3. PHYSICAL INSTALLATION

This chapter describes the procedures required to perform the physical installation of the FF-800 Repeater Controller. This chapter will only detail the connection of power, audio, COS, transmitter PTT, and some preliminary transmitter audio adjustments. The installation of other features such as analog inputs, voter logic inputs, etc... will be dealt with in chapter 4 with the various command sections that deal with these external operations. Appendix B shows the parts placement diagram and schematic of the FF-800 and the user should refer to this appendix to locate the various connectors that will be discussed. For those purchasing the FF-800 chassis, the user should also refer to the Chassis Supplement for wiring and installation information.

Most connections to the FF-800 are made via Molex connectors (supplied) -- although the transmitter and receiver connections are duplicated using a 4 pin "mini-DIN" style connector. The Molex connectors are easily installed once the method of attaching the pin inserts is mastered. Figure 3.0.1 illustrates a typical Molex pin insert. Notice that there are two flanges near one end of each pin insert. Prepare each wire to be attached by stripping 0.1" of insulation -- do not pre-tin conductors.

The wires are attached by crimping the inner flange (1) on the exposed conductor and then applying a small amount of solder to secure the connection. Once the connection has cooled, the outer flange (2) is crimped around the insulation to provide strain relief. If an appropriate crimp tool is not available, use a pair of medium needle-nose pliers to carefully bend the flanges around the conductor. Make sure that the crimped connection is reasonably secure before soldering.

If too much solder is applied to the connection, excess solder may wick up to the contact loop (3) and/or the locking clip (4). If this happens, the pin insert is ruined and must be replaced. Only use the minimum amount of solder and heat to establish a good electrical connection.

Figure 3.0.2 illustrates a typical Molex housing. Pin one is located by orienting the housing as shown. Alternately, the last pin (opposite of pin 1) on the housing can be located by looking at the bottom face of the housing. For a 9 pin housing, the number "9" is imprinted in the housing next to the appropriate hole, a 7 pin housing has a "7", and so on... . Thus pin 1 is the hole at the opposite end of the housing.

The mini-DIN connectors are comprised of a contact array, two metal inner shells, two plastic outer shells, and a plastic connector housing. Figure 3.0.3 illustrates the pin diagrams for both the 4 pin and 6 pin connectors.

There are two steps to assembling the mini-DIN connectors: the inner assembly and the outer assembly. The inner assembly involves cable preparation and connection and figure 3.0.4 illustrates the steps involved. First, prepare the cable (preferably shielded) by exposing 3/8" of the conductors as shown. Next, place the outer hood over the cable (see figure 3.0.5) and attach the wires to the contact assembly. Be sure to note the color code of each connection for later reference. Next, place a small piece of electrical tape around the soldered connections -- one wrap is sufficient, too much tape will prevent the top and bottom shells from mating properly.

Place the top and bottom shells around the contact assembly and then do the same with the left and right shells (as shown in figure 3.0.5). Be sure to properly orient the left and right shells as shown or they wll not mate properly. Finally, push the connector housing over the outer shells until it is flush with the inner shells at location (A) in figure 3.0.5. Be sure to hold the outer shells in place until the connector housing is pressed into place. Once the assembly is complete, the connector is ready to install -- the alignment mark on the connector housing should point "up" when inserting into the female mini-DIN connectors.

3.1 Power

The FF-800 Repeater Controller requires an input voltage source of +12Vdc(+/- 15%) @ 350mA. This connection is made via P1 which is located along the edge of the FF-800 near U22. Pins 1, 2, 3, and 4 are connected to ground -- while pin 5 is the +12V input. Pins 6 and 7 provide positive (pin 6) and negative (pin 7) 5 volts for use in external circuits as necessary. Each output can source up to 50mA maximum.

