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Wireless DECTheadset forHAM-radio transceivers

Discussion in 'Ham Made Gear' started by PA3VOS, Dec 30, 2017.

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  1. PA3VOS

    PA3VOS Ham Member QRZ Page

    Hand free with a DECT headset for HAM Radio …


    More than 10 years ago, I was very active with mobile operation on HF and VHF bands. Especially during the fairly long rides to and from my work, time was spent by making QSOs with my highly appreciated ICOM IC7000. One of the things I was most unsatisfied with was the annoying microphone cable with its long curling cord, which was always in the way of shifting and steering. That needed a solution. There were already nice little Bluetooth headsets available on the market! Why would not that be useless! After some research on the internet, I found at the Jabra A210 interface. This was easily available on eBay for an amateur-friendly price. This interface can be linked to the tranceiver in a simple way and linked to BT headsets.

    After gaining experience several years with BT headsets (both in the car and in and around my house) my final conclusion was that this technology worked well but has its limitations.
    Artifact, latency, limited battery life and limited setup capabilities eventually led me to a different solution. Due to the frequent calls at my QRL I noticed colleagues using a wireless DECT headset, the idea popped up to investigate the possibilities for use in our hobby. Remarkably enough, after hours of Googling, I only found one publication, which was already several years old. It involved Jabra's GN9120 (how coincidentally can it be!).


    The description on the VK3KBC site ( was clear and simple and all necessary information including the software was available. Soon I became a happy owner of this headset via a Dutch -used products -site. This was an version with a double earspeaker. Personally, I also think that's a lot easier to hear because you hear the sound in both ears. After removing the base station of its housing with (some attention and love), it was clear that my mainboard PCB looked something different from the one on the VK3KBC site. Although the description and the scheme versus the pictures appeared already to have some mistakes, the PCB was basically equal to my PCB. This became a real challenge ...

    The different PCB that clearly uses another radio interface.

    On my interface, the resistors as described in the PTT interface of Gerald VK3GJM were not found. However, the idea of using the PDTC114EU NPN Digital Transistors with good arguments, was not such a bad idea. After a few hours I finally found the points where I could find the desired signals. As a result, unfortunately I was forced to use one optocoupler.
    The PDTC114EU is a very small SMD version. Anyone who would rather use a somewhat larger digital transistor (TO-92 housing) would rather use the FJN3302R.
    The description of the connections on the PCB of the Gerald PTT interface, as found on the VK3KBC site, is very unclear about the resistors to which the LINK, MUTE and CHARGE are connected are exactly the same. After some measurements on the PCB of VK3KBC, the information is shown in the picture. Not an easy spot and very difficult to solder. It cost me a base station! It is therefore preferable to solder the wires parallel across the LEDs. If the 100R resistor to the optocouplers is replace by 150 Ohm, the reduction in light is very much less. Who rather uses the SMD transistors is advised to make some kind of strain relief. I did this by using a small piece of circuit board and sticking with double sided tape on the DECT RF interface

    To test the unit with headset on your transceiver, it is convenient first to connect the TX and RX audio to the unit. To do this, it is necessary to remove the 2 separation transformers. It is also useful to remove the RJ12 connectors. They aren’t used anymore and together with removing the transformers, you will get more space for the PTT interface. Although Gerard VK3GJM has chosen not to remove all RJ connectors.

    How to connect the audio cables to the transceiver can be determined by yourself. However, keep in mind that many tranceivers including my IC-7000 have a so-called floating ground for the MIC ground. I have used a universal audio separation transformer as shown in the picture. There is also my PTT relay connected to the PTT interface. Therefore, I isolate the PTT completely.

    The PTT interface

    Because of the very simple interface schematic, I chose not to build a nice PCB for the interface, but just to use experimental board. It is recommended to press the PIC controller in an IC socket. In case you need to replace it or reprogram it, you can remove it easily. It is advisable to keep the wires to the LEDs as short as possible, and to twist the wires. Although I did not experience any problems or interference with 100 watts RF on HF. I chose to mount the interface with 3M double-sided on the print. The advantage is that this tape is "sticky", almost a kind of chewing gum, and stays in place.

    The supply voltage
    In order to use the device in the mobile I used a 7808 with a series diode at the output so that the power supply is recharged to 7.4V. This is also the output voltage of the 110-230V adapter normally supplied with the GN9120.


    The PTT function is actually derived from a number of signals that can be found on the PCB and are influenced by a number of function keys on the headset. In addition, we want to prevent the tranceiver from transmitting unwanted if your headset comes out of range from the base station, but also when you turn the headset into the charger (base station).
    The most important condition to be met to be able to send is that LINK is "on" and CHARGE "off". If these two conditions are met, the MUTE function enables the PTT to turn on and off. The LINK is activated in two ways; If the headset is removed from the base station, or if the multifunction key is pressed on the headset. After that you must already be able to listen / receive. Then the MUTE function is activated (by pushing the "-" button on the headset twice shortly), the microphone is deactivated and the UNIT is ready to activate the PTT. You can hear / receive everything but hear every 15 seconds a soft double tone indicating that the microphone is MUTE. Then press the "-" key twice again, then the PTT and your microphone will be activated and you can speak. To switch back to receive mode, simply press "-" the headset twice again. I can’t tell much about the software. I just downloaded it from the VK3KBC site and programmed into the PIC with my K150 programmer.

    It appears that the GN9120 is available on the market in two versions; GNnetcom and Jabra. My strong impression is that the GNnetcom is the version as described by VK3KBC. Personally I prefer the Jabra. On the side of the headset you find which version you have.
    It takes some patience and caution to remove the case of the base station. It's almost impossible to explain this on paper, but on YouTube I've put an instructional video that can help. (Search for YouTube on PA3VOS). The reports I get have been very positive and worth all the work. For those who want to operate mobile hands free, this is a very nice solution. Keep in mind that a 8 volt voltage voltage regulator (eg LM7808) with a series diode is required to get the 7.4 Volt. Or an LM317 can also do the job.
    The range of headset to base station is more than 100 meters, giving you the freedom to relax in and around your home and make your QSOs simple. In order to control my transceiver (IC-7000) remote I use the App PocketRXTX on my smartphone.

    For those HAM radio amateurs who are not capable to get thismodification themself; I have some modified sets including audiotransformer but excluding the MIC-connector (which will be typical foryour RIG) available for $129,- excl. international shippingcosts

    Suc6 with building,
    PA3VOS / Fokko Vos in

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