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« on: July 18, 2011, 01:54:30 AM »
PankajC
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Guys,

I was looking at various radios and there were terms like FHSS and FASST (Futaba), DMSS, DSMX and DSM2 (JR/Spektrum), AFHSS (HiTec), FHSS-3 (Sanwa)
Each tries to claim that their radio is better protected against interferences, but this is all Greek to me.

Can anyone explain in plain terms as to what they mean and how or in what circumstances one is preferred over the other?

Pankaj
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« Reply #1 on: July 18, 2011, 08:35:27 PM »
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Seems like no one has noticed this thread
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« Reply #2 on: July 18, 2011, 08:43:50 PM »
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I am not sure anyone has done the comparison you have asked for.  The merits of some of these were discussed to death in some earlier threads.

In summary, it is clear that "frequency hopping" is the way to go, and the only one that does not hop is DSM2.  JR/Spektrum is now jumping on the frequency hopping bandwagon with their DSM-J and DSMX systems.  Having said this, there are thousands who are flying with their DSM2 systems, without any issues.
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« Reply #3 on: July 18, 2011, 09:09:51 PM »
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So, to a dummy like me, are these jargons just fancy names for frequency hopping?
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« Reply #4 on: July 19, 2011, 12:27:43 AM »
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Same here I want to know about this radio jargaon. which is the radio to go for.
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« Reply #5 on: July 19, 2011, 08:43:35 AM »
anwar
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So, to a dummy like me, are these jargons just fancy names for frequency hopping?

There are differences in encoding schemes, number of hops in a given amount of time etc.  It is like many other things... how many types of diesel engines are there now ?  Do we really know/care about the details how CRDI engines work differently from others... etc etc.

From what I saw in US forums etc, Sanwa/Airtronics has the lead in terms of reliability. And DSM2 was rated the least, as become evident later on when it was replaced with DSMX and DSM-J.  It is important to remember that the "problem"s associated with any of these brands and even others like the Turnigy/FlySky 9X, purely based on radio links themselves, are few and rare. There may be material and build quality issues with some of the cheaper / non-premium brands, so a premium brand is recommended if your are flying a really costly model.  If you are flying smaller models, pretty much any radio would work just fine.
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« Reply #6 on: July 19, 2011, 12:46:41 PM »
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thanks Anwar, so for now, Ill stick to my dsm2 till I learn to fly properly
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« Reply #7 on: July 19, 2011, 01:43:36 PM »
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did some googling on the problems related to Spektrum's DSM2. It turns of that the technology was designed for a max of 40 2.4GHz radios to be 'on' simultaneously. Now I don't know how many fields in India would be having 40 pilots at the same time.

So for most of us this talk of interference is theory rather than a problem

 
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« Reply #8 on: July 19, 2011, 04:32:11 PM »
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There have been many issues with DSM2 lately, which were reported by me on this forum.

http://publications.horizonhobby.com/read/archive?id=3714

You can go read some gyan on 2.4 ghz radio tech here:

http://www.rcmodelreviews.com/spreadspectrum01.shtml

Hope it helps.



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« Reply #9 on: July 19, 2011, 08:01:19 PM »
anwar
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So for most of us this talk of interference is theory rather than a problem

Not really.  DSM2 is said to have a higher number of "unexplained crash" issues (per US forums).  Some others who made their research before getting a new radio have also noticed this :

http://www.rcindia.org/for-sale/futaba-14-ch-rx/ (see reply #13 from Sushil bhai).

For more DSM2 discussion, see this :

http://www.rcindia.org/radios-and-receivers/jr-going-completely-fhss-parting-with-spektrum-dsm-dsss/

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« Reply #10 on: July 20, 2011, 01:23:34 PM »
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See the way i see it is that while 2.4GHz systems by themselves are pretty reliable, but the choice of technique to shield from interference is still evolving.

Agreed, lot has been said and discussed on the US forums on the unreliability of the DSM2 systems. But, if we consider where we fly (in open deserted places) and how many of us fly at a time (max 4-5 birds up at a time).

With all the members present in this forum, I do not think anyone has reported a crash or a signal lockout using any of the 2.4 systems. This is primarily we have fewer planes than the US. In such a situation, the chances of interference would negligible - further in our weekend flying type of situations, it would not matter even if the Tx did not 'hop'.

Having said that, I don;t think any one with an expensive setup or in a competitive environment would even think of going in for a system that had some negative comments.

Hence my claim that for most of us, this problem is more of theoretical  importance was meant for newbies like myself and not at the pros around.


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« Reply #11 on: July 20, 2011, 03:14:24 PM »
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I have witnessed several lockouts on Spektrum, JR and Futaba. One of them was a jet that meant a write off of several lakhs.

Few and far between but there, nevertheless.
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« Reply #12 on: July 20, 2011, 03:54:26 PM »
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I take back my words on not being reported on this forum :-)

But then I take it the jet in question was not using DSM2 right? must have been one of the 'more' reliable brands. Is so then the question of reliability is still an issue :-)
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« Reply #13 on: July 20, 2011, 08:37:19 PM »
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Hence my claim that for most of us, this problem is more of theoretical  importance was meant for newbies like myself and not at the pros around.

