TandemGeek

Ok, here’s one for the MSEE’s and other electron chasers to ponder.

We’ve used wireless computers on our steel tandems for going-on 5 years now. The captain’s is a no brainer: works just like a single bike with a front wheel pick-up. The stoker’s wireless became a no-brainer when Polar’s higher-end HRMs started to come with transmitters with medium or long-range jumper settings. So, with the exception of those times when batteries would weaken every two years or so, the rear wheel pick-up mounted just under the rear brake caliper had no problem sending a signal to Debbie’s receiver/computer on her handlebars.

Now, as many of you know (and are probably sick of hearing about), we recently took possession of an unpainted all-carbon tandem: this is where it gets interesting. The new tandem actually moved the transmitter a little closer to the receiver so fat-dumb-and-happy, I slapped the transmitter and receiver on the carbon tandem and simply assumed it would work just as it did on the steel tandem: wrongo…

For reasons that still aren’t clear, the transmitter’s signal just doesn’t seem to play well with the carbon frame. Hold the receiver at a right angle and away from the bike and the transmission distance returns to the 30” or so that’s been the norm. However, once it must transmit through or around the frame the transmission distance is reduced by nearly 6”, or to a point where the receiver needed to be either 3” behind the center of the handlebars, or out towards the curve of the bar to pick-up the transmitter’s signal.

So, I change the transmitter battery just to make sure it’s at full strength: no improvement. I try the chain stay: no improvement. I put the transmitter and receiver back on the steel tandem and it works like a charm. I even put the receiver on the carbon tandem’s carbon handlebars (thinking maybe they are the problem) and with the steel and carbon tandems side-by-side with bars touching and it still picks up the signal from the transmitter on the steel tandem: OK, it’s the carbon frame. I check with our builder and he’s never heard of any problem like ours but notes that carbon can become charged with static electricity so maybe that’s what’s happened. Despite a wash down and other tricks intended to deal with any static energy, no improvement and I’m starting to think my only solution is write a check for a Garmin GPS unit which really gets me thinking because that’s clearly a last resort.

About 30 minutes after giving up on simple solutions and while searching for an Internet deal on a Garmin Edge 305 GPS & HRM unit I have a flash of brilliance (I know, hard to believe): what would happen if I changed the orientation of the receiver? In other words, instead of mounting the wrist unit around the handlebars per normal using the bar-mount, what would happen if I turned it by 90 degrees? Well, son of a gun… it started receiving the signal loud and clear and with a few inches to boot! Great, now I just need to convince Debbie that reading her computer at a right angle won’t be all that hard to do. Well, at least on the workstand, I was able to move the watch back to about 35 degrees off center without losing the signal which even to me and my bad eyes seemed to make the computer’s face easy enough to read. Fingers crossed, it will hopefully continue to work once Debbie’s on the bike and we’re rolling down the road.

Anyway, if any of the cone heads who understand this stuff have any suggestions as to what is really going on or how one truly “neutralizes” a carbon frame, please let me know. In the mean time, if you’re riding behind us at a rally and you see Debbie’s head cocked to the left and down she’s not asleep… she’s just checking her Heart Rate.

twilkins9076

That's interesting...I've had nearly the same experience with the wireless cadence pickup of my Garmin edge on my carbon fiber single. I never could figure out why the silly thing worked on the tandem (where I didn't really want it because of the Flight Deck's virtual cadence) but wouldn't work on the Giant. Now that you've got me thinking, I wonder of simply moving the Garmin unit to the same side of the bike as the transmitter might solve the problem...

BloomingCyclist

Very interesting! You've probably already read more than I have or will but I did a little to see that carbon fiber does absorb rf. It's hard for me to imagine that the carbon fiber layers would be aligned in a way to polarize the transmitted signal but my stoker and I had a good laugh when she finally told me she could never read the cell phone screen when she would pull it out of my jersey pocket. She wears polarized sunglasses and the cellphone screen is polarized at 90 degrees to her glasses. When she turns the phone sideways she can read it just fine.

