XPS installation

[Bobs]

I just installed an XPS receiver in my Intrepid gasser and mounted it on top of the battery pack using quarter-inch foam to isolate it from the battery itself. This is the same location as the old receiver, however, the XPS instructions say to mount the receiver two inches away from any metal, wires, servos, carbon fiber, batteries, etc. Just curious if anyone else mounted their XPS receivers any differently than this. On top of the battery pack seems to be the only possible location. Thanks.

[MarkWebber]

You'll be the first I've heard of on an Intrepid gas. I'm interested to know how it works out. I'm looking at their system, also.

[Bobs]

Mark, I did fly it yesterday and it performed flawlessly. Check my gallery, I'll post a couple pictures of the installation. I also have a newly built Spectra G that I installed an XPS receiver in but have not flown it yet (see gallery).

[MarkWebber]

Interesting. My only concern would be shadowing it behind the engine at high altitudes for AP. I'm a fan of redundancy and would like the second antenna that some other systems use but I've been hearing good things about XPS. So far, I've not read complaints about signal shadowing.

[flyingrhino]

I was thinking about the XPS for my EB also. I'm torn between the XPS, waiting for the JR 9303 coming out next month, or waiting for the XPS 900 mhz to come out as Mark suggested.

[rccardude04]

900MHz should give better range, no?
-Eric

[MarkWebber]

Is that not how it works, longer wave lengths travel farther for a given power level?

[rccardude04]

That's how I understand it :)
Was just making sure :D
-Eric

[kgfly]

Mark,

XPS allows you to connect up to 255 satellite Rx if you want antenna diversity/redundancy.

Theoretically 900MHz has more range but since you get between 5000ft and 25000ft with the 2.4 I doubt range will be a problem. The real benefit of 900Mhz is lack of shadowing and reduced multipath affects.

It does seem a good idea to separate your video downlink and R/C between 900MHz and 2.4Ghz, but it's not clear to me which gets most advantage from each band. Probably doesn't matter too much, but I suspect range for the video would be more of an issue than for the R/C and hence might benefit more from 900MHz :dontknow

[MarkWebber]

Kenneth,

Range was not my concern. My reasoning for going with 900mhz was the reduction in shadowing and actually getting to fly at events, such as IRCHA. Even with 2.4, they are going to end up limiting the number of pilots that can be on at one time. I can't remember but doesn't one of the 2.4 manufacturers limit the number of systems that can be on at once to 20? Something like that. If I had 900mhz, I'd bet that would increase my odds of flying, greatly. Much like the 50mhz guys but without the HAM license. :D

[kgfly]

Mark,

Yes, Spektrum divide the ISM band into 79 1MHz channels and each Tx/Rx link uses two channels so there is a limit of 39 simultaneous users.

XPS divide the band into 12 5MHz channels but their system allows for 120 simultaneous users.

Futaba have not released any technical details nor have I seen a statement from them about the number of simultaneous users, but it would be safe to assume it is in the region of 20 to 100.

Of course although all these systems can happily coexist, you won't be able to reach the maximum number of parallel users on all systems at the same time. I imagine none of these limits will be a problem except perhaps at really large events. Although there is the question of Tx powered up in the pits/carpark (since they can be without risk of shootdowns) competing for airtime with those on the flightline. It is certainly going to be interesting to see how this pans out over the next year or two.

If XPS are the only ones to release a 900MHz R/C solution then indeed the users of that system will, at least initially, have similar 'clear air' advantages to those currently on ham FM frequencies. Of course it also depends somewhat on what other non-R/C users there are on that band.

[jrohland]

...Yes, Spektrum divide the ISM band into 79 1MHz channels and each Tx/Rx link uses two channels so there is a limit of 39 simultaneous users.
This tells only part of the story. In Spektrum, each transceiver pair has a unique ID. As such, there is no theoretical limit on how many systems can be on at the same time. It is true that only the fist 39 might get their own channel but, many more than that can operate simultaneously.

For example: Take a WiFi scanner into an apartment complex in any major city. You will find dozens of wireless Ethernet networks in operation on channel 1, 6 or 11. These can all work together because they are uniquely identified. In addition you will have 2.4GHz phones, Bluetooth, baby monitors and who knows what else.

Spektrum systems will not interfere with each other nor will they be interfered with by other 2.4GHz devices. The worst case is there may be many retransmits to get the packet through. This might, under extreme circumstances, cause a sluggish reaction between the controller and the aircraft.

Of course, if you have a 2.4GHz device right next to your transmitter of receiver the signal could be so strong as to cause problems. I've heard some folks have problems with Spektrum and 2.4GHz video on the same heli. When I fly with my Bluetooth cell phone earpiece in, I have to lean my head so the earpiece is closer to the phone if I am flying while on the phone or, I get static in the earpiece.

jrohland

[kgfly]

It is true that the unique IDs prevent an Rx from decoding a signal from anything except its bound Tx. All other transmissions in the band from any source look like noise.

I do not think it is correct that you can have more than 39 Spektrum systems operating at the same location, not according to Spektrum. When scanning the band during power-up I believe that the Spektrum Tx requires a very low noise threshold in a logical channel before it will deem it to be available for use. The presence of another Spektrum Tx in a channel will raise the noise floor enough for the channel to be deemed to be "in use". It is unknown how many FASST or XPS systems would have to be active before a Spektrum Tx would be unable to find two "clear" channels.

Note that the channelisation of the band is quite arbitrary. XPS for example divides it into 12 x 5MHz channels but can support up to 120 simultaneous users at the same location. There is no official information about FASST but some sources indicate 12 x 5MHz channels while others 32 x 2MHz.

It is true, and has been demonstrated by users, that multiple users of these various systems can all operate at the same location without any problems. The limits on the numbers in the mix are unknown so far and unlikely to be precisely determined any time soon.

It has also been clearly demonstrated that high-power/wideband 2.4GHz video downlinks can trash the band for all R/C systems which is a problem for some users. It is one reason XPS are bringing out a 900MHz version of their system.

[PaulH]

Read the president's note in this month's MA magazine. His way of handling the 2.4 GHz systems is for clubs to create a separate field for 2.4 GHz "park flyers" and leave the normal field to people with 72 MHz systems since those are "full range". :bomb:

[Bobs]

UPDATE: I have now flown over two gallons of fuel through both my Bergen and Spectra G with the XPS system and am happy to report that it works flawlessly in both.

[lperagallo]

Posted: Sat Jul 28, 2007 8:46 pm Post subject: Reply with quote Edit Delete

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Paulh,

That's for the park flyer systems that have shorter ranges. The Spektrum DX7, XPS, Fasst are full range radios and can fly happily with the 72mhz guys. The DX6 is a park flyer short range radio and receiver that does not use DSSM2.

Lou