Re: does anyone have OI and RC radio issues
 

I bet an update will come out soon saying that old radios will be allowed.:D

Re: does anyone have OI and RC radio issues
 

We were doing some testing tonight (finally!) and during the first 5 minutes our driver was driving backward, the bot kicked into high gear and started flying backward. the driver let go of the controls and the bot kept moving. Luckly, we were using a dead man's switch to cut the power and we were able to stop the bot and nobody got hurt (the bot survived as well). the RC antenna was not surrounded by any metal, there was a direct line of sight between the antennas and the distance was about 10' or so. We switched to last years antenna, and everything seems to be ok.

Re: does anyone have OI and RC radio issues
 

The RF decks in the eWave designed radios were made by Uniden, and those were no longer available. It is reasonable to conclude that the modules were made for consumer cordless phones, and products of that type. These are channelized, narrow bandwidth, analog FM full duplex transceivers operating as unlicensed devices in the 902-928MHz ISM band.

Re: does anyone have OI and RC radio issues
 

Dan, We did the same thing as well today. Everyone in the room 1 by 1 would call their voicemail with their cell phones. We noticed an interesting pattern, while my service ( Sprint ) never seemed to cause the robot to lose radio contact, EVERY SINGLE TIME a cingular or AT&T serviced cell phone was used the robot would immediately lose radio signal. We also found that each time the phone would reconnect with the towers to re-establish signal the robot would break the frequency.

My service is Sprint, and the other sprint phones also never-( or atleast noticeably ever ) tripped the radio. Now the way I understand it Sprint uses a different cellphone technology than both Cingular and At&T. Its this technology that we believe is tripping the radios. We know for a fact that the cell phones would trip the radio, because we tested repeadtly for about 15-25 minutes, turning them off walking away hiding them then calling them or making calls with them.

I don't claim to have any clue whats going on, this is probably apparent due to the vagueness of my post however I do realise there is a problem. During our skrimmage yesterday, there were many times where people came very close to being hurt because of the radio frequency loss, then the robot suddenly coming to life near the sides of the fields. You don't have to be an electrical engineer to realise this is a problem. This type of problem not only can greatly corrupt the competition, it could also cause some significant safety issues, or even potential damage to our robots, I'd hate to see a robot lose radio contact as its driving up a ramp and flip over causings thousands of dollars in damage.

I really hope that IFI will do something soon. I completely agree with you Dan this is a HUGE issue. In the case of the bane bots, if problems occured, at the very worst we could always change companies, or come up with custom solutions. With IFI there is no other option. I know they realise this, and trust they will come up with a solution as they always do. Lets hope it comes before regionals, otherwise get ready to see some of the most interesting/unsightly regionals in years.

Re: does anyone have OI and RC radio issues
 

Sprint and Verizon actually use the same technology (CDMA). The more important difference is that Sprint's network is entirely in the 1900MHz band, while Verizon primarily uses 800MHz. So, your findings are not surprising. Verizon's phones are using frequencies very close to those used by the radio modems (902-928MHz).

Re: does anyone have OI and RC radio issues
 

To a certain extent, IFI's hands are tied in terms of being able to solve this problem. If they were to modify the design, it would most likely require recertification for the FCC equipment authorization.

I'll again echo my previous statements that in all other respects, my experience with IFI has been timely, professional and reasonable. While I'm sure they can solve the problem, the bigger question is whether they'll be able to do it in both a timely and legal manner.

Based upon what I saw today at the local regional in Sussex, WI, many teams operated successfully, and there appeared to be some interference issues with teams operating on the same channel, however even when the event organizers dutifully checked to make certain everyone was on the correct channel, there were still some teams experiencing problems to the extent that it affected the outcome of the match.

In a couple of instances, I was able to see the lights on the robot's radio showing the radio going into standby and then attempting to find its operator interface again... and this is with less than 10 feet between the OI and the robot.

Instances where more than one radio pair attempted operation on the same channel is quite easy to spot as the Tx/Rx LED's on the radios will be almost constantly illuminated as opposed to the normal alternate flickering. So once you know what to look for, it is pretty easy to see the difference between interference and a radio that has just lost communications with its partner.

One of the teams at todays event simply chose to use the older radios.

While its good to hear that many, and perhaps most, teams are not experiencing an obvious problem, unfortunately our team is not one of those.

Teams experiencing problems, should make all attempts to make your FIRST contacts aware of your individual situations.

