Why don't we have better radios? Don't we deserve it?

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Why don't we have better radios? Don't we deserve it?

Postby skyguy04 » Wed Jun 09, 2010 7:26 pm

I am curious why we continuously spend $100+ for receivers and over $1000 for transmitters, which have clearly demonstrated faults. We've got jets that scream at over 400mph. But many of those jet pilots still trust the name brand leaders. Result? A big ball of fire that luckily didn't kill anyone at Joe Nall. As consumers, it is our responsibility to demand better.

After listening to many different opinions about these technologies, I've got some questions...

DSM2...
Why must the receiver/transmitter stay locked on 2 channels? In the event a channel becomes "lost", why not switch to another open channel? Example: Video transmitter clobbers 1 channel. System detects that channel is busy and switches to a different channel. Ie. 2-way communication

Why does the system not use some logic to make sure channels are spaced apart sufficiently?

I'm going to ask this question because i hear it all the time, but i believe i understand the answer already...
It is a very common theory that blinking lights mean a "partial bind". There is plenty of documentation around the web that very clearly states that blinking lights simply mean a voltage drop has occurred. Ie. If you turn the receiver off and on without also turning the transmitter off and on, the lights will blink signalling a "voltage drop". Just to confirm, a bind while the lights are blinking is no worse than a bind with solid lights. Correct? You just won't be able take advantage of the voltage drop detection "feature".

If i'm wrong about the above... Why would the system allow a bind at all, if it were "partial"? And what exactly is a "partial bind"?

Futaba...
Hypothetically, what happens if 90% of the channels are full? Does it show sluggishness while it searches for an open channel to "hop" to? Or, does using multiple channels at a time (all hopping) solve any sluggishness that might be perceived?

If the new trend in radio technology is to use MORE channels at the same time, won't that just cause MORE interference in the long run? Is it just me, or do others think these systems should be smarter? It seems perfectly logical to me that a radio system should be able to lock on to 2 or 3 (at most) channels at a time, and then only change frequencies when a channel is lost. I'm no radio expert, but it seems like this would be better than any of the options out there today.

Your thoughts?
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Re: Why don't we have better radios? Don't we deserve it?

Postby skyguy04 » Wed Jun 09, 2010 8:39 pm

Hmm... could this be a better solution?

http://en.wikipedia.org/wiki/Cognitive_radio
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Re: Why don't we have better radios? Don't we deserve it?

Postby RCModelReviews » Wed Jun 09, 2010 11:30 pm

skyguy04 wrote:I am curious why we continuously spend $100+ for receivers and over $1000 for transmitters, which have clearly demonstrated faults.

Because some companies spend a *lot* of money convincing us that there's value associated with their brands. That money has to be recovered from somewhere so it ends up significantly hiking the price of the products involved.

I guess that when i started RCModelReviews I could have jumped on the "payola" bandwagon and published only rave reviews of brand-name products -- thereby pocketing a small fortune in advertising.

Or, I could have accepted money to have negative comments and reviews carefully removed (ever noticed that there's *NO* mention of the new HK Orange DSM2 receivers on RC Universe's RC forum?).

Instead, I decided it was time people learned how products perform based solely on that performance and nothing more.

DSM2...
Why must the receiver/transmitter stay locked on 2 channels? In the event a channel becomes "lost", why not switch to another open channel? Example: Video transmitter clobbers 1 channel. System detects that channel is busy and switches to a different channel. Ie. 2-way communication

Why does the system not use some logic to make sure channels are spaced apart sufficiently?

You have to remember that DSM was the first to market and, at the time, Spektrum designed their system to be as good as they could make it, given the limitations of the technology and the price/performance ratio the market would accept.

It's now several years since DSM was introduced and technology has moved on markedly. It's now possible to deliver vastly superior frequency-hopping solutions at much lower prices but Spektrum has opted (quite sensibly from a commercial perspective) to stick with their original system and thus retain backwards compatibility with all the earlier equipment they've sold.

As a result, there's nothing wrong with continuing to use Spektrum if you're already a user but if you're just making the jump to 2.4GHz there really are much better (more modern, cheaper, higher-performance) systems available today. Why buy into technology from a previous decade when you don't have to?

If i'm wrong about the above... Why would the system allow a bind at all, if it were "partial"? And what exactly is a "partial bind"?

I have no idea.

Futaba...
Hypothetically, what happens if 90% of the channels are full? Does it show sluggishness while it searches for an open channel to "hop" to? Or, does using multiple channels at a time (all hopping) solve any sluggishness that might be perceived?

