神控（蓝宇等）的优越性，从FHSS与DSSS的优缺点比较

 

which is best?
Under normal circumstances, in a relatively benign environment with say 6-10 transmitters all operating at the same time, some Bluetooth activity and maybe a WiFi system in the distance, both DSSS and FHSS will work perfectly adequately. This is proved by the number of flying-fields all over the world where, every weekend, groups of people gather and fly models on 2.4GHz without any problems at all.

At such gatherings you'll usually find a good mix of the different systems, all operating without interference, despite sharing the same 2.4GHz band.

But what happens when we start pushing the boundaries?

What about large events such as SEFF and Joe Nall, where there can be dozens or even hundreds of people all trying to use the 2.4GHz band together? Which system provides the most protection against lockouts or getting shot down?

Well all-else being equal (which it's often not, thanks to sub-standard power systems, and poor installations), the FHSS system should have an edge over the DSSS system when it comes to retaining control of your model.

As my own tests have shown, when a DSSS system like the Spektrum encounters strong interference on its two operating channels, it loses link and control is lost. Sometimes, if you're unfortunate enough to have your system select two very closely spaced parts of the band, your system can fail, even though the other 80% of the band is completely free of interference.

By comparison, all of the FHSS systems I tested showed their ability to continue working even after 80% of the band was saturated with interference and only a small portion was free.

So, in theory and in practice, a good FHSS system will keep working long after many 2-frequency DSSS systems have locked out.

However, that's not the whole story.

Because the FHSS systems are using much (or all) of the band, there are situations where they can be badly affected while a DSSS system is not affected at all.

This can occur if the band is heavily congested except for a small portion and the DSSS system chooses that portion on which to operate. It's signals may be allocated to the clean part of the band and thus provide faultless communications, while the FHSS one loses a good percentage of its data to noise because it's hopping through interference.

Experience shows however that this scenario is far less likely than the converse one, where the DSSS systems shut down while the FHSS ones continue to provide a measure of control

If you look at the anecdotal evidence from large meets such as SEFF and Joe Nall it becomes apparent that there were far more "issues" and radio-related crashes associated with the Spektrum DSSS equipment than with FHSS systems of other brands. Now this will be at least in part due to the popularity of the DSM2 system and hence -- the more DSM2 radios in use, the more they'll be represented in the crash statistics.

However, it's still very clear that DSSS systems are less tolerant of very noisy environments than FHSS systems and lockouts are more common with Spektrum/JR than with FASST and other hoppers.

I'm sure that Horizon would say "there were hundreds of DSM2 systems at these meetings yet only a very few experienced radio issues" -- to which I would ask in reply "the DSM2 flaw I discovered only occurs with about the same regularity - could these crashes have been related to that problem?"

The Bottom Line
It strikes me that, as the 2.4GHz band becomes more congested with RC fliers, the number of problems being experienced by DSSS fliers seems to be also increasing disproportionately to the number of those systems in use.

Theory makes it clear that a constantly agile system (FHSS) should be more resilient to noise on the band and this seems to be born-out in practice.

If you've got a DSSS system and had no issues then don't rush out and swap it for FHSS just because of the small theoretical and practical extra level of insurance it may offer.

However, if you're looking to buy a new RC system, think carefully about the benefits FHSS might offer before committing to a system (DSSS) that is quickly losing favor in the RC marketplace (even JR is switching to FHSS elsewhere in the world).
If you do opt for a DSSS system, try to choose one that uses at least three or more different frequencies. This will give you maximum use of the band and reduce the chances of encountering the kind of interference that forces your radio into failsafe.

And remember -- there's far more to reliable 2.4GHz operation than just choosing between DSSS and FHSS. You've also got to have very good batteries (A123s rule!) plus a good installation with receiver antenna(s) well clear of wiring and other metal parts.

