pages Current consumption
of the FT-817
A Front-panel view of the FT-817.
Where does all of the
One of the "complaints" that I've heard about the '817 is its
consumption. Its average power consumption is certainly much more
than that of a typical HT - and some believe that the fact that it can
run off batteries must mean that it can do so efficiently. (For
on operating the '817 from various types of batteries,
look at the Lithium-Ion
page as well as the NiCd/NiMH/Alkaline
page. Also, take a look at K6XX's
FT-817 pages for power consumption information.
Well, the fact is that the '817 does pull a fair
of current in comparison with your typical battery-powered radio.
There are a number of mitigating factors that can help one understand why
current consumption is what it is. (Disclaimer: I'm sure
exceptions may be found to most of the points below, but that's why
is just an article and not a novel...)
There is a lot of circuitry in this
though it pulls roughly 300 milliamps when sitting idle on receive,
is certainly less than most any other
HF transceiver that you'll likely find. (Yeah, yeah, I'm sure you
can come up with an exception or three, but I did say "most.")
This receiver uses a fairly high-level mixer. On receivers,
select high dynamic range (i.e. the ability to avoid receiver
in the presence of strong signals) or you can opt for
current consumption: In general, you can design for performance or
low current consumption - but not both.
There is no provision for a "battery saver" mode of
HT's nowadays actually do consume quite a bit of current
- in some cases, well over 100 milliamps for (true) dual-banders such
the FT-530. The "battery saver" mode operates by turning off most
of the receiver's circuits and then, every so often, they are turned
on to see if a signal is present: If there is a
then the receiver circuits are left on. Since a channel is likely
to be quiet much of the time, the average current
is greatly reduced. This sort of "battery saver" operation is
effective during FM operation and somewhat less practical in SSB or
It is a shame that no battery saver modes are available on the '817 to
use - or not.
Mechanical relays are used extensively for routing RF through the
and each relay consumes approximately 20 milliamps when it is
Why not use PIN diodes or latching relays? This would involve extra cost and PIN diodes (especially
in an HF transmit path) would not necessarily reduce current
A number of power-saving tricks are used in the '817. For
when a mode is changed that affects the required circuitry (i.e. going
from SSB to FM) the unused circuitry for the deselected
is powered down rather than "muted" or bypassed, thus minimizing
For SSB, CW and HF data modes, DDS (Direct Digital Synthesizers)
are used on both the main synthesizer as well as the BFO. These
circuits, being rather complex and operating at fairly high speed,
consume a fair amount of current (30-40 mA each) and thus contribute to
the overall consumption.
There are also a number of mode/band/option selections that can
affect current consumption. Below is a list of various parameters
that can affect current consumption. These measurements were
at 9.0 volts:
How much current does the radio consume from its
batteries when it is shut off?
Like most modern TVs, VCR, and radios, the FT-817 consumes a
current even when the radio is turned off!
Why? Well, you may have noticed that the power
a pushbutton. Pushing the switch does not
the radio's power supply, but rather it applies power to the computer
the radio, which then turns the rest of the radio on. It may come
as no surprise that this circuit consumes a small amount of current to
perform this function.
How much current?
At 8 volts, this is between 100 and 200 microamps, going up to
as 300 microamps at 16 volts, with the exact amount depending on
(lower temperature = lower current.)
What does this mean? At a continuous current consumption
microamps it will deplete the useful life out of a set of AA alkaline
within a year - more or less.
In other words: Don't leave batteries in
for a year and expect them to work!
When powering the radio from the rear panel, things are
If rechargable batteries are installed, the '817 trickle
pack at 10-15 milliamps - even when the radio is off. This small
amount of current is unlikely to damage any cells (due to overcharging)
that are left in the radio - even for long periods of time - but you
keep this in mind if the voltage to the rear panel is supplied by a
One "gotcha" to be aware of: If you are using the
power to the adapter is applied at all times - and 10
of current is consumed whether the radio is on, off, internally, or
Display backlight: 27 milliamps, regardless of color.
Rear antenna: 20 milliamps of additional
consumed when the rear antenna connector is selected owing to the relay
Noise Blanker: 13 milliamps of current is consumed by the
Compared to 10 meters (with all other things like mode being
on 30 meters to 160 meters consumes approximately 3.5 milliamps less,
and 6.6 milliamps less on the AM broadcast band, 10.2 milliamps less on
70cm, and 12 milliamps less on 2 meters and the aircraft band.
