Uncover use a LiteVNA for precisely measuring FPV antenna SWR, a vital side of antenna efficiency indicating energy reflection. This information covers all the things from preliminary setup, calibration, to conducting exact SWR measurements, making certain optimum antenna efficiency on your FPV drones.
Try the instruments I like to recommend for constructing FPV drones: https://oscarliang.com/fpv-tools/
What’s a LiteVNA?
LiteVNA stands for Lite Vector Community Analyzer.
A Vector Community Analyzer is an instrument that may measure numerous properties of a antenna, reminiscent of their tuned frequency and the way nicely they’re tuned to this frequency.
Historically, lab-grade vector community analyzers have been extremely costly, costing hundreds of {dollars}. The LiteVNA, nevertheless, is a small and inexpensive Vector Community Analyzer that breaks this worth barrier, retailing for round $130. The newest LiteVNA64 mannequin can measure as much as 6.3GHz, protecting the 5.8Ghz band generally used for FPV drones. For example it could actually show Smith and SWR charts from 5.6GHz to six.0GHz, and it additionally works with decrease frequencies like 433MHz (radio hyperlink), 868/915MHz (radio hyperlink), 1.3GHz (fpv hyperlink), 2.4GHz (FPV hyperlink and customary RC hyperlink), and many others.
The LiteVNA can be utilized for measuring antenna SWR and tuning antennas (if you happen to’re making them), evaluating filters, and figuring out faults in coaxial cables. Whereas not as correct as their lab-grade counterparts, they’re sufficiently exact for hobbyist use. There are cheaper SWR meters out there for FPV use, just like the OwlRC SWR Meter, however they lack the reliability and intensive options of the LiteVNA.
Get your LiteVNA from these distributors (IMPORTANT: guarantee it helps as much as 6.3GHz!):
What’s SWR?
SWR, or VSWR, is an important consider antenna efficiency, standing for (Voltage) Standing Wave Ratio.
This metric signifies the quantity of energy that’s mirrored again to the supply. Ideally, all energy from the transmitter would journey as much as the antenna and be emitted as radio waves. Nevertheless, in actuality, every antenna has a selected tuning, a number of the power will get mirrored again and turns into warmth, your most vary is subsequently lowered. The VSWR worth will differ relying on the frequency you’re on and the antenna’s tuning.
When an antenna is used for transmitting, a excessive SWR can doubtlessly injury the radio. Conversely, if the antenna is for receiving, a excessive SWR gained’t hurt the receiver, however could degrade sign reception.
Study extra about Antenna SWR in my antenna information: https://oscarliang.com/best-fpv-antenna/
Whereas some antenna producers listing the SWR worth on their product pages, these figures aren’t all the time exact and should not specify the frequency at which they’re measured. Over time, injury to an antenna can alter its SWR worth. Having a software to measure this will help you assess the situation and efficiency of your antennas, and resolve which channel can be finest to apply it to.
For instance, take into account the SWR diagram of the RushFPV Cherry antenna under. Between 5600MHz (Marker 2) and 6000MHz (Marker 3), the bottom SWR is 1.113 at precisely 5.8GHz, which is great. Even at 5600MHz and 6000MHz, the SWR is barely round 1.4 and 1.6 respectively, making this antenna ultimate for FPV utilization.
How a lot sign loss and vary discount for SWR 1.1? Let’s look it up on this desk I made. It’s about 0.2% sign loss and 0.1% vary discount, which is principally nothing. For SWR 1.4 and 1.6, the vary discount is 1.4% and a pair of.7% respectively.
Additional Readings:
The right way to Use LiteVNA
Show Hint
Out of the field, the LiteVNA shows all 4 traces, which will be fairly messy. Since we’re primarily fascinated by SWR, you may take away the opposite 3 traces:
- Navigate to “Show” and deselect all traces aside from Hint 0.
- Underneath “Format S11”, change to SWR.
- In “Scale/DIV”, set it to 0.5 and allow “Present grid values”.
