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Pumpkin drop event

Which TX Antenna do I use for a 33Km space flight?

Which video transmitter do I use?


  • Total voters
    7

UBCrazy

Junior Member
#1
What TX Antenna do I use for a 33Km space flight?

Hello FT forums.

I am sending a Raspberry Pi 33Km into the atmosphere in a custom 3D printed space probe.
I would like a live video link that has an effective range of 33Km, as the probe will start it decent at 33Km and the video link need not reach any further.

I have most of the video transmission and reception equipment worked out however I cannot figure out what TX antenna to use.
Here is the list of components that I have worked out so far:

RX: http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_34_44&products_id=1020

RX Antenna: http://www.readymaderc.com/store/in...duct_info&cPath=11_45_52_100&products_id=1157

TX: http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_30_38&products_id=919

(all on 1280Mhz band)

I will also be using a GPS antenna tracker for maximum reception.

Please can you help me to find a suitable TX Antenna. :(

Thanks
 
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#2
a Cloverleaf or Pinwheel should do the job,

a few things to consider for your project,
its really cold up there
your gps will stop working about 18 Km high, rendering antenna tracking useless,
air is thinner, keeping a high power transmitter cool could be a problem (despite the cold)

good idea, just make sure you do your homework or it will end in tears.
 

UBCrazy

Junior Member
#3
Thanks for the reply

1) Custom heating elements have been designed to compensate for the tempuratures, they are controlled to work only at high altitudes to prevent overheating at low altitudes.
2)I have created a custom GPS module and software to allow for 40Km max height.
3)I may use a 1.5W transmitter, or just mount the 2W transmitter onto the control systems to keep them warm.

Thanks for the reply, all the cloverleaf and pinwheel antennas I have been looking at have very small gains.

Is it possible for you to suggest an antenna that I could use from readymadeRC (1.2-1.3Ghz)?
Is a 2W transmitter neccessary?

Thanks
 
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ivan747

Junior Member
#4
I think this would be answered much better in an electronics forum. I am thinking of several points where your design could fail, but I don't have much experience with this. For 33km range you will probably need an amateur radio license. If I'm allowed to, I'm going to suggest you ask this on eevblog.com/forum

If that's against the rules, please remove that bit.

Good luck.
-Ivan
 

UBCrazy

Junior Member
#5
Thanks Ivan for the support!

I have access to a full radio license anyway also a VHF License, marine band license, short wave license and aircraft telecommunications license. I have not given the full details of my mission yet, there will be an entire website dedicated to this with a live video feed as the mission happens. Thanks for the response anyway :).

I only have two questions now:
Which transmitter antenna (A/V) from this list:
http://www.readymaderc.com/store/index.php?main_page=index&cPath=11_45_52_100

Which A/V transmitter:
http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_30_38&products_id=919
or
http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=11_30_38&products_id=917

^^^These are my only questions as of now ^^^

Everything is worked out :)
 

vk2dxn

Senior Member
#6
Sounds like you might want to do some research on licencing and regs for what you can and can't do. A marine operators licence will not help you for this project.

Good luck mate
Subscribed
 

vk2dxn

Senior Member
#7
Sounds like you might want to do some research on licencing and regs for what you can and can't do. A marine operators licence will not help you for this project.

Good luck mate
Subscribed
 
#8
Sounds like a cool project!

you don't want a high gain antenna on your craft, unless you can be sure you can point the antenna on the craft at your ground station. If you can, you could use a helix or crosshair, but theese are heavy and quite large.

david maneged to get pritty high with a 1w tx with pinwheel and gatling. If you want more gain i would find someone with a dish
 

UBCrazy

Junior Member
#9
@vk2dxn what I meant to say was I have access to a full radio license and the others I listed, also checked local law recently, no radio license is needed in my area for this kind of project.

Thanks for the support and subbing though, I will be sure to message everyone who posts on this thread a link to the mission website.
 
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xuzme720

Dedicated foam bender
Mentor
#11
That seems like the best option as you'll definitely need a wide pattern from the plane. The trick will be to have a decent gain at the ground with a fairly directional Rx antenna where the weight isn't such an issue. I think I am preaching to the choir here though...Good luck with the attempt! I will be keeping an eye out for this one!
 
#12
to put some science into it,
1.5W vtx is a bit over 31 dBm,for now i will asume tx antana has a gain of 0 so the transmitting power is 31 dB,
those receivers have a sensitivity of about -85, coupled with the Gatling antenna with a gain of 16 will give you -101dB,
your free space loss over 33km @ 1280 mhz is 125 dB.
so you will have 101+31 - 125 = 7 dB head room, this is not taking into account humidity cable and connector loss, interference ect.

going to a 2W transmitter would only give you a another 2.5 dBm
but i have not done Manny long range flights, so i cant back up thees numbers :p
 

PaulT

New member
Mentor
#13
Isn't this like Kurt Busch asking the guy at the ticket booth what tires he should be using in the final ten laps on a rain soaked course with nine laps of fuel on board?
Ahh...use the transmitter that works is my answer! LOL
 

UBCrazy

Junior Member
#14
@Steadly1, I'm not sure what your trying to say...

Yes 1.5W VTX is the way to go?
Is 7db enough head room?
David Windestal did over 32,000m on a 1W VTX with a lower gain TX antenna.

Thanks
 
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vk2dxn

Senior Member
#15
Within out atmosphere (line of site) 1w is more than enough. You just need an omni directional antenna. Circular polarized will combat multi path interference however if you run linear polarized antennas then you just need to ensure that you maintain the same polarization on the receiving antenna.

Edit; look up long distance records set by ham's on the band you intend to use
 
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#16
@Steadly1, I'm not sure what your trying to say...

Yes 1.5W VTX is the way to go?
Is 7db enough head room?
David Windestal did over 32,000m on a 1W VTX with a lower gain TX antenna.

Thanks
yes 7 dB should be enough head room,
not meaning to be confusing or anything, i was just trying to validate your system theatrically (turns out in theory you could push for 66km :cool:)
 

UBCrazy

Junior Member
#17
To all,

Thanks for the support and interest. All my questions have been answered I just need to build the whole thing and hope that the parachute works xD.

Will make sure to MSG you all with a link to the official website when it goes up.

Thanks