18 replies to this topic

[Scoots]

I've wondered for some time why there are so many, let alone any antennas on the nose of F1 cars. Certainly they could conceal them in the bodywork ... right?

[DOHC]

Concealing the antennas can't be that much of a problem, I think. But not everything sticking out is an antenna. You also have the pitot tube, for measuring (air) speed, and that can't be concealed, it must look the way it looks.

[Scoots]

I thought one of those looked like an airspeed sensor (pitot?). Why do they need to measure air speed 10cm up from the nose? I imagine that if it was 1cm up it would be affected by the aerodynamics, but wouldn't that be a constant they could calculate out? Couldn't they find another place for it?

-S

[Chickenman]

Why not eliminate antenna's? Because CarbonFibre is a very good blocker of RF signals.

[Scoots]

That's the beginning of a reason, thanks. Couldn't they put multiple antennas flush against the bodywork to ensure they can always get a signal through?

IIRC an antenna perpendicular to the air flow has alot of drag ... if nothing else they could lean them back and make them more aerodynamic.

[DOHC]

Originally posted by Scoots
I thought one of those looked like an airspeed sensor (pitot?). Why do they need to measure air speed 10cm up from the nose?

That's to measure "free flow" airspeed. You don't want the boundary layer (air next to the bodywork) influence the measurement. On commercial airplanes you sometimes see similar pitot tubes.

About the antennas, I wonder why fixed "stub" antennas aren't used? (Again compare airplanes, both commercial and military.) It should be possible to integrate them well with the body work. That doesn't mean they have to be behind carbon fibre.

[BRIAN GLOVER]

Pitot tubes are on all airplanes. As with F1 cars, the system requires a static vent/s that are insensitive to yaw. They are tiny little holes and I am not sure of their location on the car. The vent/s are there to allow ambient pressure on the other side of ram air side of the system for indicated airspeed measurement. It functions like a leaking altimeter. If the ambient or static pressure side is blocked, the airspeed indicator will show an increase in speed with altitude gain. This can happen if the de ice system is not activated and many an inexperienced pilot has come to an end when he pulls back to a stall.

Dont ever touch a pitot tube when you see a parked plane. It will scold your hand even after 2 hours after a decent.

The location of the tube is obviously placed in clean air and in some cases, the tube protrudes way ahead of the nose of the plane.

In the case of a F1 car the position is optimised and on top the nose seems to be the norm in that high drag location, however, in some test situations, I have seen pitot tubes mounted at the level of the front and rear wing. The density of the air can be a lot different at the front wing and the back wing. The track surface can get quite hot and the ground effect wing was more sensitive to density.
The indicated airspeed is crutial to a pilot, but the F1 driver does not need this information. It is transmitted real time to the pits and takes current conditions into account including prevaling wind to set up the car. Ross Brawn would tell MS to perform his qualifying attempt, when a cloud moved over the track.

At the end of the straight at Indy on a hot summer day, the difference in indicated airspeed can vary by 30% over a winter day. The wing produces less lift on a hot day and the indicated speed will be a lot less. On a standard day(10.13 millibars @ 15'c @ sea level), the indicated airspeed will equal the cars actual speed. The true aispeed can be calculated.

An airplanes performance envelope is always at indicated airspeed, but when you land in Santa Fe New Mexico in the summer, you will use up a hell of a lot more runway, because the true aispeed will be much higher.
One of the antennas transmits this info to the pits. The airspeed can be referenced at other locations on the car with the use of pryometers.
Ive seen as many as 8 antennas, transmitting such info as shaft speeds, engine telemetry, etc.

The longest antenna, is for the tranceiver and the shortest is the transponder. None can transmit at more than 4 watts and the am frequencies are very low and line of sight. The sin wave requires a vertical antenna and are lenght critical.

Originally posted by DOHC


That's to measure "free flow" airspeed. You don't want the boundary layer (air next to the bodywork) influence the measurement. On commercial airplanes you sometimes see similar pitot tubes.

About the antennas, I wonder why fixed "stub" antennas aren't used? (Again compare airplanes, both commercial and military.) It should be possible to integrate them well with the body work. That doesn't mean they have to be behind carbon fibre.

[Powersteer]

Metal strips as antenna mounted on top of the airbox???I wonder how much visual disturbances does the current arrangement of antennas are to the drivers.

