I set up some sims with the EF Mini in a 24mm rocket tonight and the 18g Cris quoted me earlier today plus 6.5g 1S battery is screwing things up. Lose apogee altitude, but that's expected. The problem is the extra weight is making the rocket maintain speed while coasting more effectively, and the velocity at deployment is too high. Taking some mass out helps.

 

[Voyager1]

Is there a lighter-weight antenna that will work, like a "just a wire" antenna that could be adapted?

I set up some sims with the EF Mini in a 24mm rocket tonight and the 18g Cris quoted me earlier today plus 6.5g 1S battery is screwing things up. Lose apogee altitude, but that's expected. The problem is the extra weight is making the rocket maintain speed while coasting more effectively, and the velocity at deployment is too high. Taking some mass out helps.

Yes. A 1/4 wavelength of Brass wire approximately 80mm long soldered onto the TX PCB. Use some heatshrink over it for insulation.

 

[cerving]

Is there a lighter-weight antenna that will work, like a "just a wire" antenna that could be adapted?

I set up some sims with the EF Mini in a 24mm rocket tonight and the 18g Cris quoted me earlier today plus 6.5g 1S battery is screwing things up. Lose apogee altitude, but that's expected. The problem is the extra weight is making the rocket maintain speed while coasting more effectively, and the velocity at deployment is too high. Taking some mass out helps.

Sounds like you need to use electronic deployment...

 

[SolarYellow]

Sounds like you need to use electronic deployment...

That's another layer of complexity I'm hoping to avoid getting sucked into. At least for now.

 

[Andrew Brown]

A monopole only functions as a monopole if the appropriate ground plane under it is present. Otherwise, it's an unbalanced dipole with the tiny ground acting as the other pole. If you have lots of room, an end coupled half-wave would work with probably slightly better efficiency. Having said that, and the previous posts are right on, it is "good enough" assuming your ground station has a decent antenna. The transmitter is only a small portion of the equation. Most of the slop is taken care of by the receiver sensitivity.

 

[SolarYellow]

I'm only looking at 5000-ish ft sims.

 

[Voyager1]

A monopole only functions as a monopole if the appropriate ground plane under it is present. Otherwise, it's an unbalanced dipole with the tiny ground acting as the other pole. If you have lots of room, an end coupled half-wave would work with probably slightly better efficiency. Having said that, and the previous posts are right on, it is "good enough" assuming your ground station has a decent antenna. The transmitter is only a small portion of the equation. Most of the slop is taken care of by the receiver sensitivity.

Totally agree. Unfortunately, just about every telemetry module used in amateur rocketry that employs a monopole antenna will not have that appropriate (proper) ground plane. In fact, in many cases, the antenna will be installed in an avbay alongside Steel all thread rods, further changing its characteristic impedance and radiation pattern. Clever installation in a nosecone does give you an opportunity to have that proper ground plane if the NC diameter is sufficient to include it.

 

[user 30299]

Keep in mind that any antenna will work fine at 5,000 ft. or 15,000 ft. when the rocket is up in the air and you have
the most perfect line-of-sight. It's when the rocket is 5,000+ feet away on the horizontal, down in the brush or corn
or over the rise, that's when quality antennas and av-bay setups are important. The antenna is probably laying on
its side and no longer giving you that perfect radiation pattern when it was on the rail or in the air.

 

[ksaves2]

Keep in mind that any antenna will work fine at 5,000 ft. or 15,000 ft. when the rocket is up in the air and you have
the most perfect line-of-sight. It's when the rocket is 5,000+ feet away on the horizontal, down in the brush or corn
or over the rise, that's when quality antennas and av-bay setups are important. The antenna is probably laying on
its side and no longer giving you that perfect radiation pattern when it was on the rail or in the air.