Anyway, counselguy's stoker has a cateye 300 with cadence on their Calfee. The transmitter sits on the chainstay. I see that Cateye has a new unit, the V3, out in March using 2.4 GHz band long range transmission with cadence and heart rate.
https://www.cateye.com/en/product_detail/460

I'm curious to see what you hear from others.

Bloomington, IN

dvs cycles

Does Calffe plan on marketing the new STEALTH tandem?

TandemGeek

There is a lot of irony in that aspect of this anomaly... having worked in Burbank, California during the 80's before relocated to lovely Georgia in the 90's.

Ever read Lil' Abner?

DBC Steve

Skunk Works?

zonatandem

The sacrifices one has to make when buying a state of the art tandem . . .
Looks like a new niche market coming up: c/f-compatible HR monitors . . .
Pedal on TWOgether!
Rudy and Kay/zonatandem

swc7916

I spoke to our wireless guru yesterday about this (I am an engineer in an R&D group developing test equipment for the Boeing 787 airplane, which has an all carbon-fiber body) and he could come up with no obvious reason why this is occuring. Carbon fiber and resin is non-conductive, so the frame shouldn't be shielding the signal from the receiver. It's possible that the signal "bends" around the steel frame and becomes oriented correctly for the receiver's antenna, whereas the signal just passes through the carbon frame as is, which is out of phase.

dvs cycles

If he told you he'd have to kill you.
I know a friend of a friend and he was telling us about his time during the developement of theF117 which was denied to exist for years and how Skunk Works disguised their tracks on this project.
He went on to work on the B-2. When I asked him about the "Aurora" He and his wife, who worked for the same company got deadly quiet.
I thanked them for answering my question

I didn't know they went to Georgia though.
Maybe disguised as a BOILLED PEANUT factory?

TandemGeek

Yup... that is the crux of the weirdness.

I can't think of a logical explanation for why the transmission range is shortened OR why the darn Polar receiver has better reception when it's turned out of its designed alignment position when mounted on handlebars.

swc7916

From your description of the problem, it appears that the transmission range has not been shortened; otherwise, rotating the receiver wouldn't help any. The fact that it works when you rotate the receiver indicates that the signal is polarized and what you have done is to align the antenna in the receiver with the signal. To mitigate this problem, some receivers - like in your Bluetooth phone - have two antennas oriented at 90 degrees to each other.

You could try something dumb as an experiment, like wrapping the frame tubes in aluminum foil, and see if it works then.

TandemGeek

If I wanted and tandem made from recycled beer cans I would have bought a Robusta!! ( just kidding)

Actually, I did play around with some metallic shielding / backstopping around the receiver to no avail... before giving up the first time and surfing the web for a Garmin.

It was the thought of spending another $300 for a friggin' bicycle computer/HRM (I swear the bicycle industry is simply trying to out-FARKLE the motorcycle industry) that brought about the epiphany with respect to the antenna orientation of the receiver and transmitter. It's that apparent modification, bending, or polarization of the transmission signal that I can't figure out.

TandemGeek

True, but John's Calfee is painted and clear coated... not au naturale.

There's a reason that 'coatings' are applied to stealty aircraft** instead of paint.
(**Open source data can be found in Bill Sweetman's books).

swc7916

So you bought a bike made of pencil leads instead?

More ideas (that you probably already thought of): Is there a way to change the orientation of the transmitter? If it's on the trailing side of the stay, could it be moved to the leading side? How about moving it to the chainstay instead?

TandemGeek

Actually, it's made from polyacrylonitrile resins: a co-polymer. Well, that and epoxy resins just to hold it all together.

As for the transmitter, it's been right side up and upside down on both the seat and chain stays with no change in effect.