At this point, the reasonable and conservative answer would seem to be the use of the old radio's. I'm sure most of us have 18 other design implimentation issues that our time would be better spent on.

Re: does anyone have OI and RC radio issues
 

A quick correction to Dan's post: it was the Cingular and AT&T phones causing the repeatable interruption.

My Verizon and and others' Sprint phones caused no interruption as far as we could tell.

Re: does anyone have OI and RC radio issues
 

Yes I'm sorry my bad, it was late when I made that post. It was Cingular and AT&T, Verizon and Sprint were seemingly safe.

Re: does anyone have OI and RC radio issues
 

For those interested in some additional background...

Both the old (eWave) and new (IFI) radios use unlicensed (Part 15) frequencies in the 902-928MHz band. Both radio designs use relatively narrow channels, as opposed to a spread spectrum design. Both designs operate full duplex, with the OI and RC radios transmitting near either end of the spectrum.

"Cellular" carriers use spectrum allocations in the 824-849MHz and 869-894MHz, with the subscriber units transmitting in the lower channel block.

"PCS" carriers use spectrum allocations in the 1.8-2GHz range.

Cingular/AT&T uses GSM (Groupe Special Mobile) as the air access standard for their subscribers. GSM is a TDMA (Time Division Multiple Access) standard which assigns each subscriber a fairly precise time slot in which your device transmits a burst of data, representing compressed voice and control information. The packet frames are sent at a relatively low repitition rate of 217Hz or one of its submultiples.

That 217Hz packet rate results in a rapid on/off keying of the transmitter in the phone. The resulting modulation is AM (amplitude modulation) which can be problematic for many devices, whether they are radios or not. The succeptability some devices have is that components like diodes and transistors make good receivers because they will rectify the incoming signal, and by extension components like operational amplifiers (op-amps) that have transistor inputs are among the most succeptible for near field signals.

CDMA (Code division multiple access) is a spread spectrum technology that assigns each subscriber a PN (Pseudorandom Number) sequence with which to scramble their transmissions. The transmitter technically remains on the air while the frequency that it operates on is rapidly changed in a psueudorandmon manner. Phones that use this technology will typically not impact succeptible devices as much as a device using a TDMA/GSM type of modulation scheme.

Cingular and AT&T Wireless, pre-merger, both held "Cellular" and "PCS" licenses across the country, the local use of which was determined by how they came to own the licenses in a given market. Both companies heritage, in some markets, trace back to the wireline LEC (local exchange carrier) license grants in the early 80's where the LEC was given one 'cellular' channel block, and a wireless carrier was given the other 'celluarl' channel block.

Starting in the 90's, the newer 'PCS' spectrum was auctioned to new carriers, and companies such as Sprint got into the cell phone market, and established cellular carriers also bought spectrum in other markets.

Sprint uses PCS channels for their national system, and is CDMA.

Verizon Wireless came out of the merger's of Bell Atlantic Mobile Services (BAMS), GTE and Vodaphone, and the combined holdings and subequent acquistions and expansions have all utilized CDMA technology as their digital air access standard. In markets where Verizon's heritage is traceable back to the origional LEC, largely in the east, they primarily operate on celluar channels, though many areas both celluar and PCS are used for capacity. Local to me, Verizon uses PCS channels obtained through their acquistion of PrimeCo wireless which had constructed systems in the midwest, and if I remember correctly also had a prescense in Florida.


If celluar phones utilizing GSM/TDMA technology are found to drive the IFI radios nuts, then I suspect that Nextel subscriber units would also have the same potential for problems.

Nextel is neither a cellular nor PCS carrier, they are a SMR (Specialized Mobile Radio) licensee that has a patchwork of 800MHz spectrum holdings in which they have constructed a cellularized, full duplex, two-way radio network. Nextel uses a Motorola propriatary TDMA technology marketed as iDEN (integrated Digital Enhanced Network). iDEN's packet rate results in the subscriber devices transmitter typically being modulated at 22Hz.



In our teams situation, I've not attempted to torture the radio's with any cellphones, nor has anyone been on their phone's nor has any phone alerted (i.e. rang) during our tests. In many cases, I've been the only one present, and my phone is Verizon CDMA using PCS channels.

I'm not saying that there isn't a problem with susseptability from cellphones, just that in our case, I believe we are being affected by a different problem, as our packet loss events appear to always be tied to large demands on our electrical system.

Re: does anyone have OI and RC radio issues
 

This evening I implimented code to watch for packet loss, for more information see the details and example code in this thread.

