njkayaker

Ignorance by choice seems to be your mindset.

Yet, you still are arguing.

PromptCritical 

They use Santa's elves in the off-season!

Seriously, one of the testing methods is to try the device in large (very large building) in this case, document the results, make changes and try again. As an interesting aside, back in the '70s when the first stealth fighter was being developed, a small model was mounted on a stand in a very remote part of the Mojave desert and tested the design by aiming search and also firecontrol radars (different frequencies) at it in different orientations.

The bike radar may have been developed using similar methods during the early development phase before being tested on actual roads. Perhaps the used something like remote control cars with radar reflectors. Just guesses on my part.

PromptCritical 

I personally really appreciate the BF's ignore list functionality

SoSmellyAir

Theoretically, the base technology can be used outside. But since I cannot find any commercial embodiments, I am just not sure what range it can achieve at a reasonable power requirement.

njkayaker

Why would the power requirements be significantly larger than the Varia (which has a similar range)?

The interior presence detectors are (usually) plugged in but it's possible they could be run off a battery for 6-7 hours (which would be impractical indoors).

MMWave does doppler and range (time of flight).

https://sumitomoelectric.com/sites/d...nts/E92-16.pdf

PromptCritical 

I looked into a large number of outside motion detectors. Some were radar based and some laser based. Many of them had long (100+ feet, I don't recall exact numbers) and they had fairly reasonable power supply requirements. Well within what would be necessary for a bicycle application.

I think the bigger challenge is developing the software package. The radar emitter and receiver and just a radio of sorts.

SoSmellyAir

I did not say that the power requirements would be significantly larger (or smaller) than a Varia. And I understand that mm wave radar can detect speed and range via Doppler effect; after all, that is pretty much the definition of radar, regardless of wavelength, right? It is just that every paper I have seen discusses mm wave radar with respect to motor vehicles, and since I have not seen any commercial embodiments, I just do not know what the power requirements are for radar range comparable to the 140 m frequently cited for the Varia. While mm wave radar presence detectors are readily available on Amazon.com and Best Buy, they are intended for use in interior spaces presumably much smaller than 140 m in any direction.

PromptCritical 

The range is not directly dependent on the wavelength of the radar. That is a function of the power (getting an adequate return) and the software package (setting up "gates" to minimize erroneous or unwanted returns"). The military has used mm radar in anti-aircraft missiles for decades, so range isn't a fundamental issue.

SoSmellyAir

Yes. My question with respect to mm wave radar is about the power requirement at (i) a range useful for cycling (e.g., 140 m like Varia) and (ii) duration (e.g., 10 hours on blinking like Varia).

njkayaker

Here, it appears you are talking about the power possibly needing to be larger than the Varia (which seems to be what a "reasonable power requirement" would be) to give a similar range.

MMWave does range by time-of-flight (according to the link I provided). Which isn't the Doppler effect. Right?

The interior sensors are about 15-30 feet (I think). The Carback might not be mmwave but it might be similar technology. In any case, the existence of the interior mmwave sensors suggests it's possible to get (approximate) location and speed in a small low-power device.

MMWave is more sensitive than is needed for a bike radar. Couldn't longer frequencies be used in a similar less-sensitive way? The Carback appears more sensitive than the Varia (but not by a huge amount). The range is supposedly better too.

njkayaker

The bike radars have this configuration:



The mmwave boards used in interior presence sensors look like this:




The mmwave boards are smaller but organized similarly.

Seems like the technology is similar.

PromptCritical 

I don't know the specific answer to this. I'm not an electrical engineer, just a recovering (my friends say the recovery is going poorly) systems engineer (many years ago), but find these things fascinating.

Koyote

I don't think the lane indication, even if it worked, is an important feature. The radar's purpose is to alert you to an oncoming car so that you can move over to the right; if you're going to move into the lane or turn left, you still have to look over your shoulder. In other words, it's not meant to be a substitute for the other things we're already doing.

