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WiFi hamradio projects

Bidirectional WiFi amplifier for 2.4GHz ISM band - WiFi Link Extender Rast2432 [NOT AVAILABLE]

PDF WiFi amplifier application schematics [490k - 21/01/2006 - PDF]
WiFi extender in   WiFi extender out
WiFi Link Extender RX GAIN   WiFi Link Extender TX GAIN   OFF -> ON switching time   ON -> OFF switching time
This project is a bidirection amplifier which permit to achieve up to 30Bm of output power from commonly used access points or WiFi cards (PCMCIA, PCI, USB). Also, it amplify the RX signal by 20dB, so now it's easy to extend covered distance!
Also, this amplifier can be used to amplify ATV (Audio/Video) signal, both in RX and in TX: you can connect directly to the antenna, to improve RX and TX regarding to the coax cable loss, using the optional mast box.
Improving WiFi coverage is simple using RAST2432, in both indoor and outdoor environment, due to its large output power, high sensitivity and out-of-band noise filtering (look at the RX characteristic above)!
Due to its high output power, this project can be used by licensed amateur radio operators only.
Caratteristiche Tecniche
Frequency:2400-2480MHz (2.4GHz ISM Band)
Supply:10-14Vdc through external plug or coaxial cable from the access point
Input current while receiving:80mA
Input current while transmitting:800mA
Maximum output power:30dBm (1W)
Maximum TX gain:15dB
Maximum RX gain:20dB
RF connectors:SMA female
Dimensions:61x92x30mm LxWxH
Case:Additional PVC watertight box, which can be mounted on the antenna mast, can be supplied at the cost of 5 EUR

