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Old Aug 13, 2012, 06:24 AM
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433 Mhz oscillator , correct me if i'm wrong !

HI guys , i totally newbie with RC here . So pls correct me . I just take a look at those 35 - 72 mhz RC , and see that , it have a quatz crystal to creat oscillator at the frequency we want .
What if we creat a 433 Mhz oscillator and connect with rc instead of crystal ,so we will have UHF transmitter .
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Old Aug 13, 2012, 08:15 AM
Oxford Panic
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Simply put, no.

The remainder of the circuitry in the transmitter is tuned to the band it was originally designed to operate on. I've heard of 35 MHz receivers working on 40MHz with only a crystal change but even that's a stretch to hope it would work at anything like peak efficiency.

If you were thinking of controlling some flying model on 433MHz, this is the band used for all sorts of other controls and telemetry so it would not be sensible to consider it.

A.
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Old Aug 13, 2012, 04:31 PM
RIP Ric
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What Andy says is correct. Put in another way, however, oscillators have multiple components that have to be designed to operate at the correct frequency. The crystal just makes it extremely stable and accurate..
..a
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Old Nov 09, 2012, 11:35 AM
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Can some one explain me , why 433 Mhz with just 500mW - 1W output ,but the range is far better than 35 Mhz transmitter . What make the different ? Does it work the same like a fm transmitter that it combine the PPM signal to transmitt frequenz and send ? Thanks
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Old Nov 09, 2012, 02:13 PM
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Originally Posted by noname2x View Post
Can some one explain me , why 433 Mhz with just 500mW - 1W output ,but the range is far better than 35 Mhz transmitter . What make the different ? Does it work the same like a fm transmitter that it combine the PPM signal to transmitt frequenz and send ? Thanks
First, the power level is much lower then 500mw. Think in terms of a remote door lock (key fob) for autos which operate at 315 MHz.

Next it is possible to have a real quarter wave antenna at 433, if you had a real quarter wave antenna at 35 MHz it would look like a telephone pole.

Whether it is AM, FM, OOK or anything else does not have anything to do with the frequency. 433 radios can be anything.

Here is one of many sources of radio modules that could be used for radio control:

http://www.mouser.com/Embedded-Solut...33+mhz&FS=True

I have used similiar modules for radio control and they work very well. You do have to know about data encoding and something about antenna design. I used them to control a combat robot and the shorter wavelength worked much better then the longer wavelength 75 MHz radios in the steel battle cage.

I did some range testing outside and the range was futher then I could see the robot.

You also buy transmitters that operate in the standard AM or FM radio bands and even the TV bands. At low power levels you can operate at many different freqencies. Another option is to use a cordless phone, the base station makes a good transmitter and the handset would be the receiver. With a computer modem they will operate at 56K baud or with Manchester encoding you would not need a modem.

With HDTV most TV is now in the UHF bands and the VHF bands are unused. In the US there are very few VHF stations anymore and the ones left are in the VHF high band.
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Old Nov 09, 2012, 05:41 PM
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But why its range is more than 35 Mhz ? And do i need to build a amplifier for those module from mouser.com
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Old Nov 09, 2012, 06:15 PM
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But why its range is more than 35 Mhz ? And do i need to build a amplifier for those module from mouser.com
Depends, what is it you are trying to do ?
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Old Nov 09, 2012, 06:25 PM
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Depends, what is it you are trying to do ?
I try to do nothing , i just try to understand how transmitter work , and why 433 mhz get a longer range than 35 mhz
What i mean is , i buy a module , but it just a small module with 200-500m range . Can i build a amplifier to get 10km range ?
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Old Nov 10, 2012, 03:42 AM
Stuart
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and why 433 mhz get a longer range than 35 mhz
It does not, for the same amount of transmitted power and same sensitivity for the receiver.

Physics dictates that absorbtion of RF by the atmosphere rises as the frequency rises, Its the pesky oxygen and water vapour we have to endure.

