Question about interference

[talulah]

Mark - The natural impedance of a quarter wave dipole is 37 Ohms. The receivers are probably matched to this, or maybe 50Ohms. The mismatch between 37 and 50 Ohms isnt that bad and can be ignored for most purposes.

Trial and error is certainly the best way of finishing off the design, but it is important that basic design principles are followed to start with. Trial and error wont fix a basically bad design, but it can improve a good one!

Jonas - following on from that last comment, you may or may not have problems when you come to putting everything in the box. Its impossible to say at the moment. If it all works OK, then congratulations! If not, then dont say we didn;t warn you! Good luck.

[richard_morris]

Back to earthing of the antenna shield - I wouldnt, from experience on robots and other kit. Sure - connect the antenna screen to a metal box around the receiver, but dont link it to the chassis - keep it floating. We do not use the chassis as a return, but you can still get noise on it because there is just so much high current floating around in cables clipped close to the chassis - so my recommendation is to keep the antenna screen off it!

Richard

[jeremy_cuss]

I used a number of tips to increase the effective range of my transmitter from about 2m to 40m. I used capacitors to minimise motor noise, put the receiver in an aluminium box, used a separate receiver battery, used co-ax cable within the robot to carry the aerial signal, earthed the shield to the battery negative (but did not earth the chassis), extended the length of the aerial to ~1.1m, and used sprung steel for the aerial to hold it away from the chassis. Each one of these elements had a positive effect. When at a later time I had to move the on-off switch to make it more accessible I used graphite cores at both end of the wiring. Surprisingly the reception didnt seem to change with or without these cores.

Jeremy

[kefirtribe]

can aluminium foil work as a screen (for cables)?

[richard_morris]

It certainly can! Its just very tricky to solder - so clamp the end for a connection if you need one.

[big_nipper]

Alot of good tips on here. It seems to me that almost all of you have a seperate Rx battery and most put the Rx in a metal box. Also seems like most dont earth the chasis like we do to the rx battery.

On the featherweights we have had alot of interferance problems recently with a simple setup of the rx wire stright out of the robot without screening but with seperate rx battery and opto-isolators. Could be something to do with the single conversion mini rx! just waiting now for a new Tx & Rx setup.

[talulah]

Petter, Its best to buy screened cable. Screening your own is very unlikely to be effective.

Jeremy - interesting post that. I dont suppose you have figures for how much extra range you got with each individual improvement do you? That would be very interesting.