Re: Mounting of router
 

OK,
When trying to impart the wisdom of others, one thing to point to is the signature of guys like Don and I. I am a broadcast engineer and Extra Class Ham Radio operator. Don is a Ham with significant digital experience. Alan is a trusted network and software specialist with a lot of wireless experience.
Aluminum at 5 GHz might as well be lead.
For everyone, the DAP-1522 has two antennas mounted on the board. They are verticaly polarized with respect to the bottom of the AP/Router. That means they are most sensitive to radiation out to the sides, front and back of the radio. The circuit board is a ground plane effectively blocking all reception in that direction (out the bottom of the radio). The nature of 802.11N is that both antennas are required for max bandwidth to be achieved. Both are used for receive and transmit. In addition to the shielding effect provided by metallic objects, the metal serves to de-tune the antennas making them less effective. This effect, of course, is distance dependent. As Alan has pointed out, there is some significant noise generators on the robot. Of those that are the worst for interference is open frame motors (those that you can actually see sparks through the openings in the sides of the motors), the five volt convertor power supply, and the supplies in both the PD and the DSC. These noise sources not only interfere with radio reception, they also impart noise directly to the electronics on the board.
Having the radio mounted in the robot such that is "visible" to the antennas on the field, it is not mounted near a noise source and it is not surrounded by metal of any kind is the best of all worlds.
One word on "visibility", inspectors want to be able to help you and insure that you will play all matches at every event. If your mounting is questionable it may pass, but if you want help when you fail on the field, you have to meet us halfway. If we can't see the lights from several feet away when you are dead in the middle of the field, we have to rely on the field logs only, to try and figure out what went wrong. After repeated connection issues or a string of bad packet events we will ask you to move the radio to help you improve.

Re: Mounting of router
 

Thanks Al! This is extremely informative. I learned my lesson when we have had radio problems in the past, and ended up fixing the issues by simply moving it. I try to stress this to my current students, I will definitely pass this on to them! It's a good explanation. ... and since your a HAM, I'll say 73 AL! Thanks! :)

Re: Mounting of router
 

Seth,
If you want me to talk to your students some time, just ask. See you soon.
Al

Re: Mounting of router
 

I would like to consider the possibility of setting up a semi-official field-day-like station at FRC competitions. Who wouldn't want a Worked All Regionals certificate? :cool:

DE WB9RUF

Re: Mounting of router
 

Thanks to Don, Al and Alan for your wisdom here. In your experience, does the signal light impart any interference with the radio signals? We are currently planning to mount them near each other so that the field crew can find them easier.

Re: Mounting of router
 

Send out some really cool FRC Regional Event QSL Cards! That'd be so cool! haha :cool:

anyway... sorry, I digress!

Re: Mounting of router
 

The RSL has no real generator in it. It merely is a high brilliance LED. It contains a flasher circuit that is not used in our application. Alan, you never told me you were a ham. A demo table might be a cool thing at events.

Re: Mounting of router
 

I agree, the RSL is pretty quiet. No worries if it's mounted with the radio.

Hey Al, I also was a TV engineer for 3 years...but on the consumer electronics side of things. Now it's automotive.

I also never knew Alan was a ham, but it does not surprise me.

Re: Mounting of router
 

Please elaborate. You are saying after we have it wired, we cannot slide out the drawer for some reason? We're using connectors so we can easily disconnect sensors, solenoids and motors at the top of the deck, and then the drawer can slide out.

Can the router be placed on top of the battery? That's the best place we got where the router is the least interfered with. Other places are underneath our polycarbonate in the middle of all the electronics. My team doesn't want to agree with mounting on top of the battery because the battery could overheat or something.

Re: Mounting of router
 

Ikillee,
During match play, the battery might get hotter than normal. It also contains a lot of metal. I would think you could find a better place. If it is on top of the battery, don't you have to remove it to change batteries? You don't charge batteries in the robot do you?

What if it was mounted sideways right beside the batteries?

Re: Mounting of router
 

Here's what I believe is the best:
Motors are probably one of the worst interference, even the smallest ones. Motors use electromagnets to convert the electrical energy to kinetic motion. Motors, because of that, when in close proximity of the bridge, can cause severe problems. That radio wave will interact and deform the radio wave of the bridge, causing it to increase it's power until it's max threshold. Then, you will notice your connection continuously dropping. When you go full speed forward, you lose connection because there is a sudden load of interference. It isn't because of the voltage drop because there is a buck converter, probably containing some smoothening capacitors. What the bridge is encased in also maters a lot. Start a router and keep the device next to it. See how good your signal is. Then, go to the other side of a brick wall, and voila! You will notice an extraneous drop in signal quality. In my room, where I keep my laptop, if I keep it 3 feet higher, on my desk, I'll get a good signal. However, when I put it on the floor next to a bunch of transformers, I am lucky to get 3 bars of signal. Oh, remember that I'm running a hacked router with DD-WRT, so I can change the transmission power manually and max it out to 251mW, powerful enough to give me a .25 mile range with another DD-WRT router at the same transmission power! Also, keep the converter away from the bridge. It constantly changes in frequency so it is almost impossible to go against! As Al said, try to have your bridge high up and flat.

This year, our bridge is on a tall pole, distant from ANY radiation, except the AXIS camera. Otherwise, it is surrounded with pneumatics and a compressor 3 feet away. That aught to give a decent connection!

Re: Mounting of router
 

Ikillee,
Same but different, the battery contains a lot of lead plates and connecting bars.
Yash,
Not exactly. The motors can produce interference due to the sparking that is normal in DC motor brushes and commutators. Think spark gap transmitters. The closed motors tend to reduce this spark interference but RF does stray along the motor leads as it leaves the motor case. Twisting the motor leads can help somewhat. Your results will vary.
The effect you experience with a brick wall may be more due to the materials inside the wall than to the wall itself (Pipes, conduit, steel structural materials, wire). If that wall has plaster on the surface for instance, it is likely to have a steel mesh screen (lath) to help the plaster stick to the wall. The convertor makes a lot of RF noise because of the way it switches current to the internal transformer. This produces significant, high slew rate, pulses with lot's of ringing. While the frequency of operation is relatively low, (likely around 100 kHz) it is the ringing that is much higher in frequency and that which causes the interference. when placed close to the bridge, the comparative signal strength from the convertor is orders of magnitude higher than that received from the other radio. This tends to fall off rapidly with distance (following the inverse square law).
I would be remiss if I didn't say something about exposure here. The radio output from wireless home routers is intended to keep exposure limits low and maintain FCC specifications. Please consider what you might be exposing yourself to when making power adjustments to a product of this type, particularly if you spend a great deal of time in one location near the source.

Re: Mounting of router
 

Well, if I have my way, I will be making a change to it today. The mentor that was against moving the router up and quit Saturday! He's our head mentor. Kind of weird to quit just before build is over. I won't have time to get it out of the drawer but if we get a chance before bagging it, I'm going to put an angled piece of plexiglass aiming it up at about 40°. The mentor that quit was fine that the lights only showed thru the heavily smoked Plexiglas, which I think would have been behind the bumpers anyway.

If worse comes to worse, 1 hole and some Velcro on the deck and we can mount it up there at competition.