Developing a New Wireless Hardware Product? Here’s Your Most Important Decision
When developing a new wireless product there is one decision that matters most. This decision not only affects technical specifications like transmission range, battery life, signal quality and product size, but it also dictates where you can even sell the product.
This priority one decision that you must make as early as possible is the selection of the carrier frequency. This is the frequency of the signal that is used to “carry” the data from one device to another. Granted an electrical engineer will be needed for this process, but any entrepreneur or startup developing a wireless product should also understand the process at a high level.
The choice of frequency can have a huge impact not only on performance, but also on your ability to sell your product outside of your own country or region. Choosing the frequency gets really complicated if you plan to sell your product in multiple countries, and especially if sold worldwide.
Multiple radio frequencies are allowed around the world, and each country has its own set of rules.
Transmitting on many of the available frequencies requires the device’s operator to have a special FCC license similar to radio stations, TV stations, and HAM operators. No operator’s license is required for receiver-only products, like a radio, or GPS.
Unlicensed transmission devices, which include most new products, must use one of the following frequency bands in the U.S.:
Industrial, Scientific, Medical (ISM)
Short Range Device (SRD)
Personal Communications Service (PCS)
Family Radio Service (FRS)
Table 1 below lists some of the more common unlicensed frequency bands. It shows unlicensed bands that are available at both low and high frequencies.
However, any frequencies lower than 27 MHz are prohibitive for most products because of the large antenna size required. Although some applications still use a low frequency with a non-optimized antenna length.
Frequencies higher than 5.8 GHz don’t have enough range, especially for indoor applications. For most products a frequency between 433 MHz and 5.8 GHz is ideal.
Table 1: Available Unlicensed Frequency Bands
|27 MHz||276 cm||Worldwide|
|40 MHz||184 cm||Worldwide|
|315 MHz||12.6 cm||U.S. and Asia only|
|433 MHz||17.3 cm||Europe, Asia, Australia, U.S. (limited)|
|465 MHz||16.1 cm||FRS for use only North America|
|868 MHz||7.8 cm||Europe only|
|915 MHz||8.2 cm||U.S. and Australia only|
|1.227 GHz||6.1 cm||GPS L2 band|
|1.575 GHz||4.8 cm||GPS L1 band|
|1.9 GHz||3.9 cm||PCS for use in North America|
|2.4 GHz||3.1 cm||Worldwide|
|5.8 GHz||1.3 cm||Worldwide|
The rules can be quite complicated, especially for any frequencies not classified as “worldwide”.
For example, 433 MHz is normally thought to not be available in the U.S. because it is considered a licensed frequency that is only used by HAM operators.
However, under part 15 of the FCC regulations if the device only transmits data at very low duty ratios and if the transmission power is kept below a certain threshold then a product can operate at 433 MHz in the U.S.
So for certain types of products, 433 MHz can offer a worldwide solution. In fact, I recently designed a radio system using 433 MHz that will be used worldwide.
Another example is the Family Radio Service (FRS) band that is used mainly by walkie-talkies to transmit up to two miles. This band is only for use in North America. Originally it was only for voice communication. But GPS maker, Garmin, got the FCC to modify the rules to allow transmission of GPS coordinates over FRS for their Rino line of GPS/Radio products.
Lower frequencies will go further than a higher frequency signal for the same amount of transmission power. RF receivers are more sensitive at lower frequencies which also helps increase the range at lower frequencies.
There is a proportional relationship between transmission range and frequency. For example, a product operating at 433 MHz will have a range 5.5 times (2,400 / 433 = 5.5) larger than one operating at 2.4 GHz for the same amount of transmission power.
The transmission power can be increased at higher frequencies to help compensate for this fact, but there are limits placed on the maximum power allowed for various bands depending on the region.
The higher frequency bands have larger bandwidths which allow the transmission of larger amounts of data simultaneously. Bandwidth is simply the range of frequencies that can be used for a certain band.
For example, the 2.4 GHz band allows frequencies between 2.4 GHz to 2.5 GHz, which gives a bandwidth of 100 MHz. But if using 433 MHz your available bandwidth is only 1.7 MHz (433 MHz – to 434.7 MHz).
As shown in table 1, the higher the frequency the smaller the antenna. This fact, along with higher data transfer rates, is why 2.4 GHz has become so popular as product sizes continue to shrink.
Bluetooth, WiFi, and countless cordless phones and baby monitors use 2.4 GHz. The primary limitation with 2.4 GHz is the reduced range compared to lower frequency bands.
At lower frequencies the antenna size becomes so large as to be prohibitive for many products.
Some bands are very crowded, especially 2.4GHz, making sensitivity to interference a real problem.
Techniques such as Frequency Hopping Spread Spectrum (FHSS) allow designers a way to avoid interference problems. FHSS is what allows Bluetooth and WiFi to operate simultaneously at the same frequency without interfering with each other.
A FHSS system constantly hops between frequencies (within the defined band) so any interference is only a short momentary issue.
One final consideration is battery life. For a given range, the lower the frequency the lower the necessary transmit power. So more transmit power will be required at higher frequencies which drains batteries faster.
