Repeater Mods

D-STAR Modifications

Repeater Modifications

While the repeater modules look nice, there are always things that can be done to make them work better. :)

Of course, it should go without saying that if you undertake any of the modifications listed on this page, you do so at your own risk. Further, you will probably be voiding your ICOM warranty, so you're on your own.

While we will try to be as accurate as possible in the information we provide, there are no guarantees that it will work with your equipment. Something as simple as a manufacturing change may render this information inaccurate.

Under the Hood

There are some interesting things to notice when you peek under the hood of the repeater equipment.

This is a picture of the ID-RP2C (click for zoom):

Not really too much to see here. Below is the block diagram of how it works.

Interesting to note is that the ASSIST ports (ID-RP2L 10GHz link) connect via a 10MB/s ATM connection using LVDS (low voltage differential serial).

There is a 16Mbitx8 Boot ROM (flash) (IC12), 32Mbitx16 Flash ROM (IC11), and 4Mbitx32 of SRAM (IC2, 3, 6, 7) on board.

Also of note is that J6 is an RS-232 interface directly connected to the CPU (IC5). The pinout of this connector appears to be:

	Pin 1 - RTS
	Pin 2 - TX Data
	Pin 3 - RX Data
	Pin 4 - CTS
	Pin 5 - GND
	Pin 6 - GND

Now, the IC-RP2D. This appears to be nothing more than perhaps an ID-1 in a rackmount case, presumably with some slightly different firmware.

Some investigation will be required to see if the radio responds to other commands on the USB port (as defined in the ID-1 interface specification).

Since the RP2D can only operate half-duplex, it only needs an integrated transceiver.

On the other hand, the repeater modules that need to do duplex require seperate transmit and receive units.

This is what the IC-RP2V looks like inside:

RSSI

It seems that the pinout of the RJ45 on the rear of all the repeaters is the same. The pinout of this connector is:

	Pin 1 - TC (Transmit Clock)
	Pin 2 - TD (Transmit Data)
	Pin 3 - Ground
	Pin 4 - TE (Transmit Enable)
	Pin 5 - RE (Receive Enable)
	Pin 6 - RSSI (Receive Signal Strength Indicator)
	Pin 7 - RC (Receive Clock)
	Pin 8 - RD (Receive Data)

Now, something that is immediately interesting about this is that all of the repeater modules have an RSSI signal that they send to the controller.

This RSSI signal comes pretty much directly from the receiver IC (MC3356 in the RP2D, or TA31136 in the RP2V). It is NOT used by the RP2C.

This signal is an analog voltage, that appears to be in the range of 1-4.5VDC (depending on signal level).

An RP-4000V was tested by applying a CW signal to the antenna connector, and measuring the corresponding RSSI voltage as the level was changed.

With no input, the RSSI voltage was 1.078VDC. The signal was swept from -128dBm to -60dBm in 4dBm steps (source was an IFR 1200S). The resulting data was graphed to produce the following:

You will notice that the curve is basically linear right up to about -72dBm, at which point the detector circuit obviously saturates (4.5VDC).

The receiver was also swept with a CW at both +/-12.5kHz from the operating frequency. As you can see, it takes a stronger level from the adjacent channel interference to cause the RSSI to rise, but it still affects the RSSI.

The actual selectivity of the receiver was not tested at this time.

Further tests on the other repeaters will be performed as the opportunity presents itself.

Discriminator Tap

While there isn't currently any test equipment on the market that can encode and decode D-STAR, there are some work arounds.

Right up to the modem chip, the RX radio is still an FM receiver. So, all the standard tests can be done to check the RF performance of the radio by utilizing the discriminator audio prior to the modem chip.

In the RP-4000V, this is relatively painless. If you remove the top cover of the RX radio, you will see the RX interface board. Near the middle of that board is the CMX589A modem chip. Right near that chip is a test pad labelled "DET". Yep, you guessed it, that's good old FM Detector audio.

