Kenwood TK-931 Repeater How-To

The TK-931 as a Repeater Receiver

The TK-931’s make an excellent repeater receiver or link radio. If you would like to use any model TK-931 as a repeater receiver the VCO will require one small modification. The modification requires the addition of a 2.2pF or 3pF ceramic disk or surface mount capacitor. This value capacitor will allow the VCO to function on receive from 902 up to ~907MHz, adding more capacitance allows the VCO to receive higher in the band. Pictured below is where to add the capacitor.

931VCOmod1

931VCOMod2

931VCOmod3

 

 

 

The pick off points for COR and low level, filtered, de-emphasized audio can be found pictured below.

931 pick points

 

 



The pick off point if you would like to use Pre-Emphasized, detector audio. Pick off point for this is on a small pad on the bottom of the TK-931, near IC104.

931DetAudio

 

 

 

The receivers original ceramic bandpass filters will need to be removed and ones that will pass 902MHz or thereabouts, installed in their place. The filters listed in the TK-931 Filter Changeout section of this website for the normal conversion process will work, as well as ones centered at 902.5MHz, which also exist. The radios ceramic bandpass filters can also be removed and jumpered. My personal opinion of that method is what one might call the “Mickey Mouse Method” as I do not like the idea of doing this; however, with a good duplexer and bandpass filter this is acceptable.  
Programming a receive frequency on 902.xxxMHz can be done by hex editing the saved *.F90/*.B90 file and using the KPG-5D software OR you can use Kenwood Burn to do this BUT make sure you leave the repeater offset set to -39MHz, if you change the offset to -25MHz then it will not work!

To program the TK-931 for a 902.xxxMHz receive frequency using the Hex edit method and KPG-5D, create a new data file and ensure you set the radio with transmit inhibit enabled, and any other settings you desire, save the file. Using the Hex editor of your choice, in the saved *.F90/*.B90 file on line 230, column one and two is where you want to add your receive frequency. Then save the hex edited file and write it to your radio using KPG-5D. For example: your repeater receiver frequency is 902.100MHz on line 230 your first column (starting from the left side) should read B8 and second column should read 8D.  The chart below shows all 902.xxxMHz repeater receiver frequencies and their corresponding hexadecimal values. 

Frequency Hex  Frequency Hex 
902.0125 B1 8D 902.2625 C5 8D
902.0250 B2 8D 902.2750 C6 8D
902.0375 B3 8D 902.2875 C7 8D
902.0500 B4 8D 902.3000 C8 8D
902.0625 B5 8D 902.3125 C9 8D
902.0750 B6 8D 902.3250 CA 8D
902.0875 B7 8D 902.3375 CB 8D
902.1000 B8 8D 902.3500 CC 8D
902.1125 B9 8D 902.3625 CD 8D
902.1250 BA 8D 902.3750 CE 8D
902.1375 BB 8D 902.3875 CF 8D
902.1500 BC 8D 902.4000 D0 8D
902.1625 BD 8D 902.4125 D1 8D
902.1750 BE 8D 902.4250 D2 8D
902.1875 BF 8D 902.4375 D3 8D
902.2000 C0 8D 902.4500 D4 8D
902.2125 C1 8D  902.4625 D5 8D
902.2250 C2 8D 902.4750 D6 8D
902.2375 C3 8D 902.4875 D7 8D
902.2500 C4 8D 902.5000 D8 8D

Frequency Hex  Frequency Hex 
902.5125 D9 8D 902.7625 ED 8D
902.5250 DA 8D 902.7750 EE 8D
902.5375 DB 8D 902.7875 EF 8D
902.5500 DC 8D 902.8000 F0 8D
902.5625 DD 8D 902.8125 F1 8D
902.5750 DE 8D 902.8250 F2 8D
902.5875 DF 8D 902.8375 F3 8D
902.6000 E0 8D 902.8500 F4 8D
902.6125 E1 8D 902.8625 F5 8D
902.6250 E2 8D 902.8750 F6 8D
902.6375 E3 8D 902.8875 F7 8D
902.6500 E4 8D 902.9000 F8 8D
902.6625 E5 8D 902.9125 F9 8D
902.6750 E6 8D 902.9250 FA 8D
902.6875 E7 8D 902.9375 FB 8D
902.7000 E8 8D 902.9500 FC 8D
902.7125 E9 8D 902.9625 FD 8D
902.7250 EA 8D 902.9750 FE 8D
902.7375 EB 8D 902.9875 FF 8D
902.7500 EC 8D