That's where the last known position fix comes in. Gets one within the ground footprint. Once the rocket is down and I know the general direction, on goes a 900Mhz directional Yagi. The Yagi does increase the ground footprint quite a bit. Porting the output to a mapping program as I did some years ago is even better. One gets an idea of the terrain and what obstructions there are getting to the rocket. Sometimes it's best not to go in a straight line to do the recovery. You know the last known position and at times it's easier to take a circular route to get to the rocket. Kurt

 

[user 30299]

That's where the last known position fix comes in. Gets one within the ground footprint. Once the rocket is down and I know the general direction, on goes a 900Mhz directional Yagi. The Yagi does increase the ground footprint quite a bit. Porting the output to a mapping program as I did some years ago is even better. One gets an idea of the terrain and what obstructions there are getting to the rocket. Sometimes it's best not to go in a straight line to do the recovery. You know the last known position and at times it's easier to take a circular route to get to the rocket. Kurt

These are good tips for the people new to using GPS trackers.

 

[SolarYellow]

Sounds like you need to use electronic deployment...

Okay, been looking into it and I'm liking the Quark more and more.

Any chance you could throw one of the antennas you include on a gram scale and see how much of the combined weight is that part?

I'm playing with MD 18 and 24mm rockets in OR and the 18g + battery + OpenLog is impacting performance notably. On some, that approaches 2x the airframe mass.

 

[cerving]

An Eggfinder Mini with the antenna weighs about 14 grams. 6 grams of that is the antenna, so if you got rid of it and used a piece of wire instead (say, 1 gram) you'd get it down to about 9 grams. A Quark weighs about 5 grams. So, if you had both of them it would be 14 grams, + the wiring, connector, screw switch, and 2S Lipo battery. Figure on 30 grams total... close to the 1 ounce slug that they used to use for payload lifting events.

 

[SolarYellow]

Thanks!

 

[ksaves2]

That's another layer of complexity I'm hoping to avoid getting sucked into. At least for now.

Which is harder to do with smaller rockets due to space limitations. So now one has a battery for the tracker and the deployment altimeter plus how does one deal with on-off switching? Turn the tracker on before going out to the pad and the deployment electronics while on the pad. Throw in a long wait that may happen at a busy, major launch and if the battery capacity is not up to snuff, an off-nominal flight can occur when the launch button is pushed.
A whole bunch of trade-offs plus a smaller rocket can be tougher to find. I once had a relatively thin long-necked black tubed (that was the color of the tube not painted) rocket 38mm tube with 24mm RMS motor.
Might of been a 38mm motor with internal retention. I forget. Anyhow nice nominal flight. Landed a fair distance away that I had a GPS tracker in. I believe it was an Eggfinder product. Saw it land visually too.
I track by porting the data to a mapping program so I get a picture on a laptop. GPS on the laptop shows my position relative to the rocket's last known position. Anyhow, I get out there and "my" red dot was right on top of the "rocket's" red dot. NO rocket. I didn't have room for a noisemaker on the harness and I'm getting viable position updates from the rocket TOO. Hmmmm, I wander around a short bit as this would be embarrassing to lose a GPS tracked rocket with a nominal flight and good positions coming in after landing.
It occurred to Dr. Stupidhead here to hit the zoom option on my laptop mapping program and sure enough, I was like 30 to 40 feet away and walked right up to it! Still have that rocket today.
I highly recommend a noisemaker on the harness because one's ears are a potent tracking device. I was launching on a no-till corn field and the dark dirt did a good job camouflaging the black tubed rocket.
Scared the heck out of me as it would be a shame to lose a perfectly good rocket that is easily accessible upon landing. I've found a small enough noisemaker for it and use noisemakers on all out of sight flights along with the GPS trackers. If one has enough space in the nosecone for the tracker with a removable bulkhead, that's a good place for a tracker. Put it on a sled with the battery on the other side and a switch on the bulkhead. Make sure bulkhead retention is beefy enough to handle the deployment forces and things will be cool. Of course with smaller rockets not viable. Kurt

 

[jhill9693]

Totally agree. Unfortunately, just about every telemetry module used in amateur rocketry that employs a monopole antenna will not have that appropriate (proper) ground plane. In fact, in many cases, the antenna will be installed in an avbay alongside Steel all thread rods, further changing its characteristic impedance and radiation pattern. Clever installation in a nosecone does give you an opportunity to have that proper ground plane if the NC diameter is sufficient to include it.

