Antennas: gain, type

[tiberiu.gindu]

Hi all,

anybody tried different antenna types? More precisely, I wonder how important is the antenna gain (dBi) for the START/FINISH gate width and/or for the read rates.

Also - I am curious if anybody has tried a mat antenna, what type/cost, and with what chips/bibs.

Setting antennas on the side and having shoe-lace tags seems OK (easy to RF read through skinny legs); however the distance between an ankle bib and a mat antenna should ensure even better performance, I guess. 

Regards,
t.

[Ohio Race Day]

The question about mat antennas is near and dear to Brian's heart.  LOL.  I bet he answers it with every purchase of the software.  We've had plans to test the shoe tag (I'm not interested in putting RFID inlays on bib numbers) on a mat antenna.  There are some cheapy mat antennas made by Chinese vendors on Alibaba but the communication barrier and the uncertainty of what exactly they are selling has prevented me from diving into that pool.  We are on the wait list for a rental mat antenna from Times-7.  They supposedly rent them for $200 for 1 month.  I'd like to give it a try.  I ran the Akron Half Marathon over the weekend and noticed that the big boy timing company had a mat antenna (that's normal) AND two side antennas like us at the finish.  Hmmm.

http://www.times-7.com/rtas-uhf-rfid-race-timing-antenna-system.html

[edited]

[SportMadeSimple]

We purchased some Times-7 mats before I spoke to Brian about this and I would not recommend them.  Whenever I've tested them they under perform the side antenna.  It is a cheap plastic connection between mats that gives too much when they are on grass and they also get more slippery than I'd like in wet conditions.  I also had one cable end pull off the mat ... not a fan.  

[tiberiu.gindu]

Wow! under performed the side antenna...

This antenna is supposed to have a 10 dBi gain (pretty good). Most antennas (including those proposed by Motorola for RFID applications with FX7400) have 6 dBi only.

4 dB more means the signal power is 2.5 x (2.5 times!) stronger.

I was expecting that the combination of higher gain, smaller distance-to-tag as well as avoiding having several bodies between the antenna and the chip would provide better results.

Was it the same antenna indicated bu Ohio Race Day? (SlimLine RTAS...)

Was the tag close to the antenna? (for example - near the ankle of the runner / cyclist) ?

thanks!

[tiberiu.gindu]

I'll be waiting the feedback : )

One should mind (on the finish line setup) the radiation pattern of the antenna: these are directive antennas; the radio waves are spreading in certain directions (usually a lobe towards the front of the pannel); thus - if the finish line is 5 meters wide and the mat antenna is only 1.2 meters wide, it won't catch signals from the edges. Sorry if I'm detailing on obvious matters : )

thanks,
Tibi

[SportMadeSimple]

Sorry .. I should have been more clear.  I've been using wet inlays on bibs so the proximity to the mat is not ideal, but it is still generally closer than the side antenna.  When I look at the read data it is always the side antenna first and more often.

The Side antenna I use has Gain: 9 dBic  -  http://www.atlasrfidstore.com/MTI_MT_262006_TRH_A_K_RHCP_Outdoor_RFID_Antenna_p/mt-262006_trh_a_k.htm

The mat is 10, but it is under the mat and has a different pattern (as you mentioned) http://www.atlasrfidstore.com/Times_7_A5530_LP_RFID_Antenna_902_928_MHz_p/70890.htm 

[tiberiu.gindu]

Thanks a lot!

now maybe we'll see Ohio Race Day's feedback (when ready)  : )

[Brian Agee]

Mike is right, mat antennas and bib tags are two topics that are sure to get me up on my soap box. :)

I should start by saying that I've never personally tested mat antennas even though I've had plenty of offers to receive them at no cost so that I can try them out. Here is why I have no interest in mat antennas:

1. I know how RFID works, so I can tell just by looking at them that they will not work well. Here is why:

When I first started playing with and learning about how RFID works it didn't take me long realize that RFID works extremely well as long as you don't break the rules that I laid out in the topic labeled "Ensuring the highest read rates". These are well known concepts with RFID, pay special attention to the 3:35 - 4:00 mark of the following video: https://www.youtube.com/watch?v=rSbSYp2hexs&list=UUUrisPGQP-tDwzwAv9kcgWw

The problem with mat antennas is that the RFID waves coming out of it are pointing straight up - so if you have RFID tags on the bib the tags are coming across "knife edge" to the antenna. This is why the read rates are so poor with mat antennas. Most people report around 60% read rates when using only mat antennas with bib tags.

