# Improve RF range with a boost converter?

This might be a stupid idea, but I will try anyways:

I have a RF 433MHz TX module (datasheet) which can be supplied with 1.5V...12V. My understanding is the range increases with higher voltage as the module can draw more power.

My power supply is a 5V 10W wall adapter. Suppose I cannot simply change that to a 12V adapter.

If I increase the voltage from 5V to 12V using a boost converter, or a charge pump, would that have the same effect as having a 12V supply in the first place? Can the RF TX really draw more power through a boost converter?

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To answer your questions: yes, you can, in general, deliver more power to a load, if you insert a boost converter between source and load and yes, in this specific case, the RF module will probably transmit with a higher RF power, if you insert such converter. It is hard to tell, because the datasheet is quite poor. However, both switching and (especially) charge-pump converters produce a lot of noise, at their outputs. Forget about charge pumps. If I used a switching converter there, I'd probably insert a low-dropout linear regulator (LDO) between the switching converter and the RF transmitter, to have a cleaner supply.

Also, by inserting a boost converter, you do increase the power that you can deliver to the load, but only up to the limit given by maximum power that your wall adapter may deliver (10 W in your case). In this case, the maximum power that the RF module may admit at its input (which is 12 V · 8 mA = 96 mW) is well below that 10 W limit, so that number will not limit anything.

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The charge pump will also only double the 5V to 10V, you won't get 12V. –  Federico Russo May 27 '12 at 15:05
@FedericoRusso "will also only double". Wrong. He could use a charge pump to generate (5 V)·3=15 V, and then use the LDO to go down to 12 V. We're not giving detailed schematics here. Just ideas. –  Telaclavo May 27 '12 at 15:10
My point was that it generates whole multiples. Sorry if that wasn't clear. –  Federico Russo May 27 '12 at 15:13
That was what I was looking for. Good info about the noise of the converters as well. –  henning77 May 27 '12 at 17:40

The output power will be maximum at maximum input voltage. It just mentions a typical and maximum: 14dBm typical, which is 25mW, and 32mW maximum.

But it also says maximum supply current is 8mA. At a low supply voltage like 1.5V that would mean it consumes 12mW. In that case it can't possible transmit 25mW, so at lower voltages the power will be indeed limited.

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The datasheet is poor but, clearly, the maximum current (8 mA) won't happen when the voltage is minimum (3 V or 1.5 V, who knows, because the datasheet contradicts itself). The schematic in the datasheet does not show any boost converter in it. –  Telaclavo May 27 '12 at 15:15
@Telaclavo - and then we're not even talking about efficiency. Even if it would consume 25mW (3V and 8mA) it can't possibly output 25mW. –  stevenvh May 27 '12 at 15:19

What range are you wishing to achieve?

If I increase the voltage from 5V to 12V using a boost converter, or a charge pump, would that have the same effect as having a 12V supply in the first place?

Yes. as long as the supply can provide the required current the transmitter does not "care" how the 12V is provided.

Can the RF TX really draw more power through a boost converter?

It can really draw more power with more supply voltage - whether from a boost converter or otherwise.

RF can have more output voltage than supply voltage due to resonance but an order of magnitude check of result is often useful. A 12V rail to rail signal = +/- 6V. RmS value is 0.7071 of that or about 4.2V. Say 4V.
Power = V^2/R and R = V^2 / Power
To get 32 mW at 4V then Rload = V^2/Power = 16/.032 =~~ 500 ohms. As typical antennae used with such devices are liable to present impedances of 50 ohm or 75 ohm for whips or dipole or 300 ohm for a folder dipole. Either way, there is enough supply voltage at 12V to meet the 32 mw spec.

If you want substantial range you are liable to get best return for effort by implementing a formal antenna (ie not just a random untuned piece of wire of unknown characteristic), driving it well (impedance matched, low VSWR). If you need more than what simple whips etc will easily provide you can implement multi element "beams" or cantennas with relative ease. 432 MHz is a bit low for good gain cantennas but you are unlikely to need much.

Loop

Skewplanar - from here includes dimensions for 432 MHz.

http://www.n2jrf.com/antennasforvhfabove.htm

)

Classic turnstile

etc

Mainly 2.x GHz - things to learn:

Oh Yes !!! :-)
The photo below is from this page which is all in Arabic unless you allow translation, when it's 98% in Arabic and the gear shown is largely aimed at 2.x GHz BUT it's very worth looking at regardless.

[They seem to think they know what they are doing :-) :

Or in Turkish - not as good. 2.4 GHz

Spanish 2.4 GHz excellent
The aerial with a rod with circles twisted in it can be adapted to 432 MHz.

2.4 GH - v good

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