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.
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...
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.
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.
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.
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.
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