TandemGeek

The Skunk Works is alive and well and living adjacent to Air Force Plant 6 in Palmdale, California. Unlike the old days, the moniker is now a trademark emblazoned on the side of a hangar. However, rumor has it that some of the Skunks and spooks who haven't retired have moved elsewhere over the years, some even moving formerly unacknowledged programs like the F-22 Raptor elsewhere for production as what was the original Lockheed Aircraft Company, and later the Lockheed California Company, divested itself of its original home in Burbank, Ca. Or, so I've read.

swc7916

Ummm.....According to Calfee himself (see https://www.calfeedesign.com/GradesofCarbon.htm )polyacrylonitrile (PAN) is a fiber, not a resin, that is a precursor to carbon fiber. What they use are the carbon fibers that are made from PAN in a process that uses heat to remove all elements except the carbon. So the frame is made of carbon fibers that are held together by resins. Here at Boeing we use carbon fiber that is in the form of a tape and lay this tape around an airplane-sized mandrel. After impregnation with resins, the mandrel is placed into a giant oven to cure.

just me

From a friend who designs small RF devices, I trust his judgment.

"The steel in the bicycle frame acts as a ground or counterpoise for the rf signal...it's like the antenna is one side of a two wire system and the bicycle frame is the other wire to connect the circuit, more properly called a counterpoise. Without the "ground" or counterpoise, the antenna system does not work. Pure carbon is a metallic conductor, unfortunately carbon fiber is to a great extent epoxy resin, which is used as an insulator in printed circuit boards. The carbon fiber is now an insulator. I could be more helpful if I had the instrument in hand and could physically measure the signal on my spectrum analyzer, but I suspect that it is less than a milliwatt......"

Jack

oldacura

I say dump the Calfee (at a huge loss) & keep the wireless computer!

TandemGeek

Actually, he mis-spelled it as 'polyacrylanitrile' and fiber vs. resin is probabaly more an issue of semantics than anything else. Whatever-the-hell it is, it makes for an incredibly sweet riding tandem.

Just me's source, yours, and the others are probably on the right track to the root cause which does have something to do with the properties of the unfinished carbon structure, although I'm still not sure what that is...

I KNEW this would be an interesting thread with many tennacles.

oldacura

"Boeing 787 airplane, which has an all carbon-fiber body"

I knew that both Boeing & Airbus were using a lot more composites in their new planes but I didn't realize that the entire 787 fuselage would be CF.

paladinsfo

Initially the entire center section of the F-35 was milled from a giant slab of titanium....then they went to carbon fiber.....when they did so.....I was hired as a consultant to come aboard and work out the antenna radiation problems that now appeared, without adding any weight or external drag.....two people can lift the entire panel which acts as the duct for the fan and the wing supports...but back to your radiation problem....I just logged on as a favor for a friend...if someone will be so kind as to send an e-mail to paladinsfo@hotmail.com with the web site for the device in question and identify it for me, perhaps I can come up with a fix..Thanks....Chuck

TandemGeek

The device as in the structure the Polar S720i HRM is attached to or the HRM device itself?

The structure is a carbon tandem bicycle frame:
https://www.calfeedesign.com/tandem.htm

The device is here:
https://www.polarusa.com/Products/consumer/s720.asp

Since I have a general idea what we pay our consultants I'm hoping this is pro bono work...

Seriously, thanks for taking an interest and please pass along my thanks to whom ever referred you to our little spot here on the web. Also, please don't break a sweat on this: it's more a curiosity at this point as there are many work arounds that would cost less than the value of time spent searching for a solution by most of the folks who frequent this list.

just me

Looks like my friend has joined us.
Tandemgeek you should send paladinsfo (aka Chuck) that email, he really seems to enjoy finding solutions for little problems like this. He also has led a very interesting life, maybe he will share a tale or two with you along the way. If he helps with a solution, please pass it along.

Jack

specbill

I love this forum!!!! It is threads like this that light me up it a great way.......
It sure looks like Sir Paladinsfo is the real deal from my seat in the peanut gallery.
'Thank You' to just me for introducing Chuck to us and for his willingness to contribute, that is pretty first class in my book.
TG, I'm thinking it won't be long before there will be no need for Debbie to be turning her head sideways to read those numbers...thanks for starting a very cool thread.

Bill J.

Bill J.