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Power consumption of the Futaba 9C with various modules

I finally got one the 9C synthesized modules, and people had talked about the power consumption of them, so I went ahead and measured it. (Well, I measured current consumption, but if you really want power, assume 10 volts.)

9c with no module at all 77 mA with Futaba synthesized module, antenna down 257 mA with Futaba synthesized module, antenna extended 287 mA with 50 mHz module, antenna down 235 mA with 50 mHz module, antenna extended 200 mA with 72 mHz module, antenna down 160 mA with 72 mHz module, antenna extended 214 mA with Hitec Spectra module, antenna down 311 mA with Hitec Spectra module, antenna extended 280 mA

I was surprised at a few things --

-- that the 9C itself used so little power -- that some modules used more power with the antenna down. and some used more power with the antenna up, and that the two non-synthesized modules differed in that respect.

Readings were taken in my garage, so the readings outside, especially with the antenna extended, may be slightly different.

Reply to
Doug McLaren
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A couple of years ago I was playing with my old JR radio looking at the magnitude of the carrier on an oscilliscope - I ound that as I varied the antenna length, the strength of the signal varied. The strongest signal was achieved at about 2/3rds extention, and at that point the radio's power consumption was lowest.

I should try the same experiment with my newer radio...

Reply to
Poxy

Don't forget that the radiation pattern changes as you vary the length of the antenna. It is possible the the length providing the best match/least current consumption, might not be the best pattern for flying, though I doubt there would be any major consequence, even in a worst case scenario.

Ed Cregger

Reply to
Ed Cregger

I'm no RF expert, but I'm pretty sure that the antenna on a radio is a simple dipole with a correspondingly typical radiation pattern. I suppose it might change shape with antenna length. That said, I've got no plans to go flying with my antenna at half-mast - as it stands I can barely see my plane long before it's out of range.

Reply to
Poxy

It is well known that for a given frequency, the optimal length of a monopole antenna is lambda/4. This will maximize the conversion of power into RF. For other lengths, some power is reflected back into the transmitter and wasted.

A rough estimate, ignoring the fact that the pilot is a poor approximation of a ground plane and lots of other factors, is:

35 MHz -> 2.1 m 41 MHz -> 1.8 m 50 MHz -> 1.5 m 72 MHz -> 1.0 m

So it is perfectly normal that performance depends on both the length of the antenna and the operating frequency.

Google for "standing wave ratio", "characteristic impedance" and "reflection coefficient" for more information.

AC

Reply to
A. Caspis

The power consumption change with antenna in/out shouldn't be a surprise. The power consumption with antenna up vs. down depends on the details of the output amplifier circuit, not on whether the frequency is generated with a crystal or a synthesizer.

The amount of power consumed by the frequency synthesizer vs. a crystal oscillator should be on the order of a few milliamps. This difference will be swamped out by the hundreds of milliamps consumed by the output amp as it does it's job of generating RF so you can drive your plane.

It is a nice touch to have the power consumption go down with the antenna down -- hopefully this means that it's being more gentle to the final amplifier transistor.

Reply to
Tim Wescott

Power consumption seems to be fairly consistant...most of these modules are tuned for the antenna on the transmitter...being longer or shorter than optimum is debatable, I think. It's what comes on the transmitter...and we have to assume the factory tunes the module to the transmitter antenna length that comes with them all. Probably a better answerwould be a sensitive field strength meter placed some distance from the test transmitter/module and readings then taken with the different modules.... All things being equal..that is, the transmitter placed in a certain place and the FSM in exactly the same place, I think one could get a better idea of just how much signal the thing is radiating...right?? Frank Schwartz AMA123 W4KFK--------------- Who had to quit flying on 6 meters at my field due to strange glitches that the spectrum analyzer couldn't see.. and....the Futabe 6m on 00 seems to be working better than the JR on

00...dual conversion vs single conversion??? And finally...I have a BUNCH of JR 53.4 receiver crystals...anybody interested????
Reply to
Frank Schwartz

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