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翻译

谁是最好的？

一般情况下，在一个相对温和的环境中，比方说有6-10个控同时发射，在该区域内还有一些蓝牙以及wifi系统在活动，DSSS和FHSS将相当好的干活儿。这已经在世界上大量的飞场上被证明了，在那里每个周未，有成群的人们聚集在那里飞飞机模型，他们都是2.4GHz而且没有任何问题。
在这种聚会时节，你可以发现很多的不同遥控系统，所有它们都不受干扰地运转着，仅管都分享着2.4GHz频段。
但是当我们挑战底线的时候会发生什么？
在像SEFF和Joe Nall这样的大型活动中，在那里有成打的甚至上百的人们都一块使用2.4GHz时又如何呢？
我们互相之间都是地位相同的（经常也会不是这样，这时要感谢那些不符合标准的动力系统和那些较差的装备），当保持你的系统控制飞机时FHSS系统会比DSSS系统占据更优先的地位。
正如我亲自测试的结果表明，当一个DSSS系统（如Spektrum品牌的控）在它的两个频道上遭遇强的干扰的时候，它将失联和失控。有时，如果你不够幸运的话，你的两个频道正好处于很近的时候，你的系统会出事，而80%的其它频道确没有任何干扰。
通过比较，所有我测试过的FHSS系统确表现出它们继续工作的能力，尽管在80%的频道都已经被干扰的饱合了只剩一小部分是可用的。
因此，理论上和实践上，一个好的FHSS系统将仍保持更持久的工作而许多2-频道DSSS系统已经失锁掉了。
不过，这并不是全部的理由。
因为FHSS系统利用很多（或全部）频道，会产生这样一种情况，即它可以出现被影响的情况而DSSS系统则不会被影响。
这种情况时常会发生，即频带被严重的堵塞只剩下一小部分，而DSSS系统正好选择工作在这部分频带上。DSSS的信号正好工作在频道的干净部分，提供无故障的通联，这时FHSS则失去了大部分好数据变成了噪声，因为它要在干扰中跳频。
经验证明这种情况远不如相反的情况容易发生，DSSS系统掉了，而FHSS仍能保持有效的控制。
如果你考查一下大型轶事，比如SEFF和Joe Nall，这已经成为事实，在那些会场上出现的失控“炸机事件”与Spektrum DSSS控有关要比其它品牌FHSS的多远去了。
而且，这也上非常清楚的事实，即在非常噪杂的环境中DSSS系统的冗余比FHSS系统差，Spektrum/JR（它们是DSSS的）的失锁现象比起FASST和其它的跳频系统更是家常便饭。
我确定地平线（品牌）说过“有上百的DSM2（DSSS）系统在这些比赛大会上仅有非常少数不出现无线电事件”——我问过他们，回答是“我发现的DSM2（DSSS）的缺陷都以相同的规律发生——是不是这种炸机都与这个缺陷有关？”。

底线

它打击了我，因为2.4GHz频带被遥控飞手弄得非常的拥挤，大量与DSSS飞手遭遇的有关的问题似乎不成比例地与大量这样的系统同时使用有关。
理论已经清楚了，连续的灵巧系统（FHSS）应该是对带内噪声干扰更能很快复原的，这似乎是从实践中诞生的。
如果你已经有了一个DSSS系统并且没有任何问题，你不必冲出去把它换成FHSS，因为在理论和实践FHSS在小的水平上提供多一点的保险。
不过，你正想购买一套新的遥控系统，在提交给DSSSS系统之前仔细想想FHSS将带来的益处，DSSS是一个在RC界很快就会失宠的系统（甚至JR正在世界其它地方转向FHSS）。
如果你偏要选择一个DSSS系统，好吧，你要选择一个至少3个以上的不同频率的系统。这将给你最大的频带利用和减少被干扰而导致失控保护的机会。
切记！——在保证2.4GHz的可靠使用上有更多的比在DSSS与FHSS间选择还重要的事情要做。你要选择好的电池（A123定律）再加上良好的安装接收机的天线以和良好的布线和布置其它金属部分。

FHSS与DSSS优劣比较的视频
 
Which one is better? interference 
谁更好？干扰
图中大致意思是——左为FHSS（下面的代表厂家有Airtronics、Futaba），右为DSSS（代表厂家有Spektrum、Radio Post）。都位于2.4301-204302GHz频带上，里面分了10个频道。FHSS有3个频道同时发送，但下一时刻这3个频道会跳到别的3个频道上，这3个频道随机的跳。DSSS10个频道同时发送相同的信号。当有一个频道上有固定的干扰（红色）时，DSSS将无法避免地要接收到这个信号，因为它必须同时接收这10个频道。而FHSS此时刻3个频道里接收到了这个干扰，但下一时刻有机会跳到别的3个没有干扰的频道上，这样的机会至少有7个频道。所以，当某个环境有干扰时DSSS不行了，FHSS还有机会。所以FHSS更好。

Distance?
距离？
图中两种设备都是发射100mW功率。DSSS以10个频道同时发射，每个频道只有10mW。而FHSS只以3个频道发射，每个频道33.3mW，所以可以发射更远的距离。

Price?
FHSS便宜。

最后，Futaba（中间）将两者的优点结合在一起，有了它家的FASST。