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	<title>FHSS | Model Power Boat Association</title>
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	<title>FHSS | Model Power Boat Association</title>
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		<title>2.4Ghz Radio</title>
		<link>https://www.mpba.org.uk/2019/01/20/2-4ghz-radio/</link>
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		<pubDate>Sun, 20 Jan 2019 17:18:14 +0000</pubDate>
				<category><![CDATA[Technical]]></category>
		<category><![CDATA[2.4Ghz]]></category>
		<category><![CDATA[Antenna]]></category>
		<category><![CDATA[DSSS]]></category>
		<category><![CDATA[FHSS]]></category>
		<category><![CDATA[Radio]]></category>
		<category><![CDATA[Transmitter]]></category>
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					<description><![CDATA[<p>Spread Spectrum Radios Welcome to the 2.4GHz spread spectrum radio revolution! No other advancement in RC radio technology has changed our hobby in such a profound and positive way. As big as PCM was – it doesn’t come close to the freedoms that all spread spectrum radios have. Interference issues are more or less all gone! No more frequency conflicts! [...]</p>
The post <a href="https://www.mpba.org.uk/2019/01/20/2-4ghz-radio/">2.4Ghz Radio</a> first appeared on <a href="https://www.mpba.org.uk">Model Power Boat Association</a>.]]></description>
										<content:encoded><![CDATA[<h4>Spread Spectrum Radios</h4>
<p>Welcome to the 2.4GHz spread spectrum radio revolution! No other advancement in RC radio technology has changed our hobby in such a profound and positive way. As big as PCM was – it doesn’t come close to the freedoms that all spread spectrum radios have.<br />
Interference issues are more or less all gone! No more frequency conflicts! No more Worries!<br />
Actually, the RC radio world has been rather slow to adopt 2.4GHz spread spectrum technology considering it has been commercially available since the 90’s with cordless phones, cell phones, and later wireless computer technologies such as Wi-Fi and now Bluetooth. In fact, spread spectrum was co-invented way back during WWII to prevent radio signal jamming of torpedoes by a famous actress of the day <a href="http://www.women-inventors.com/Hedy-Lammar.asp" target="_blank"><u>Hedy Lammar</u></a></p>
<p><!--The main idea behind spread spectrum is to spread the radio transmission out over a wider range of the radio spectrum - thus the name <strong>SPREAD SPECTRUM</strong>. This makes a spread spectrum signal much less likely to run into interference or jamming issues that are common with all narrow band radio transmissions. 

Even many spread spectrum radios all transmitting at the same time are very unlikely to interfere with each other as the spread of radio signals are random, changing, or coded. In most cases any signal conflict happens for such a brief moment, you never even notice it. 
<img decoding="async" src="https://www.mpba.org.uk/wp-content/uploads/2019/01/futaba_16sz.jpg" alt="Futaba 16SZ" width="150" class="size-full wp-image-10363" srcset="https://www.mpba.org.uk/wp-content/uploads/2019/01/futaba_16sz.jpg 300w, https://www.mpba.org.uk/wp-content/uploads/2019/01/futaba_16sz-150x150.jpg 150w, https://www.mpba.org.uk/wp-content/uploads/2019/01/futaba_16sz-90x90.jpg 90w, https://www.mpba.org.uk/wp-content/uploads/2019/01/futaba_16sz-75x75.jpg 75w" sizes="(max-width: 300px) 100vw, 300px" />


<h4>How Does A Spread Spectrum Radio System Work?</h4>


There are essentially two different types of spread spectrum technologies that today's 2.4GHz RC radios use... FHSS & DSSS. 