Sweep Vary
That is the place you’ll set the frequency vary you want to analyze:
- Go to “Stimulus”, choose “Begin”, and enter the bottom frequency you’re fascinated by observing.
- Choose “Cease” and enter the best frequency you want to observe.
- Sometimes, for FPV, I set the vary from 5.6GHz to six.0GHz.
Keep in mind, it’s really useful to recalibrate your VNA every time you regulate the sweep vary.
Calibration
It’s necessary to calibrate your LiteVNA earlier than performing any measurements. Utilizing an uncalibrated VNA renders the outcomes unreliable, primarily making them ineffective and deceptive.
The LiteVNA comes with a set of calibration instruments (open, quick, and cargo connectors), that are important for the calibration course of.
Navigate to the calibration menu, and connect the “open connector” (which has no center pin) to the primary port. Choose “Open” within the menu.
Repeat the method for the “Quick” and “Load” connectors. Word that each of those connectors have a middle pin; nevertheless, the “quick connector” is shorter, whereas the “load connector” is taller. Guarantee it’s tightly screwed on to ensure a very good connection.
For those who’re testing filters, you’ll additionally have to calibrate “Through” by connecting Port 1 to Port 2 utilizing the offered cable. Nevertheless, if you happen to’re solely testing antenna SWR as demonstrated right here, you may skip it.
As soon as full, click on Executed. You’ve the choice to save lots of this calibration in reminiscence, which is able to routinely load upon the system’s subsequent startup, together with all settings and the frequency sweep vary. This characteristic lets you save a number of calibrations with completely different setups and swap between these profiles within the “Recall” menu, providing vital comfort.
Moreover, you may confirm your calibration utilizing the Smith chart. The quick level needs to be on the center-left of the circle, the load level straight on the heart, and the open level on the center-right of the circle. Keep in mind, it’s advisable to recalibrate your VNA every time you regulate the sweep vary.
Utilizing an Adapter or Cable
For those who intend to make use of any adapter or cable throughout testing, it’s essential to recalibrate with the adapter linked. This step helps eradicate the potential influence of your check cable or adapter skewing the outcomes.
For those who lack a calibration set with the suitable connector, you can also make changes utilizing “Electrical Delay”. First, calibrate the VNA with out the adapter, then join the adapter. You’ll discover the open level has shifted on the Smith chart. You may rectify this by navigating to “Scale”, then “Electrical Delay (E. Delay)”. Enter a worth till the open level realigns to its right place. This sometimes ranges between 50-150 picoseconds for SMA adapters (or an extended delay for cables).
The right way to Measure Antenna SWR
To check an antenna along with your LiteVNA, first, connect the antenna to the primary port. Guarantee it’s tightly secured to ensure a strong connection. Place the antenna away from any metallic or conductive supplies. The VNA will then show a graph displaying the VSWR inside your specified frequency vary.
Vital:
- Guarantee the encompassing space is clear and freed from obstacles through the check. Particularly, maintain the setup away from metallic or any magnetic materials.
- Moreover, examine the SMA connector to make sure it’s clear.
Most antennas have a dip within the graph, indicating the frequency to which they’re finest tuned. Whereas some antennas could not present a pronounced dip, having a comparatively low SWR worth inside the desired frequency vary is mostly acceptable.
For a VSWR of two, solely about 10% of the facility is mirrored, which is taken into account excellent. With a VSWR under 2, variations in real-life efficiency are hardly noticeable, however in fact, the decrease the higher.
Establish the frequency with the bottom VSWR to find out the finest FPV channel to be used. It’s advisable to pick out an antenna for the receiver that matches the tuned frequency for optimum efficiency.
Conclusion
Utilizing LiteVNA gives an in depth perception into your antenna’s SWR, serving to you choose the perfect frequency for unmatched efficiency. It may also be used for checking in case your antenna is any good for FPV. The LiteVNA stands out as an inexpensive and sensible software for hobbyists, offering reliability and a breadth of options to fine-tune and consider your antennas effectively.
Get your LiteVNA from these distributors (IMPORTANT: be certain it helps as much as 6GHz!):