 

The TK-931 as a Repeater Exciter
The TK-931’s can be used as a repeater exciter for driving a Milcom/Crescend/Powerwave, DB Products, or Motorola cellular amplifiers. For example a 15 watt TK-931 or TK-931(D) can be adjusted so that the power output is as low as 7 watts output for driving a STF2520A Motorola Cellular amplifier to 115+watts out.

Using the pre-drive module (M57781), the TK-931 or TK-931HD can be arranged to get 200mW out or 350mW out for driving a Milcom or DB Products amplifier (depending on the amplifier drive power required padding might be needed to drop the power out to even less). The modification to create a low power exciter is the same for both the 15W and 30W TK-931's. In either the 15 or 30W TK-931's you will need to remove the MHW820-3 Hybrid Module (Blue Brick). As an added note, on the 30W TK-931HD you DO NOT need to remove the Motorola MRF847 Final PA module- the pictures below show it removed- this was because it was reused in another radio that had a dead PA. To get the RF from the low power pre-drive module M57781 you can then connect a small length of RG-316 coax to the output of the pre-driver module (M57781) which is Pin 11 and jumper it to the antenna terminal directly.

For 200mW of RF output leave the SMD resistors R406, R407, R408, and R409 in place on the output of the pre-drive module, this is a PI attenuator network.

If you need 350mW out, REMOVE the SMD resistors R406, R407, R408, and R409 and add a small INSULATED jumper (the center conductor with the shield removed from RG-316 coax works well) from Pin 11 on the output of the pre-drive module to the terminal shown on the pictures below.

For BOTH 200mW or 350mW RF Output you will need to remove the SMD Cap C441 near the antenna terminal, the L412 Coil on the top side of the board near the antenna terminal, the MHW820-3 Hybrid Module (Blue Brick), and finally you will need to remove the thru-hole terminal and cut the trace that connects to pin 2 (the bias pin) of the MHW820-3 Hybrid Module as shown below. The MOST important step is to reinstall the RF shield on the bottom of the radio and ensure that you cut an opening in the shield so that the coax can pass under the shield without being pinched. This setup will give you a very reliable low power exciter on 900MHz, with no cooling fan required!

 

 


Shown below is a 15 watt TK-931 used as a repeater exciter. The main board is a 15 Watt TK-931 that has been removed from the short heatsink chassis and remounted in a 30 watt TK-930HD (800MHz) chassis- taking advantage of the larger heatsink. The chassis was salvaged from a dead TK-930HD that was also used for parts. The HD 30 Watt chassis are the exact same as the low power short heatsink chassis, so the swap is easy! Please see the "TK-931L" section of this website for the TK-931 long heatsink how-to! With the radio output power set to 7 watts in this configuration you can run this radio at continuous duty cycle to drive a Motorola STF2520A cellular amplifier to 120 watts out.  It should be noted that you do not want to run the radio below ~7 Watts because the switching transistor, Q401, will fail due to heat caused by turning back the power below 7 Watts. This radio used as an exciter at 7 to 10 Watts runs cool in continuous duty operation and as added protection (if need be) a thermal switch was mounted just above the PA module to power on a cooling fan (not shown) if unit reaches 140deg F.

tk931linktop

tk931link

 

 

 

TK-931 Repeaters in Service

W7UVH Kalama, WA Repeater, 927.2750MHz QT 114.8Hz

 

 

 

N8WAC Ohio Group Repeater, 927.0250MHz QT 131.8Hz
Repeater has since been replaced.

 

 

 

KD6VPH Bush Mt., WA Repeater 927.7500MHz Repeater, QT 114.8Hz
Repeater has since been replaced.