<h4>FHSS:</h4>


FHSS is exactly how that first WWII spread spectrum system worked. 
Frequency hopping, as the name suggests, transmits within a specific frequency band (such as 2.4 GHz),  but changes the precise frequency of the transmission hundreds of times a second. It's sort of like switching between channels on your TV (channel hopping) if the same show was on several different channels at the same time and you were trying to avoid any adverts for a commercial free watching experience. The commercials in the TV example here are interference.
For FHSS to work, the receiver has to know the frequency changing pattern so it can hop to the different frequencies in the same order and time frame as the transmitter does. The time spent on each specific frequency is so short, even if there was interference on several of the frequencies, it changes so quick, you wouldn't detect it.
FHSS theoretically has better interference immunity than DSSS as more channels are used to hop around on but the other hand a FHSS only RC radio would have very poor/limited range due to something called "Process Gain". Even radio brands that "market" their radios as using FHSS technology are not telling us the whole story since they also use DSSS. All our spread spectrum RC radios use DSSS technology. Some combine it with FHSS, that is all.
<img decoding="async" src="https://www.mpba.org.uk/wp-content/uploads/2019/01/graupner_mc26.jpg" alt="Graupner MC26" width="150" class="size-full wp-image-10362" srcset="https://www.mpba.org.uk/wp-content/uploads/2019/01/graupner_mc26.jpg 300w, https://www.mpba.org.uk/wp-content/uploads/2019/01/graupner_mc26-150x150.jpg 150w, https://www.mpba.org.uk/wp-content/uploads/2019/01/graupner_mc26-90x90.jpg 90w, https://www.mpba.org.uk/wp-content/uploads/2019/01/graupner_mc26-75x75.jpg 75w" sizes="(max-width: 300px) 100vw, 300px" />

<h4>Direct Sequence Spread Spectrum DSSS:</h4>


Unlike frequency hopping, direct sequence as the name suggests uses random PN code sequences and picks one or more pseudo randomly selected frequencies out within the band (such as 2.4 GHz).
The idea is with several randomly selected frequencies, along with random code sequences, it's very unlikely all of them would ever experience interference at the exact same time within the unique code sequence. Using our TV example from above, DSSS would be somewhat similar to watching several TV's with the same show on each TV all on different channels.
 
At any one time, adverts will be on some of the channels, but never on all of them at the same time allowing you to watch your show commercial (interference) free by simply looking at (processing) all the TV images and ignoring any that were commercials. This brings us to DSSS main contribution our hobby - improved radio range. I touched on Process Gain above in the FHSS discussion, but this is why DSSS technology must be used in all 2.4GHz RC radio's regardless of brand.
DSSS is capable of high bit processing speeds and the higher the bit process rate, the greater that range can be with a set amount of transmitter output power (which by the way is pretty low for off the shelf RC radios). It's not that a DSSS RC radio signal will travel any further out than the same powered signal using FHSS or just plain old 2.4GHz noise of the same power level; but due to the higher bit processing rate, it can process and extract more clean data packets out of that noisy environment - even as the signal gets weak at extended ranges.    
These are very, very basic explanations of both spread spectrum methods and for most of us, it's simply enough knowing that the systems work,  and work well. 
The video below also provides an easy to understand explanation of how DSSS works.

<center>

<h5>Spektrum DSMX Video

<h5>
<a href="https://youtu.be/aZGcyuezMik" target="_blank"><img decoding="async" src="https://www.mpba.org.uk/wp-content/uploads/2019/01/dsss_video.jpg" alt="DSSS Video"></a></center>