Best to start with a better 35\72mhz system in the first place, 200\500M is little more than a park flyer type set. Most decent TX and RX sets will allow you to control a model as far as you can see.
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Old Nov 10, 2012, 09:21 AM
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In real life, I think you will find that the range of 35 MHz is far greater than the 433MHz if both transmitters are working at the same power levels. The hard part is having both receivers with the same sensitivity in order to make such comparisons. Receiver design is usually the most difficult and critical aspect especially if physical orientation of the receiver antenna to transmitter antenna varies.
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Old Nov 10, 2012, 09:41 AM
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In real life, I think you will find that the range of 35 MHz is far greater than the 433MHz if both transmitters are working at the same power levels. The hard part is having both receivers with the same sensitivity in order to make such comparisons. Receiver design is usually the most difficult and critical aspect especially if physical orientation of the receiver antenna to transmitter antenna varies.
and why FPV pilot ,going to buy a Dragonlink if 35 mhz is far better ?
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Old Nov 10, 2012, 09:47 AM
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But why its range is more than 35 Mhz ? And do i need to build a amplifier for those module from mouser.com
Every country has laws that limit the allowed power that can be used so amplification may not be an option. The power allowed in the 315, 418, 433 and 915 bands are very limited as all sorts of devices use these bands. Cordless phones, baby monitors, wireless mics, garage door openers, key fobs, etc. all have to share these bands so the power and range is limited. If you jump in with a 1 watt transmitter you will cause many problems and be a real jerk.

As pointed out, there is no difference in range between 72Mhz and 433Mhz. At 433Mhz it is possible to use tuned antennas at both the receiver and transmitter to get better range at the same power levels.

While many or most people will argue that the 72MHz receiver antenna is tuned, it is really just a hunk of wire and is a crappy antenna.

At 2.5Ghz the antenna size is very small and these devices can actually have tuned antennas with an effective ground plane or a dipole.

A mono pole antenna is worthless without a ground plane to work against. At 72Mhz the transmitter box is too small to be an effective ground plane. What happens is that the user is capacitive coupled to the transmitter box and becomes the ground plane. At the receiver end the cloud of wiring and control rods in the airplane becomes the ground plane. Altogether the system is pretty crappy. At 35Mhz the antenna size required for tuned antennas is even larger so the systems are even worse.
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Old Nov 10, 2012, 11:50 AM
Stuart
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and why FPV pilot ,going to buy a Dragonlink if 35 mhz is far better ?
Dunno, but I question whether this assertion on the Dragonlink page is true;

"The DragonLink is an UHF 1) FHSS 2) radio system for RC models. It is operating over the 433mhz band at 500mW. This band is legal in most countries for radio communication, and allow an extremely reliable and long distance radio link."

The band might be legal to use at 10mW in most countries , but at 500mW ???
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Old Nov 10, 2012, 04:04 PM
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As pointed out, there is no difference in range between 72Mhz and 433Mhz
For the same power output, antenna type, and receiver type, a 72Mhz system will perform better.
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Old Nov 10, 2012, 05:43 PM
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Originally Posted by mjsas View Post
Every country has laws that limit the allowed power that can be used so amplification may not be an option. The power allowed in the 315, 418, 433 and 915 bands are very limited as all sorts of devices use these bands. Cordless phones, baby monitors, wireless mics, garage door openers, key fobs, etc. all have to share these bands so the power and range is limited. If you jump in with a 1 watt transmitter you will cause many problems and be a real jerk.

As pointed out, there is no difference in range between 72Mhz and 433Mhz. At 433Mhz it is possible to use tuned antennas at both the receiver and transmitter to get better range at the same power levels.

While many or most people will argue that the 72MHz receiver antenna is tuned, it is really just a hunk of wire and is a crappy antenna.

At 2.5Ghz the antenna size is very small and these devices can actually have tuned antennas with an effective ground plane or a dipole.

A mono pole antenna is worthless without a ground plane to work against. At 72Mhz the transmitter box is too small to be an effective ground plane. What happens is that the user is capacitive coupled to the transmitter box and becomes the ground plane. At the receiver end the cloud of wiring and control rods in the airplane becomes the ground plane. Altogether the system is pretty crappy. At 35Mhz the antenna size required for tuned antennas is even larger so the systems are even worse.
Hi mjsas , your answer really help . I understand almost about 35 mhz and 433 Mhz . Thanks so much
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