AM transmitter range tweaks?

[meteor]

Hi!


I got a few micro R/C cars (MicroZ GT's), which have notoriously short range, probably around 3-5 feet! (operating in the 27Mhz range)

I'm trying to get an understanding of what actually defines range of any particular transmitter/receiver set. (does the transmitter play a larger part?)


In the past, some manufacturers have intentionally "crippled" the range of the transmitter by adding a ceramic capacitor as a hand-soldered addition to the circuit board.


Can extending the antenna on either unit help to any significant degree, and is there any particular optimal length for the receiver at 27MHz?


Ideas?



Thanks!

[Cirip]

Hi meteor,

Range is largely the result of the transmitter power and receiver sensitivity.

Steps that need to be taken to improve range might be:
-Increase the Tx output power. If the Tx is powered from a 9V battery, getting more RF power won't be easy. The battery will be exhausted quite fast.
-Increase receiver sesitivity. The cheap toys usually rely on superregenerative receivers. Not too much to be improved there. Maybe adding an RF amp could increase the range, but you'll also add a lot of noise. Superreg receivers are wide band.
-Antena length. Maybe, to some extent, but don't expect huge improvements. The antenna on those toys are usually shorter than a quarter wavelength and extending them a bit may not induce a huge mismatch, but the range gain is minimal.

The range increase is proportional with the logarithm of the output power. To get twice the range you'd need to quadruple the power.

Hope it helps,
Cirip

[meteor]

Hi meteor,

Range is largely the result of the transmitter power and receiver sensitivity.

Steps that need to be taken to improve range might be:
-Increase the Tx output power. If the Tx is powered from a 9V battery, getting more RF power won't be easy. The battery will be exhausted quite fast.
Cirip


The TX uses 4xAAA cells, so it would be pretty trivial to up the voltage a bit, but would they not have some kind of regulator to protect the circuitry, based on the wide range of expected voltages? (new alkalines vs. rechargeables)

I did quickly try alkaline cells vs. older NIMh's, and there was no perceptible difference, but I need to fully investigate this.


It seems very odd that a major retailer (essentially RadioShack in Canada) would market a car in the $40 price range that was nearly unusable.

Oddly enough, the nearly-identical non-propo 27Mhz version of the same car has probably quadruple the range!



Thanks.

[Cirip]

The TX uses 4xAAA cells, so it would be pretty trivial to up the voltage a bit, but would they not have some kind of regulator to protect the circuitry, based on the wide range of expected voltages? (new alkalines vs. rechargeables) Um, no. Usually you don't regulate the power amplifier's (PA) supply voltage. Not worth it in this kind of application. None of the transmitters I've opened so far did it.

Increasing the supply voltage may increase the output power, provided the PA has enough drive. Otherwise, the voltage increase is useless.


I did quickly try alkaline cells vs. older NIMh's, and there was no perceptible difference No surprise here.

Oddly enough, the nearly-identical non-propo 27Mhz version of the same car has probably quadruple the range! It is actually difficult to tell what the problem is without running a few tests on the circuit.

Actually, I needed an AM transmitter for indoor fllying. I am using superregen receiver for their simplicity and low weight. So, what I did was to completely remove the original FM transmitter from the remote and replace it with my own AM design. The transmitter is essentially a Futaba 6EX series (exactly the same boards) packaged in a different box. See VEX Robotics transmitter.

Cirip

[meteor]

Here's a few photos of the main PCB. The black connector goes to the "handle" which has the steering control and the batteries/charger unit.

There is a large inductor(?) in series with the antenna output, and two caps and some other device marked "L2" in parallel with those two caps, then going to that inductor.


Does this help at all?


Added non-propo, looks to have very similar output side of things. Could the receiver be the issue perhaps?


Thanks!

[Cirip]

Sorry, there's not a whole lot I can comment, other than the fact that the transmitters look very similar (both use 2 transistors, the tiny black boxes with 3 terminals) and they should probably provide the same output power/range. L2 and those 2 caps look like the PI filter responsible for harmonic attenuation. A couple of comparative measurements, even with a basic digital volt meter might shed some light.