Futaba doesn't "search for an open channel to hop to" -- it hops blindly. If a channel is noisy it still transmits on it and chances are that part of the data will be lost -- but it doesn't really matter unless almost the whole band is really filled with high noise levels. Most 2.4GHz systems send the data for each frame more than once -- so that any data missing from the first transmission will be filled in by the second (or third).

In the case of a FHSS system, this means that the effect of noise on the band is far more progressive than with a fixed-frequency DSSS system. A FHSS system will become increasingly sluggish before it stops altogether as you wind up the noise on the band. A DSSS system will usually just go into lockout with little or no warning, and then you're stuffed.

If the new trend in radio technology is to use MORE channels at the same time, won't that just cause MORE interference in the long run? Is it just me, or do others think these systems should be smarter? It seems perfectly logical to me that a radio system should be able to lock on to 2 or 3 (at most) channels at a time, and then only change frequencies when a channel is lost. I'm no radio expert, but it seems like this would be better than any of the options out there today.

The problem with locking onto fixed channels and switching only when interference appears is that, once the link between transmitter and receiver is lost (ie: the fixed channels are overwhelmed by noise) there's no way for the ends to re-negotiate another set of frequencies. They can try to use pre-set alternatives but if they're also filled with noise you're stuffed. And, the longer it takes for the transmitter and receiver to "find each other", the more time you're going to be in "lockout".

The current FHSS systems are probably the best solution because unless the band is totally obliterated by noise, they'll always provide at least some measure of control. ie: if the band is 90% filled with noise, then you'll probably end up getting 3-4 full frames of data through each second. That will mean your controls will be slow and laggy but they *will* still work. Anyone who doesn't land at the first sign of such sluggishness deserves to crash anyway :-)
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Re: Why don't we have better radios? Don't we deserve it?

Postby skyguy04 » Thu Jun 10, 2010 2:56 am

Thanks for the very detailed response! As always. I am really growing to love this site and find myself checking it regularly every day. Can't wait for your DSMJ review.


The problem with locking onto fixed channels and switching only when interference appears is that, once the link between transmitter and receiver is lost (ie: the fixed channels are overwhelmed by noise) there's no way for the ends to re-negotiate another set of frequencies. They can try to use pre-set alternatives but if they're also filled with noise you're stuffed. And, the longer it takes for the transmitter and receiver to "find each other", the more time you're going to be in "lockout".


I only have one question/comment from what you mentioned above...

I wasn't really talking about "lockout". If 1 channel has to re-negotiate, the other channel is still operating. Or is that not possible? Even if it's sluggish, it's still better than waiting for the channel to free up. Also, if it's too sluggish...3 channels would solve that. If any one must re-negotiate, there are still 2 good channels to transmit on. Would this not be superior? Is it possible?
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Re: Why don't we have better radios? Don't we deserve it?

Postby RCModelReviews » Thu Jun 10, 2010 4:10 am

Yes, if there was a channel still operative then you could renegotiate -- but given how well the FHSS system works I think that KISS is a better approach. The more complex you make things, the more chances there are for something to go wrong and the more expensive things get.

For example, with an FHSS system, the only time it will totally stop working is if more than 90% of the band is hit by extremely strong noise.

If you have the adaptive DSSS system you suggest and all three channels happen to get hit by noise that may still only saturate 60% of the band -- that system is going to fail because it won't be able to renegotiate working frequencies due to the total loss of link. Meantime, the FHSS system will keep on working.

Glad you like the site and yes, I can't wait to see how the DSMJ system performs.
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Re: Why don't we have better radios? Don't we deserve it?

Postby Toumal » Fri Jun 11, 2010 6:50 pm

skyguy04, the sad fact is that RC radio makers have not researched what's "out there". I'm professionally involved in the aviation industry, and stuff like VDL Mode 4 (http://en.wikipedia.org/wiki/Self-Organ ... ple_Access) et al.

There are plenty of well-established standards out there that go beyond the simple distinction between FHSS and DSSS, and some of them are actually designed to evade a deliberate interference. Yes it's true that the 2.4 band is smaller than what's usable by many airborne communication systems, but my point remains that there's a lot of blind faith going on in our hobby.

"Surely selecting two different channels will be enough..."



One thing I believe is important to keep in mind is the actual bandwidth that we RC modelers need - it's ridiculously tiny! We're literally sending little drops through a massive pipeline. Actual experience has shown that it takes a LOT of drops to flood that pipe. What was the practical record so far? 100 TX? 150? Something like that.
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