Most ground antennas are also Linear antennas. If you buy a Linear antenna then only are you fighting against the bad angle, but you also have to worry about every tag coming across at the perfect orientation.

2. Cost

With mat antennas is that you'll spend around $1,000 for about a 6 foot wide coverage area that provides poor results when you could have spend around $100 for a single panel antenna that offers a 20 foot wide coverage area and excellent results (if tags are worn on the side of the body like I recommend). For less than half the cost of a single mat antenna you can have multiple read zones throughout your finish line.

3. Maintenance

Storage and transportation of a mat antenna is not as easy as with panel antennas. Additionally I'd imagine that the wear and tear of a mat antenna would be greater than with a panel antenna sitting off to the side of the finish line.

4. If it aint broke, don't fix it.

Again, I've had a few companies that sell RFID equipment try to get me to recommend their mat antennas but I've turn them all down. If I'm reliably achieving 100% read rates why would I be interested in changing anything? Even if mat antenna did reliably achieve 100% read rates there is still the problem with cost, small coverage area, storage, transportation, and wear and tear with being tampled on every race.

So far, every report I've received back from those that have tried UHF mat antennas (using many different tagging methods and brands of antennas) has been negative and the customer regrets the purchase. If any of you have a different experience then please let us know.

I will say that Ipico offers what is probably the best mat-antenna based system because they are using a lower frequency RFID than what we're using. Lower frequencies cannot pick up tags very far away, but they do better at reading through skin. I've never used their system, but just knowing how RFID works, I can imagine that they probably get pretty good read rates. Again, even if the read rates are good, all of the other factors listed above make me prefer the side-mounted panel antennas.

[joshspiker]

I have used mat antennas (and have not used side antennas although have used overhead) and for larger races (with a dense starting line) bib tags offer some big advantages although as several have stated cost significantly more. I am still relatively small time but did time a 5K with two 13' ground mats and had a 99% read rate at the start (with people who wore there bib and ran under the arch...fun to watch videos of some starts where people run around an arch or truss) with a single tag (dogbone) with a foam spacer on the back of the tag. 

Although this was not a huge race it was convenient for the race to hand the participant a bib and shirt and be done (no collection and no separate instructions.)

Again I have not timed a large race like that with side antennas but wondering what kind of read rates it would get at the start.

I spend roughly 40 cents for the disposable tag, encoding, foam spacer, and paying some to put them together. I order rolls of pre-encoded tags which saves a lot of time.

[joshspiker]

Sorry was typing too fast...that race had 1400 people so was a lot of people coming across at the start in a very short period of time.

Right now I have three different softwares I use...Agee, Race Director, and Race Result.

Here is the system: http://www.raceresult.com/en-us/solutions/DatasheetRRS.pdf

Not sure if you can buy just the mats. I bought the system and the mats and then paid extra to be able to use my own chips.

Have been intrigued by the mats RM uses: http://www.rmtimingsystems.com/Shop/Detail/RM-Timing-Performance-Mat-Antenna

Found their main site and if ordered in quantity can get the price down but would definitely want to try them first. I did get to see them at Running USA and they had a seemed really nice.

[tiberiu.gindu]

Interesting.

Indeed, I was thinking of mat antennas not in "ordinary" situations but mainly for:
a) chip-time capturing while lots of people are crossing the start line almost simultaneously;
b) triathlons (here - the usual solution is to have a velcro-tied chip near the ankle).

But even in simpler races we had problems with those guys tying their shoe-lace chips otherwise than instructed : ) 

Thanks for the fdbk.