<h4>2.4GHz Limitations</h4>


You should know by now almost nothing in this world is perfect and spread spectrum radios are no exception. As I mentioned earlier, transmitting and receiving in the 2.4GHz high frequency range certainly gets you out of a fair amount of naturally occurring RF (radio frequency) noise that occurs below 300 MHz. 
You have probably also noticed that all 2.4GHz devices from cordless phones, WiFi routers, and of course RC spread spectrum radios have very short antennas. This is because the frequency or wave length is so short, a short antenna is all that is required to transmit and receive 2.4 GHz. This has made the long unsightly and usually difficult to route RC receiver antenna wire a thing of the past. It has also eliminated the long telescoping antenna that would always get bent on the RC radio. 
So what’s the issue? 
Blocked and reflected signals. 
Unlike the longer wave lengths used in 27-75 MHz RC radios that pass through almost anything, 2.4GHz short wave lengths are easy absorbed or reflected by many objects just like a light wave. Absorption and reflection of the 2.4GHz signal by parts of the model could lead to fail-safe lock out control loss if the signal is not strong enough for the receiver to hear or identify if from shielding or reflecting. 
This is not so much of an issue with fiberglass hulls; but it certainly can be a problem for hulls that use carbon fibre. 
<img decoding="async" src="https://www.mpba.org.uk/wp-content/uploads/2019/01/aurora_9x.jpg" alt="Aurora 9X" width="150" class="size-full wp-image-10361" srcset="https://www.mpba.org.uk/wp-content/uploads/2019/01/aurora_9x.jpg 300w, https://www.mpba.org.uk/wp-content/uploads/2019/01/aurora_9x-150x150.jpg 150w, https://www.mpba.org.uk/wp-content/uploads/2019/01/aurora_9x-90x90.jpg 90w, https://www.mpba.org.uk/wp-content/uploads/2019/01/aurora_9x-75x75.jpg 75w" sizes="(max-width: 300px) 100vw, 300px" />


<h4>The Solution… Diversity</h4>

 
By mounting at least two receiver antennas in different locations and orientations within the model (or on the exterior or carbon models), even a couple inches apart at a 90 degree angle to each other; pretty much ensures at least one of these receiver antennas will always “see” a clear & strong signal.
By having two or more receiver antennas placed in different orientations, no matter how the model is orientated, one of the antennas will have enough longitudinal exposure to "see" & receive the radio waves from your radio's transmit antenna.  
 
Transmitter antennas radiate RF out of the sides of the antenna, not out the tip, the same way receiver antennas receive RF along their length. This is why you will often see people driving with their 2.4 GHz antenna bent sideways on the radio.
When the antenna is straight, there is a null zone out the tip where the RF energy is not that strong; so if you always fly with the tip on the antenna pointed directly towards the model, you are going to limit your range. Bend it sideways and more RF energy reaches the model; Remember, there is that null zone of weak RF energy out the tip of the antenna so as the model travels a long way downrange inline with the tip, it's going to be coming into that null zone. 
<img decoding="async" src="https://www.mpba.org.uk/wp-content/uploads/2019/01/multiplex_sx16.jpg" alt="Multiplex SX16" width="150"class="size-full wp-image-10360" srcset="https://www.mpba.org.uk/wp-content/uploads/2019/01/multiplex_sx16.jpg 300w, https://www.mpba.org.uk/wp-content/uploads/2019/01/multiplex_sx16-150x150.jpg 150w, https://www.mpba.org.uk/wp-content/uploads/2019/01/multiplex_sx16-90x90.jpg 90w, https://www.mpba.org.uk/wp-content/uploads/2019/01/multiplex_sx16-75x75.jpg 75w" sizes="(max-width: 300px) 100vw, 300px" />


<h4>Dual Diversity RC Radio Antennas</h4>


This is why the latest generation of spread spectrum radios sometimes use two antennas on the radio (one pointing up vertically and one in the back handle positioned 90 degrees horizontally). Just like having dual receiver antennas placed in different orientations onboard the boat to improve diversity; doing the same thing with the transmitter antenna also improves diversity. With this arrangement, you don't have to worry about which way the radio antenna is pointed.
When the boat is directly in front of you, the horizontal antenna will be proving the most RF energy back to the model. As the model travels along the lake to the left or right, now the model will be seeing the most RF energy from the vertical antenna.

