Uncover find out how to use a LiteVNA for precisely measuring FPV antenna SWR, an important side of antenna efficiency indicating energy reflection. This information covers the whole lot from preliminary setup, calibration, to conducting exact SWR measurements, making certain optimum antenna efficiency on your FPV drones.
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What’s a LiteVNA?
LiteVNA stands for Lite Vector Community Analyzer.
A Vector Community Analyzer is an instrument that may measure varied properties of a antenna, reminiscent of their tuned frequency and the way properly they’re tuned to this frequency.
Historically, lab-grade vector community analyzers had been extremely costly, costing 1000’s of {dollars}. The LiteVNA, nevertheless, is a small and reasonably priced Vector Community Analyzer that breaks this value barrier, retailing for round $130. The most recent LiteVNA64 mannequin can measure as much as 6.3GHz, masking the 5.8Ghz band generally used for FPV drones. As an illustration it could 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 normal RC hyperlink), and so on.
The LiteVNA can be utilized for measuring antenna SWR and tuning antennas (in case you’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 accessible 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 a vital 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. Nonetheless, in actuality, every antenna has a particular tuning, a number of the power will get mirrored again and turns into warmth, your most vary is subsequently diminished. The VSWR worth will differ relying on the frequency you might be on and the antenna’s tuning.
When an antenna is used for transmitting, a excessive SWR can doubtlessly harm the radio. Conversely, if the antenna is for receiving, a excessive SWR received’t hurt the receiver, however could degrade sign reception.
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Whereas some antenna producers record the SWR worth on their product pages, these figures aren’t all the time exact and will not specify the frequency at which they’re measured. Over time, harm to an antenna can alter its SWR worth. Having a instrument to measure this may also help you assess the situation and efficiency of your antennas, and resolve which channel could be greatest to apply it to.
For instance, contemplate 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 simply round 1.4 and 1.6 respectively, making this antenna superb 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 couple of.7% respectively.
Additional Readings:
How you can Use LiteVNA
Show Hint
Out of the field, the LiteVNA shows all 4 traces, which will be fairly messy. Since we’re primarily interested by SWR, you may take away the opposite 3 traces:
- Navigate to “Show” and deselect all traces apart from Hint 0.
- Beneath “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 interested 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.
Bear in mind, it’s advisable to recalibrate your VNA every time you alter the sweep vary.
Calibration
It’s essential to calibrate your LiteVNA earlier than performing any measurements. Utilizing an uncalibrated VNA renders the outcomes unreliable, basically 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 fasten 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. Notice 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 great connection.
If you happen to’re testing filters, you’ll additionally have to calibrate “Via” by connecting Port 1 to Port 2 utilizing the offered cable. Nonetheless, in case you’re solely testing antenna SWR as demonstrated right here, you may skip it.
As soon as full, click on Finished. You’ve the choice to save lots of this calibration in reminiscence, which is able to mechanically load upon the system’s subsequent startup, together with all settings and the frequency sweep vary. This function lets you save a number of calibrations with completely different setups and swap between these profiles within the “Recall” menu, providing important 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 instantly on the heart, and the open level on the center-right of the circle. Bear in mind, it’s advisable to recalibrate your VNA every time you alter the sweep vary.
Utilizing an Adapter or Cable
If you happen to intend to make use of any adapter or cable throughout testing, it’s essential to recalibrate with the adapter related. This step helps get rid of the potential influence of your check cable or adapter skewing the outcomes.
If you happen to lack a calibration set with the suitable connector, you may 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 possibly can rectify this by navigating to “Scale”, then “Electrical Delay (E. Delay)”. Enter a price 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).
How you can Measure Antenna SWR
To check an antenna together with your LiteVNA, first, connect the antenna to the primary port. Guarantee it’s tightly secured to ensure a stable connection. Place the antenna away from any steel or conductive supplies. The VNA will then show a graph displaying the VSWR inside your specified frequency vary.
Essential:
- Guarantee the encircling space is clear and freed from obstacles in the course of the check. Particularly, maintain the setup away from steel 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 greatest 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 after all, the decrease the higher.
Determine the frequency with the bottom VSWR to find out the greatest 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 presents 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 reasonably priced and sensible instrument for hobbyists, offering reliability and a breadth of options to fine-tune and consider your antennas effectively.
Get your LiteVNA from these distributors (IMPORTANT: ensure that it helps as much as 6GHz!):