What is this ground plane of which you speak?

 

[cerving]

Ideally, a 1/4 wave antenna would have a ground plane counterpoise perpendicular and underneath it at least 1/4 wave in radius. That works fine for mobile antennas on a car roof/trunk, not so good for rocketry. So, the compromise is that the ground plane on the transmitter circuit board acts as the counterpoise. It definitely reduces the efficiency of the antenna... generally not enough to make a significant difference for most sport flyers. You may see this if you put an Eggfinder Mini and an Eggfinder TX in the same rocket... you'll probably get a better signal and quicker GPS fix out of the TX due to its much larger ground plane area on the PC board. We try to maximize the ground plane area on the transmitters... but it's a balance between size and cost. A 4-layer board would be nice but they're a lot more expensive to produce, harder to design, and MUCH more prone to being damaged during soldering.

 

[Voyager1]

What is this ground plane of which you speak?

Like this one. Some have the passive ground plane elements at right angles to the vertical driven element. The reason they are bent down at about 45 degrees in this one is to optimise the impedance matching. You could also use a metal disc.



This is not mine, but I have built ones similar to this one. Credit for this image goes to https://lowpowerlab.com/wp-content/uploads/2017/04/image11.jpg

 

[Off Grid Gecko]

Ideally, a 1/4 wave antenna would have a ground plane counterpoise perpendicular and underneath it at least 1/4 wave in radius. That works fine for mobile antennas on a car roof/trunk, not so good for rocketry. So, the compromise is that the ground plane on the transmitter circuit board acts as the counterpoise. It definitely reduces the efficiency of the antenna... generally not enough to make a significant difference for most sport flyers. You may see this if you put an Eggfinder Mini and an Eggfinder TX in the same rocket... you'll probably get a better signal and quicker GPS fix out of the TX due to its much larger ground plane area on the PC board. We try to maximize the ground plane area on the transmitters... but it's a balance between size and cost. A 4-layer board would be nice but they're a lot more expensive to produce, harder to design, and MUCH more prone to being damaged during soldering.

Just tossing this out there for thought... if you have room you can run a ground wire in the opposite direction from the circuit the same resonant length might help or might not. Thinking 10-40m ham radios where they run a ground wire back from the active antenna (antenna goes one way, ground the other) and either coil it up somewhere, ground it to a hard point (a physical ground like a water pipe in the shack), or run it straight the opposite direction from the primary feed, effectively making a kind of dipole or a full dipole depending on how you work it in.

I'm not sure how much good it would do for a small wattage tx but dipole-ing the antenna? I dunno, maybe worth a shot. I might be looking into your trackers soon, might give it a try. I has solder.

 

[Off Grid Gecko]

Like this one. Some have the passive ground plane elements at right angles to the vertical driven element. The reason they are bent down at about 45 degrees in this one is to optimise the impedance matching. You could also use a metal disc.

View attachment 533442

That looks sooo much better than the last one I tried to make, lol. I didn't buy any special hardware so I was trying to solder wires to this tiny SMA connector with a square base and mounting holes.

 

[cerving]

You can theoretically make a decent 1/4 wave antenna for a rocket with a couple of pieces of copper tape in opposite directions, soldered to a coax. I've been meaning to try it on the outside of a CF rocket... haven't had a chance to test it yet. Half the battle of making a good antenna is workmanship... personally, I'm not that good at soldering coax.

