Radio Boost/Range Extender?

Hey CD Forum!

I have a question about the FIRST radios supplied in out kit. Our team wants to be able to control our robot [on the off season, not at competitions] from a far greater distance than we currently can with our radio connection.

In this scenario, limitless tether cables won’t do the job. So, I was wondering if anyone had found – or could find – a rather simple modification of the the FIRST supplied radios to extend its range.

We want to be able to control the robot on a playing field from the top of the bleachers.

Our team also has some of the older radios to work with, so the answer doesn’t need to specifically deal with the revised radios.

Thanks for all of you help and comments!

How far of a range do you want? The FRC radios have a pretty decent range for normal use. What kind of application are you thinking of?

I’m not trying to discourage you, but I can’t think of anything offhand. I’m also curious as to why the extension is needed.

We want to be able to control the robot on a playing field from the top of the bleachers.

Last fall my dad and I built a bot for Holloween and had it driving down my sidewalk a good 200-300 FT. I believe that is way more than bleachers to field.

-Mike AA

Have you tried this range. Not knowing how large your gym is, but if it’s a typical gym, you shouldn’t have a range problem at that distance.

Now, if you’re talking a stadium…

If you don’t have any kind of tether running from where you are to field-side (i.e. to allow the regular radios to be closer together), then you need to create some kind of wireless relay system.

I think we’d like to hear back as to weather you simply tried it first. Then we can work from there.


On a similar note, our team 2158 has experienced a drastic reduction in radio range recently for one of the new radios. We were doing a demo in a parking lot and we only had about 30-40 feet of effective distance. That’s bad, seeing as we have a 13-foot forklift. We can’t really have our signal cut out at full speed.

On our OI board, we have the radio box screwed down underneath the OI controller (on standoffs), and the antenna sticks out from the side. Any problem there?

XBee Radios have an effective range of about 300 feet outdoor, and about 150 feet indoor, its just a RS232 connection so you could probably just hook them up and you’d be running, just like the FRC radio’s. You’d have to set up the network but its not too hard.

Yes, there is a problem.

These radios have two antennaes. The external one, and the internal one. In addition, these are standard dipole antennaes. That means that the shape of their “field” is like a donut, with the antennae sticking through the hole of the donut.

Putting the radio on it’s side means that at times, one or both of the antennaes will be pointing AT the operator interface antennae. Contrary to what may be intuitive, this is the absolute worst orientation to have the antennae. Both the antennaes and the robot antennae “box” should be vertical for best reception.

You might be able to build a directional Yagi type antenna to use on your controller. Boosting the signal (adding watts) could be a violation of FCC laws and you would need to add filters to reduce harmonics also. The contollers should work fine for line of sight over a distance of 300". Look up some of the ham sights on how to add a “director” and “reflector” elements too the controller antenna. If done right you should be able to more than double your range.

The kit radios are FCC certified as a radio and antena modual. It’s against FCC regs to modify the antena, But who is going to catch you.

It has been spotlighted that someone (I forget who) said “Stop it with the “Break the rules, just don’t let anyone know” already!” (approximate quote)

Don’t modify the antenna if it’s against the regulations. I don’t care if you will/won’t get caught. Professionalism forbids it (let alone Gracious Professionalism).

I can not condone this action as the FCC can impose a $10,000 fine and confiscate any and all radio transmitters in your possession/home if you are caught. They can also make it illegal for you own any radio transmitters in the future. That includes your garage door opener, cell phone and cordless phone etc. It’s not worth the risk. As for modifying the antenna, I’m not sure if it is illegal to add a reflector and director elements to the antenna but warrants investigation. Reflectors and Directors are just elements of a certain length in front and behind the active antenna with no DC electrical connection the active antenna. The simply direct and collect the RF energy in designate direction. FIRST states that is not legal to modify the controllers for competition.

You could always do a range test. From what I’ve read in this thread, people are getting very different max ranges. I know we tested ours at school at got a little over 500 feet, and that was with a 20 ft dirt hill between the operator and the robot.

For starters you may want to look into changing the wireless link into a 802.11x based system. That way you can legally use YAGIs or omnis and and higher power units.

I’m not clear if you are allowed to modify the antenna or not. From my understanding FCC regulates the power emissions of wireless devices. E.g. 200mW for user 802.11 devices. What antenna, using RX amps, or how many of such devices within an area shouldn’t be a problem.

In addition to some of the good info here, the best reception using the antennas supplied is to have them parallel. The minimum coupling between antennas takes place when they are at right angles to each other. The radios do in fact, have two antennas, one external and one internal. At the RC modem, the external antenna is receiving data from the OI, and the internal antenna is sending data back to the OI. Although the dashboard data is affected by this antenna, the software will allow communications with errors on this return link. (according to IFI reps)
As always, mounting any antenna near metal, causes it to detune. This effect is at it’s worst when the end of the antenna is near or touching other metal parts. By their nature, antennas of this type, mounted on robots that travel near the ground, would have the best coupling when in a vertical orientation. That is why the IFI supplied antenna farm at competitions is in the vertical orientation.
To use another type of antenna would require retuning the output coupling of the radio, something most teams are not equiped to handle. The band that our radios use have specific limits set by the FCC that allow unlicensed operation in that band. One of those limits is Effective Radiated Power, ERP, which is affected by antenna gain and output power. The majority of teams would not be able to measure ERP so it is ill advised to try to increase that specification.
You can however, move the radio closer to the field and feed it with a longer serial cable. Be careful that the cable you use has low loss as the power for the radio also runs in that cable.


There are two things you can do with antenna location to improve range, in addition to the suggestions already made in this thread. The first is to mount both the robot’s and the base’s antennas as high as conveniently possible. This gets the direct transmission path between the antennas as free of obstructions as possible, and reduces the effect of the ground reflection. Since it’s just for a demo and not a competition, you could mount the radio on a separate, higher mast to raise it. The second is that if you can’t get the robot’s antenna very high, at least make sure that it’s got as much clearance between it and the metal in the frame and manipulator as you can manage.

Al’s suggestion of moving the driver’s side radio closer to the field with a longer serial cable is a great cheap way to get a lot of the extra range you’re looking for. Good luck with your demo.

  • Steve

The FCC is who.

Anyway: To maximize range read Al S’s post twice and do what he says. Specifically: Parallel antennae, and ALL of BOTH modules as far from all metal as possible.

You should see 200 feet reliably.