NormS
Posts: 36
Score: 100
Joined: 6/15/2006
Last Login: 11/7/2009
From: Hopkinton,
MA, USA
Status: offline
|
quote:
ORIGINAL: Mike Sieniarecki
Mike, I think everyone agrees that DSSS and FHSS systems work well with each other once they are up and running, but I have read on other forums that frequency hopping systems like Futaba's interfere with Spektrum's ability to find two clear channels and link up the transmitter and the receiver at startup. I have no idea if this is fact or rumor; can you please specifically address this issue?. BTW, if it helps, Futaba's announcement says that their system hops every 2mS. If it uses all 160 channels, does this mean that on average, once every 160mS a single Futaba system will "hit" a Spektrum system on one of its two channels?
Thanks a lot.
quote:
NormS,
I’m not sure this is a true rumor; however, I do think sometimes by simply asking the question, it can create unclear answers until someone can help educate on the issue. So, in this case, I will speak to the Spektrum side of the issue to hep clear up the uncertianty.
When the Spektrum radio is turned on, it searches the 80 available channels. As we know Spektrum allocates two of those 80 channels for redundancy. If the scan sees any one of the 80 in use (say a Futaba system or other for example), it will continue to scan until it finds two dedicated, unused channels. If the system is unable to find two dedicated, unused channels when turned on, it will not transmit until two become available. So in essence, the answer specifically to your question is no, there will not be interference from Futaba or other with the Spektrum system.
One more note on this issue, if an FHSS system hops to a Spektrum dedicated channel for the stated 2mS, the signal will not have Spektrum’s patented Global Unique Identifier (GUID) which is required by the receiver to operate; this virtually eliminates the chance of a stray signal from interfering with the Spektrum system.
Does this help, or did I make it more confusing LOL?
Mike, please understand that I have no axe to grind here, I'm simply looking for information. In that regard, your response has helped me understand how the things work, and I guess that the worst thing that should happen is that a Spektrum system may take a little longer to sync up in the presence of hopping systems, but only if it happens to be checking a channel that a Futaba system has hopped on to, and only if it sees the collision as interference.
Concerning the GUID business, I'm sure that the unique ID code will keep a receiver from responding to a non-errored frame from a different transmitter. The question, however, is what happens if someone hops on to one of the Spektrum's channels, and I think the answer is simple radio theory: they will interfere with each other on the RF level to an extent dependent on the relative signals strengths of the two signals at the receiver(s); both transmit frames are likely to be affected. This is the way radio transmission works, regardless of the frequency or modulation (AM, FM, PM, etc). However, this should not be a big deal because it sounds like the Spektrum system will ignore the bad frame and probably just use the good frame from its second channel. The hopping system may or may not lose a frame, depending on how many bits it lost and the amount of foward error correction it has. Some might consider Spektrum to be a more robust solution, but this comes at the expense of higher bandwidth utilization.
Thanks a lot.
Norm S
Hide Signatures
|
Search This Thread
Printable Version
All Forums >> Radios, Batteries, Clubhouse and more >> RC Radios, Transmitters, Receivers, Servos, gyros >> RE: Spektrum DSM2 2.4Ghz modules for Futaba and JR announced 
RE: Spektrum DSM2 2.4Ghz modules for Futaba and JR anno... - 