With a packet loss counter displayed on the operator interface, I had a couple of Cingular (i.e. GSM) phone users setup calls within proximity to the 2007 radios, and boy did the packet loss counter take off. This was not a difficult problem to reproduce at all, nor did the phones appear to need to be particularly close to the radios. We didn't do range testing to see how far away they would still cause problems.

With eWave radios, the problem could still be produced, but the phones had to be within about 12-18" before some minor packet loss was noted.


My CDMA phone affected neither.


I also tested with a /\/\otorola 450MHz 5W handheld and found that it was fairly difficult to disturb the 2007 radios, but when I did, they took quite a while to recover, and it seemed to be longer than it normally takes for the radios to sync in the first place.

When I tried the same test with the eWave radios, I found that they were actually more succeptable to interference from the commercial handheld radio than the 2007 radios were. However, the eWave radios never experienced anything more than a few packets being lost when the commercial radio was keyed, whereas the 2007 radios lost sync for up to 20 seconds as a result of a single transmission on the commercial handheld.


With regard to the V14a firmware, my test code seemed to indicate that the robot controller will disable the outputs when 8 consecutive packets are lost. My number could be off a bit, as I sometimes saw as many as 12 missing packets prior to the RC disabling the outputs, but its right in that area somewhere. In otherwords the outputs will be disabled 200-300ms after packet loss starts to occur.


With the packet loss counter displayed on the operator interface, over several minutes of operation, both the eWave and IFI radios showed occaional packet loss counts during the regular course of operation, however the packet loss rate was higher for the IFI radio than the eWave radio. I won't quote specific numbers nor quantify that statement as I wasn't making a specific expermient to instrument packet loss.

The environment that I was testing had no other 900MHz signals present, as verified with a spectrum analyzer.

Overall, the IFI radio design appears to be quite a bit more succeptable to cellular phone interference than the eWave design, however the eWave design was more succeptible to 450MHz two-way transmission.




From a design curiosity standpoint...

Additional testing shows that the IFI designed radios are FSK radios using channels spaced 150kHz apart. The RC radio channel 1 starts at 902.100MHz and works up from there. The OI radio channel assignments are less obvious, and not sequential, operating in the 922-928MHz portion of the band.

The eWave designs operate on 50kHz channels with the RC side transmitting on the lower frequency channels, just like the IFI design, and appear to be AFSK. Presumably the AFSK approach avoids needing to design the transmitter/receiver to be able to essentially pass/recover data down to DC. The latter results in a slightly more complicated synthesizer design because the PLL reference needs to be modulated in addition to modulating the VCO.

The IFI FSK signal appears to contain a ~3ms pre-amble prior to the data, which I presume is to center the recievers data-slicer, then sends the data, and then sends what appears to be a post-amble. Given that the data is true FSK, its not clear why a post-able burst could be helpful.

I also noted that the signals didn't appear to be properly pre-emphasised, so the higher frequency content of the signal didn't deviate as widely as the lower frequency data, nor was the signal necessarily well balanced. Depending upon the data-slicer design, this could certainly result in a reduction of performance.

While a bit hard to tell, the signal encoding didn't appear to particullarly try and place a limit on long strings of 1's or 0's as long periods of mark and space were evident, which again can make the design of the data slicer a bit more challenging.

Again, this last bit is offered just as insight into the radio's design. I have no reason to believe that the modulation methodology plays into the performance problems that I've noted, and believe are tied to power supply issues, nor should they play a great part in the receivers succeptablility to GSM/TDMA type transmissions... that is unless the succeptability problems are related to RF getting into post receiver circuitry.

Re: does anyone have OI and RC radio issues
 

Makes you want to think that the AGC delay release is set a little too long doesn't it.

Re: does anyone have OI and RC radio issues
 

So is playing with broken radios this year a part of the game challenge?
..

Re: does anyone have OI and RC radio issues
 

They should tell everyone with Sprint & AT&T service to shut off their cell phones :D

Re: does anyone have OI and RC radio issues
 

Ben,

People don't turn off their phones in restaurants, movies theaters, meetings or Broadway shows. They text message while driving down the interstate. They even ignore FAA regs and jeopardize their very lives by using phones while taking off on commercial jets.

What chance do you think you have in getting people to turn off their phones at a robot competition?

JMHO.

Mike

Re: does anyone have OI and RC radio issues
 

our radio channels are different RC is 32 and OI is 40 anyway to fix and i'll try it at regionals