 

[Off Grid Gecko]

You can theoretically make a decent 1/4 wave antenna for a rocket with a couple of pieces of copper tape in opposite directions, soldered to a coax. I've been meaning to try it on the outside of a CF rocket... haven't had a chance to test it yet. Half the battle of making a good antenna is workmanship... personally, I'm not that good at soldering coax.

The other half is testing it and trimming and retesting with a signal meter, lol. I tend to agree with some of the earlier stuff, if it's technically working you are going to do a LOT more with the Rx side. Boosting the Tx signal at that VHF and UHF also tends to make the signal bounce off of everything and harder to pinpoint a stronger transmitter.

I made a little 433 with my PI and didn't have any problem detecting the signal. Homing in on it was another problem. Course I'm in the woods so there's lots of signal bounce. Good for walkie talkies, not so good for testing tracking devices.

 

[OverTheTop]

If you are looking at tuning antennas check out this thread I did which used a Vector Network Analyzer to tune antennas.
https://www.rocketryforum.com/threads/tuning-a-telemetry-antenna-with-a-vna.164715/

 

[SolarYellow]

Got my parts from Cris.

My first goal (after building and testing) is to put the Eggfinder Mini in an Alpha, in anticipation of MD launches. Due to packaging, the only real place for it is in the PNC-50 nose cone, which won't fit with the standard antenna. There are a lot of things I could do to make a longer forward section and make a BT-based ebay, but I'd like to keep it more like a standard Alpha, at least at first. (I bought an Alpha bulk pack for $50 off fleabay, so I have ill-defined plans to try a bunch of variations.)

The brass wire sticking out the point of the nose cone will work, allowing the PC board to fit, but I've seen comments about such a configuration being "unsafe." It's vulnerable to getting bent when landing, but wire is cheap, so I'm not worried about that. The safety concern is that it's a needle added to the tip of the rocket in the event of a ballistic descent. Is this something that is really that much worse than the rocket coming in with just the nose cone? Is it unreasonably more dangerous than a much larger, heavier rocket coming in ballistically, perhaps even with a pointed aluminum tip (which we try to avoid, but still happens without the world ending). There are scale models that include antennas on the tip. Are they that much different? Are there RSOs that wouldn't let it fly? One factor is that my planned launch sites are high desert dry lakes. Local flights will probably be with a ceiling and at a site where the EF wouldn't really add anything over a normal altimeter.

I can chew on this and logic it out, weighing risks, for myself, but I'm kinda interested in if there's already a consensus about acceptable/non-acceptableness of such an installation, or if someone has some horror anecdote where everything went wrong "perfectly" that I wouldn't think of by myself.

ETA: Down the road, I'm also looking at setting up a Black Brant III as MD. I think the Mini will fit quite a bit better in that long, conical nose cone with the additional straight section at the base, and I also have plans for mid-body break, etc., but I want to sent some Alphas too high and get them back before I go there.

 

[Voyager1]

You could swap the thin brass wire that Cris supplies with a similar length of insulated solid Copper wire, similar to that used in network cable. It would represent less of a hazard, and would bend easily. You could also use an equivalent length of flexible wire that just flops around, but doesn’t represent any hazard. However, this is far from ideal when you consider the effects on the wire antenna’s radiation characteristics, and not something I’d personally do, but it will still work and be very safe.

 

[RocketDestroyer]

Antennas like this can actually work quite well. Many moons ago I made one to access the 2M uplinks of the Oscar 6 and Oscar 7 ham radio satellites. I made lots of CW contacts with just 10W and an antenna like this.

Like this one. Some have the passive ground plane elements at right angles to the vertical driven element. The reason they are bent down at about 45 degrees in this one is to optimise the impedance matching. You could also use a metal disc.

View attachment 533442

This is not mine, but I have built ones similar to this one. Credit for this image goes to https://lowpowerlab.com/wp-content/uploads/2017/04/image11.jpg

 

[AllDigital]

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.

-Mike


Example dipole printed antennas ("long" 433mhz)