Uncover learn how to use a LiteVNA for precisely measuring FPV antenna SWR, a vital facet 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 in 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 numerous properties of a antenna, equivalent to 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 6GHz, masking the 5.8Ghz band generally used for FPV drones.
The LiteVNA can be utilized for measuring antenna SWR and tuning antennas (in the event 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 out there for FPV use, just like the OwlRC SWR Meter, however they lack the reliability and in depth options of the LiteVNA.
Get your LiteVNA from these distributors (IMPORTANT: guarantee it helps as much as 6GHz!):
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. 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 diminished. The VSWR worth will differ relying on the frequency you’re on and the antenna’s tuning.
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Whereas some antenna producers checklist the SWR worth on their product pages, these figures aren’t at all times exact and should 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 help you assess the situation and efficiency of your antennas, and resolve which channel can be greatest to apply it to.
For instance, contemplate the SWR diagram of the RushFPV Cherry antenna beneath. Between 5600MHz (Marker 2) and 6000MHz (Marker 3), the bottom SWR is 1.113 at precisely 5.8GHz, which is superb. Even at 5600MHz and 6000MHz, the SWR is barely round 1.4 and 1.6 respectively, making this antenna splendid 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 mainly nothing. For SWR 1.4 and 1.6, the vary discount is 1.4% and a pair of.7% respectively.
Additional Readings:
Tips on how to Use LiteVNA
Show Hint
Out of the field, the LiteVNA shows all 4 traces, which might be fairly messy. Since we’re primarily thinking about SWR, you’ll be able to 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 thinking about observing.
- Choose “Cease” and enter the very best frequency you want to observe.
- Usually, for FPV, I set the vary from 5.6GHz to six.0GHz.
Keep in mind, it’s really helpful to recalibrate your VNA every time you regulate the sweep vary.
Calibration
It’s vital 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 fix 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 an excellent connection.
Should you’re testing filters, you’ll additionally have to calibrate “Via” by connecting Port 1 to Port 2 utilizing the offered cable. Nevertheless, in the event you’re solely testing antenna SWR as demonstrated right here, you’ll be able to skip it.
As soon as full, click on Accomplished. You might have 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 characteristic means that you can save a number of calibrations with totally different setups and swap between these profiles within the “Recall” menu, providing important comfort.
Moreover, you’ll be able to confirm your calibration utilizing the Smith chart. The quick level ought to be on the center-left of the circle, the load level instantly on the middle, 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
Should you 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 impression of your check cable or adapter skewing the outcomes.
Should you 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 possibly can rectify this by navigating to “Scale”, then “Electrical Delay (E. Delay)”. Enter a price till the open level realigns to its appropriate place. This usually ranges between 50-150 picoseconds for SMA adapters (or an extended delay for cables).
Tips on how 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.
Most antennas have a dip within the graph, indicating the frequency to which they’re greatest tuned. Whereas some antennas might not present a pronounced dip, having a comparatively low SWR worth inside the desired frequency vary is usually acceptable.
For a VSWR of two, solely about 10% of the facility is mirrored, which is taken into account superb. With a VSWR beneath 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 an antenna for the receiver that matches the tuned frequency for optimum efficiency.
Conclusion
Utilizing LiteVNA affords an in depth perception into your antenna’s SWR, serving to you choose the most effective frequency for unmatched efficiency. It can be used for checking in case your antenna is any good for FPV. The LiteVNA stands out as an inexpensive 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: be sure it helps as much as 6GHz!):
