Running D-STAR on a GE MASTR Exec II

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GE MASTR Exec II
By Ron Wright N9EE

The GE MASTR Exec II can be configured to pass/repeat D-STAR data. The problems that must be addressed are with the transmit data. Simply taking the data from the receiver discrimentator is fine for the receiver. But as with most FM radios the transmitter audio input is processed to the point the D-STAR data is distorted preventing user's radios decoding.

For this article, the MASTR Exec II mobile radio has been converted to a full-duplex repeater and the D-STAR was added to it. The techniques used here could probably be applied to other MASTR-series radios.

Exec II D-STAR Transmitter and Receiver Interface:

The Exec II's exciter is phase modulated and this will not pass digital data. A direct FM transmitter is needed for data.

D-STAR data is frequency shift keying with a logic 1 being 1 kHz above the transmitter carrier and logic 0 being 1 kHz below the carrier.

The Exec II can be modified to do direct FM using the exciter's crystal holder's frequency temperature compensation circuitry. This compensation circuit is located on the exciter and feeds a voltage to a varacitor diode in the exciter's crystal holder. This same voltage is fed to the receiver's crystal holder via the SAS (System Audio Squelch) board. You can find documentation on the SAS board here.

Modifying the Exec II:

Cut the temperature compensation voltage line between the exciter and receiver on the SAS board (see this diagram).
Insert a 10k resistor between these two crystal holders.
Install a capacitor on the receiver's side of the resistor.
Insert the D-STAR data on the exciter's side of the resistor. The data will directly Frequency Modulate the exciter, but not modulate the receiver's oscillator.

The transmitter data is to be connected to J904 (mulit-frequency board) pin 6. This is the location of the 10k resistor and the exciter temperature compensation line. This allow D-STAR data to direct frequency modulate the exciter, but the 1uf capacitor at the other end of the 10 k resistor filters the data preventing modulating the receiver crystal holder.

The receiver D-STAR data is taken from the discriminator and can be found at many places on the SAS board. One location is at P908 (timerout timer board connector) pin 5.

PTT is on P908-pin 6 and ground at pin 3.

This diagram shows the modifications to the SAS board. The SAS PC board run is cut to separate the temperature compensation voltage between the exciter and receiver crystal holders. A 10k resistor is inserted and a 1uf 16V capacitor to ground is connected to the receiver side. D-STAR data is then inserted at the exciter side of the resistor connecting the D-STAR data to the exciter. This allows D-STAR data to direct frequency modulate the exciter, but the 1uf capacitor filters the data out, allowing the temperature compensation DC voltage to pass through while preventing modulation of the receiver crystal.

The ARS D-STAR Repeater Controller (DRC):

A D-STAR controller that works very well is the D-STAR Repeater Controller (DRC) from Advanced Repeater Systems. This controller is designed to recognize D-STAR data, condition and delay the data by 250 milliseconds (to give all radios time to stabilize and lock onto the signal), and provide a PTT signal (pull to ground) when the controller senses D-STAR data. Here's a photo of the DRC:

The DRC can be interfaced to any repeater through a DE-9P connector. Main connections are: 12VDC, ground, receiver discriminator, transmitter PTT (pull to ground) and transmitter data, as shown in the following table:

Signal Pin# Location on Exec II SAS

12VDC Power 9 P904 pin 8

Ground 5 P908 pin 3

Discriminator (receiver) Input 3 P908 pin 5

PTT (pull to ground) 4 P908 pin 6

Transmitter Data 1 P904 pin 6 (end of 10k resistor)

Signal	Pin#	Location on Exec II SAS
12VDC Power	9	P904 pin 8
Ground	5	P908 pin 3
Discriminator (receiver) Input	3	P908 pin 5
PTT (pull to ground)	4	P908 pin 6
Transmitter Data	1	P904 pin 6 (end of 10k resistor)

P908 is the "Timeout Timer" connector and P904 is the "Multi-Frequency board" connector on the SAS. These boards are not used in a repeater.

There are other places to pick up the receiver data (discriminator) and PTT, but these are out in the open and are easy to get to.

Adjustments:

All adjustments are performed on the DRC. The input level is set with pot PT2 to 1 Vp-p at test point "RX A" using D-STAR data, not open squelch audio. Transmitter level/deviation is set to 1.2 to 1.5 kHz with pot PT1 using a service monitor. Exceeding this level can prevent user's receivers from decoding the data.

An alternative is to use an ICOM D-STAR hand-held or mobile radio signal as a reference and set the repeater's output to match this level.

D-STAR Data Problems:

Other issues with D-STAR is the data must be "right side up" or not inverted as can occur in some receivers and exciters.

D-STAR data is frequency shift keyed with a logic 1 (one) being 1 kHz above the carrier frequency and a logic 0 (zero) being 1 kHz below the carrier. The D-STAR data must be in this configuration so the receiving station radio knows when there is a 1 or 0 in the data.

There is a jumper on the DRC that inverts the data, which can happen in some repeater exciters and/or receivers. The jumper is present to handle this situation. In an Exec II with low side receiver local oscillator injection, the data is not inverted and the jumper is not installed, but if high side injection is used, the jumper must be installed.

Analog Operation:

If both D-STAR and analog operation of the Exec II repeater is desired, then the normal analog audio interfaces to the exciter and receiver are used, but the above D-STAR data interface must be used. This will allow for both analog and D-STAR operation. However, the D-STAR data needs to be removed during analog operation or the data from any D-STAR controller could interfere with analog audio. A DPDT relay can be used to do this switching with the DRC's PTT energizing the relay to apply the data and PTT to the repeater transmitter. Make sure a diode is across the relay coil to suppress the high voltage spike from the relay coil when turned off.

Contact Information:

Ron is the owner of Micro Computer Concepts (MCC). He is not affiliated with ARS.
He can be contacted at: mccrpt [ at ] tampabay [ dot ] rr [ dot ] com.

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This page originally posted on Tuesday 23-Dec-2014.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.