Best Yagi Antenna for Altus Metrum

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JEtgen

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Now that I have mt technician license, I’m getting some of the tele line from Altus Metrum. The one question I have is what is the best antenna to purchase for the ground station?

Jenni Etgen
TRA9801. KI5TWN
 
Now that I have mt technician license, I’m getting some of the tele line from Altus Metrum. The one question I have is what is the best antenna to purchase for the ground station?

Jenni Etgen
TRA9801. KI5TWN
Congratulations!

Its a fun hobby! (Plus now you get to buy really cool hardware! :clapping:
 
My Altus Metrums and TeleGPSes are received just fine with the rubber ducky antenna on my THD72 and D74. The BT RX dongle gets an MFJ magmount on the roof of the car. I have both Arrow yagis but really just not needed.
 
I regularly fly to around 10k' and I receive just fine on a Diamond antenna which has two loading coils on the whip. That makes the radiation pattern less dependent on the ground plane. Since the antenna is mounted on a corner of the car the pattern could otherwise be quite asymmetric.

Diamond SG-7900

sg7900_1_.jpg
 
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My Altus Metrums and TeleGPSes are received just fine with the rubber ducky antenna on my THD72 and D74. The BT RX dongle gets an MFJ magmount on the roof of the car. I have both Arrow yagis but really just not needed.
When we were doing Fox Hunting in our HAM radio club, the rubber duck antenna would get you in the general direction by just turning your body around with the handheld radio in front of you, then when you got closer you would have to attenuate the signal by removing the rubber antenna and inserting a straightened out paper clip in its place.
 
Our highest successful flights have been 38k. Plan on higher than that. But we also fly between 3k and 17k.
Good info. You should be able to look at telemetry from your earlier flights and work out how much you have to spare in your link budget. That will be a pretty good indication of how much you will need to increase your gain by using a more directional antenna. You want to have enough gain for reception, but not so much that pointing the yagi (or whatever) becomes problematic. There is a trade to be made.
 
While the rocket is in the air you really don't need/want a long antenna.

I use a "Crossed Moxon Loop" antenna with my TeleGPS trackers. It is not the easiest antenna to build but it seems to work well. It does help to have a NanoVNA to build it but it isn't required. It has a few dB of gain overhead and less gain down on the horizon and it is circularly polarized so the relative position of the rocket antenna to the receive antenna is not important. It should be noted that there is a 3 dB loss associated with using a circularly polarized antenna to receive signals from a linearly polarized antenna. I have used it sucessufully with rocket flights to around 20,000' but still had plenty of margin left. For what it's worth I have also used it to listen to some of the ham satellites. Setup is a breeze, I just put it on a PVC tripod about 6' above the ground, turn on the TeleBT and I'm done.

https://www.oocities.org/w9bci/VHFUHFSatelite.pdf
 
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In the air a simple whip is fine for pretty much anything under 30k ft agl from my experience. Because you have line of sight to the transmitter you don't need a directional antenna.
Yagi's are useful for getting the 'final packet' once the rocket is on the ground from farther away when compared to a whip though.
 
From reading this thread, it sounds like almost any antenna can pick up the Altus Metrum GPS data packets during descent (7, 5, 3-element yagi directional down to simple whip).

Has anyone ever had an issue in flight from "too much" directionality on the 5 or 7-element yagi's and loosing telemetry due to misaiming the antenna?

For context, I'm flying to the 5-15K' range and using a DIY 5-element yagi on a TeleBT to get data from a TeleGPS. The problem is that I am always stressed about potentially misaiming the yagi and loosing the signal after I have already lost visual tracking (no longer have youthful eyes).

Am I being silly and overly worried, or would I be better off "downgrading" to something less directional like a 3-element or even a high-quality whip for the antenna on the TeleBT? Yes, in theory, I can listen to the directions from the phone app to know where to point, but I am hoping to do less mental processing in the middle of flights so I can just enjoy the moment.

I guess another way to ask this... what is the margin for error on aiming (in terms of degrees) on a 7, 5, or 3-element yagi and still catching data packets?
 
what is the margin for error on aiming (in terms of degrees) on a 7, 5, or 3-element yagi and still catching data packets?

Yagis generally have a beam width of +/- 30 degrees. That's to the 3dB point, larger angle loses half the signal level.

Bottom line: point the antenna straight up and it'll be fine for any nominal flight.

