Parabolic antenna vs Yagi-Uda antenna?

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Gym_Class_Hero

Gym_Class_Hero

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I'm considering building a homemade receiver for my recovery transmitter (not sure what brand, it's kind of old, but I've still got the frequency info so all good). I've noticed most people use Yagi-Uda antennas (the ones that look like scaled-down television antennas), but I've never seen anyone use a parabolic antenna or dish. I'm tempted to try a dish, though. What do you guys think? How would a dish be at picking up the signal from a transmitter in a rocket? I can imagine it being quite an efficient design to focus in directly on the source of transmission, compared to the need to sway the antenna back and forth like when I've used Yagi-Udas.

Also, would an old satellite dish be a good base for such a project?
 
Here's a dish calculator: https://www.satcom.co.uk/article.asp?article=22

Here's a cheap yagi: https://www.iw5edi.com/ham-radio/?cheap-yagi-antennas-for-vhf-uhf,93

At 432MHz, 15dbi gain and assuming 50% efficiency you would need a dish 1.75m in diameter vs a 60" 11 element cheap yagi at 14dbi. Depending on the feed, dishes are very good for circular polarization. Yagis, not so much.

Now on the other hand, if you want a dish, here's a dish :)
k1rqg.jpg


via
https://www.nitehawk.com/rasmit/gallery.html
 
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I would agree that a yagi will give you better results for what you are working to achieve. Keep in mind that a standard TV satellite dish is for KU band (12-18GHz) and that the lower you go in frequency, the larger the antenna will be for the same given fractional wavelength. Translation is that you are talking one big dish.

As polarization was mentioned before, realize that the polarization of you transmitter will change between each phase of the flight. Circular polarization accommodates this but can also be achieved in a yagi if using it for a tracker or using an "egg beater" for receiving telemetry.
 
For me, the tradeoff point is at 2.3GHz--a 2' dish has 1 dB more gain than a long Yagi, but the long Yagi has less wind load, and is easier to mount in a big multiband array. At higher bands, I used dishes. On lower bands I use Yagis. Actually, I use loop Yagis on 2.3 and 1.3GHz, as they are much easier to build if you have a sheet metal shear at your disposal.

An audio/ultrasonic dish might be more practical for rockets--particularly if you want extremely narrow beamwidths.
 
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If I recall correctly, the ideal dish diameter is 5X the wavelength, so if you are using anything under 1 GHz, the dish is gonna be big and clumsy.

A good 5 or 7 element Yagi is plenty directional enough, lighter, easier to pack up, and winds don't affect it as much as a dish.

In short, what Zack said. :)
 
By the way, haven't seen ya in awhile.

Ya going to be making the rounds this season? Say Hi to your dad for me.


CJ
 
Thanks for your input everyone, it was very helpful. As I'm sure you can tell, I'm a bit of a newbie when it comes to the technicals of radio equipment, but I'm getting better everyday. Yagi it is (my transmitter is 273Mhz, so WAY under the point where a dish would be viable). I guess I can put the elements on hinges so it can fold up into it's central core (might even find a way to holster it :D).

Though a Ku band rocket transmitter would be a good project to bring out to BALLS one of these years. But I perish the thought about how much the equipment to put out a signal like that must weigh.

blackjack - Yeah, I probably will. Been out a couple of seasons cause of money and other stuff that came up, but I'll hopefully be back a bit this coming spring. I'm hoping to Level 2 before I head off to college in the fall, then maybe I'll Level 3 next year.
 
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bobkrech said:
This antenna autotracker from FPV Hobby is an interesting device for tracking a rocket.
Click to expand...

From a short glimpse into the manual, it appears that this devices relies on the plane to transmit its GPS coordinates. This will make it hard to use with rockets, that usually loose GPS-lock during the boost phase of the launch.

One could make an autotracker that only relies on the emissions of the aircraft - roughly equivalent to what is used in the AGM-88 HARM - but I haven't seen anything like that in the hobby space.

Reinhard
 
^That's awesome. :D

Just wondering, are there any commercially available transmitters out there that produce a wavelength small enough to justify a dish?
 
The issue is going to be that when you get to using dishes, you are in the microwave range. Utilizing frequencies up there requires pure line of site (if your buried down in brush you aren't going to get a signal).
 
It would be an interesting research project for getting a lock-on during flight, up until the point of landing.

Imagine this: An omnidirectional microwave transmitter in the nose cone of the rocket, and an omnidirectional microwave receiver back on the ground. Before launch they establish a line-of-sight signal lock-on with each other. Assuming the motors on each can move fast enough, they should be able to keep a lock-on throughout the flight, and as soon as it lands one should have an immediately established line to follow to retrieve the rocket.

For areas that might have RETs or other high foliage it might be a problem (but if you've got a good line established before it hits the treeline, it should still be an easy track down). This would be best utilized in the southern playa.

Again, just a thought experiment for something to bring to BALLS eventually.
 
Gym_Class_Hero said:
It would be an interesting research project for getting a lock-on during flight, up until the point of landing.

Imagine this: An omnidirectional microwave transmitter in the nose cone of the rocket, and an omnidirectional microwave receiver back on the ground. Before launch they establish a line-of-sight signal lock-on with each other. Assuming the motors on each can move fast enough, they should be able to keep a lock-on throughout the flight, and as soon as it lands one should have an immediately established line to follow to retrieve the rocket.

For areas that might have RETs or other high foliage it might be a problem (but if you've got a good line established before it hits the treeline, it should still be an easy track down). This would be best utilized in the southern playa.

Again, just a thought experiment for something to bring to BALLS eventually.
Click to expand...
There's plenty of 2.4 GHz and 5.8 GHz transmitters and receivers out there for cheap so microwave frequencies are no longer an issue. A simple whip antenna in the NC is more than enough to transmit. The issure is receiving, however a parabolic antenna is probably not the way to go. The angular field of view is only about 10 degrees or so for 24 db 5.8 GHz parabola antenna from FPV Hobby, so if you'r not aimed directly at the rocket you don' t get any data. An amplifed patch antenna is a better option. Available 5.8 Ghz patch antennas from FPV have lower gain but a larger FOV. An 11 dB gain patch antenna has a 60 degree fov, a 14 db gain patch antenna has a 45 degree fov, a 18 db patch aintenna has a 20 degree fov.

Bob
 

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