[Scoots]

http://www.schlegelm...ix/0213-34.html
http://www.schlegelm...ix/0213-36.html
http://www.schlegelm...ix/0213-38.html

Some interesting pics

[DOHC]

Originally posted by BRIAN GLOVER
The longest antenna, is for the tranceiver and the shortest is the transponder. None can transmit at more than 4 watts and the am frequencies are very low and line of sight. The sin wave requires a vertical antenna and are lenght critical.

Are there regs prescribing what type of radio transmission is allowed as regards frequency band, transmitter power, digital vs analog data transmission (apart from what is allowed by radio/telecom authorities)? All of these are factors that affect antenna type and design. With modern designs, antennas don't have to stick out that much.

Also you mention low am frequencies that are line of sight, but isn't it rather FM frequencies that are line of sight, while AM "bend" more easily?

Finally, why use different antennas and frequency bands for different types of data?

[BRIAN GLOVER]

Howdy DOHC,

Beats me why they have so many anntenni in such a high drag area. They spend millions on wind tunnels, why cant they have a pitot that retracts on the high speed sections.

I dont know too much about this, but nobody else has responded, but why cant they combine all transmitters on one antenna? Either a freqency dependent multi frequency antenna that transmits close freqencies or multiplex many channels of information into one frequency. Why cant they have some fibreglass sections so that they can hide the antennas or at least put them in a faring?

I mention 4 watts, because of FCC liscencing limitations for transmitters, in the States anyway, but they could even transmit at less power, say 2 watts on the telemetry. With a high enough tower at the pits, that will more than ample.
The short antenna is the transponder, which transmits in 1/4 wave lengths , and intigates signals from the pits and sends it back in car specific codes. This must be at least 17" from the transceiver antenna. The power of most coms is 117.95 to 134.95 MHz. Transponders or Xponders need more power, say 100 to 150 watts.
Such antenni are $5ooo to $6000 on aircraft, a mere drop in the bucket for F1 teams. There must be more to it than I am telling. How much do they spend on wind tunnels and such?

Originally posted by DOHC


Are there regs prescribing what type of radio transmission is allowed as regards frequency band, transmitter power, digital vs analog data transmission (apart from what is allowed by radio/telecom authorities)? All of these are factors that affect antenna type and design. With modern designs, antennas don't have to stick out that much.

Also you mention low am frequencies that are line of sight, but isn't it rather FM frequencies that are line of sight, while AM "bend" more easily?

Finally, why use different antennas and frequency bands for different types of data?

[BRIAN GLOVER]

That should read, interrogate.
[QUOTE]Originally posted by BRIAN GLOVER
[B]Howdy DOHC,
The short antenna is the transponder, which transmits in 1/4 wave lengths , and intigates signals from the pits and sends it back in car specific codes.

[DOHC]

Originally posted by BRIAN GLOVER
I dont know too much about this, but nobody else has responded, but why cant they combine all transmitters on one antenna? Either a freqency dependent multi frequency antenna that transmits close freqencies or multiplex many channels of information into one frequency. Why cant they have some fibreglass sections so that they can hide the antennas or at least put them in a faring?

Exactly my thought. They already have that top camera pod. Wouldn't that be a nice location for a fiberglass stub containing the antenna? And wouldn't it be possible to also put the pitot tube up there, so you could make it a straight pitot instead of the 90 degree bent unit they have now? I would guess that the flow is clean enough if you let it protrude some 20 cm (8-10", the location would essentially be right above the driver's head, but well above it, and well clear of the airbox intake's level).

On the other hand, the speeds are not so high after all, at least if you compare to aviation. So while you would certainly dismiss the solutions you find on an F1 car for aviation use, it's perhaps not so critical for total drag in F1. Nevertheless, from on-board F1 cameras we have many times seen the anntenas vibrating heavily from the induced von Karmann vortices. It could be done in a better way, I think.

[BRIAN GLOVER]

Howdy DOHC,
I e mailed a buddy who is a communications engineer and this is his reply. Knowing Russ, we are going to learn more about this than we ever want to know.
I cant answer his questions.

Hi Brian,

Based upon the photo, it appears that the four
antennas operate at four discrete frequencies, with
each falling somewhere between 80 MHz and 2 GHz. (The
higher the frequency, all things being equal, the
shorter the antenna. The "rubber duck" spiral wound
type will be physically shorter than the straight rod
type antenna.)

I'd guess that the biggest problem is keeping each
data stream clean and uncontaminated (free of
"crosstalk") by the others. It appears that they do
this through frequency separation.