The Altus app will tell you where to point as the rocket descends. I keep a magnetic compass handy to help with azimuth aim. Elevation, yeah, within 30 or 45 degrees.
 
Has anyone ever had an issue in flight from "too much" directionality on the 5 or 7-element yagi's and loosing telemetry due to misaiming the antenna?
Yes. I had a multi-element Yagi that was entirely too directional. I pointed it straight up and it would not pick up signal when the rocket was on the pad. Surprising really. Taught me to be a bit less enthusiastic with beam-width. Note that this was with one receiver. The other one had a whip antenna on the car and was fine for the pad content. It was also fine for the whole flight for any flights around 10k'.

Yagis generally have a beam width of +/- 30 degrees. That's to the 3dB point, larger angle loses half the signal level.
Depends on number of directors on the Yagi.
 
You might gain (pun intended) some added benefit in using a cross-polarised Yagi. However, I agree with pretty much everything above.

So far this discussion has concentrated on the ground station, but you also need to consider how/where you install the telemetry unit, specifically the antenna, in the rocket. You want to optimise the radiation pattern and antenna matching.
 
Yagis generally have a beam width of +/- 30 degrees. That's to the 3dB point, larger angle loses half the signal level.
Depends on number of directors on the Yagi.

And element spacing, etc.
But yes, in general more elements mean lower beam width which means more accurate pointing required or more accurate direction if used for RDF.

It is a shame Arrow does NOT publish the antenna specs on their web site.
Beam width for a hand held Yagi is of interest.
 
And element spacing, etc.
But yes, in general more elements mean lower beam width which means more accurate pointing required or more accurate direction if used for RDF.

It is a shame Arrow does NOT publish the antenna specs on their web site.
Beam width for a hand held Yagi is of interest.
Rule of thumb is a hand held Yagi is easy enough to point at a rocket in flight on the 2 meter (144-148Mhz) and 70cm (420-450Mhz) bands. In the 33cm band (902-928Mhz) which is where most of the no license required units function, it has been said the beam width of a Yagi is too narrow to track a rocket reliably while in flight. I don't know about that. I was going to try it with a 33cm band Egg-Finder but went on flying hiatus after death in family.
That said, I've proven to myself that a 33cm band multi-element Yagi DOES increase the ground footprint of a downed rocket on the ground. Easy to point in the general direction of the rocket as it's generally standing still. Sure, yes so what? With GPS tracking will get to the last known position which usually close to the touch down point. The only benefit of the 33cm Yagi is one gets the final lie position sooner rather than later. I kinda like knowing "sooner" that my rocket is intact rather than later. That's my quirk. When I bought my 33cm Yagi, prices weren't that much. Actually a 33cm multi-element Yagi isn't that hard to carry. Put receiver/decoders in a one handed box and can point the Yagi. Kurt
 
Here's a free online Yagi beamwidth calculator:
https://www.changpuak.ch/electronics/yagi_uda_antenna_DL6WU.phpJust put in the frequency, the size of the elements etc. just like shown on the opening screen. Click on "Show me the details" and the sample screen will show the calculations. Is the boom isolated from the parasitics? Yes is a good answer here. If one is using a wooden boom for a homemade Yagi, "yes" in the answer for obvious reasons. Kurt
 
One thing that's not been called out here but I feel worth mentioning is that all of our transmitters (for the most part) are using 1/4 wave whip antennas. These antennas have polarisation, as do yagi antennas. Last year I was tracking a TeleGPS and noticed my SNR was lower than I expected. I could rotate my 5 element yagi 90 degrees to where the elements were in a vertical orientation and my SNR would improve dramatically. I didn't really catch onto what was happening until I got to the rocket. It was in a sea of canola and the chute had caught itself in the canola which resulted in the nose cone hanging off the canola in a vertical orientation. So my transmitter antenna was in a vertical orientation, and turning my yagi to match that orientation improved SNR dramatically.

TLDR, if you aren't getting a good signal on the ground try rotating your yagi 90 degrees.
 
Excellent point plugger.

This is why RocketDestroyer in post #16 uses a circular polarized antenna.
This has a 3dB loss but is independent of TX antenna orientation whereas a horz RX antenna to Vert TX antenna is more than 6dB loss.

A circular Moxon as linked in post #16 would be a nice fixed antenna for capture during flight.
Once the rocket is on the ground the TX signal tends to be weaker and may be very weak if beyond a hill. Then a Yagi is helpful to get a signal and bearing.
 
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