Compared to SSB/CW/Digital modes, the AM mode consumes 16
The AM mode does not require BFO circuits, and these may be powered
Compared to SSB/CW/Digital modes, the FM mode consumes 11
The BFO and product detector circuits are not needed and are powered
Compared to SSB/AM/CW reception 10 meters, reception on the FM
band consumes 38 milliamps less. Much of the RF/IF circuitry is
when in this mode because a completely separate receiver chain
of a single chip) is used for FM broadcast band reception.
When squelched, current consumption reduces by between 9 and 11
depending on band and mode. This is mostly a result of the front
panel signal indicator LED being illuminated.
Reception on 6 meters consumes an extra 7.7 milliamps - mainly
6 meter (only) preamplifier built into the filter unit. (Note
this preamplifier is in addition to the one selected by
Powering the '817 via the battery connector (as opposed to the
power connector) reduces power consumption by 5 milliamps. (I'm
sure why - I'll have to look into this...)
IPO on/off: When the preamplifier is on (i.e. IPO is off)
2.5 milliamps is consumed.
Depending upon the exact position of the main tuning dial,
may vary by 2 milliamps due to the illumination (or lack of) the
in the rotary encoder.
Depending on the exact position of the "Select" knob, current
may vary by 500 microamps.
Attenuator: The difference between the attenuation on/off
Selecting the optional SSB/CW filter does not change current
by more than 100 microamps.
AGC mode/selection doesn't affect current consumption measurably.
The amount of audio from the internal speaker can increase the
consumption by more than 120 milliamps. This is, of course,
on volume and the content audio being amplified.
When an OFF command as sent via the serial
FT-817 will continue to draw approximately 10 milliamps (due to the
being powered) if powered via the rear power
If powered via the internal batteries, this current consumption will
occur as the microprocessor is powered down - and it will not
respond to an ON command. If the '817 is then
powered by the rear connector, the 10 milliamp current consumption will
resume. Note: This current consumption will occur
if the OFF command was used.
When the Yeasu CAT interface is plugged into the rear panel, an
milliamps (approximately) will be drawn by the FT-817 powering this
This will occur whether the '817 is on or off or using internal
or an external source.
Table relating current and power
power supply voltage.
While the current consumption is only slightly affected by the
voltage, power consumption is much higher at the
voltages. Since power is determined by current multiplied
by voltage, even if current consumption were to not increase, power
would still increase. The table shows current and
consumption under the following conditions: 10 meters, receiver
minimum volume, USB mode, noise blanker turned off, front antenna
and backlight turned off.
As can be seen from the table, while the current consumption
only by 8% or so from 7.5 volts (the lowest voltage at which the '817
operate without much degradation) to 16.0 volts (the highest rated
the power consumption more than doubles!
What does all of
From this information, there are several things to do to minimize
consumption when trying to conserve battery power. The most
of these are as follows:
Turn off the backlight: This is, perhaps the
knock about 10% off the current consumption. (Yes, it is
annoying that the "auto" backlight function is disabled when using the
rear panel power connector.)
Use the front antenna connector: This reduces
by about 6% by de-energizing the selector relay.
Turn off the noise blanker: If you are running on
you are probably well away from noise sources and turning off the
will shave the current consumption by about 4%.
Enable the IPO: You probably don't need to have
enabled on HF anyway. Turning the preamplifier off (i.e. the IPO
"on") tends to reduce the magnitude of background noise, which also
to reduce the amount of power consumed by the audio amplifier trying to
amplify this noise.
Use the squelch: This is most easily done when
although if signals are strong, this can also work on HF. This
save not only current used by the audio amplifier (see below) but it
cut current consumption by about 3% when squelched even when the volume
is turned completely down. (It will save even more power if the
isn't blasting noise all of the time...)
Use minimum speaker volume: Next to the radio just
the audio amplifier can be one of the largest factors affecting current
consumption, and minimum volume is the best way to reduce this
Current may be further reduced by using headphones instead of the
speaker. This current saving can easily average between 10 and
when listening on a noisy HF band.
Use minimum operating voltage: The radio consumes
less current when running at 8 volts as opposed to 16 volts. More
importantly, though, is that the power consumption is less
half at 8 volts compared to what it is at 16.
power consumption in this way may not be particularly convenient when
batteries, but using modern switching supplies, it is
as demonstrated on the "Optimizing the
of the FT-817" page.
Use minimum transmit power: Transmitting (even
power) consumes several times as much power as receiving does so it
sense that the lowest transmit power is conducive to lowest power
In short, just turning off the backlight, using the front
antenna connector, and turning off the noise blanker will reduce the
consumption by 20%. Using headphones and minimum transmit power
also go a long way toward battery longevity as well.