Range Issues

[Rhino90]

Hello everyone,

I’m not getting much more than 15ft of range before my sub loses signal. I’m running a vex radio / 75Mhz ND S3 receiver. I thought I had cut the antenna to the right length, wasn’t getting range much farther than 15 or so ft so the soldered back on what I cut off.

Not sure if this is antenna issue or something else. Anyone run into this previously? Would greatly appreciate any advice. Here’s a couple pics as well.

thanks,

Ryan

[trout]

Ryan,
check for any nicks or cuts in the antenna. Water touching the bare wire will greatly interfere with transmission. Wait, are you having issues in the water or dry on a bench? If on the bench you may have a receiver or transmitter that are not quite in tune. The antenna of the receiver could be a starting place.

[Rhino90]

Thanks for the advice Trout. I’m not sure what range to expect, but it’s definitely worse in the water. On the bench, I get about 50-60 ft range.

I’ll take a close look at the antenna as you suggest for nicks, thanks for getting back to me.

Ryan

[He Who Shall Not Be Named]

I assume it's a glass layup, not carbon or Kevlar?

David

[Rhino90]

Hi there David. Yes, it’s fibreglass. The hull is a 1/96 Permit.

[mike27283]

Hello Ryan - there may several problems.

- Have you tried your transmitter with another receiver? I've had issues with the transmitter before that caused range problems. Led to the infamous 'Mike's Type VIII caught under a pipe at Groton Dave had to rescue' incident...
- I'd also purchase a new receiver (ensure your transmitter is good as mentioned above - and both have fresh batteries) - then try the new receiver with the transmitter.
- Are you sure your crystals are fully seated and match? Perhaps they prongs need to be cleaned (some rubbing alcohol and a toothbrush would do the trick).

75MHZ will penetrate clear water to 1/4 wavelength so you'd only get about 12 feet while submerged anyways... (12 feet depth). Realize the antenna is coiled up and not streaming at full length so that causes range issues also - not to mention the slant range through the water counts against the ~12' at 75 MHZ water penetration...

- Have you unplugged your servos and plugged in a new servo just to be sure nothing is grounding out?

- As Tom mentioned above (and I have had to do) your transmitter / receiver may need to be tuned. I've sent mine off to Radio South to have this done before...not sure what other businesses offer that service anymore.

I hate to say it ... but cutting the antenna is likely the problem here - even though its soldered back together it changes the impedance...and therefore the tuning (as I understand it...) - I personally never cut receiver antennas...

All that would be a good start.

[RCSubGuy]

Great stuff above.

Another thing to realize is that the VEX transmitters are basically de-powered Futabas. They were designed to be used in close proximity to robots, not controlling them from hundreds of feet away like hobby radios. You will never get similar range out of a VEX unit that you will from Hitec, JR or Futaba.

From what I understand, you can actually throw additional voltage at the VEX to increase power. This can be done safely up to around 30% I believe.

[Rhino90]

Thanks Mike and Bob for the advice, much appreciated. I don’t have another transmitter or receiver to try…. Yet. I’m open to recommendations if you have any. As Tom suggested I’ve attempted to re-seal the antenna in the event water is getting in, going test it this afternoon. I’ll try cleaning and re-seating the crystals too.

anyone know the typical range from vex transmitters? I just assumed that 20 or so was too short.

Aside from that going to look into another receiver and a back up radio just in case.


thanks again everyone,

Ryan

[RCSubGuy]

Based on our experience with VEX, I'd say you could expect maybe 100ft or so in open air. Get the boat underwater and that will drop depending on your depth. You should get at least 50ft, though...

[Rhino90]

Thanks Bob, that gives me a baseline, thanks for letting me know. I’ll keep muddling with it, stay tuned for progress.

Ryan