Radio problems

[glen]

hello,

im having really bad radio problems at the moment with the main problem being the areial/antennae.

i was just wondering, what options do i have in making a better aerial (i want to remove the reciever wire)? ive heard CO-AX cable can be used as can piano wire. but i have absolutely no idea how to connect it to the reciever itself etc.

btw im running 29mhz AM

help desperately needed,
Regards,
Glen

[big_nipper]

Radio problems

29MHz is not allowed, niether is 27MHz unless its an ant weight. Changing the aerial will not (usually) improve the signal as the wire is matched to the Rx, it will only make it worse. Try using a 40MHz FM set.

[team_ireland]

Radio problems

One thing that i think alot of people overlook is foam around the receiver. The most common casue of model aircraft and car crashes is either a servo falling out or worse the crystal falling out. Considering we dont mind paying 75quid for speedos 30quid for motors etc. i dont think the 2-3pounds for the foam to go over the receiver should be a problem.

As for aerials i am not too sure but the best i can recomend is to use green wire to replace the rx aerial wire and try to keep it the same length as the origional.

Regards
Ian Mc Donald

[craig_anto]

Radio problems

Funny you should mention Electron Magnetic interference
Tim Mann from Stinger has produced an information pack on how to deal with it
should be on the FRA site soon Ill find out and post back when I know

[Guest]

Radio problems

I notice from his profile that glen is from australia so 29 Mhz may well be their equivalent of our 27Mhz, I would check with any australian robot groups (?) regarding which frequencies are allowed.

Personally i would not use an AM set unless it is unovoidable as they tend to be more prone to interference than FM.

On Thorak we simply cut the ariel wire about 4 from the reciever and cut a length of Piano wire the same length as the off cut and then use this in a peice of tubing that we got from the hobby shop. I believe its usually used for aircraft control wire lining or something to stop the ariel from coming in contact with the metal casing of the robot.

[glen]

Radio problems

thanks alan, ill try that.

basically we over here have 36mhz FM, which is your 40mhz equivalent and 29/27mhz AM.

eventually i will be changing over to 36mhz FM, but with the IBC (http://www.robowars.orgwww.robowars.org) it doesnt get the jitters as much as you would think.

[big_nipper]

Radio problems

Should have checked your location. I assumed that you were in the UK. Even when we first put a 40MHz PCM Rx we started with alot of problems. Most of the EMI came from the motors even with the suppression capacitors connected, try removing the brushes if you can and see what increased range you get without altering any of the wiring. I even went to the trouble of designing a filter to put on the motor wires to get rid of most of it. The probelm was the filter needed to cope with 120Amps and it was huge. We solved the probelm by simple putting everything to do with the Rx (battery,mixer) in one metal box and earthed the chasis to the Rx battery (not main battery). Got some SMB mini co-ax connectors and used co-ax right up to the point that the areial left the robot where we used piano wire (30-40cm long) and have had no probs since. The only reason to use piano wire is its strengh and when upsidedown our spiked wheels dont rip it off. The Rx is matched to the wire attached to it when you get it. Altering the length and even the thickness degrades the signal to the Rx but the wire is not strong enough for an areal so its a compromise.

[m2xt]

Radio problems

The document to which craig refers to is also available in the Technobots Technical Guidance Notes section http://technobots.co.uk/en-gb/pg_19.htmlhttp://technobots.co.uk/en-gb/pg_19.html It is G6: EMI and how to deal with it. It is nice to see this black art of what we generally call radio interference presented in an easy to understand way. Document author Tim Mann (Stinger Team)

Paul

[glen]

Radio problems

back on this topic ive now got some 75ohm coax and the rx is in a metal box.

how should i go about earthing the box? i know you earth it to the frame but should i earth it to the reciever battery negative (i use an ibc so no rx batts)?. and should any wires going into/out of the reciever metal box pass through ferrite cores etc.

also with the coax. should i earth the shield to the frame and to the rx battery negative as well?

any help appreciated.

[knightrous]

Radio problems

Glen, just put a capacitor between the shield braid and the earth to the negative, mainly to stop any currents that may some how short or back spike down the IBC battery eliminator circuit regulator. This will stop the problem that we had in Robowars 2003. I dont think ferrite cores will be necessary, we only have ours could out the box straight with no gromets or ferrites and our radio reciever is tops right now.

[talulah]

Radio problems

I have loads of information about radio and emi in sections of my website:

http://homepages.which.net/~paul.hills/Radio/Radio.htmlhttp://homepages.which.net/~paul.hills/Radio/Radio.html
http://homepages.which.net/~paul.hills/Emc/Emc.htmlhttp://homepages.which.net/~paul.hills/Emc/Emc.html

[talulah]

Radio problems

Aaron, are you using a BEC? If so, dont!

[knightrous]

Radio problems

We use the BEC on the IBC, so it powers the reciever. Saves having to worry about another battery pack that has to be maintained. We havent had any problems since our first earth loop issue.

[talulah]

Radio problems

Sorry, that comment should have been directed to Glen...

Glen, are you using a BEC? If so, dont! Is your radio receiver optically isolated from the speed controllers? If not this is highly likely to be the source of the problem.

[knightrous]

Radio problems

Glen is running the same setup as me Paul, both of us have IBCs using the BEC function. I believe Glen just needs to make a base loaded coil like on your site to fix his problem, because it damn sure fix all of our radio problems!