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HiTec Spectra Module getting hot

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Old 07-28-2004, 01:19 PM
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Baretta92
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Default HiTec Spectra Module getting hot

Hi,

I am using a HiTec Spectra module in my Futaba9C. I have seen several fellow modelers do this without any issues on both PPM and PCM. My question is, do you notice that the module gets rather warm? Mine does. It transmits just fine and I have no control issues but it just gets really warm. I notice that my power consumtion on my transmitter pack has gone way up. I just assumed that the module needs more juice to run. Is this a correct assumption?


Thanks,

Baretta92
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Old 07-28-2004, 02:59 PM
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Default RE: HiTec Spectra Module getting hot

The spectra module in my Eclipse 7 does get warm but not hot by any stretch of the imagination.

One reason for excessive heat would be if the load presented by the antenna on the Futaba was different to that presented by the antenna on the Hitec transmitters.

Transmitters have to be tuned to match the characteristics of a particular antenna length/capacitance in order to assure that the power coming out isn't reflected back and then dissipated as heat. This matching is often referred to as the standing wave ratio (SWR). The lower the SWR the better since it means that more of the transmitter's power is radiated by the antenna rather than wasted as heat in the transmitter circuitry.

Since the Spectra module isn't actually designed for the Futaba transmitter it's always possible that it operates with a higher SWR in a Futaba environment.

The effect of a higher SWR may not be particularly noticeable in terms of operating range (since halving the radiated power won't halve the range) but it could make the module run warm.

Perhaps it might be worth asking this in the Hitec Support forum.
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Old 07-28-2004, 03:22 PM
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Default RE: HiTec Spectra Module getting hot

Uh-oh... I been down this road. Get your flame-retardant suit ready once the boys see what you're doing. LOL
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Old 07-28-2004, 05:04 PM
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Default RE: HiTec Spectra Module getting hot

Xjet is right in that cutting the radiated power in half doesn't just cut the range in half, it cuts it by 4 (down to 1/4 normal range). First off, the Hitec module is not legal to use in the Futaba--should you be involved in a misshap, your insurance through AMA would be null and void and any other insurance would have legal grounds to invalidate your claim. Also, if you run at more than a few minutes with the antenna collapsed--even partially collapsed--you will get much more heat dissipated in the module. This is true with all transmitters, its just that most of them have the final output transistor deeper into the case and the operator doesn't notice the heat rise as easily.
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Old 07-28-2004, 05:37 PM
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Default RE: HiTec Spectra Module getting hot

ORIGINAL: Rodney

Xjet is right in that cutting the radiated power in half doesn't just cut the range in half, it cuts it by 4 (down to 1/4 normal range).
You've got that a bit backwards actually.

The inverse square law says that to double the range you must increase the power by a factor of four.

Hence, halving the power will reduce the range by a much smaller amount than you'd actually expect and certainly not the 75% reduction you suggest :-)

I'm too tired to do the math but a 25% reduction in range is probably closer to the truth.
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Old 07-28-2004, 05:41 PM
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Default RE: HiTec Spectra Module getting hot

WOW!

I did not know it was illegal[X(] The thought never even crossed my mind. I understand the heat dissipation theories and I do have some time where I am running it with the antenae collapsed while I am getting ready for a flight. I extend the antenae right before I take off. As far as the legality, who deemed this to be illegal. Just curious....



Thanks for the information,


Baretta92[&o]
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Old 07-28-2004, 09:10 PM
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Default RE: HiTec Spectra Module getting hot

Told ya it was comin'! LOL
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Old 07-29-2004, 09:50 AM
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Default RE: HiTec Spectra Module getting hot

Baretta92, who makes it illegal--the FCC-- Xjet, you are correct, the range would be reduced by the square root of 2 or would now be approx. 71% of the original range if power were reduced by half. sorry for my goof, I really do know better.
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Old 07-29-2004, 11:02 PM
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Default RE: HiTec Spectra Module getting hot

I have been using the Spectra with 9C for more than two years, without a problem. Range is as good as the stock module, actually a get a few more meters on ground test (antenna collpsed). It just get a little warm and draws more current (20-30% less battery time). I have more than 10 planes/heli, on different frequencies, and I notice that i gets warmer when I use lower channes (12 and 14).
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Old 08-01-2004, 11:57 AM
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Default RE: HiTec Spectra Module getting hot

Ditto---
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