Look at modern warships, which bristle with antennas
of all sorts. They face similar problems. For this
reason, shipboard receivers are especially selective
and their transmitters are especially free of spurious
emissions. The rf components in F1 cars probably have
similar requirements regarding out of band signal
rejection.

You're correct: in theory the data could all be
multiplexed, in both the receive and transmit
directions. This could in theory be done at the rf
(radio frequency) level, but signal losses in the rf
components might make this impractical.

A cleaner approach would be to multiplex the data
before they modulate rf signals, and then just
transmit and receive proportionally wider bandwidth rf
signals, via one wide bandwidth antenna. However, in
general the efficiency of an antenna and its bandwidth
are inversely proportional, so an antenna that's used
to receive/transmit a narrow signal may not work as
well with a wide bandwidth signal.

In the end, my guess is that the F1 car designers kept
the rf systems discrete because it's simple and offers
rf component redundancy that a multiplexed system
wouldn't.

Questions:

1) Does the transponder (which I normally think of as
an airborne pulse system related to external radar
systems) respond to an intermittent interrogation
signal from the pit? What frequency does it operate
at?

2) Do you have an idea of how much data (in terms of
bps or Hz bandwidth needed) are transmitted and
received, and for what duty cycle?

I hope that this helps.

Regards,
Russ

p.s. I've copied our messages to friends who may have
some ideas.

[BRIAN GLOVER]

..........Regarding the idea of somehow plaing all antennas
within one housing:

In general, antennas should be spaced *at least* one
or two wavelengths from each other to minimize their
electrical interaction. (A second antenna within the
near field of another antenna will detune the first
one.) At a frequency of 150 MHz a wavelength is about
2 meters, at 450 MHz it's about 3/4 meter. The
spacing shown in the photo is probably less than a
wavelength, so there's probably some interaction
between antennas resulting in less than optimum
radiation efficiency, but they live with it.

Regards,
Russ

by the antennas in the photo, it looks like
the frequencies in use are somewhere between 100 MHz
and 2 GHz. I'd guess that each antenna is fed by a
discrete transmitter, receiver, or transceiver.
Multiplexing at this level would be tricky (but
theoretically not impossible) because of signal loss
(especially troublesome in the receive direction)
within the rf components.

If you wanted to multiplex, a better place to do it
would be before the (rf - radio frequency) transmitter
/ receiver stage. Then you'd need wider bandwidth rf
components, including the (single) antenna. Depending
upon how much data are being transmitted / received,
this may be tricky. Antennas have one optimum
frequency; their efficiency decreases as you move up
or down away from this frequency. You can think of
them as tuned circuits. Generally speaking, the most
efficient antennas have very sharp responses (and
would be poor choices for wide bandwidth signals);
wide bandwidth antennas are usually inefficient.

Look at modern warships. They bristle with antennas,
one or more per rf system. This places a requirement
on the transmitters that they be clean (no spurious
emissions) and the receivers that they have sharp
passbands (no spurious responses). Keeping each
system's data uncontaminated while in the vicinity of
so many rf signals is tough on the receivers
(especially) and transmitters. To some degree, these
cars may have similar problems -- I don't know.

In the end, my guess is that each rf system is
discrete because nobody thought much about trying to
integrate them, and since their weight is minimal,
they sort of liked having the redundancy that keeping
them discrete buys them. Keeping their data
uncontaminated is probably provided by rf frequency
separation. (Notice the unique appearance -- and
probable frequency of operation - of each antenna.)

Hope this helps.


Regards,
Russ

[Ross Stonefeld]

Why cant they put the pito extended out the tip of the nose like on older spec fighters? The secondary benefit would be subtle tire deflation on the car ahead

[DOHC]

Hi Brian -- interesting stuff you got!

In the end, my guess is that each rf system is discrete because nobody thought much about trying to integrate them, and since their weight is minimal, they sort of liked having the redundancy that keeping them discrete buys them. Keeping their data uncontaminated is probably provided by rf frequency separation. (Notice the unique appearance -- and probable frequency of operation - of each antenna.)

This is very plausible. Sounds like the radio systems have been added, one "on top" of the other, as the needs or possibilities of using new or more telemetry data arose.

[BRIAN GLOVER]

More stuff from Russ and Richard. Told you, this stuff would keep coming.

Hi again Brian,

As I mentioned, the biggest problem is contamination
of one data stream with another. The setup that's
pictured provides for isolation through both frequency
and spatial isolation. The spatial isolation though
looks marginal. I wouldn't want to reduce the space
between those antennas! In an ideal world I'd want at
least one or two wavelengths' separation.

