v16 power draw at idle

[kubark42]

The v16 manual says this about the supply current:

RX: 0.3A at 13.8V, TX: 2.5A at 13.8V, TX into 50 ohm dummy load.

However, it's not clear to me if the published RX load is while driving a speaker, driving headphones, or simply in idle state waiting for an incoming transmission.

I fly gliders, so having a minimal idle load is important to preserving the battery. I love what I'm learning about the v16, and I especially love the public ICD. Here's hoping that the idle power draw is tiny, making this the perfect unit for my application.

[rainier]

The v16 manual says this about the supply current:

RX: 0.3A at 13.8V, TX: 2.5A at 13.8V, TX into 50 ohm dummy load.

However, it's not clear to me if the RX load is while driving a speaker, driving headphones, or simply in idle state waiting for an incoming transmission.

I fly gliders, so having a minimal idle load is important to preserving the battery. I love what I'm learning about the v16, and I especially love the public ICD. Here's hoping that the idle power draw is tiny, making this the perfect unit for my application.

Measuring a current unit on my desk - at a supply of 13.8V it draws 0.205A. That is without receiving a signal. With a 30% modulated signal at 70% audio output level into a 300 ohm aviation headset headset it goes up to 0.21A. Note that switch-mode power regulators are used which means current will increase as supply voltages gets lower and it reduces when voltage increases. Electrical power draw remains the same though.
Typical output power (transmit) of current production units tends to be around 12W at 13.8V supply at the units supply pins on the DB25 connector.
The unit on my desk produces about 13W of TX power at a supply current of 2.4A into a perfectly matched load. Note that any non-perfect load (such as a real antenna in most cases) will reduce the current somewhat as less power will be transferred to the antenna.

So it's fair to say our official performance figures are somewhat conservatively stated...

On a side note: The power draw during TX is fairly low by standards. This is a direct result of a very efficient transmitter design (which is so efficient it does not need much cooling). So with about 2.2A at 13.8V going into the transmitter you can calculate an efficiency of about 43% (actual RF power out at 127Mhz vs input power). This of course includes the remainder of the transmitter, not just the output stage.

It can actually do well over 20W but in order to ensure maximum reliability and robustness with respect to abuse and miss matched antennas it has been derated to 10W (a bit more in reality - the 10W is minimum but no radio leaves here under 11W).

[kubark42]

Thanks for the bench test. Understood completely about the SMPS current vs. power ratio.

Out of curiosity, what's driving the idle power load? Unless I misunderstand the Becker AR4201 specs, it's idle current consumption at 13.75 V is 0.07mA, or just under 1W.

From the Becker manual:

Power consumption at 13.75 V without panel lighting:

• "Standby" reception mode <= 70 mA

• Reception mode <= 500 mA

• Transmission mode <= 2.5 A

99% of my time gliding is spent in the boonies where there's no one talking, so the idle load is one of my bigger draws. I can see, however, how there might not be a true apples-to-apples comparison here, since you gave me an actual power draw and Becker is just publishing a figure.

[rainier]

70mA is about right for an analog radio. The V16 is digital - most of the current is used to run the fast CPU which has to process the radio signals at high speed in the digital domain. Second in line for current is the digital PLL circuit that creates the reference clocks (digital oscillators run at around 5Ghz which needs power). As this is a zero-IF receiver it is actually two receivers running in parallel - one providing a slightly time shifted signal to the CPU. The CPU reconstructs the original signal effectively from the difference of the two signals in the time domain. The last item that tends to suck a bit of power is the RF-preamp. One of the design goals for the V16 was to be able to match or better the requirements for the new ICAO IP3 requirements with respect to nearby FM radio station interference while at the same time not degrading receiver sensitivity as is common now with competing products (reducing the sensitivity to the minimum allowed helps achieve these goals). So in effect we need a receiver that is able to receive extremely weak signals in the presence of interference sources at nearby frequencies that actually exceed as much as +15dbm at the receiver input. It's a huge challenge - one of the building blocks to make that happen is a very good RF pre-amp that can handle large signals with good IP3 performace - you guessed it - that needs power...
In part - the decision to try and get a zero-IF radio to work for this was the unmatched selectivity such a design can provide due to a complete absence of mirror frequencies and undesired mixing products in the intermediate frequency stages (the zero I receiver does not have such stages). The selectivity is achieved by digital filtering directly in the baseband. The traditional downside of such a receiver is poor dynamic performance (so they are popular for digital data transmissions where levels are constant). The V16 avoids this issue completely and actually does better than a traditional analog receiver as there is no automatic gain control (which requires a control slope) - the signal "amplification" needed is a simple multiplication...
As far as I know - the V16 is the only radio of this kind used in aviation so far that is able to match or better all performance requirements.

But the V16 is only an intermediate solution - the real solution is a digital receiver that directly samples the radio spectrum using an extremely high speed analog to digital converter. These exist and the technique is widely used but not yet in any way practical for something like the V16 - you still need several amps to run these things and the cost of these converters far exceeds the cost of a V16. But this is where it will ultimately go...

[kubark42]

That's an excellent description. I guess this is one of those rare moments in science where analog components wind up burning through *less* energy than their digital equivalents.

That's quite some clever SDR you've got going. Silly question, but how hard would it be to get to the 157MHz frequencies so this radio could also work for marine VHF?

[rainier]

That's quite some clever SDR you've got going. Silly question, but how hard would it be to get to the 157MHz frequencies so this radio could also work for marine VHF?

In principle yes but it would need some modifications - that big silver rectangle you see on the PCB close to the antenna connector is a surface wave acoustic filter - it is a very precisely cut piece of quartz that is made to resonate at the frequencies of interest - in this case the filter passes VHF frequencies from the NAV band starting at 108Mhz to around 140Mhz with extremely steep attenuation beyond these frequencies.
So this filter would need to be changed. There also a more traditional band filter (LC based) before it with a much wider range and more slack skirts intended to prevent far away interferes (such as mobile phone stations) from overdriving the SAW filter. That would need to be tweaked as well.
Lastly - the firmware would need changing - we are now looking at FM modulation rather than AM, different channel dynamics etc - but that can all be done in firmware. FM is much easier to do than AM. To get AM with good audio quality and wide dynamic range going on what is to some extent a SDR design - it took me quite a while to get that right. The two signal paths have to match each other to an incredible degree to avoid beat frequency products and distortion of the audio signal. With FM it almost does not matter...