3.2 Receiver audio

The audio inputs are routed through P2 and P3 and also through P11 - 14. P2 handles RXA, RXB, RXC, and RXD -- P3 handles the Local MIC and Control RX. P11 through P14 each handle a single receiver (A through D, respectively). Figure 3.2.1 illustrates a simplified model of the receiver audio input circuit. Not shown is the audio multiplexer that mutes audio from all but the selected receiver -- this allows either squelched or discriminator audio to be utilized. The min/max limitation of 0.8/4.0 Vpp is due to the op- amp output constraints. The non-inverting op-amp stage is used to provide a high input impedance to prevent loading of the receiver audio. The input impedance of 50K is the result of the parallel combination of the DTMF decoder input and the 100K bias resistor used at the non-inverting input buffer. This may be of significance because there are times that the DTMF decoder will not be connected (ie., if the control receiver COS is active, or there is a control autopatch in progress) which will cause the input impedance to be that of the bias resistor alone (100K). This should only be of concern where the output impedance of the receiver(s) is greater than 10K. The high pass filter formed by the decoupling capacitor and the bias resistor has a cut-off of less than 3 Hz so the response of the audio section is flat across the 100 to 3000 Hz voice spectrum.

The next stage is an inverting amplifier that utilizes a digital pot in the feedback path to provide gain or attenuation of the receiver channel. The equation shown in figure 3.2.1 can be used to calculate the output voltage based on the POT setting for a particular receiver input (the mixer and output gain = 1) assuming that the corresponding output level settings are at maximum. This stage also has a 100pF capacitor in parallel with the feedback resistor to prevent the op-amp from oscillating due to parisitic high frequency poles in the feedback circuit. This results in a low-pass filter with a minimum 3db cut-off of 16 Khz (at POT = 99%) and a maximum 3db cut-off of greater than 1MHz (POT = 1%).

3.3 COS and Logic Inputs

COS inputs parallel their corresponding audio inputs on P2 and P3 and P11 - 14. The FF- 800 uses a zener diode and series resistor to protect the digital inputs from the outside world -- figure 3.3.1 illustrates the logic input circuit. This input circuit is also used by the voter logic, CTCSS, and command trigger inputs. A logic low or "0" is any voltage below 0.8 V -- A logic high or "1" is any voltage above 4.2 V (or open circuit). Circuits driving these inputs must be capable of sinking or sourcing 0.02 mA (minimum) for proper operation. The upper limit for input voltage on these pins is determined by the power limits of the 50K pull-up resistor. The absolute maximum voltage is 80 volts -- however, some latitude should be given to this limit and the user is recommended to limit the input voltage to no more than 40V.

For inputs that do not sink current to ground, a load resistor to ground must be added to the logic input. This resistor should be in the range of 470 to 1000 ohms. The load resistor pulls the logic input to a logic zero (0.1 V for R = 1000 ohms) and requires that the input device be able to source at least 5 ma to create a logic 1. If the input device has a high impeadance drive circuit, it may be necessary to add a transistor buffer to the appropriate logic input(s). Figure 3.3.2 illustrates a simple NPN transistor switch that is suitable for buffering high impeadance circuits. The base resistor can be varied in accordance with the drive characteristics of the sourcing circuit.

Another situation that may require some external buffering occurs when an input signal does not vary below 0.8 V or above 4.2 V. The NPN switch can not be used with signals that don't vary below 0.8V because the transistor will never turn off, thus a different circuit is required to provide the logic levels required by the FF-800. Figure 3.3.3 illustrates an op-amp comparator circuit with hysteresis that is used to indicate weather the input voltage is above or below the reference voltage. If the op-amp of figure 3.3.3 is powered from +5V only, the output of the op-amp will directly drive the input to the FF-800. If the input is above the reference, the op-amp will drive its output to +V and if the input is below the reference, the op-amp will drive its output to ground.

3.4 Local microphone

The local microphone channel is designed to provide the user with a local input source -- however, this input can also serve as a receiver/transmitter port if the user determines that a local microphone is not desired. In order to use an electret or DTMF microphone, the user must provide an external pre-amplifier to provide the FF-800 with the proper input level (the FF-800 chassis has a built-in pre-amplifier). Figure 3.4.1 illustrates the pre-amplifier circuit. The op-amp is not critical, the LM1458 is quite popular and can be readily obtained through many electronic parts outlets.