<strong>Q. Is it true that 2.4GHz is immune to interference?</strong> 
A. It is true that you can't be blocked by another 2.4GHz radio control system but there is still always a chance that other forms of interference can cause you to lose control of your model. The 2.4GHz band is used by a very wide range of other electronic equipment from wireless internet to microwave ovens. There's no guarantee that one of these other devices won't interfere with your RC set. 
<strong>Q. Are there disadvantages to a module-based 2.4GHz system?</strong> 
A. There are some disadvantages to using a module based system over a totally 2.4Ghz one. The newer non-module-based 2.4GHz systems often offer higher resolution and faster response. The JR native 2.4GHz systems also offer a unique feature (Model Match) that eliminates the risk of running with the wrong model memory selected in your transmitter. 
<strong>Q. Can I use my existing servos with a new 2.4GHz system?</strong> 
A. Yes, all of the currently available 2.4GHz systems are compatible with conventional (analog or digital) servos. There is talk of a new generation of totally digital servos becoming available specifically for advanced Spread Spectrum RC gear but nothing has yet been seen. The only exception to this is that some Hitec digital servos may not work reliably (or at all) with some Futaba FASST receivers due a lower than expected voltage on the signal line. 
<strong>Q. What causes lockouts on 2.4GHz?</strong> 
A. Spread spectrum radio sets work in a way very similar to PCM ones in the way they respond to strong interference. If you're unlucky enough to experience interference so strong that the link between transmitter and receiver is lost, your receiver will enter "hold/lockout" mode and then go to failsafe mode (if set). 
The cause of such a lockout/failsafe resets can be almost anything including, but not just limited to, interference. In fact, in the case of spread spectrum systems, experience has shown that lockouts are far more likely to be caused by inadequate batteries in the model or bad installation. 
<strong>Q. Should I switch to 2.4GHz now or wait?</strong> 
A. this depends very much on your own situation. If you've never had a problem with your existing narrowband RC system and have no problems with frequency control at your club lake then there's no reason why you should rush out and buy a 2.4GHz spread spectrum set. However, if you do live in an area where interference on your existing set is not uncommon, or if there are long queues for frequency pegs then the move might be worthwhile. 
If you're just starting out in the hobby and don't yet have any RC gear then it probably makes sense to go straight to 2.4GHz. 
<strong>Q. Why are good receiver batteries so important on 2.4GHz?</strong> 
A. Inside every spread spectrum receiver are an array of tiny computer chips that must perform millions of complex instructions without mistakes every second. In order to function reliably, these computer chips require a steady stream of electricity. If that steady stream is interrupted, even for a tiny fraction of a second, the computers can crash or stop working briefly. 
This means that if your receiver batteries, BEC or regulator aren't up to scratch then you will almost certainly have real problems with your new 2.4GHz radio. 
Unless you're running with servos that can't handle the extra voltage, it is strongly recommended that you use a 5-cell receiver pack (6V) or even (6.4V) to further reduce the risk of voltage-related receiver problems. 
Many of today's hi-torque servos can draw very high amounts of current and if your battery isn't up to the task, this can cause the voltage they deliver to be drastically reduced. Should that voltage drop below the 4.5V that some receivers require to function, a lockout or reboot may result. Remember that when the computer in your 2.4GHz receiver crashes, it's quite likely your boat will also crash. Good batteries of adequate capacity and well-charged are absolutely essential to safe running. 
<strong>Q. Can I use a 2.4Ghz system in my carbon boat</strong> 
A. Unfortunately carbon acts as a pretty good shield against 2.4GHz radio transmissions. This means that if you put a 2.4GHz receiver inside a carbon-fibre hull, it will be affected. 
Most 2.4GHz receivers such as those from Futaba have extended antennas that make it easier to route them through to the CF he outside world. It's still very important to make sure that at least one antenna is visible from every angle.
--></p>
<h3>Read the full article on :<br />
<a href="https://www.rchelicopterfun.com/spectrum-radios.html" target="_blank"><strong><u>www.rchelicopterfun.com</u></strong></a></h3>
<p><a href="https://www.mpba.org.uk/posts"><u>Back to News Articles</u></a> | <a href="https://www.mpba.org.uk/category/technical/"><u>Other Technical Articles</u></a> </p>The post <a href="https://www.mpba.org.uk/2019/01/20/2-4ghz-radio/">2.4Ghz Radio</a> first appeared on <a href="https://www.mpba.org.uk">Model Power Boat Association</a>.]]></content:encoded>
					
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