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Thread: Kenwood tk-3000 repeater idea

  1. #1

    Default Kenwood tk-3000 repeater idea

    Hey, so I was thinking about an idea of making a portable repeater from 2 kenwood tk 3000. I have checked the pin outs of the headset plug and saw that there is maybe a chance that with those signals and some transistor or timer its can be made .

    How do you think its can be made ?
    Thank in advance!

  2. #2
    Super Moderator 5B4AJB's Avatar
    Join Date
    Mar 2008
    Meneou, Cyprus


    It's fairly common practise to have a small isolating transformer between the audio connections, I have used such interfaces without, however.

    A good (free) source for these components is old modem cards, they are usually the only transformer on the board and fit nicely into a small project box.

    So, the 2.5mm stereo connector will have one input on the tip & another transformer input on the ring. Ground the other side of both the coils to the spk- and take your signals from the other windings.

    A picture says 1000 words...

    Here are some nice interface designs, scroll down to the echolink one. Notice he has included a preset resistor for setting sensitivity.

    I recommend using an opto-isolator (4N25) for the PTT line...

  3. #3

    Join Date
    Dec 2008
    Elgin, Illinois


    Hello Trzcrz,

    Your post isn't very clear whether you understand how repeaters are configured, early in my career in the Land Mobile Two-Way Radio Industry I had a good beginning testing, troubleshooting & repairing Analogue Base Stations / Repeaters at Motorola. After 4-1/2 years I transferred into an engineering group that built up portable repeaters from the ground up. What I mean by this is I had to test & troubleshoot any initial problems on the handheld transceivers, the RF amplifier boards, select & tune the correct the RF Duplexers using a HP Spectrum Analyzer / Tracking Generator with a HP Signal Generator for a +5 MHz Offset for UHF repeaters for the U.S. or unusual splits for International customers. These repeaters had our own designed Audio Squelch Gates that took the audio from the handheld's receiver's Discriminator circuit into the Squelch Gate / COR and into the second handheld transmitter stage. These units were spread apart approximately 18" because everything was built into a metal attaché case. All of the RF cables were double shielded coaxial cables and this self contained portable repeater was tested at room temperature, then at -30 C degrees and finally at +60 C degrees. The unit contained it's own +13.6 VDC Power Supply, some +8 VDC regulators for the handhelds, could operate off of the internal batteries at 2 W Output or 25 W Output with the internal Power Supply, 121 / 240 VAC or an External Battery Pack at 12 VDC at 60 Amperes. The portable repeater shipped with a modified +3 dB Mobile Antenna or the end user could connect a Base Station +5 dB Gain Antenna using 1/2" Heliax Coaxial Cable mounted in a high location.

    Now for your Kenwood Programmable TK-3000 handheld, I would recommend to place them approximately 2 to 3' apart because of the internal synthesizers as they will interfere with each other. You can purchase 5 MHz UHF Mobile RF Duplexers off of eBay like these:

    These UHF RF Duplexers will tune down into the 440 to 450 MHz Amateur Radio Band, as the ones that I used had BNC connectors that were manufactured for Motorola exclusively. Whereas these use N Type connectors, top end RF connectors and triple Notch Cavities a must have for low power repeaters. Here's a Motorola MSR Audio Squelch Gate that could be modified for your UHF Repeater as this module operates off of 12 VDC and isn't very expensive.

    Before adding a 40 Watt RF amplifier into the RF transmitter portion, make absolutely sure that the two TK-3000s operate properly using 4 Watts of RF Power, if they do -- Fine but if they don't you'll be pulling your hair out -- cussing up a blue streak.

    I will recommend to use an External Antenna +3 to +6 dB Gain and LMR-400UF (Ultra Flexible) Coaxial Cable between the RF Mobile Duplexers Output Connector and mounting the Antenna as far (50 to 100') away and high in the air as humanly possible.

    Well, Good Luck!


  4. #4

    Exclamation ROIP between Kenwood TK 3000


    I am awfully new to the walkie talkie world & about a month back bought 20 nos of kenwood TK 3000 M6 radio for my company employees.

    Problem I am facing is my factory spreads on over 6 acres of land & I am not getting clarity (in most cases) / connectivity (in some cases). My vendor was at first trying to sell 3-4 repeaters, each costing a fortune, and now ROIP solution.

    Since I am new to this subject & the way my vendor has been changing statements, I am looking for some advice & help with same. All I need is my radio to work within a 10-12 kms radius & looking for a solution that is economical.

    Any help is greatly appreciated.


  5. #5


    Hello guys.... sorry for "hijacking" this thread , but can what your talking about be adapted to a Mobile radio interface? using the pinouts on the front RJ45 jack / the accossory jack on the back of a Motorola LCS2000..... im trying to find out how to build a simplex repeater interface for Motorola LCS2000 wich dousnt have COR out..... i would imagine the audio just needs to be connected with a few "components" in between but activating the PTT on the TX radio with one of the signals from the RX radio is where i get stuck......... ( i dont have skills in designing eletronics ciruits ) but could build one from instructions....

    Thx in advance.

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