regarding antena.

[manz]

if i were to have 2 remote control (same brand) for remote 2 control cars (just a simple batery powered one) can i share the antena for the same brand controller but have 2 diff frequency (eg: 27 htz and 40 htz) and use it both at the same time.what will be affected by doing that?or do i still need 2 antenas for those 2 controller.

thanks

 

[Papabravo]

No. Antennas are part of a resonant circuit. If you use one at a frequency for which it was not designed you will loose a considerable amount of your output power which will be reflected back to your output stage possibly resulting in its destruction.

Second it is unlikely that your frequencies are 27 Hz. an 40 Hz. More likely you mean 27 MHz. and 40 MHz.

 

[manz]

oh yes,it is 27MHZ and 40MHZ,sorry for the typing error. just to describe more about the controllers and just to reconfirm,both of the antenas and controllers are identical (same brand,size,pattern,circuit) accept for the frequency.the thing is,i`m using both of the reciever to trigger somthing else and should be controlled by both of that identical reciever (diff frequency) simultaniously,so im combining that controllers into one plastic box, so that`s why i`m asking should or shouldn`t i use just one antena?

base on the explaination given, so that`s mean i shouldn`t do that (use 1 antena) and still need to use both of the antenas for each of the circuit isn`t it?

thanks anyway

 

[Papabravo]

For receiving you might get away with a single antenna. I thought you were going to be transmitting and receiving with the same antenna. Putting RF transmit power into an unmatched antenna is a recipe for heartbreak.

 

[RadioRon]

It is possible to attach both transceivers to one antenna, but it is typically a bit beyond the beginner to do so. There are two problems. One has been mentioned already, that is, that each radio should be impedance matched to the antenna for maximum power transfer, but they operate on different frequencies so you need a fancy impedance matching circuit that works for both. While this is essential with higher transmit powers, like greater than 10 dBm, you can get away without it at low powers, where you just live with inefficiencies of the impedance mismatch.

The other big problem is that the transmit output from one transceiver will interfere with performance of the receiver in the other transceiver. The severity of this problem depends on the transmitter output power. If the power is, say, 20 dBm or higher, it is possible for this power to actually damage the other receiver. At any useful power level, the transmitter signal will also potentially drive the other receiver into overload and desensitize it to the point where it doesn't work.

So, the way that you can solve these problems is to include a duplex or diplex filter (I'm not sure which term applies, but I think it should be diplex). This is a three port circuit, with terminals for ANT, Radio 1, and Radio 2. The connection from ANT to Radio 1 provides a 50 ohm impedance match at both ports only for 27 MHz. The connection from ANT to Radio 2 provides a 50 ohm impedance match at both ports only for 40MHz. The isolation from Radio 1 to Radio 2 port is high for both frequencies so transmit from one radio doesn't get into receive of the other radio.

This kind of filter is common in cellphones, except that those ones work at much higher frequencies. I think they are also common in newer dual band VHF/UHF transceivers that Hams use. If you want to give this a try, you will have to find some design information in radio design texts, perhaps for radio hams. Its a very difficult filter to get right even if you have the expensive RF instruments needed, so I don't recommend building one. It definitely is easier to use two antennas.

 

[manz]

ok i`ve got the point.i just use 2 antenas then.thanks to all for the info.

for the antena problem solved (that is to use 2 antenas) i`ve got another unexpected problem(for me though).here`s the situation:

1.how come does the 27MHz transmitter (controller in this case) signal, caught by the 40MHZ receiver and by the 27MHz reciever as well at the same time.

2. this still happened even when i totally switch off the 40MHz controller.

3.but the signal from controller 40MHz only being recieve by the 40 MHz reciever (just like how it should be)

4. this situation still happen even when i seperate both of the controller (coz i happen to put both of the controller in the same box with 2 antenas in the 1st place) so i guess the reciever is messed up. is that any posibbility that the 40MHz signal interfere with the 27MHz reciever?(i expect it wont, since the frequency are a lot different)

5. just for the info (if needed) the reciecers share 1 power source (battery) and being place quite near (less than 1 feet).both the reciever have own antenas.

6. so i guess the problem is at the reciever side and not at the controller.

is there any way to solved this problems?anyone,feel free to give your thought.just to give a general info for what the heck that am i doing, its a simple remote control battery powered helicopter.it only have 2 basic movement that is up /down and rotational.so im combining 2 of these helicopter (diff frequency) just to add extra movement to this helicopter that is forward/backward.basically i`m just adding another dc motor (from another helicopter) and controlled it with diff frequency.ignore the stability of the helicopter coz somehow i manage to balance it quite good by placing the motor at the right central of gravity.

thanks

 

[audioguru]

Try completely separate batteries for the receivers. If this stops the interference between them then add a 0.1uF ceramic disc and a 100uF electrolytic filter capacitors and/or voltage regulator.
If it doesn't make any difference then the receivers are too simple and cheap.

 

[manz]

dear audioguru

thanks for your thought.alright,i`ve tried seperating the battery and the interference is still there buging each other.it should be at least 1 1/2 feet away then it would be stable.i think the receivers really are too simple and cheap. so nothing that i can do to solve the problem is it? yes if i change the reciever to something a litttle bit better and stable i guess.but other than that?by the way, may i know what does the 0.1uF ceramic disc and a 100uF electrolytic do and affect the reciever and how to actually connects it?it should be just parallel with the power supply isn`t it?

 

[Nigel Goodwin]

I would suggest that the radio control system is only a toy!, you can't do what you're wanting with it - buy and install a proper R/C system and do it properly.

 

[manz]

i guess so.hm thanks anyway to all.