Overview:
Kenwood makes several variants of the TK-X90 radios. These are all heavy duty, Mil-spec environmentally rated radios. The TK-690 is basically 30MHz-50MHz, the TK-790 is 136MHz-174MHz and the TK-890 is 400-500MHz. I am going to focus on TK-790 variant, but all of this applies to the 690 and 890, and all of the accessories can be used with the 690 and 890.
Rear of main radio body:
The 4 pin connector, lower left, is power input. 2 positive and 2 negative. 15amp fuses on both the positives. Above that is the 9 pin molex connector. The 25 pin d sub connector is top right. The antenna coax is lower right.
Highpower vs standard power (110w vs 45w)
The TK-790 comes in standard (TK-790) and high power (TK-790H). The standard is 45w, the H is 110w. The standard is about the size of a normal VHF radio. Either variant can come with a fixed head (head and radio body are one piece) or remote mount head (radio body attached by cable to just the display). The 45w is most commonly made with a fixed head, the 110w is most common remote mount.
110w remote head:
45w fixed head:
Fixed head 45w vs fixed head 110w:
Simple head vs Complex Head add pictures
The head on either radio can be either a KCH-10 (simple head) or a KCH-11 (complex head). The simple head has a built in speaker. The complex head does not. The complex head has a bigger display and more buttons. For our application, the simple head is the better option, but it is much less common and more difficult to find. The biggest issue with the complex head is it requires the use of a remote mount speaker. The simple head does not require an external speaker.
Simple Head:
Complex Head:
Rear of Remote Head:
Access cover removed:
Rear cover of remote head removed: You can see the connector and the ground wire.
Internal (simple head) vs external speaker:
If you have the simple head, you can use either the internal or an external speaker. For internal speaker use, there is a 9 pin (pin diameter .062) molex connector on the back of the main radio body. On this connector, you would need a jumper between pin 3 and 6 . If you use an external speaker (KES-4 or KES-5), you put the black lead in pin 2, black and white lead in pin 6. It shouldn't matter which cable goes where as long as it's pin 2 and pin 6. It is very important that you use pin 2 and 6 though, you cannot just ground one side of the speaker. You can also use the 12 pin molox connector on the back of the remote mount head to power the remote mount speaker. This is pin 10 and 11. If you use the remote mount head, the speaker power will be limited 5W. Coming from the 9 pin on the main radio will get you 13W. You cannot use the 12 pin connector if you are using a simple head; must use the 9 pin on the main radio. If for some reason (like using an intercom, or an in cab and outside speaker) you want to use 2 speaker outputs, see the section below for using 2 speaker outputs just below the intercom section.
See the simple head pictures above for internal speaker.
External speaker:
eBay purchasing:
If you want a good affordable radio, either the standard or the high power versions will work. The standard is much easier to mount, and can generally be had for about $180 including everything you need. The high power version is significantly larger and more difficult to find space to mount but can reach out to distances a lot better. It can generally be had for about $300-$350, although occasionally I have seen the complete setup on eBay for about $200. It is easy to get suckered into a high power radio on eBay that looks like a great deal but isn't. We bought 3 TK-790H radios with remote mount heads for $200 each, thinking it was a great deal. They came in and didn't have the cable to the remote head ($80), speaker ($40), mounting bracket ($50), power cable ($15) or microphone ($80). The great deal wasn't so great after buying all the other crap that didn't come with. It still wasn't terrible, especially considering these radios go for about $1300 brand new from PCI. Point being, be careful what you're buying, look at the pictures really well and ask questions of the seller. Parts are plentiful, but add up quickly.
Intercom:
These do work with an intercom, however you have to do some internal modification. I took mine to JES and Sons in Indy to do the soldering on the circuit card. There is a zero ohm resistor, basically a jumper, that is soldered to a circuit board inside the radio. This resistor can either be put on the circuit card at R640 or R641. It should be configured in "data" mode originally. The resistor will be present on R641 for this configuration. To work with the intercom, it needs to be removed from R641 and put onto R640. This configures the radio to accept an external microphone source.
After fixing the resistor, you change the programming of the radio to accept an external push to talk source. I used a Rugged Radio harness to go to the Rugged intercom. This harness has a 25 pin d sub connector that interfaces with the back of the radio and a 9 pin molex connector that interfaces with the back of the radio. The molex connector has 2 pins used, the speaker output pins. The 25 pin D sub has 3 pins used. There is mic+ (pin 13), mic- (pin 25), and external push to talk (pin 2). In the programming of the radio, there is a "Edit" tab, in the dropdown is a section called "Function Port". Within that is a section there is a few rows for "Head" functions, then several rows for "Radio" functions. For the Rugged harness, set Radio AI1 to "Ext PTT" so that the radio will know to look on that pin for external PTT input. PCI makes a jumper also, I believe it uses only the 12 pin connector on the back of the remote mount head. I don't know much about this but I would guess you set Head AI1 to "Ext PTT". The biggest issue I have with the intercom is that it turns off the speaker function and the external microphone function, so you can only hear or talk through the intercom helmets unless you set the radio up for 2 speaker outputs.
Ext PTT set: You can set any of these inputs/outputs to different functions from the dropdown menu.
Using 2 Speaker Outputs (for intercom, PA system speaker, etc.):
I played with radios tonight and found that I can switch between multiple speakers from the face of the radio. This is hugely beneficial for an intercom situation, but can also be used if you have a radio mounted inside of a pickup or something and want to mount an external speaker, you could then switch between the two by pushing a button. Focusing on the intercom application: The molex 9 pin connector on the rear of the main radio body has 2 speaker outputs. Speaker A is the primary, Speaker B is the backup. They call Speaker B the PA speaker. The speaker A uses pin 2 and pin 6. Speaker B uses pin 7 and 8.
If you have a complex head without a built in speaker, the Rugged jumper uses Speaker A output for the intercom, so you can put the KES-4 speaker leads into pin 7 and 8 and then program the radio to have a button be "internal/external speaker". Then when you hit this button, an indicator on the display lights up and it provides speaker output to Speaker B, your external speaker and you can hear the incoming transmissions without having a helmet on. When you are on Speaker A, the incoming transmissions go to the intercom and into your helmet.
If you have a simple head, you need remove the speaker output from pin 2 and 6 from the Rugged harness, put them into pin 7 and 8, and then jump pin 3 and 6 together. The set a key to "internal/external speaker" in the programming. This configuration will setup the intercom helmet output as speaker B and the built in speaker in the simple head as the primary speaker. You will most likely need to hit the "internal/external speaker" button every time you turn the radio on. Kind of a pain but best I can come up with now.
