Hey y’all, I’m looking for advice on what might be the best way to use the krakensdr for VHF on a fixed wing drone. I’m going to be building it and will probably be using carbon fiber poles to locate the antennas in the circle radius regardless of what the final wingspan ends up being.
My question is would making a simple dipole by soldering wire to the coax shield and conductor (approx 19.5") work ok? I could also use the mag mounts and make a ground plane by embedding chicken wire/hardware cloth in the uav but that adds weight and complexity. I also want to know if it would be useful to use a balun in this case. I would think any interference coming from the uav itself would be picked up on the antennas as well as the coax, I’m more thinking to get the best signal to noise ratio possible on VHF.
Has anyone already done the work of designing the UAV? If so I would be very interested in those designs.
The data connection to the app will be an integrated onboard LTE modem and connect to the app over cell data and a vpn. Latency will be high but I do expect it to still work, even if the total round trip exceeds 2-3 seconds (2000-3000ms).
The design I have will be fully autonomous, using arduplane and a suite of sensors to automatically follow a waypoint mission. The idea is to create a search pattern and launch shortly before a fox begins transmitting, then stream those bearings down over LTE to the app where I can navigate to the location.
I realize this is a huge project but if it works it’s going to be awesome.
A dipole without a balun might work poorly, because without a balun the feedline becomes part of the antenna, and it can make weird radiation patterns that can affect the DFing performance. You could try and see if a simple ferrite choke balun is enough, or you might need an actual balun from Minicircuits.
I’ve used a ferrite choke balun (thats where you wind the coax through the ferrite ring, right?) for HF, I could just get the proper mix from like palomar for vhf. What is an “actual” balun? How does it differ from what i could make by myself?
A proper balun converts a balanced antenna like a dipole to unbalanced feedline. That stops the feedline ground sheath acting as an antenna. A proper balun is a type of transformer.
But a cheap way to get a similar effect is to use a ferrite choke on the feedline which chokes currents on the ground sheath. This is not actually doing any balanced to unbalanced conversion, but the choking effect might be sufficient to stop the main problem with dipoles (at least in our application), which is the feedline becoming part of the antenna and distorting the radiation pattern
If you were to use a 1/2 wavelength antenna you would not need a ground plane at all. Perhaps some antenna modeling software could be employed? These types of antennas are often used on boats and airplanes due to the limited availability of electrical conductive materials.
BTW: I am really excited about this project and would like to be involved in it. I myself am an FAA 107 pilot and operate sUAS in Public Safety missions on a routine basis. I’ve been considering several Tethered options related to radio for disaster communications.
I did not know you can use a half wave long antenna without a ground plane. So all I would do is take some coax, run it to the spot, and solder the center onto a half wave wire? Of course we’ll still need baluns (ferrites etc) I need some good ideas for stiff-ish wire then. Not sure what would work best. Cruising speed for the aircraft looks like it’ll be about highway speed so as long as 3 foot long wires can be stiff enough not to bend i think it’ll be fine. Maybe I could join the tips of the antennas to give it some rigidity?
We commonly use brazing rods for antenna elements. Do you plan to use these vertically off the top of your fixed wing aircraft or do you have a method to mount underneath? Since you are not transmitting with these antennas a balun may or may not be needed. It definitely does not need to be a high power capable setup. I would look at some of the PCB type options where there is a small coil soldered to the board with an input connector (or even directly to coaxial cable) and the antenna element at the other end. The PCB would become your mounting point to the aircraft itself. I routinely use my Kraken without a balun, it could be useful in some instances, but mainly due to a change in noise floor from what I am reading. A balun become more necessary when transmitting as you want to protect the transmitter from a mismatch. Yes RF is still RF even on receive, but the damaging voltages are usually not present. An RF filter may be more appropriate (band pass for your frequency range for example).
I mistakenly replied to the E-Mail and it didn’t post to the thread earlier.
I’m going to mount these to the top of the aircraft. 2 on the wings, one on the nose, and 2 on the tail. the geometries are pretty close to correct, so the radius will flex a bit to fit everything. I cant have them on the bottom because I still have to land it.
As far as balun I will be using it because the coax cannot be part of the antenna and still be a uniform circular array (UCA) like the kraken requires. That’s based on the kraken team’s advice on #2 in this thread.
See that is where I am a little surprised because from what I can tell the Kraken Antenna kit does not have baluns either. They are essentially a quarter wave antenna in the 144-148 MHz frequency range.
Just a few options. You may even want to consider having custom PCB created just for your specific use. Weight is key. I honestly would try it without a balun first, see if it is really needed for your application.
Hey again. I’ve been continuing to look into this and I think I may have found a good, lightweight solution. I think I will use what is called a “Pawsey Balun”, where you arrange the coax with another stub in the following way:
The shield of the stub is used at both ends, the center is not. Would a dipole arrangement like this work? For the antenna elements, I’m considering nitinol wire, which will require some exotic acid flux soldering. This would put 5 vertical dipoles around the centerpoint, and it should be flexible enough to land on, provided I avoid abrasive surfaces like asphalt.
If you want ideas from people who have done similar work (certainly not me ), try checking out the hobby balloon launch/track sites.
On the other hand, since the KSDR is receive only, the only issue with a mis-matched antenna is a little signal loss. Given the altitude advantage, unless it’s a VERY weak signal, I doubt you’ll have issues with whatever you use. Just try it! - and let us know how it works… Happy Hunting!
PS- If you want exotic but that might be a good fit, check out slot antennas.
), try checking out the hobby balloon launch/track sites.