Within the above limits, I'd guess that all the
antennas (with adequate spacing) could be placed
inside a fiberglass fairing(s). though I'd want to first
test the proposed fiberglass for signal loss at these
frequencies. I don't think that carbon fiber would
work, as it conducts rf at most frequencies.


Reason for keeping antennas separated:
---------------------------------------------------------------

Despite rf equipment manufacturers' claims, signal
contamination -- specifically cross-modulation -- can
and does occur within receivers (specifically their
first stage) themselves. The degree to which this
takes place is a function of the first stage's
selectivity and its dynamic range.

Ideally, receivers' bandpass characteristics would be
such that they would receive the desired signal and
nothing else. However, because physical things
(inductors, capacitors, insulators) aren't perfect,
receiver front ends have some out of band response.
Read good military receiver tech specs carefully and
you'll find cross-modulation and desensitization
specs. Most commercial receivers won't have these
specs. Or, perform the test yourself using two or
more signal generators and a signal mixer to generate
your own desired signal and interfering signal(s).
True, if the system designer knows the exact
frequency(s) of interfering signals(s), notch
filter(s) tuned to the interfering frequency(s) may be
used ahead of the receiver to minimize cross-mod.

It sounds like the teams aren't sending / receiving
all that much data. From an overall system design
standpoint, the first factor to consider is how much
data need to be transmitted and received, and whether
some channels can be simplex (transmit first, then
receive, then transmit) which will save bandwidth.

Once the bandwidth requirements are known for both
receive and transmit directions, informed decisions
(i.e., digitize and multiplex all of the information?,
modulation type, frequencies, antenna type) about how
to accomodate these can be made. Who knows, maybe the
best solution is to keep all data streams separate,
with a discrete frequency and antenna for each.


Has this added to the confusion?

Regards,
Russ.


Hi again Brian,

IEEE spec 802.11 is for wireless LAN (local area
network) applications. Its bandwidth is 11 Mbps
(equivalent to state of the art 10 year-old *wired*
LANs), so it could probably handle a car's bandwidth
requirement. It's normally used within office
buildings to provide on-line portability for users.

The problem with 802.11 (an unlicensed service) is
that its nominal center frequency (it uses frequency
hopping to provide diversity and security) is 2.4 GHz,
which is strictly line of sight. Maybe repeaters
could be placed at the far ends of racecourse?

Richard is an old friend and mentor. He really
knows rf, from both theoretical and practical points
of view. For the past few years he's been working on
applying his employer's 802.11 chips to systems.

-Russ

--- Brian Glover wrote:
> Me again, I cant answer these questions. The
> transponder is for lap times
> and maybe speeds at a point on a track. The pitot
> tube is used for wing
> adjustment depending on atmospheric conditions. A
> quick adjustment can be
> made to the wing if it starts raining.
> Brian.
> >


Hi Russ,

The real savy commercial equipment does specify and therefore control the quality of the receiver performance. For example, the 802.11 WLAN protocol does specify minimum Adjacent Channel Rejection performance (and a whole array of other meaningful performance specs), so any Wi-Fi certified equipment should perform adequately.

The real problem, as with most good things in life, is that receiver performance (i.e. Dynamic Range) is a delicate trade-off between linearity, filtering (often referred to a "roofing"), current drain and cost. Like the punch line of an old joke states, "you can have any two of the three!"

Of interest, there is a big difference in philosophy between the FCC's mandate and that of the other compliance agencies (e.g. ETSI and TELEC). The FCC was only given the mandate by Congress to control radiation (e.g. transmitter performance and Local Oscillator radiation). The other compliance agencies police both transmitters and receivers. One interesting exception to this is that, somehow or other, the FCC usurped the power to control the Noise Figure of UHF TV tuners (but that's a whole other story unto itself).

So, 802.11's Wi-Fi consortium is a very necessary exception to the normal rule. Performance of most receivers sold in the U.S. is more or less "caveat emptor". Practically, however, various economic forces do maintain some de-facto quality standard for receivers.

Richard



[QUOTE]Originally posted by DOHC
[B]Hi Brian -- interesting stuff you got!

[biercemountain]

Originally posted by Ross Stonefeld
Why cant they put the pito extended out the tip of the nose like on older spec fighters? The secondary benefit would be subtle tire deflation on the car ahead

Hey Ross, don't give those NASCAR boys any ideas! Of course with a fendered car you would need to put the pitot tube sticking out the side of the car, ala "Ben Hur"