My old FM-VHF battery-only radios will run for months on a set of 4xAA batteries. I also have a Sony pocket digital FM radio that, with regular and frequent use, will run for many weeks on two AA batteries. Can anyone explain why DAB/FM battery receivers consume batteries at an absurd rate (on mine about 10 hours) when used only on FM?
Quick check with DMM showed that the DAB-FM radio had a battery current of 129mA on DAB, and 204mA on FM (in both measurements with volume control at zero). Surely they don’t leave the heavy consumption DAB processing circuitry running in FM mode. Even if they do (incredible! Why?), I don’t understand why the current consumption should be nearly twice as much in FM mode.
Any thoughts appreciated!
Quick check with DMM showed that the DAB-FM radio had a battery current of 129mA on DAB, and 204mA on FM (in both measurements with volume control at zero). Surely they don’t leave the heavy consumption DAB processing circuitry running in FM mode. Even if they do (incredible! Why?), I don’t understand why the current consumption should be nearly twice as much in FM mode.
Any thoughts appreciated!
Thanks. The radio is a Roberts Gemini 49 - about 10 years old, so hardly state-of-the art. Manufacturers only claim about 10 hours battery life (6xAA) - and that's presumably for DAB. I don't expect much better from it when in DAB mode, so the measured consumption seems predictable for that. But why should it be more (or even as much) when in FM? As far as I know, there isn't any fault - that's just the way that it is as originally designed. But, again, why? I have seen claims somewhere that modern DAB radios actually use less power than FM sets, and I don't understand how that could be.
Page 53 of the manual refers to Pause Plus storage and Back light recommended
as being off when using batteries
http://www.aeldownloads.com/robertsradio/userguides/RD1 ISSUE.1.pdf
Maybe try as they suggest to see if improves. But can only think the DAB section is remaining on
for some reason when FM selected, but not the other way round when DAB is .
The manual also on page 5 states
We would recommend for economy that your radio is used
via the AC adaptor whenever possible with battery operation
for occasional or stand-by use only.
as being off when using batteries
http://www.aeldownloads.com/robertsradio/userguides/RD1 ISSUE.1.pdf
Maybe try as they suggest to see if improves. But can only think the DAB section is remaining on
for some reason when FM selected, but not the other way round when DAB is .
The manual also on page 5 states
We would recommend for economy that your radio is used
via the AC adaptor whenever possible with battery operation
for occasional or stand-by use only.
I don't know much about the specific model of radio you have, or DAB in general since it is not available here. I did however design two way radio circuitry for Motorola for 20+ years.
Early FM radio use a discriminator or ratio detector circuit as the demodulator for FM. Some versions drew virtually zero current since they could be made with a pair of diodes and a phase shift network.
Since you radio had digital demodulation capabilities, it probably digitized the received signal at some low Intermediate Frequency, and does the demodulation in software, or a logic array. There are several algorithms for demodulating FM, each with its own advantages and disadvantages. We used an algorithm that was developed in house and patented. It was designed for maximum noise immunity and intelligibility in the recovered audio (police and fire walkie talkies). The FM demod consumed more DSP MIPS than the APCO 25 digital volce mode, and therefore drew more current. The culprit was the heavy use of multiplication in the algorithm.
It's likely that you radio uses the same hardware for both modes, and the DSP code (or logic array) was optimized for DAB.
Early FM radio use a discriminator or ratio detector circuit as the demodulator for FM. Some versions drew virtually zero current since they could be made with a pair of diodes and a phase shift network.
Since you radio had digital demodulation capabilities, it probably digitized the received signal at some low Intermediate Frequency, and does the demodulation in software, or a logic array. There are several algorithms for demodulating FM, each with its own advantages and disadvantages. We used an algorithm that was developed in house and patented. It was designed for maximum noise immunity and intelligibility in the recovered audio (police and fire walkie talkies). The FM demod consumed more DSP MIPS than the APCO 25 digital volce mode, and therefore drew more current. The culprit was the heavy use of multiplication in the algorithm.
It's likely that you radio uses the same hardware for both modes, and the DSP code (or logic array) was optimized for DAB.
Yes. Most DAB/FM radios use digital techniques for handling FM, so one might expect that they have similar power consumption for both. Other things being equal, which they are not. Decoding DAB is essentially a matter of doing an FFT and then lots of bit twiddling which is not too different from what happens in a CD player. Modern FFT algorithms are very clever and have been heavily optimised. FM may be harder to handle digitally - certainly reviews seem to suggest that the outcome is not very good when compared with analogue methods. One might suggest that the FM decode has to be poor so the bad sound of UK DAB is not shown up too much!
Digital radio demodulation is done in chunks. Collect a packets of bits since they come to the radio in digital form, process them, stream them to a DAC. The CPU or DSP spends some time in idle mode drawing minimal current. A lot of improvements in processor and software have occurred in the past 10 years, so newer radios are not this bad. One of our first digital phone prototypes would run the DSP so hard that it would unsolder itself (before lead free solder was invented).
FM involves continuously digitizing an RF (actually a lower frequency Intermediate Frequency) data stream and continuously performing math on the stream before sending it to the DAC. There is usually two paths I (in phase) and Q (quadrature, or 90 degrees out of phase) this is needed to determine if the modulation is increasing or decreasing in frequency. This is analogous to the I and Q channels on a rotary encoder, needed to determine which way the knob was turned.
Our algorithm used continuously differentiating and cross multiplying the I and Q streams to recover a single audio stream. If the radio is stereo, then demultiplexing the left and right channels is done.
FM involves continuously digitizing an RF (actually a lower frequency Intermediate Frequency) data stream and continuously performing math on the stream before sending it to the DAC. There is usually two paths I (in phase) and Q (quadrature, or 90 degrees out of phase) this is needed to determine if the modulation is increasing or decreasing in frequency. This is analogous to the I and Q channels on a rotary encoder, needed to determine which way the knob was turned.
Our algorithm used continuously differentiating and cross multiplying the I and Q streams to recover a single audio stream. If the radio is stereo, then demultiplexing the left and right channels is done.
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