In many wireless devices the power used to transmit a radio signal is the largest drain on the batteries.
However, the lower frequency necessitates a larger antenna which then leaves less room for the battery.
There is no doubt that selecting a frequency is a complicated process, unless your application requires a protocol with a predefined frequency, such as with Bluetooth, WiFi, and ZigBee.
If your product doesn’t use one of these standard protocols then you have many options to consider when selecting the right transmission frequency.
If you have any questions or feedback please be sure to post in the comment section below. This is usually the best way to get me to answer your question, so go ahead and leave a comment;)
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- Hiring an Electrical Engineer to Develop Your New Electronic Hardware Product
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- Understanding Certifications for Electronic Hardware Products
Hello , can anybody tell me which frequency is used for automobile remotes in Australia, 433,434 or 315 or??
Hi Michael. I believe it is 434mhz. I know that here in the US, it is 315mhz.
clarifying 433 & 920 mHz in the USA: The primary user in of these bands is the U.S. government, in the form of the DoD. Amateur radio operators – hams, lower case please, are secondary users of the band. Part 15 users are third tier users. Part 15 users have nothing to complain about if they get clobbered by a ham with 1500 watts, or the government with thousands of watts. The license makes amateurs the legal tenants of these bands where the government is not using them, if we get into a conflict with Part 15 users they automatically lose.
Part 15 devices are Certified with an antenna attached. this certification verifies that the device produces an acceptable amount of power as delivered by the manufacturer. If you change the antenna for a higher gain antenna, it is no longer a Certified device. Amateur radio operators can run up to 1500 watts, and use a high gain antenna.
Amateur radio operators can use modules with >20dbm power like the 30 dbm RFM23BP devices, but you have to periodically transmit an ID
Thanks for the informative comment.
I think that hams get away with too much, they should get restrictions as well. Hams have too many frequencies to pick from. Also the f.c.c is out of control with allowing ham radio operators going Gaga on radio frequencies. The ism bands are swamped with low power devices, with the greatest loss of power, and total interferance. Ham radio operators have gone too carried away with power on their transmitters. It is pathetic and sad! They have 5 bands to get away with what ever they want, but yet leaves nothing for the non licensed user to explore with. That’s not fair. Some people don’t have the the comprehension, or understanding on how some of this stuff works. My boyfriend has tried taking the test to get his ham license, and failed more times than he cares to admit! But he has the know how to build. Hams should go narrow band, and trunking just like the rest of us. I would love to file a petition to give the third party users the right to operate on at least a few new frequencies to explore with better options to choose from. And yes we are going to complain untill our voices are heard! Police have taken 25 or so frequencies for there communications! Why not give us a few. We only have the ism band, and I feel that it is bull! You have hundreds of people breaking the law every day, and no one complains. But yet if we break a law we end up in jail, you are a full of it! Your lucky I have to keep my post clean, because I would love to tell you what I really like to say! But that would violate every word known to man. Well if my boyfriend makes something, and it violates the f.c.c rulls so be it. You guys are not above the law! Your less than human for talking that way on this post. Your a sick person with no reguards of the saying, everybody is to be treated equal, reguards to race, religion or other. My boyfriend will be transmitting on vhf radio in the 150mhz, and if you don’t like it tough! No license! Have fun reading this post!
Radio Amateurs can indeed run a max power level of 1500 Watts. But there are exceptions to that rule with regard to operation in the 70cm band. (420-450MHz)
There are power output restrictions around Beale AFB, California, Clear AFS, Alaska and Cape Cod, Massachusetts where the USAF has PAVE PAWS radar installations that also use 70cm. Transmitter power in the aforementioned areas is limited to 50 Watts.
According to CFR 47 Part 15.231 low power periodic devices are allowed on 868 MHz. Or am I reading it incorrectly?
what modulation do they occupy
Great article! I have seen many of our customers faced this problem when they come to us for fixing wireless connectivity issues and passing operating standards.
Thanks for the comment!
In the US the 315/915 freq, are all devices able to transmit these freq’s to be prepared for new technologies as they hit the market? Cell phones, tablets extra…..
I am developing a new product and your article has been very helpful.
Hi, The article was very informative. I want to know whether we can operate in frequency bands other then 2.4Ghz and 5Ghz and still use Wifi?
I’m gathering info on 433 license free usage worldwide and have some doubts that you may help me solve.
How can you be sure that 433MHz is license free in Asia? In Europe and ITU region 1 it’s ISM band, but in Asian countries normally you need to check local regulation, as region 2 doesn’t have 433 as ISM.
Moreover, in the case of Australia you’d need a license, right? http://acma.gov.au/theACMA/spectrum-at-434-mhz-for-low-powered-devices
433 is license fee in Indian sub-continent. You just need a type approval for your product to get it in to Indian Market. Please refer-
I’m currently studying towards a degree in Computing and IT – The article “The Most Important Decision You Must Make When Developing a New Wireless Device” was very formative and exciting to read.
Keep up the great work,
Thanks Andy, I appreciate the positive feedback!