If you look on the main board, right near the front, you'll see some more test pads, "MIN" which appears to also be detector audio, and "RSSI" which is the receive signal strength indicator pin.

RP-4000V Internal Jumpers

It has been reported by others, and confirmed also on our unit, ICOM in their infinite wisdom indeed used RG-58A/U for the jumper cables between the RX and TX units to the back of the chassis.

They probably could not have picked a worse cable for this application. It isn't the loss that is a problem (about 0.2dB), its the lack of shielding.

Put a 25W UHF radio right beside a sensitive receiver, and you're asking for desense when you use cable with only 95% braid (if you're lucky).

These are the factory installed jumpers:

In order to eliminate the RG-58, and improve the shielding, we replaced the factory jumpers with some semi-rigid coax jumpers instead. These jumpers happened to be surplus out of another application, and fit the bill. They are N(f) bulkhead on one end, and SMA(m) on the other. A high quality SMA(f)-N(m) adapter was used to attach to the radio.

The result:

On a side note, these are obviously nothing more than modified mobiles that make up the repeater... if you've used a ham mobile in a high RF environment, you know how the front end is wide open like a barn door and will get hammered by strong adjacent channel interference.

Since there is so much room inside the chassis, you would be well advised to add a tuned RF preselector in front of the receiver to try and keep some of the "crap" out.

A surplus out of a Daniel's Electronics UHF receiver would work perfectly inside the chassis. We use an external Sinclair Laboratories receiver multi-coupler ahead of ours that contains a bandpass filter and pre-amp. It makes a BIG improvement.

Output Power

The RP-4000V was checked for its output power by applying 3.3V to the TE line on the RJ45 connector (you can find 3.3V on one of the accessory connectors inside the transmit radio).

On low power, the radio puts out 2.2W (seems low, should be 5W?).

On high power, it puts out 24.7W (on spec).

Input Current

The RP-4000V draws about 400mA idle (RX). During TX (low), it uses about 2A, and on TX (high), about 5A.

TX/RX LED

One of the biggest things that the repeater modules lack is an indication of whether the repeater is transmitting or receiving.

Instead, all you have on the front panel is a nice, green LED to tell you that the power is on.

However, all is not lost, it seems that ICOM did include all of the circuitry on board to give you a TX and RX LED, its just not brought out to the outside world.

This modification was first tested on the IC-RP2D 1.2GHz Digital Data repeater. It is confirmed to work with this unit. It has also been proven to work on the IC-RP2V 1.2GHz Digital Voice repeater. The difference on the IC-RP2V is you will need to pull the RX from one radio unit and TX from the other.

Open up the repeater to expose the radio unit. You will also need to open the top cover of the radio unit to expose the logic board.

On the logic board, near the front of the repeater, you should see three series of three through-hole plated vias.

The set of holes on the left are connected to the bias resistors of the TX/RX LED circuit.

Note that the picture of the board layout is actually of the under side of the board, when you are looking down from the top, R114 (TX) is actually the LEFT hole, and R113 (RX) is the RIGHT hole.

Since the bias resistors and drivers are already installed, all you have to do is install some LED's!

Our prototype used a bi-color, common cathode LED. We connected the green anode to the RX line, and the red anode to the TX line.

This is a picture of our prototype in "proof of concept":

Once we proved that it actually worked, it was time for a more permanent solution.

The factory power LED is pretty much an idiot light. As long as the fan is running on the back, there is power. We re-located the power LED from the top of its PC board to the bottom (you'll need to rotate it 180 degrees so the pinout is correct when you do this).

This freed up room behind the little frosted hole in the chassis to install our TX/RX LED without having to drill holes in the case.

Extend the LED with a nice piece of shielded wire, hot glue it in place, and you get this:

On the IC-RP2D it flickers nicely red and green as data is being moved. On the voice repeaters, you will usually find the bi-color LED will be amber/orange since both TX and RX will be active at the same time.