Wireless Installations · Topic 2 of 3
Wireless Cards
Learn how to choose a MikroTik wireless card, what band, chains, transmit power and sensitivity mean, and how to read the card properties from RouterOS.
- 5 min
- A card is chosen for its band, standards, chains, power and sensitivity.
- A chain is one transmit and receive path with one antenna connector.
- Sensitivity is better when the number is more negative.
What it is
A wireless card is the radio module that sends and receives the signal for a RouterBOARD.
It sits in a miniPCI or miniPCIe slot, or it is built onto the board. RouterOS shows it as a wireless interface, and its properties set the limits of every link you build.
A card is chosen for four main things. These are the bands it supports, the standards it speaks, how much power it can transmit, and how well it hears weak signals.
How it works
A card is defined by its band, its chains, its transmit power and its receive sensitivity.
Bands and standards
A card is built for 2.4 GHz, for 5 GHz, or for both on different radios. It also supports a set of standards, such as 802.11a, b, g or n. A card that does not support 802.11n cannot use the n data rates, even if the access point offers them.
Older cards use the older standards only. Newer cards add 802.11n, and with it more than one chain.
Chains
A chain is one transmit and receive path with its own antenna connector. A one chain card has one connector, and a two chain card has two. More chains allow the higher 802.11n data rates, and they need a matching number of antenna ports.
Chains are explained again in the 802.11n chapter. For now, remember that a two chain card needs two antenna connections, or a dual polarised antenna, to use its full speed.
Transmit power and sensitivity
Two numbers describe how strong a card is on air:
- Transmit power is how much power the card puts out. It is measured in dBm, and it is limited by the country rules.
- Receive sensitivity is how weak a signal the card can still decode. It is also in dBm, and a more negative number is better.
Sensitivity depends on the data rate. A card hears a weak signal at a low rate but needs a stronger signal for a high rate. This is why a link that works at a low rate can fail when a high rate is forced.
Higher power does not fix a card with poor sensitivity. The other end must be able to hear you, so both directions matter.
Reading card properties
RouterOS lets you inspect a card:
/interface wireless print
/interface wireless info hw-info wlan1
/interface wireless print detail where name=wlan1/interface wireless printlists the interfaces and their basic state./interface wireless info hw-info wlan1shows the hardware information for that card.print detailshows every setting on the interface, including band and frequency.
Connectors
Cards use small connectors for the antenna cables. Make sure the cable and the pigtail match the card connector. Fit an antenna to every chain that you use.
Do not transmit on a chain that has no antenna fitted, and do not fit a card that the board does not support. Check the board documentation first.
Matching card and country
A card has a list of channels and power levels that it can work on. The country setting then limits those to the rules of the place where you operate. The country topic comes later in this guide.
If a card seems to lack a channel that you expect, check the country first and the card second.
Card comparison
| Property | What it tells you |
|---|---|
| Band | Which frequencies the card can use |
| Standards | Which data rates the card can use |
| Chains | How many antenna paths and how fast the n rates can be |
| Transmit power | How loud the card is on air |
| Sensitivity | How well the card hears weak signals |
What to remember for the exam
Six points are worth knowing about cards.
- A card is chosen for its band, standards, chains, power and sensitivity.
- A chain is one transmit and receive path with one antenna connector.
- Sensitivity is better when the number is more negative.
- Sensitivity depends on the data rate, and low rates need weaker signals.
- Transmit power is limited by the country settings, not only by the card.
/interface wireless info hw-infoshows the properties of the card.
When two cards are compared, look at sensitivity as well as power, because both ends of the link must hear each other.
Common mistakes
Four errors come up often when choosing or using cards.
Buying for power only. A powerful card with poor sensitivity can send to the far side but not hear the reply.
Forgetting the second chain. A two chain card with one antenna cannot reach the speed that the data rate table promises.
Assuming the card sets the channel list. The country setting trims the channel list and the power, so a channel can be missing even if the card supports it.
Mixing bands. A 2.4 GHz card cannot join a 5 GHz network. A band mismatch is a common reason for a client that never connects.
Check yourself
Work through these three questions.
What is a chain on a wireless card?
A chain is one transmit and receive path with its own antenna connector. More chains allow higher 802.11n data rates.
Why can a link work at a low data rate but fail at a high one?
The card needs a stronger signal to decode a high rate than a low rate, because sensitivity depends on the data rate. The signal is enough for the low rate only.
Which command shows the hardware information of the radio called
wlan1?/interface wireless info hw-info wlan1shows what that card supports.
Topic 2 of 3 in Wireless Installations
Test yourself on Wireless Installations
The full MikroTik MTCWE question bank has 447 questions, with timed practice exams and an explanation for every answer.
This study guide is independent and is not affiliated with, endorsed by, or sponsored by MikroTik. Vendor names, certification names and exam codes are trademarks of their respective owners and are used for identification only.