3.5 Control receiver

The control receiver audio and COS are connected at P3. The same switching circuitry is used for the control receiver which means that squelched or discriminator audio can be used. Control receiver audio is passed only to the DTMF decoder, not to the main mixer -- thus, control commands can be entered at the control receiver without disturbing a transmission in progress. The input impeadance is 100K, and is AC coupled through a 1.0 F capacitor. It should be noted that only one input can be connected to the DTMF receiver at a time. Thus, the highest priority active receiver input will have sole access to the DTMF receiver.

3.6 Transmitter audio

The four transmitter audio outputs are located at P4 (and P15 through P18) and the local output is located at P25. Digital pots control the output levels for ports A through D. The digital pots can be adjusted from either the DTMF or the serial terminal port (the serial terminal port allows real-time adjustment). For best results, each output level should be set at maximum, and the level should be reduced (padded) at the transmitter (either by a potentiometer or the transmitter deviation control). This helps to increase the noise margin on the audio signal. Of course, if this is not possible or practical, the level can be adjusted at the FF-800. Figure 3.6.1 illustrates a model of one of the TX audio outputs. The output impeadance of the op-amp is about 75 -- thus, with the series resistor the output impeadance is roughly 175. The op-amps are all biased at zero volts which means that there is no bias on the output signal. The audio outputs are all DC coupled and the user must install a capacitor in series with any audio feeds that require AC coupled audio. The size of the capacitor will affect the low frequency roll-off of the FF-800 output. If CTCSS signals are to be passed through the system, the coupling capacitor should be in the 50 - 100 F range. For applications where CTCSS passing is not an issue, the capacitor may be in the 1 - 10 F range.

3.7 PTT and Logic outputs

All of the on board logic outputs (including the PTT outputs) are of an open-drain MOSFET type. Each output can sink up to 500 mA of current. No pull-up devices are present, so the user must provide them based on the type of load the output is connected to (a relay load would not need a pull-up resistor, but a CMOS logic device would). Device limitations force the user to de-rate the output current rating if multiple outputs are used to draw high current levels. The curve of figure 3.7.1 illustrates the maximum output current vs number of "on" devices. As the curve shows, a room temperature device with all eight outputs on is rated at about 250 mA per output. The user will also note that the output current rating must be de-rated with temperature. If the FF-800 is to be operated in an environment where the ambient temperature can exceed normal room temperature (25 C or 70 F) the total allowed current per output is reduced. Any outputs that drive an inductive load (such as a motor or relay) must have a spike supression component (such as a diode) installed at the load device as shown in figure 3.7.3.

Each output has an associated "active level" which is much like the active level settings for the COS and Voter Logic inputs. The active level settings for the outputs determine whether the output is "on" with a path to ground, or "on" with an open circuit. For the relay of figure 3.7.3, "on" should be active low, while the LED circuit of 3.7.2 would require an active high output so that the LED would be on when the output is "On". The factory default level settings are active low so that any "On" output represents a low impeadance path to ground. The Active Level command is be used to modify the active level status of the outputs and PTT signals.


One possible difficulty with the FF-800 outputs relates to the fact that while they can sink a significant amount of current, they can not SOURCE any current. This causes difficulty when a voltage output that can source current is desired (to key an exciter strip, for example) without using a relay. In this situation, the user must supply an external PNP transistor to act as an inverter/buffer combination. Figure 3.7.4 illustrates the circuit that is required to convert the open-drain, current sink outputs of the FF-800 to an open-collector current source. There are several transistors that can be used for this circuit, the choice of which largely depends upon the amount of current that is to be sourced. Loads that require less than 200 mA can be driven by a 2N2907 PNP switching transistor. The TIP32 PNP switch is capable of collector currents of up to 3 A, and the TIP34 can handle currents up to 10 A. Since the circuit of figure 3.7.4 drives the transistor into saturation, the typical Vce voltage drop will only be about 0.1 V, which means that the power dissipation in the transistor will typically be very small and only a modest heat sink may be required for currents greater than 1 A. Any FF-800 output that is to drive a circuit like the one in figure 3.7.4 should be configured for active low output because the transistor is turned on by grounding the base resistor.

3.8 Telephone line

Telephone Line connections are made through the standard phone line connector at P21. This connection is all that is necessary for basic phone patch operation (including auto patch, control auto patch, and reverse auto patch). However, if this phone line is shared with other services, there are additional connections that must be made to prevent interference to and from the other services sharing the line.

