Librem 5 SAR (or DAS)


#21

That’s funny :slight_smile:

@2disbetter So you’d buy a pocket that shields radiation (if working as advertised), making the phone send at maximum power trying to find a station, sucking your battery (yes, phones adapt their power, depending on how good the connection is).
Instead of just pushing the hardware button, turning the radio off.

To be fair, the secondary use, putting it in the outer pocket, seems legit.

However, note that the whole SAR story is about using the phone. You know… making a call.
After all, that’s where, by far, most radiation occurs.
And the bag is not helping here. SAR is reduced by good engineering.


#22

How about this 100% plausible and legitimate product? :laughing:


#23

Intriguing. And the price surely tells us about its superior quality.


#24

Sorry for reviving this topic.

I still did not buy this phone as I am still concerned about the SAR. From @nicole.faerber we know that you are trying to reduce the SAR as much as you can. I appreciate that and from what you wrote you will not be able to tell us any SAR values at least until April or May.

However reading @TungstenFilament 's post and the FAQ to NFC I have doubts.

And from https://puri.sm/faq/will-the-phone-have-nfc-technology/

Will the phone have NFC technology?
Most likely not. We want to have a metal case and that is already a challenge with the three other antenna systems that we have to support: Cellular, WiFi/BT and GNSS (GPS…). NFC Antennas, likewise wireless charging, are pretty large. Last but not least they add another radio emitter which can cause additional EMC issues.

Would this mean high SAR values? I am no expert on this topic, is it planned to release SAR values before shipping in Q3 or would we have to wait for numbers after the official release?

I would like to add that I admire your work you are doing for the FLOSS Community! :slight_smile:


#25

It might be too much effort to release SAR values early. However, the given information does in no way hint to bad SAR:
If the case is not the antennae, the signal must be stronger, but only as much as the case absorbs.
If the case is the antennae, energy would be distributed instead of coming from one spot, which likely would mean lower SAR.

In reality, I think the most significant properties are distance between antennae and surface (could be really good in a thick phone)
and preferably, the display side should not be the only side where radio waves can pass easily.

I would expect at least average SAR.
To reduce exposure, you could always use a head set.


#26

look a librem 5 is already weird enough running Libre software and beeing manufactured from the hardware side to be more in-line with the privacy/security/freedom respecting principles of our digital world https://puri.st/

why not make it even weirder and add an external antena. in combination with iems and a good 1 inch away from the body (with a holster) you could maybe not have to worry too much about SAR values (that is not true when in contact with your body though but you could just use it on a need-only basis)


#27

I’m not entirely sure if this is satire, but in case it isn’t, lets explain how this stuff works.

Let’s start with the basics: What even is SAR?
It stands for Specific Absorption Rate, which is a measure for the absorbed radiation, converted to heat, in a human-like tissue sample.

This is only ever really relevant in a situation where the transmitter is very close to the tissue, because the potential for heat transfer decreases drastically with distance.
This would mean, an external stub-antenna, as common in early GSM phones and earlier analog mobiles, which increases the distance to the head by about 20 mm compared to an internal antenna, could improve the situation.

However, in reality this is not the case.
Modern 3G and 4G phones have very little power budget, and use relatively high frequencies with poor penetration.
A well designed phone needs to make sure, that said power is radiated in a way that causes least possible attenuation to work well; for a phone with internal antennas this means, a design will need to avoid radiating towards the head.
Not only because the head attenuates the signal (it does), but mainly because modern phones have a huge display and very little free space on the head-facing side, which usually has a metal shield, and a large PCB behind it.
This causes far larger attenuation than the head itself (which would only absorb a small amount of the radiated energy, while the displays metal shield will reflect a very large portion).

Because of this, most phone designs of the last decade tended to use the most obvious solution: place the antennas on the top backside of the device, where neither device, nor head, nor hand are in the way.
This causes them to radiate the vast majority of its power away from the head.
Since the antenna designs can typically achieve very little directionality, this is also caused by the displays shield, which reflects radiation away from the head.

Stub-antennas on the other hand have no such limitations - they radiate in a near isometric pattern, or to make it more understandable in a donut-shape around the antenna.
In turn this means, that even though the antenna now has a little more distance, it will actually radiate a larger portion of its power towards the head, since no reflector is in the way, and the radiation pattern is even less directional.

So a well done antenna internal antenna design will actually produce lower absorption in the head tissue (which may or may not be reflected in SAR measurements, depending on how they are done).

Stub antennas have in fact the advantage of less interference and tend to produce a more reliable connection, since omnidirectionality is what you want to have in a mobile device.

So why does nobody do it anymore?
First, it is just impractical. Such antennas make phones larger, customers much less likely to buy them, and are either bulky or get damaged easily.
Mainly however, it is, because we no longer have just one antenna in the phone.

We now need a least 2 antennas for LTE, and 1 or 2 for WiFi and Bluetooth.
Doing this as a stub antenna would make the phone look about like a walky-talky with a at least 50 mm tall plastic cover housing the 2-4 antennas.

So what does this mean?
Stub-antennas are more optimal for reception.
They are less optimal for SAR.
They are far less optimal in practicality.
They are more expensive, less robust, and consumers hate them.


#28

and that’s why i’ve used the word “add” not “replace” refering to the internal design.

as you’ve said

as such give us options to use both ( internal for phone like comunications while mobile and external stub for static 3g/4g modem/router type scenarios )

we will choose to use one or the other based on circumstance. removing the stub antenna for mobility as you’ve pointed out (and the rest concerning practicality) and mounting the stub antenna while indoors or when using the phone as a 3g/4g modem/router indoors or some static scenario.

the part about the metal shielding the head makes more or less sense to me but it might actually be true. that beeing said i think that adding the option for external antenna would not complicate the design too much. and if it’s a question of including the external antenna in the package - that won’t be neccesary as each user could decide if he/she really needs such a thing in the first place.


#29

any update on this?

there was mention of april/may for knowing more… now june… just wondered.

this is the issue that determine if i come back to having a phone.

ps,

Such antennas make phones larger, customers much less likely to buy them, and are either bulky or get damaged easily.

not this customer.


#30

it’s q3 2019 for the librem 5 - that is untill late september - so anytime in between july-september


#31

I don’t think you can expect an update on this before the actual phone has been built. Even if you know which modem and antenna is used, most components in the phone will have some kind of impact on the radiation.