BaldEagel

The problem with locking onto two channels is they could be adjacent in which case the interferance does not have to be over the whole band to lock you out.

Mike

siddus74

I found this video and the others in his collection very informative ... I made my decision on my radio on many factors, but this info sure helped.

[youtube]http://www.youtube.com/watch?v=Vy7Gg6Tj57Q[/youtube]

[link=http://www.youtube.com/watch?v=Vy7Gg6Tj57Q]http://www.youtube.com/watch?v=Vy7Gg6Tj57Q[/link]

Scott.

luv2flyrc

My Feedback: (6)

Although I appreciate what you are suggesting is possible, it is still highly improbable.

If you had the worst luck on the planet, your radio may pick two adjacent channels , then you may encounter interference that wipes them both out at the same time yet, leaves the rest of the band open for everyone else.

The combined chances of it happening are so low that it makes both the 2 channel system and the hopping system equally safe from a stats perspective.

Where the hopping system has an advantage is in the possible # of users and this is what JR/spektrum has stated is the advantage of the DSMX system.

A system that locks onto 2 channels is limited to 40 users when there are 80 channels available. The frequency hopping system can accommodate more users as they all roll across the band in a random order there is again (statistically) less chance of conflict but, it only has its advantages when there are many users.

Mike

DominicM

Only if it has a CE mark on the back.

rhklenke

My Feedback: (24)

This is an old, old discussion, but what you are saying is not the case, a DSM2-type system can support more than 40 users because each user only uses the channels for a short period of time. Two DSM2-type systems can co-exist locked onto the same two channels. More than 40 DSM2 users can operate safely at the same time. This has been shown and proven.

Also, it *has* been shown that locking onto two channels that are closely spaced does happen quite often with DSM2, and there *are* disadvantages to that happening even in the face of no broad-band interference sources. That being said, it *is* possible for an interferer, such as a 2.4 GHz FM video transmitter, to wipe out two closely spaced DSM2 channels simultaneously, but in spite of what the proponents say, that is *not* the major disadvantage of the DSM2/DSMX systems...

Bob

luv2flyrc

My Feedback: (6)

Bob, I agree with what you have stated regarding channel usage although, in theory at least, my understanding is the RF should not transmit unless there are two free channels available as it looks for open channels before it turns on. Is this not the case?

I have checked my own 12X a variety of times with a 2.4 scanner, certainly not every time I've used it but, I have yet to have it pick two channels that I would consider even remotely close together.

Mike

rhklenke

My Feedback: (24)

This is a quote from one of Cal Orr's (FlyRC) early articles on DMS2:

There is anecdotal evidence from many flyins like Joe Nall and IRCHA in the old days when DSM2 was the only thing out there, that it would ,in fact, work with more than 40 transmitters on.

Its probably likely that they have changed the firmware to avoid the "two closely spaced frequencies" problem, but you can see evidence of it here:

http://www.rcmodelreviews.com/dsm2flaw.shtml

and we saw it enough in the field with the DSM2 stuff we were using on a UAV project that we added checking (with a spectrum analyzer) the output frequencies and rebooting the TX if it happened, to the pre-flight checklist...

Bob

BaldEagel

"There is anecdotal evidence from many flyins like Joe Nall and IRCHA in the old days when DSM2 was the only thing out there, that it would ,in fact, work with more than 40 transmitters on.

Its probably likely that they have changed the firmware to avoid the "two closely spaced frequencies" problem, but you can see evidence of it here:

http://www.rcmodelreviews.com/dsm2flaw.shtml

and we saw it enough in the field with the DSM2 stuff we were using on a UAV project that we added checking (with a spectrum analyzer) the output frequencies and rebooting the TX if it happened, to the pre-flight checklist...

"Anecdotes" and "Probably likeley" is not reassuring in any way.

Mike

Selleri

Well on the bottom it did but it fell off last fall... [:@]