• PMR446

    01/02/2021 at 14:58 0 comments

    Yaesu FT-65E

    European version of the FT-65 can listen to PMR446, but not transmit on that band.  Transmission on PMR446 is only allowed with PMR446-certified radios (fixed antenna, TX-power limited to 0.5W, ...), which the FT-65E is clearly not.

    It's however technically possible to use a Yaesu FT-65E on PMR446:

    1. Expand TX-range of a Yaesu FT-65E outside the ham-bands using this guide here.
    2. 8 : CTCSS : set up the same as a PMR446-radio.  On Kenwood PMR446 handsets, this will be called "Quiet Talk (QT)" setting, but it's effectively the same thing.
    3. 29 : SQL Type : TSQL
    4. 32 : TX Power : LOW
    5. 37 : WIDE/NAR : NARROW (+/-2.5kHz deviation instead of +/-5kHz) (Optional)
    6. Set the TX-frequency equal to that of a PMR446-radio.

    Kenwood TK-3201T

    • analog FM: about 500m range in residential area
    • manual can be found here.
    • NiMH batteries don't last very long.

    dPMR

    • technical info
    • 4FSK :  (-1050, -350, 350, 1050Hz), deviating index = 0.29
    • 2400 symbols/s, 2bits/symbol

  • 70cm band Antennas

    12/08/2020 at 20:20 0 comments

    General

    Understanding Antenna Specifications and Operation : Application Note AN-00501

    • The quarter wavelength on 433MHz is 17cm.
    • VSWR < 2.0 is acceptable.  Less than 10% of the power will be reflected back to the transmitter.
    • Baluns avoid RF-radiation and noise pickup from the feed line:
      • These baluns should be placed as close as possible to a balanced type antenna (feed point). 
      • Not needed for monopole antennas because they're unbalanced.
    • FCC CFR Part 15 forbids standard connectors like SMA.  RP-SMA is allowed.
    • The frequency of lowest VSWR is not necessarily equal to a resonant frequency of the antenna.
      • lowest VSWR = antenna impedance closest to 0 on Smith chart.
      • resonance = antenna impedance is purely resistive, on X-axis on Smith chart.

    Antenna testing

    VSWR measurements on quarter wave monopole antennas don't mean much in reality.  So the measurements below should be taken with a grain of salt.
    The λ/4 monopole antenna performance strongly depends on the size and orientation of the ground plane and hand capacity etc...
    An antenna with a good VSWR in a lab setup (using a large perpendicular ground plane) doesn't guarantee it will perform well in real life conditions, when it's connected to your HT.

    λ/4 Monopole antenna characteristics

    • Zin = 36Ω at the resonance frequency (over an infinite ground plane)
    • Maximum gain = 5.15dBi (3dB more than dipole antenna)
    • The go-to antenna here is a ground plane antenne.  The resonant frequency can easily be tuned by cutting the monopole, while the impedance can be tuned by folding the radials.
    • Monopole antennas need a ground plane, so you shouldn't use them with a u.fl to SMA cable assembly.  Dipole antennas can be used with u.fl-SMA cables.
    • Monopole antennas can be used with edge soldered SMA-connectors.
    • All 433MHz whip antennas on the market seem to be monopoles.  I guess dipoles would make them too long.

    AliExpress WirelessLink store PM433-ZB165BM (71A, 433MHz 16.5cm ZT SMA)

    The characteristics have been measured with a direct connection to the VNA.  No ground plane added.  This will impact bandwidth as well as center frequency.

    The default antenna frequency is by no means 433MHz, as can be seen in the first graph.

    VSWR of antenna directly connected to VNA.(https://cdn.hackaday.io/images/5866921607457173224.png)

    Monopole antennas should always be measured with a reasonable size ground plane (radius > lambda/4).

    VSWR measurement of antenna on serving tray.  This seems pretty good!(https://cdn.hackaday.io/images/8070311607457349499.png)

    Measurement on Smith chart with serving tray as gnd plane:

    • Resonance: Z = 27 + 0j ohm at 408.3MHz
    • Minimal VSWR: Z = 28.5 - 3.8j ohm at 404.9MHz

    Measurement when SMA taped with Cu-tape to the edge of Al-GND plane (800x2000mm)

    • Resonance: Z = 78 + 0j ohm at 417MHz
    • Minimal VSWR: Z = 74.5 - 5.6j ohm at 414MHz

    AliExpress WirelessLink store PM433-ZB165BM (71A, 433MHz 16.5cm ZT SMA) : manually shortened

    Inexperienced as I am,I cut away a few centimeters to improve the impedance match in the 430MHz region.  The open end has been protected by double folding heat shrink tube over the end and then adding extra heat shrink tube over it.

    VSWR measurement of shortened antenna, directly connected to VNA.(https://cdn.hackaday.io/images/7954321607457539146.png)

    Of course, when...

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  • RFID

    11/10/2020 at 15:26 0 comments

    RFID Writers

    RFID Copier Duplicator 125KHz Key fob NFC Smart Card Reader Writer 13.56MHz Encrypted Programmer USB UID T5577 EM4305 Cards Tags

    • Only works on Windows.  On Linux dmesg shows a lot of errors.  It's not recognized as virtual com-port or anything.
    • When connected to the PC, it shows up as flash drive that contains the reader software.
    • The reader software consists of a left side for 13.56MHz, the right side is for 125kHz.
    • Bring a 125kHz tag within range.  A double beep will indicate that the tag is recognized.  Then press the "read EMID" or "write EMID" button.
    • For 13.56MHz tags, the functionality is unclear.
    • It can write empty 125kHz tags delivered with the 5YOA reader, but it can't overwrite them
    • Also reads my own created RFID tag.

    Handheld 125KHz EM4100 RFID Copier Writer Duplicator Programmer Reader + EM4305 T5577 Rewritable ID Keyfobs Tags Card

    • Based on a PSoC.  Nothing much left to hack.  No method to extract read tag data.
    • Doesn't read my own created tag.
    • Use: bring tag within read range and then press read or write button.
    • Can rewrite the tags delivered with it.

    Own designs

    RFID Reader modules