Review: Corona 2.4GHz DSSS module and receiver (Part 2)

PUTTING THINGS TO THE TEST

The first and most obvious thing to check was exactly how the Corona DSSS system makes use of the 2.4GHz band. To do this I fired up the recently-reviewed WiSpy 2.4i spectrum analyzer and got this pretty picture:

It is immediately apparent that this system actually uses three parts of the band (strangely similar to the FlyDream 2.4 which claims frequency-hopping).

This is good, very good. In effect, the Corona DSSS system is a bit like the Spektrum DSM2 system on steroids. Whereas Spektrum uses two separate parts of the band, Corona is using three -- in theory offering up to a 50% potential improvement in interference resistance, nice!

Compare this to the much more limited use of the band that the cheaper FlySky 2.4 system offers and you can see that the Corona is a better choice in environments where interference might otherwise be an issue.

My only concern with the DSSS transmitter module (as with the FHSS one) is the amount of heat generated internally when run on a transmitter which uses an 8-cell battery. The module itself gets quite warm in such cases and things get even worse when a 3-cell lipo is used for the transmitter battery.

The life and reliability of electronic components is adversely impacted by excessive heat and I'm a little concerned at that the fact these modules might be wasting over three-quarters of a watt of electrical energy as heat. An extended flying session in the middle of the day during a hot summer might really be pushing things to the limits in some cases.

The module did run much cooler in my modified FlySky/iMax 9X however, thanks to the 2S lithium-ion battery pack. Yet, in my JR9XII/9303 with an 8-cell NiMH pack, it got decidedly warm to the touch after 15 minutes operation.

And now to the receivers.

These are nice, end-pin units which appear well designed and constructed.

The very long link-time (as much as 8-9 seconds) did concern me a little though.

If these receivers had problems with brownouts then such a long link-time could be disastrous, just as with the early Spektrum equipment.

I was extremely pleased, and somewhat relieved, to find that the Corona DSSS receivers perform incredibly well under low-voltage/brownout conditions. When I performed my usual test of slowly reducing the receiver voltage until the receiver LED was extinguished and the servos no longer responded to the sticks, the Corona just kept going, right down to an incredible 2.25V.

At this stage the servos themselves were quitting due to a lack of voltage but the receiver recovered instantly as soon as the voltage went back up to 2.35V. What does this mean?

Well the Corona is very resilient to fluctuations in the battery/BEC voltage.

Chances are that in a low-voltage situation, your servos will stop working before the Corona DSSS receiver does and, when the voltage is restored, you'll get control back almost immediately.

In fact, so far the Corona DSSS system has the best brownout performance of any receiver tested and I believe it's on a par with that of the Futaba FASST receivers (to be tested in an upcoming review).

Corona claim that the range of the system is 1.5Kms, a figure that I would consider to be conservative in the situation where the model is actually flying and the transmitter is held by a pilot on the ground. I will be doing some carefully conducted simulated range tests with all the systems I test in the very near future but I know that no range issues have been experienced during test-flying, despite taking models to the limits of reasonable visibility (around 1km or so).

FHSS/DSSS, why so different?

I wont mince words, Corona's FHSS system was a huge disappointment, so how come I'm so enthusiastic about their DSSS system?

Well there are a number of very good reasons why the FHSS system sucks.

They're using a chipset that has bugs and the onboard processor seems to be running out of power trying to keep everything coordinated.

The DSSS system however, is a whole lot less stressed and doesn't push the RF chipsets hard enough that the bugs become an issue. In short, they've kept it simple and that's paid big dividends.

The result is a module-based 2.4GHz system that is pretty damned good. At last Corona have scored a well-deserved goal with this system.

In fact, it would be almost perfect -- except for one thing...

There's no useful user-set failsafe system.

If Corona's DSSS system did have user-set failsafes, I'd be converting my existing PCM systems to it tomorrow. Unfortunately, it's just reckless (and in some countries *illegal*) to fly large, fast and jet-powered models without a failsafe facility in your RC system.

If I could get Corona to make one change, it would be to respond like FlyDream have promised to and implement a simple but effective user-definable set of failsafe permanently memorized positions for the servo-outputs.

However, for the vast majority of fliers, the lack of failsafe won't be an issue -- after all, we flew for decades on FM receivers that offered no failsafe either.

Summary

At last, I've got something amongst the pile of "dud" Corona products that I've been accumulating under my bench, which actually works, and works damned well.

By keeping it simple and delivering a solid, robust, smooth, module-based system, Corona have finally come up with a really competitive option for those wanting to move from FM/PCM spread spectrum on 2.4Ghz, without breaking the bank.

I had a sneaking suspicion that Corona may have gotten this product right when they offered a sample for review (manufacturers have to be pretty sure of their products to send them to RCModelReviews).

Given the current state of development, the Corona DSSS is perhaps the best Chinese-made 2.4GHz module-based system I've tested so far (Note: I'm about to test some more products due to QC concerns that have appeared since this review was originally written). I'd be happy to switch to Corona's DSSS system for all but my largest and fastest models. What's more, if they added failsafe, I'd even use it in my jets and gasers.

Pro's:

• It works! (although some users report issues)
• Triple frequency use offers a robust link
• A good range of receivers
• Excellent resilience to brownouts/reboots
• Futaba module works equally well in Hitec radios

Con's:

• Module gets hot, especially with a 3S lipo
• No useful failsafe capability
• Some users have reported problems -- I'm investigating

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