900 MHz or 2.4 GHz what is better - Page 5 - RC Groups
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Nov 19, 2017, 11:44 AM
Thermals, Tom
RyanNX211's Avatar
Jim:
That hasn't been my experience. While I can affirm that XPS will operate down to the lowest voltage and easily has the best range, interference is possible and I've had to remove the Nano from two aircraft. I have been unable to interfere with either Futaba FASST or FHSS.

Spektrum and FrSky are the absolute easiest to screw with. Spektrum also had voltage issues.

I have no first hand experience with HiTec because I've only used my A9 with an XPS module. Friends on the west coast report no issues with Airtronics.

I have some videos I can post and could make some more under controlled conditions.

What's ACKS?
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Nov 19, 2017, 04:32 PM
Like I said, Futaba/FrSky/Hitec all use the exact same over-air protocol. You could have a single receiver compatible with all 3. Likewise, XPS/JETI/JR DMSS are all the same. Spektrum is the only one using their over-air protocol.

ACKs are acknowledgements. The XtremeLink system is the only system on the market that requires that the reciever send a response to the transmitter. If the transmitter doesn't get an ACK (acknowledgement) from the reciever within 862us of the data being sent, the transmitter will automatically re-send the packet. That repeats until either the receiver response gets through or the next frame occurs, at which point the new data will be used.
Last edited by JimDrew; Nov 19, 2017 at 04:37 PM.
Nov 19, 2017, 06:38 PM
Registered User
Sounds like frequency hopping to me .....
Nov 19, 2017, 11:15 PM
No, this is in addition to the frequency hopping.
Nov 21, 2017, 07:40 AM
Thermals, Tom
RyanNX211's Avatar
There are many under appreciated benefits to XPS
Apr 14, 2018, 02:41 AM
Registered User

pissing contest about 900 mhz


yall need to drink some more lemonade. you gotta be low on piss by now.
Apr 16, 2018, 02:46 PM
Registered User
Quote:
Originally Posted by JimDrew
Like I said, Futaba/FrSky/Hitec all use the exact same over-air protocol. You could have a single receiver compatible with all 3. Likewise, XPS/JETI/JR DMSS are all the same. Spektrum is the only one using their over-air protocol.

ACKs are acknowledgements. The XtremeLink system is the only system on the market that requires that the reciever send a response to the transmitter. If the transmitter doesn't get an ACK (acknowledgement) from the reciever within 862us of the data being sent, the transmitter will automatically re-send the packet. That repeats until either the receiver response gets through or the next frame occurs, at which point the new data will be used.
How do you do that and stay in FCC limits.

I know how the channel power levels are sent on Jeti TX. It is based on the transmit period for a packet, and the frequency of packets and the number of hops and the channels are tuned so that the average power over a period is below some limit set by FCC. If jeti TX doesn't get an ACK packet back from RX, its not allow to send extra packets, as increasing the frequency would push the average transmit power over the spec. How do you get around this?
Apr 16, 2018, 10:06 PM
The average power is well within the FCC requirement. The ACK is a standard parts of all XBee modules. You can look at the FCC info for their module.
Apr 16, 2018, 10:26 PM
Registered User
Quote:
Originally Posted by JimDrew
The average power is well within the FCC requirement. The ACK is a standard parts of all XBee modules. You can look at the FCC info for their module.
So you must have the TX module running at detuned to lower power levels than would be the limiting values for the your packet period and packet frequency. IE you run with head room, not at max power continuous, so your retries do not push the average over the FCC limits.

Xbee modules aren't fixed power. If you alter the power levels or packet time or packet frequency, its not necessarily valid under the XBee FCC license. The end user device must comply with FCC. So your unit(s) don't run under your own FCC license?
Apr 16, 2018, 11:16 PM
Our transmitter modules use the singular modular certification that the XBee module provides. Our receivers and RFU have their own certifications and you can see within that FCC information the duty cycle vs. power output requirements. The XBee module is similar and runs custom firmware that was provided by Digi for our application that handles the power output and fast hopping sequence, changing the power output as necessary based on transmission frame rate.
Last edited by JimDrew; Apr 16, 2018 at 11:23 PM.


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