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Modification dnt WT 77

Extending the frequency range without hardware modification

The WT 77 from dnt  is one of many 'license free' radio-sets working in the 444 MHz range. The device works in the LPD range (69 channels) and also in the PMR range (8 channels). It is also known as TELCOM TE-150 or WT405. The basic idea of the modification origins from the the Internet (sources see below).

dnt WT77

  Freqencies WT 77

  • 69 LPD Channels 433.075 - 434.775 MHz in 25 kHz steps, Output 10mW
  • 8 Channels in PMR band, Output 500 mW. These are the frequencies:

     Channel   Frequency (MHz)
    P1 446.00625
    P2 446.01875
    P3 446.03125
    P4 446.04375
    P5 446.05625
    P6 446.06875
    P7 446.08125
    P8 446.09375
Figure 1: The dnt WT77  

There is however a third band available. The third band is the so called K-Band with 4 channels at 444 MHz.

Channel  Frequency (MHz)
K1 444.600
K2 444.650
K3 444.800
K4 444.825

Radio operation on these four channels is not allowed in Germany. In order to enable the K-Band the following steps have to be taken.

Step 1: Switch off device

Step 2: Press Volume-Key Lautstärke and ChannelUp Channel Up at the same time and switch on the device (thus pressing three keys simultaneously). Still hold all keys until a peep sounds. Now release all keys. There should be the following display.

Configuration Menu
Figure 2: Configuration Menu

The display P·L means that the device is currently being configured for the P-Band (PMR) and the L-Band (LPD). Using the arrow-keys, several configurations can be chosen from. The best certainly is P·K·L, since there will be all three bands available.

Menu PKL
Figure 3: Making all 3 bands available

Step 3: After confirmation (CONFIRM) a new menu will show up. Within this menu, the output power for the L-Band can be switched from 10mW to 500mW. I do not recommend to use the option HI. First, using more than 10mW is not allowed in Germany (even for radio amateurs when talking to non-amateurs). Second: it is just the nice thing with LPD that the batteries last much longer. So if you really need 500mW, use the P-Band then.

Power Configuration
Figure 4: Configuring Output Power

Step 4: The configuration is finished after confirming either LO or HI. There is a new item in the band-switch menu now. The K-Band is available under the name KDR.

Selecting Band KDR
Figure 5: The KDR Band (new)