Rast2432: Frequently Asked Questions

  • What does Rast2432 include
    This project includes
    * 1 enclosed and tuned amplifier
    * 1 power supply cord, 1m length, with jack connector
    * specifications sheet with application schemes
  • How the amplifier should be supplied?
    The amplifier must be supplied at 10-14Volt direct current; in transmission it absorbs about 700mA, but consider that when it is connected to a WiFi device, due to the low duty cycle of the system the average current consumtion remains below 300mA, so you can use a common power supply device which provide 12Vdc 300mA.
    It can be supply directly, through the power cord, or by the coaxial cable, using the optional device DC injector
  • Which is the best TX power which must be set to the Access Point?
    The amplifier achieve the best power working in its linear region if access point is setup to deliver 15-17dBm (30-50mW) of TX power: setting higher TX power, the amplifier works in compression, introducing a little non-linearity which lead to worse performance expecially with 802.11g (more than 11Mbps). For example, using DWL2000, to achieve best power and linearity it is convenient to set TX power as High but not Highest nor Medium
  • Amplifier does not work with my Access Point at speed higher than 11Mbps
    Really? The amplifier works with 802.11g, setting the appropriate TX power. To transmit high bitrate (more than 11Mbps) in 22MHz of band, a complex modulation is used, which provide both phase and amplitude modulation. Amplitude modulation means that the transmitted power is not constant, but changes during the time to provide a better spectral efficiency, with the result of a poor power efficency (less coverage): if you've setup a low TX power, the RF detector inside the amplifier will switch from TX to RX even during transmission, when amplitude component of the modulation is low (small periods of 5-6uS); set TX power to an appropriate value (15-17dBm = 30-50mW).
    Note that it's NOT guaranteed that the amplifier works with all access points at high bitrates: for example Rast2432 amplifier works with LinkSys WRT54g only at bitrates lower than 24Mbps!, but works well with Dlink DWL2000 at all speeds (even 54Mbps)
  • Which speed can be achieved at 11Mbps and 54Mbps, in a point-to-point link?
    The following results are calculated on a dozen of FTP transfer with a 50Mbyte file; tests using the amplifier have been performed at a distance which lead to no-signal without amplifier
    DistanceSpeed FTPConditions
    D-Link DWL900AP+ and PCMCIA card
    D-Link DWL900AP+ and PCMCIA card
    D-Link DWL2000 and Digicom PCMCIA card
    D-Link DWL2000 and Digicom PCMCIA card
    11MbpsYes2km, no visibility740kbyte/sec
    Linksys WRT54g on both sides as AP+WDS+WEP 128bit, TX power 15dBm (30mW).
    18,24,36MbpsYes2km, no visibility890kbyte/sec
    Linksys WRT54g on both sides as AP+WDS+WEP 128bit, TX power 15dBm (30mW).WRT54g does not work, with the amplifier, at 48 and 54Mbps!
    1MbpsYes110km60-110kbyte/secDlink DWL900+another amplifier + 12dB sectorial antenna on the top of mountain, PCMCIA senao card + Rast2432 + 24dB dish antenna in the plain
  • Which bitrate should I use to increase the coverage?
    To extend the distance coverage, you need to setup the access point to use power-efficient modulations, so it's recommended to set 802.11b standard (bitrates up to 11Mbps), which uses constant envelope modulations (constant power); also, consider that noise immunity increses as bitrates decreses, so to extend the coverage at the maximum value, set bitrate to 1 or 2Mbps
  • Which antenna should I use?
    BiQuad AntennaIt's convenient to use high gain antenna, because it's supposed that you need the amplifier to extend the WiFi coverage, so do NOT connect the amplifier to the small-gain antenna shipeed with the access point, but use high gain directional antennas (11-24dB gain, sectorial, log, yagi, dish) or omnidirectional collinear antennas (6-12dB gain).
  • Which connectors should I use?
    RP-SMA to SMA adapterRP-SMA to SMA adapterTo simplify cablings, the amplifier uses SMA connectors which are standard for microwave appliances, so it's easy to find the SMA male connector for the coaxial cable as like as SMA-N adapter if your coaxial cable is connectorized with N connector.
    To connect the amplifier to the access point, the following adapters are available, as shown below, which minimize power loss:
    * RP-TNC to SMA adapter, used by some Linksys devices such as WRT54g
    * RP-SMA to SMA adapter, for the other devices.
    If your antenna has a RP-SMA plug connector, I suggest you to replace it with a crimp SMA plug (shown below) or, if you cannot remove it, just connect RP-SMA plug with SMA-female inserting a copper wire with 0.8mm diameter and 10mm length to connect the internal female poles of the connectors
  • Amplifier does not work, for me... why?
    It's impossible: every amplifier has been tested for power consumption, rx gain, tx gain, tx output power, RF switching time. Before loosing your hopes, check:
    • Am I using the correct SMA connectors? SMA connectors to the amplifier should have the central pin (MALE SMA plugs, not RP-SMA plugs!!)
    • Is power supply Ok? A power supply unit with 11Vdc and at least 300mA of output current is needed, but 500mA is preferred. Is green led lighting, and does red led flash when it's connected to the access point? The red led should flash every time the wifi device transmit,for example every 100mS if you've set beacon interval to 100mS
    • Is access point set-up correctly?
      Setup right or left antenna (depending to the access point type), not both! Access point should drive power and receive only from the connector connected to the amplifier
      Set the power level to 15-17dBm (30-50mW)
      Disable 802.11g and use 802.11b
      Fix TX rates to a value less-equal than 11Mbps: lower the TX rate, longer the distance you achieve
    When you've tried all this, if it works, try to increment TX rates and change TX power to achive the best performance.
  • Which is the output power limit permitted by the law?
    The ISM 2.4GHz band can be used by any device which has less than 100mW ERP (20dBm ERP). ERP means "Effective Radiated Power", which can be calculated with the formula Ptx[dBm]-Acoax[dB]+Gant[dB].
    For example: Transmitter power: 17dBm (50mW), Coax cable+connector loss: 4dB, Antenna gain: 11dB => Perp=17dBm-4dB+11dB=23dBm (200mW ERP) => the ERP power execedded the limit by 3dB: we need to change antenna or limit the power level down to 14dBm.
    Another example: Transmitter power: 30dBm (1W), cable loss: 4dB, antenna gain: 11dB => Perp=30dBm-4dB+11dB=37dBm ERP (5W ERP) => the effective radiated power exceed the limit by 17dB.
    These two example show how is difficult to meet ISM power limit with antennas with 10dB or more gain, but if you are a licensed amateur radio, you can install WiFi devices within the hamradio band with 40dBm ERP (10W ERP) power level, or more, depending by your country laws.
  • How should I compute the gain of a dish antenna?
    The formula to compute dish antenna directivity is
    directivity=( pi * Diametre / lambda )
    where pi=3.14, Diametre is the diametre of the dish, lambda the wave length.
    For example, if diametre is 66cm, the formula become
    This is the directivity, proportional to the effective area of the antenna, but to obtain the gain you need to take into account other problems like spillover (feed radiated power outside the area of the dish) and feed loss, so, in the best way, you can reach a gain like
    gain=0.6*directivity=0.6*298=178 which correspond to about 22dB (or dBi, because it's referred to isotropic antenna model).
    Ah, to translate from linear units to dB, you need to perform the compute
    So, from a well done 66cm dish in 2.4GHz, you can expect a gain around 20÷22dB
  • I would like to reduce or remove the RX gain from the amplifier
    Removing the RX gain reduce the coverage of the device, so it's not recommended. Also, because the amplifier contains a 2400-2480MHz band-pass filter (2360-2520 is the real coverage of the filter), it's a good idea to leave the first GaAsFet RX stage followed by the RX filter to reduce the off-band noise like UMTS/GSM repeaters and other services.
    In the case the amplifier is installed in the top of a mountain where in-band noise is very high, you can remove the 2nd MMIC stage RX amplifier following the instructions on this photo: remove the MMCI at the left of the filter, then remove the inductor used to supply it, and connect with a small wire the two pads indicated.
    With this modification you'll get only 8dB of gain filtered by the band-pass filter.
  • I have several other questions: how can I do?
    The fastest way to contact me is using skype (nickname iw3grx) or sending an email to iw3grx@ir3ip.net
You can request any information and quotation sending an email to the address iw3grx@ir3ip.net, using skype (nickname iw3grx).

