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andypag

Voltage range on Airwave 612 TX

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Hi everyone.

I'm looking for some info on the Airwave 612 transmitter.

I want to avoid building a pcb for the input voltage required for the unit. I'm aiming to power it with it's own 4pack of AA cells (either rechargeable ni-cads at 1.2v each, or non recyclable 1.5v cells)

I'm not putting the unit in a plane, and although weight is an issue it's not so critical. So my 4 cell pack will come in at somewhere between 4.8v and 6v, and my question is; willl the airwave 612 transmitter accept this input voltage range or do I have to build some sort of regulator anyway? All the data sheet info says 5.0v. - will a lower/higher voltage effect performance? Does anyone have 1st hand experience on this?

I was looking at the much more expensive unit on sale at range video, which can cope with 4.0-7.4v. Will the Airwave units take the same voltage without exploding?

Andy

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You really should provide a stable 5.0V to it. Higher voltages will stress it (it runs way too hot as it is) and lower voltages will just result in reduced RF strength.

Keep in mind that when you use primary batteries, the voltage during the active discharge period can drop quite a bit. For example, if you wish to fully utilize the rated mAH spec of a 4-cell Alkaline pack, it would be considered fully discharged at ~3.2 volts. Since reliable operation is unlikely with that, more cells and a LDO VReg are needed for practical use.

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lower voltages will just result in reduced RF strength.

Have you done any propper testing at reduced voltages ?

I would be interested to run it at lower power.

Terry

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I've run it several times on a 4-cell NiMH. Including the time I used it on a skydiver doing a 4000m jump.

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Have you done any propper testing at reduced voltages ?

On my AMW612, RF power is reduced by 25% at 4.0V operation.

I've run it several times on a 4-cell NiMH.

Other than the initial high voltage when hot off the charger, a four cell NiMH/NiCD rechargeable will maintain decent voltage through its discharge curve. However, a primary battery will not.

FWIW, I have run my 5V Lawmate systems with 4-cell NiMH with good success. The short term high voltage it sees from a fresh charge has always concerned me, but nothing has smoked yet.

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Thats interesting, it may be a good way of running the 612 as it always seems to hot and current hungry to me. A 25% drop would be a good price to pay for the benifits. I would be very interested to know the usable voltage range with the current and output. Maybe we could use the 612 with switchable power levels ?

Terry

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I would be very interested to know the usable voltage range with the current and output.

On my test Tx's installation, 4V current is ~450mA. 5V current is ~530mA. The change in current draw is nearly linear with the voltages in between those two extremes.

The absolute current values will vary with each installation, but the relative differences should be similar. For example, the antenna itself can affect current draw (to normalize that issue, my values were recorded with a non-inductive 50 ohm RF load). I also noticed a variation in power out and current draw with different Tx module samples, so the numbers are not cast in stone. Lastly, I recall my test Tx started to get goofy at about ~3.7VDC or so. I suspect this threshold would vary due to component tolerances.

Maybe we could use the 612 with switchable power levels ?

It might be useful to allow the R/C Tx to control the video Tx's RF power. I don't think that in the case of the AWM612 you will buy much with that (only 80mA), but some of those 1W rigs are heat/power demons; being able to throttle them back to half that power, on demand, would not be a bad idea.

For those that want to use low voltage for power reduction, it is really a matter of trying it and then performing suitable tests to determine if you like the results. These are the sort of experiments that we do best on this forum. :)

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Its a shame its not possable to drop the current a bit lower but it dose give us the chance of keeping the 612 a bit cooler if we are using it in a position with poor cooling.

Terry

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If its any consolation, all the RF modules in this power class run quite hot. The nice thing about the Airwave modules is that the four metal corner legs are usually soldered into a host PCB. If the host board uses a copper plane layout then the resulting heatsinking helps out.

Sorry for going off topic. Hopefully the original poster's questions are already satisfied.

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Thoroughly satisfied thanks; but actually one more question: Will I toast this unit if I put 6v through it. (or am I likely to irradiate myself in the process?)

Andy

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Will I toast this unit if I put 6v through it.

I don't have the kahunas to try that. Ordinarily I would not expect it to be a good thing to try.

Assuming the electronics aren't damaged by over-voltage, I definitely would be concerned about the additional heat burden. But, maybe someone will chime in and say it is all fine and good. You just never know.

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I think on a practical note, the possible extra power would not add much to the range of the system but would require a heat sink for sure. The trade off is not good, thats why I was looking at reducing the power.

Terry

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