Yes, it is rare.  But it is not theoretical at all.  It is because it is practical that DSM2 was replaced.

http://www.rcmodelreviews.com/dsm2flaw.shtml
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« Reply #14 on: July 24, 2011, 05:06:57 PM »
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Friends...understanding the phenomena about the radio is simple..and interesting..as mentioned in the question, many companies write some tough words on their systems...for example you can see on 2.4 Futaba radio as FASST...means nothing but Futaba's Advanced Spread Spectrum technology...oh...SST...!!!  some magic..Huh?   nothing...SST means a comparatively new technology for the radio propagation.previously, we were using the radio waves in to Mega Hertz range.as country develops our government determined some frequency for the use of National Radio transmission,(radio and TV broad castings) ,police, military, and air traffic, etc..etc...so some frequencies were reserved for these purposes...so, some were also reserved for hobby purpose, while some are kept for HAM Radio.

working principle of a radio transceiver is simple.there are many tranreceiving are exists...means principle...basically a whole system holds a transmitter and a receiver.. Tx always transmit a particular frequency here measured in Mega Hertz,Mhz, to the periphery..and a Rx will receives this signal through an antenna..we can consider this signal as a carrier wave...
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« Reply #15 on: July 24, 2011, 05:15:32 PM »
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so whenever we switches on our radio set,a carrier wave will emits from the antenna of the TX..so the receiver will energized..you may notice one thing that while we connecting a radio set to our crafts...at initial stage servos of our crafts may some where...when we switches on our RX and TX you can see an instant relocation of the servos that showing the Rx is receiving the guide signal, or carrier...then none of the servos will move until we gives any stick input..
so, servo arm will move only up to stick inputs...whats happening here means, the RX already getting a carrier signal to it so it will be in a ready mode to respond for the next SIGNAL....through the carrier wave, or within the carrier wave..more clearly, imagine you are using a radio set with 27 .145 Mhz..carrier . if so whenever we switches on the TX a 27.145 Mhz carrier signal will be switched on...its only a CARRIER...then whenever we gives a stick input, an other mode of signal is transmitted in to the air, within the CARRIER wave, may be anything from an AUDIO CODE, to any other RADIO CODE....
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« Reply #16 on: July 24, 2011, 05:21:56 PM »
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for an example we can go for an other thing. suppose, that i am sending a letter to Anwar Sab..i will post it from my Vatakara post office...then the postal department takes this letter to Anwar Sab, may be to Bahrain.so here we can consider here me as the OPERATOR. (holding the TX). and postal department as a CARRIER, who carries the letter to destination..and usually no one can interfere the department.then we can consider Anwar Sab as receiver..but still we do not know that what is the content of the letter...only two of them are aware of that..me, the (OPERATOR, or TRANSMITER, and Anwar Sab, or RECEIVER..) after getting the letter in to the hand, Anwar Sab will read the matter and will do the desired actions.  just like that a Radio Carrier only carries a particular waveform to a particular destination...
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« Reply #17 on: July 24, 2011, 05:29:12 PM »
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one of the great dis advantages of the Mhz based radio is disturbances..we know our earth is constantly interrupted by many radio disturbances..like SAW..surface acoustic waves..such disturbances can also disturbs our set ups, that you can here in a normal radio reception. for an example, you can hear kirr kirrrr noise from our radio, while lightning happens.so, here it is not a problem as we are not doing anything as critical with radio. but in an RC flying, such disturbances can make a fatal crash, by altering servo setups for some fractions of a second..secondly, a same frequency also affects the system violently, that we can consider it as radio jamming or radio interrupting..

use of the radio reached in its peak in WW2..each and every country were trying to break the sending massages each other, and each and every one was trying to develop a fool proof system to send secret massages...so some extra ordinary technologies were born..for..RADIO PROPAGATION....
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« Reply #18 on: July 24, 2011, 05:45:52 PM »
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after many many innovations engineers reached a particular technology...was FH and DS  Frequency hoping and Spread code...its a vast science to say and under stand, but we can simply explain it as follows..instead of sending a simple carrier, a particular SPECTRUM or a CODE is transmitted from the TX. the receiver will be BINDED  (or PAIRED) with the TX oly to accept a particular code.when switched on, the TX will send a SPECTRUM of CODES all around, in 2.4 Ghz, and the receiver will receives all these codes but responds only for one CODE the PAIRED in BINDING proses.so none of any other disturbances never effect the system. one of the another advantage of using a Giga Hertz based system is the antenna size.all we know when frequency increases the size of the antenna decreases according to the radio principles...so Friends..buying a good radio is a must...but never consider the writings on a set..all new 2.4 Ghz sets are based on SST, or spread Spectrum Technology...there may be a slight difference in applications..but basic are same...
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