I think these are the same issue: I've never gotten a false negative (that I can recall), but the closest I've seen is when a car appears and then disappears -- which happens when it is cruising at my speed, usually waiting for a safe opportunity to pass. Once the vehicle speeds up, it appears on the screen again.

SoSmellyAir

No, I was suggesting that an mm wave radar might need more power than an mm wave presence sensor. But I have no idea whether that would be more, less, or comparable to a Varia.

You are right, I did accidentally conflate the two.

Theoretically you are right, but as I have been trying to say all along, extrapolating the technology to the range useful for cycling will likely increase the power requirement; I just have no clue by how much?

Maybe? mm wave radar is currently proposed for motor vehicles, so I am not sure the requirements for cycling is necessarily less sensitive?

I think so?

Based on the few reviews I have glanced through, I might venture that the current differences between the CarBack and Varia are largely due to maturity of implementation, rather than any inherent limits due to the supposed difference in wavelengths.

PromptCritical 

The mm radar frequency band is generall considered to be between 30 to 300GHz. IIRC, GPLama stated in. his Youtube comparison of the Varia and CarBack that the Varia operated @ 30GHZ and the CarBack @ 77GHz (my numbers may be slightly off as the most memorable part of that statement was the significantly higher frequency of the CarBack), so both are in the mm radar category.

SoSmellyAir

I should have reviewed the FCC certifications before engaging you and njkayaker in this theoretical discussion.

Trek Bicycle CarBack Radar 5301478 FCC ID 2AHXD-5301478
GARMIN VARIA RTL510 TR812413 RF test report (fccid.io)

Per the above CarBack is 76 GHz while Varia is 24 GHz; I am assuming no change from RTL-510 to RTL-515 with respect to the radar components.

tomato coupe

I've read that the Varia uses 24 GHz.

njkayaker

As long as it can run as long as the Varia with the same size, it doesn't matter. That is, it really only matters that the power isn't a lot more than the Varia. As long as that can be met, it doesn't matter if it needs more power than a presence sensor.

The cycling device has to run at least about 8 hours. Acceptable battery life for interior products are about a year (about a 1000x longer).

Some of what I ran across for cars was for small distances (like for parking). High sensitivity might lead to more "false alarms" when cycling.

The increased frequency might be a big part of it.

Steve B.

First ride today with the Varia 715. It’s as described, a game changer for situational awareness. I suspect my 1040 audible alerts are too faint for my deaf ears, I could hear the audible on my phone though. I was able to pair the Varia to my Instinct watch, but was not getting buzz notifications. In any event, this is a very useful device. I particularly like being able to see that there are multiple vehicles coming up behind and also like that I can mostly judge the approach speed. That is very useful info no obtained from a mirror. I also likes that it powers on and off when I power up or off my 1040. Overall, money well spent.

SoSmellyAir

The Edge does not allow one to adjust the volume of the Varia alert tones. My only option is to switch between a multi-tone alert -- a triple note trill, which was too much for me -- and a single beep. Whereas, the iOS Varia app does not have the same limitation.

Thanks for pointing this out! The Garmin Edge documentation is not exactly well organized.

Steve B.

My riding buddies can hear the alert tones generated on the 1040. I can't so just turned it off.

And no escaping that Garmin cannot write a manual. The 1040 is horrible, the Instinct watch only so-so. The Varia is useless.

PeteHski

I didn’t realise there were different Varia alert tone options on the Edge units. Whatever the default is on my Edge 530 I can hear it clearly on the bike.

PromptCritical 

We are on a tour of National Parks in Southern Utah and the Varia is really helpful in this setting (two lane curving roads with light traffic).

howsteepisit

For me, the Varia is a game changer. I've ridden for the better part of 60 years, some years more some years less. I still hear cars approaching from the rear just before my Varia alerts on some days, some days not. Even in town, knowing what's behind make left turns so much easier. I do look before leaping though, just in case of a false negative but in over a year and 3000+ miles I have yet to have a false negative of positive. Seems for some odd reason I just cannot twist around and look behind me nearly as easily as I could years ago.

Troul 

if the radars could determine make of vehicles, that'd be futuristic!