If the other service(s) using the same phone line have a busy detect input, the OH+ and OH- signals at P8 are used by the FF-800 to provide the line busy signal. These two signals are actually the output of a single opto-isolator (OH- is the emitter and OH+ is the collector). OH- is connected to the target service(s) signal ground while OH+ is connected to the active low busy input -- if this input does not have an internal pull-up, then one must be provided according to the specifications for the shared equipment requirements. If the service(s) in question require active high busy input, an inverter (such as a 7404 or an NPN switch) will be necessary.

The FF-800 BUSY+ and BUSY- inputs are used to detect when other services have control of the phone line. These two signals are opto-isolator inputs which are current limited and reverse polarity protected. This input can accept voltages of 5V to 20V and can be DC or AC (up to 1 KHz) -- the minimum current drive required is 10 mA. Whenever this input is active, auto patch operations are inhibited by the FF-800.

The OH(+/-) and BUSY(+/-) signals might seem a bit complicated, but they were implemented in this fashion to protect the FF-800. By using opto-isolators, the phone line interface can be electrically isolated from the rest of the FF-800 circuitry. Statistics have shown that a large percentage of lightning surge damage occurs through phone line connections. Thus, it is important to isolate the phone line and its associated circuitry to reduce the likelyhood of major damage from surges on the phone line.

3.9 Adjustments

Adjusting the audio levels on the FF-800 is not difficult, but there is a procedure that should be followed that allows one-pass adjustment for all levels. There are three phases to the adjustment procedure: 1) receiver DTMF adjust, 2) transmitter level adjust, and 3) receiver balance adjust. A service monitor or oscilliscope/receiver combination are suggested, but a good ear and a good receiver can also work well.

Each receiver level must be adjusted at the receiver to provide the optimum level for the DTMF decoder. Each receiver must be capable of providing at least 0.8 Vpp audio for DTMF detection. If a receiver can not provide this level (or if its maximum level is near this minimum specification) then the signal must pass through an external amplifier before reaching the FF-800.

The easiest way to determine if valid DTMF detection has occurred is to view the data valid (DV) LED on the FF-8010 Display Interface. For those users who do not have a display, the DV signal can be found at pin 15 of U21 (refer to appendix B for a parts placement diagram). The signal at U21 will go high (+4.0 to +5.0 volts referenced to ground) any time a valid DTMF is detected. While monitoring the DV signal, transmit a DTMF "3" while adjusting the level at the appropriate receiver. Start at minimum level and increase -- note where the DTMF valid first occurs and continue increasing until the DV signal goes low and note where this happens. the final adjustment should be half way between the lower and upper detect limits. Once this adjustment is complete for all receivers DO NOT perform any further adjustments on the receivers. These levels should not need further adjustment unless problems occur with DTMF detection. NOTE: The "3" was suggested earlier because it is typically the most difficult tone pair to detect. However, all codes should be tried (and with several radios) to verify that the adjustment is correct.

Next, choose which audio source is to run at the highest level (ie., receiver audio, speech audio, or tone audio). The selected source should be run at full level (99%) and the transmit levels are then adjusted for each connected transmitter to provide the desired deviation. For transmit levels that are adjusted using the transmitter deviation control, the user should initially set the appropriate TX pot(s) to 99% -- only reduce this setting if the FF-800 is providing too much level to allow proper adjustment at the transmitter. After the transmitter level is set, the remaining levels are adjusted to the deviation desired for each.

The last phase of the adjustment procedure involves balancing the receiver inputs. This is where a service monitor is extremely valuable. However, if a monitor is not available, a pair of transceivers can be used. The following description will assume that you are using the two-transciever (2TR) method. In the 2TR method, one transmitter transmits a test tone into the receiver under test and the listener uses another receiver to compare the original signal to the FF-800 transmitter output. This is done by flipping between the input frequency and output frequency and comparing the levels. A DTMF tone pair makes a good test signal that is easily generated by almost any radio. Be sure to use the un-mute feature, or the tone will not get to the transmitter.


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