2.4GHz Antenna alignment system [NOT AVAILABLE]

This is a Direct Sequence Spread Spectrum transceiver with high sensitivity and output power which permit to measure the signal received by a similar device and to analyze the 2.4GHz ISM spectrum to determine the free WiFi channels.
This is a hand-held device, internal supplied by 4 NiMH batteries, with charge circuitry inside; it is controlled by a microcontroller by a keyboard and an alphanumerical LCD display.
With a single device, only the spectral analysis can be performed, to look at the 2.4GHz spectrum; using a couple of devices, it is possible to measure the RXed signal which is displayed and reproduced as a tone frequency: higher is the tone frequency, higher is the strength of the received signal. In this way is very easy to perform antenna alignment.
Rast SmartPalm Rast SmartPalm
Caratteristiche Tecniche
Frequency:2400-2480MHz (2.4GHz ISM Band
Power Supply:internal, through 4 NiMH batteries (4.8V 2000mAh)
Battery charge circuitry:inside: 8-30Vdc should be applied to the Jack connector
Battery charge mode:about 8 hours with constant current, then trickle charge
Battery working time:more than 50 hours
Output power:20dBm (100mW)
Sensitivity:-102dBm (2.5uV)
Spectral analisisNoise level indication for each WiFi channel of the 2.4GHz ISM band
Dimensions:26x116x50mm LxWxH
You can request any info sending an email to the address iw3grx@ir3ip.net, using skype (nickname iw3grx).

WatchDog to avoid access point blocking/crashing

This simple circuit should be connected between the power supply and the access point to avoid troubles caused by software errors (blocking) or power supply interrupts (loss of configuration, access point bricking).
It implements a minimum of protection (fuse) and filtering (inductor and varistor), also a microcontroller provide to enable/disable the power supply looking at the low voltage detector and time (power supply is disabled and then reenabled every period, set using one dip switch).
Caratteristiche Tecniche
Power Supply voltage:10÷13.8Vdc
Power Supply current:3A max
Power Supply protection:Fuse, inductor, transient suppressor
Watchdog:the power supply will be disable after an interval set by a dip switch to 1,2,4,8,12,24,48,168 hours
Low voltage detector:it use a comparator with hysteresis to detect when input voltage falls below 9.6V (you can tune this threshold changing one or two resistors); if the voltage remains below the threshold for more than 40uS, the power supply will be disabled and a discharge circuit will be enabled to avoid troubles caused by inefficient reset circuitry inside the access point devices
High voltage detector:Using another dip switch it is possible to set the minimum time the voltage remains high before enabling power supply, to 1,2,4,8,15,30,60,120 seconds
Clocks supplied:the circuit supply three clocks, at 500Hz, 16Hz, 0.5Hz, usable for external monitoring systems or for other purposes
Signalling:one led will be activated (turned on) when the power supply is disable, due to low voltage detect or during watchdog timer expiration
The schematic, layout and PCB master are available to build the circuit by yourself.
Also, the programmed microcontroller is available at the cost of 6€

Related components available

DescriptionPhoto (click to zoom)Price each
for < 5pcs
Price each
for ≥ 5pcs
Plug RP-TNC to plug SMA adapter
Body Nickel plated 100um Contact gold plated 3um
Adattatore RP-TNC to SMA   Adattatore RP-SMA to SMA € 4,50€ 3,80
€ 3,00
SMA female - SMA female adapter
Body and contact gold plated
SMA female to SMA female adapter € 3,50€ 3,00
N female - SMA male adapter
Body nickel plated and contacts gold plated
N female to SMA male adapter € 4,50€ 3,80
Female SMA to female SMA cable with RG178 16cm length
SMA with body and contact gold plated 30um
SMA-F to SMA-F cable€ 6,50€ 5,00
€ 4,50
Male SMA plug to male SMA plug with 100cm Rosenberger UTiFLEX cable
SMA 90degrees with body and contact gold plated cable low-loss with 3.2mm diameter and PTFE dielectric
SMA-M to SMA-M 100cm cable€ 8€ 7,00
€ 6,00
SMA male crimping connector for RG178/RG174 coaxial cable
SMA with gold plated body/contact
SMA-Male crimping connector€ 3,00€ 2,75
SMA female crimping connector for RG178/RG174 coaxial cable
SMA with gold plated body/contact
SMA-Female crimping connector€ 3,00€ 2,75
SMA female crimping connector for RG58/H155 coaxial cable
SMA with gold plated body/contact
SMA-Female crimping connector€ 3,00€ 2,75
Mast box where the amplifier can be allocated
It is a waterproof housing suitable which can be installed near the antenna and permit AP to be connected through a long coaxial cable
Mast box Mast box Mast box5,00 € 4,50 € 
DC injector
Permit to supply amplifier using only the coax cable between the AccessPoint and the amplifier as shown in the PDF application schematics [490k - 21/01/2006 - PDF]
Use two SMA-female connectors
DC injector 15 € 12 € 
You can request any info sending an email to the address iw3grx@ir3ip.net, using skype (nickname iw3grx).

Electronic components SURPLUS


Other mirror sites: wifi amplifier, wifi booster, amplificatore wifi

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