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24 votes
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Why is it bad to power up a drone without an antenna on the VTX?

Short answer: Yes, this is very much true. The VTX sends out radio-frequency (RF) energy through the antenna connector and pigtail, and if nothing (or the wrong thing) is connected at the other end, ...
FlashCactus's user avatar
  • 2,997
14 votes
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What is circular polarization in antennae?

This is going to be a long answer but bear with me. First, I must discuss the phenomenon of polarization itself. As you probably know, radio waves are a subtype of electromagnetic waves, which in turn ...
FlashCactus's user avatar
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13 votes
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Can circularly and linearly polarized antennae be used together for FPV?

The compatibility of mixed polarity antennae depends greatly. For a little background in RF polarity, this diagram shows the difference between the four main types of antenna polarization available: (...
ifconfig's user avatar
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11 votes
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How much does mounting an antenna near a carbon fiber frame degrade signal reception?

This is a huge question, which is why a complete answer is not really possible without specifics on your drone frame, antennas, antenna placement etc. Long story short - Carbon Fibre is pretty much ...
Rory Alsop's user avatar
10 votes
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What is antenna gain?

Gain, as a general term, is a measure of how large or strong something (a voltage, a radio wave, a sound wave, or whatever else) is relative to some baseline value of the thing being measured. A gain ...
FlashCactus's user avatar
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9 votes
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Crossfire signal strength - comparing Immortal "L" vs "T"

The short answer is, yes. According to testing done here there is an observed 3db loss when folding the bottom half of a dipole which would be the same effect as cutting your output power in half. ...
ipaq3115's user avatar
  • 525
9 votes

Why is it bad to power up a drone without an antenna on the VTX?

Your VTX is a high-power RF transmitter. When operating with an antenna, the RF power of the transmitter is radiated out through the antenna. When the antenna is missing, the RF power is reflected ...
jpou's user avatar
  • 411
9 votes
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FrSky receiver snap-on connection problem

This type of connector is called a U.FL connector. Replacing the connectors will be super fiddly, but is possible if you are skilled with a soldering iron. The cable side is the more difficult bit ...
Kralc's user avatar
  • 6,036
8 votes
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How fragile are the SMA connectors used in FPV equipment?

According to electronics-notes.com, the mating cycle rating for the SMA/RP-SMA connector is 500 cycles. However, it is important to note that this rating assumes that the connection and disconnection ...
ifconfig's user avatar
  • 6,008
8 votes

How to mount XM+ receiver antennas?

I really like the way the Joshua Bardwell does it. He puts one on each rear arm facing forward with a zip-tie and heat-shrink over the top. It places the antennas at 90 degrees to each other and so ...
Paul Kendall's user avatar
7 votes
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Calculating the range of an FPV drone

I'm going to give you the answer first: Yes, it is worth calculating the approximate range if you're building a (very) long-range aircraft. However, theoretical calculations will usually be such a ...
FlashCactus's user avatar
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6 votes
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Can I mount my RX and VTX antennae next to one another?

The distance is dependent on the wavelength of the lowest frequency. You can calculate the wavelength $\lambda$ (m) from $\lambda = c \div f$, where $c$ is the speed of light in a vacuum (ms-1) and $f$...
Kralc's user avatar
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6 votes
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How to mount XM+ receiver antennas?

TL;DR: From purely a range consideration the 90 degree mounting is the best because of the orientations your quad might see. You'll want to get the antennas as far away from the frame as you can so ...
ipaq3115's user avatar
  • 525
5 votes

What is antenna gain?

'Antenna gain' gives you the power transmitted by an antenna in a specific direction, when compared to a theoretical antenna that radiates equally in all directions (this is known as an 'isotropic ...
sempaiscuba's user avatar
5 votes
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What is a "mushroom antenna"?

A "mushroom" is just a clover-leaf antenna. Generally they have a plastic cover that makes them look like a mushroom, hence the name.
Paul Kendall's user avatar
5 votes

Can I mount my RX and VTX antennae next to one another?

The rule of thumb here is the further away from each other the better. The problem is, that receiver is operating on different band and so it has some input filtering to not receive "out-of-band&...
LQd's user avatar
  • 71
5 votes
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How do I test if my DX5e antenna is still good?

That's probably OK, but you should do a range test. All transmitters have a mode that transmits a much lower power than normal, and if that is sufficient to control the model at 30 paces, full power ...
Robin Bennett's user avatar
5 votes

How far can you get video without a VTX antenna?

First off, DO NOT power up the quad without a VTX antenna as this can damage the VTX. And to actually answer your question, it varies. Depending on the quality of the VTX and the power output, you may ...
Drones and Whatnot's user avatar
4 votes
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In what direction should I orient the dipole antenna on my 2.4 GHz RC transmitter?

The antenna should be aligned to match the orientation of the antenna on your aircraft; generally this will be vertical, but for more acrobatic aircraft a compromise of 45° might be appropriate for ...
Kralc's user avatar
  • 6,036
4 votes

What is a "mushroom antenna"?

Some brand-name antennae actually have the word "mushroom" in their model name. In common parlance, though, unless the model name is spelled out fully (such as "VAS Mad Mushroom"), it can refer to any ...
FlashCactus's user avatar
  • 2,997
4 votes
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What are the exact specifications of a RushFPV SMA connector?

The Rush cable is slightly non-standard as it lacks the threads on the holes that the TBS connectors have. It works fine though. The SMA is a standard SMA thread, so the normal hole size for SMA ...
QuadMcFly's user avatar
  • 1,200
4 votes

Calculating the range of an FPV drone

I just want to add to FlashCactus's excellent answer... Depending exactly what you want, you can get some fairly good estimates on range on various range calculators online. You can get them pretty ...
anonymous2's user avatar
  • 1,043
4 votes
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Should Crossfire transmitter antenna orientation match receiver antenna orientation?

A dipole antenna is linearly polarised, which means it radiates most of its energy in one 'plane' relative to the antenna. For maximum efficiency, the transmit and receive antenna should be orientated ...
Kralc's user avatar
  • 6,036
4 votes

What makes mushroom antennae so good at receiving and transmitting omnidirectionally?

The primary purpose of using circularly polarised antennas is the rejection of out of phase video reflections. They tend to have lower gain compared to linear antennas but linear need the antenna ...
Gary Boulter's user avatar
3 votes
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What makes mushroom antennae so good at receiving and transmitting omnidirectionally?

Most omnidirectional antennae have two factors that work well for them. 1) They have fairly symmetrical and uniform RF profiles. This means that you are less prone to sudden drop-outs in the video as ...
Drones and Whatnot's user avatar
3 votes

Can circularly and linearly polarized antennae be used together for FPV?

To add to ifconfig's excellent summation of how the signal strength would be affected by mismatched polarizations, I must point out that in order to benefit from the reduction of multipath ...
FlashCactus's user avatar
  • 2,997
3 votes
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What is the difference between a patch and helical antenna?

tl;dr: In terms of radio performance, they're almost identical if you compare similar-gain models, so choose based on dimensions, durability, maintainability and other practical considerations. If you'...
FlashCactus's user avatar
  • 2,997
3 votes

What is the difference between a patch and helical antenna?

It is my understanding that in general a helical antenna will perform better than a patch antenna. I should really find a source for that though. However a patch antenna is flat or nearly flat and ...
5zero7rc's user avatar
  • 1,130
2 votes
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Does FPV transmitter antenna need to match the goggle receiver antenna?

No, specific brand and specs don't matter for interoperability (aside from making sure that both antennae are built to transmit/receive the same frequency). Specific specifications about an antenna ...
ifconfig's user avatar
  • 6,008

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