30.12.2017, 00:02 by Mare

I will descvribe here the USB interface between the redio station and the computer which I recently developed and tested. This post is a continuation of the first part, where I described a simple interface for controlling two digital lines using the USB / Serial Converter, where I presented simple interface to control two digital signals (e.g. PTT and CW). This time I will describe an interface that combines more functions:

Controlling several digital (switching) inputs and outputs,

Interface for controlling the station via the serial interface

Audio input and output interface (sound card)

I had some implementation issues with the microcontrollers and USB virtual com ports, which I have described in detail in the previous contribution, I decided it’s better using the tested solutions. The block diagram of the interface is swhown in following picture:

Contents

Skip to:

USB Hub | CAT module | Sound card module | Housing | Connect to FT817 | Final test and 1st QSO | Latest Revisions |

Quick links:

Gerber files: USB HUB, CAT module, Sound Card

BOM (crytical components): USB HUB, CAT module, Sound Card

Interface structure

The interface is based on a USB hub with three USB ports. On the PC side, the interface is connected only with one USB cable, which serves for data transfer and provides power. The whole interface fits inside the standard casted aluminum housing with outline dimensions of only 100x50x25mm.The interface is modular and provides several different configurations according to specific needs. There are three ports on the USB HUB. The ports 1 and 2 are always available for additional modules, and on the port 3 is shared either the CAT / PTT / CW interface that is already installed on the hub itself or the auxilary USB connector for additional external devices. The sound and CAT module can be connected to USB HUB ports to expand the functionality of the interface.

USB HUB

Each module in this interface is an USB device on its own, which is separately connected to the USB interface. It would be very uselss if each of the devices in the interface would be connected to USB interfaces with its separate cable. For this reason, I developed my own USB hub. The hub consists of a dedicated hub controller and power line switches. The hub controller is TUSB2036, which is 3-Port 12 Mbps USB full-speed hub with serial EEPROM interface for stroing own VID / PID identifiers. Most usefull feature is that this device is implemented with a digital state machine instead of a microcontroller, which means no firmware programming is required. Just solder it and it will work.

An individually port power controlled hub switches power on or off to each downstream port as requested by the USB host through external power-distribution switch TPS2044B. Also when an individually port power controlled hub senses an over-current event, only power to the affected downstream port will be switched off. A ganged hub switches on power to all its downstream ports when power is required to be on for any port. The power to the downstream ports is not switched off unless all ports are in a state that allows power to be removed. Also when a ganged hub senses an over-current event, power to all downstream ports will be switched off.

The TPS2044B power-distribution switches are intended for applications where heavy capacitive loads and short circuits are likely to be encountered. These devices incorporates 70-mΩ N-channel MOSFET power switches for power-distribution systems that require multiple power switches in a single package. Each switch is controlled by a logic enable input. Gate drive is provided by an internal charge pump designed to control the power-switch rise times and fall times to minimize current surges during switching. The charge pump requires no external components and allows operation from supplies as low as 2.7 V.There are 4 channels in TPS2044B, from which only 3 are use3d in this application.The USB HUB schematics is shown in following diagram:

There is additional USB-to-serial interface on the HUB base board. The schematic diagram for this part is shown in the following picture:

The connector for the radio station is located on the same board as well. It has place for two SIL (Single-in-Line) connectors, both in parallel with RJ-45 connector. Using standard RJ-45 can be very useful, because it’s easy to cut one old network (patch) cable in galf to have two cables for connecting the radios on this interface. The schematic for this part is shown in following picture:

Implementation of the USB HUB interface

USB HUB is assembled on double sided PCB which fits inside the Hammond 1590G casted housing. Here are GERBER files for the USB HUB PCB. I suggest ordering at one of the low-cost, fast manufacturers, like ALL-PCB. To order the USB HUB board, just use the order code H28486AST52. You will get 10 PCBs for 5 USD (including shipment).

The assembly drawings:

The bill of materials for USB HUB:

Description Designator Size Quantity Value Ceramic capacitor C1, C2, C20, C28 0603 4 1u Ceramic capacitor C3 0603 1 10nF Ceramic capacitor C4, C5, C6, C11, C13, C15, C17 0603 7 100n Ceramic capacitor C7, C8, C9, C10, C12, C14, C16 0603 7 4u7 Ceramic capacitor C18, C19, C21, C22, C23, C24, C25, C26 0603 8 22p Ceramic capacitor C27, C29 0603 2 33p SMD LED D1 0805 1 LED 0603 EEPROM Ic2 SOT23-6 1 93AA46BT-I/OT Regulator IC1 SOT223 1 NCP1117ST33T3 USB HUB controller IC3 TQFP32 1 TUSB2036_VF_32 USB 1.1 connector type B J1 1 4-1437106-8 EMI filter L1, L2, L3, L4 0805 4 BLM… 2,54mm P1, P2, P4 3 Female single row Female USB, tip A P3 1 Optional Resistor R1 0603 1 220E Resistor R2, R8 0603 2 1k5 Resistor R3, R4 0603 2 22E Resistor R5, R6, R7, R9, R18, R19, R20, R21, R22, R23 0603 10 15k Resistor R10 0603 1 0E Resistor R11, R12, R13, R14, R15, R16 0603 6 33E Resistor R17 0603 1 2k2 Test point TP1, TPG 2 Test point TPS 1 Test point U1 SO-16 1 TPS2044B Quartz SMD 5x7mm Y1 SMD 5x7mm 1 6MHz

Optional CAT interface (located on USB HUB board)

In case a CAT interface located on the main board is used it is also necessary to assemble the components listed in following Table.

Bill of materials serial interface…

There are two bridges (0 ohm resistors) connecting this optional interface to the USB hub, port 3: R30 and R31.

Description Designator Size Quantity Value Ceramic capacitor C30, C31, C32, C33, C34, C37, C38 0603 7 100nF Ceramic capacitor C35, C36 1206 2 10u Digital isolator IC4 SO16 Wide 1 ISOW7841DWR RS232 line driver IC5 SO16 Wide 1 TRS3232ECDBR USB UART IC6 SSOP20 1 FT231XS-R Optocoupler Iso1, Iso2 SO4 2 TLP124 LED SMD LED1, LED2 0805 2 LED 0603 2,54mm P5, P6, P7 HDR1X8 3 8 pin male RJ45 without magnetics P8 RJ45 1 RJ45 2,54mm P9, P10 HDR2X2 2 Dual row, 2 pin 2,54mm P11 HDR1X3 1 3 pin Resistor R24, R25, R28, R32 0603 4 1k Resistor R26, R30, R31 0603 3 0E Resistor R27, R29, R33, R34 0603 4 220E Test point TP2 En pin TP 1 CTS Test point TP3 En pin TP 1 DTR Test point TP4 En pin TP 1 DSC Test point TP5 En pin TP 1 RI Power NPN Tr1, Tr2 SOT223 2 NSS60601

After assembly of the USB hub it is time for first test.

All “crytical” components for the USB-HUB are available in this Octopart BOM.

Here is photocopy of the assembly drawing with marked values of the passive components. It might be usefull during placement of the components: scan20180103235148002812

USB hub test

When all the components are assembled, first is to check there are no short circuits on the power lines. With a multimeter, measure resistance between point TP1 and SGND (contact 4 P1, P2 or P4). There must be no short circuit here. Now, the circuitry can be connected to the USB port of the computer. Connect the USB cable between the J1 connector and the free USB port of the computer. If all goes well, the USB hub should be shown in the operating system. There might be some issues with USB 3.0. There is a chance that your PC’s won’t detect the USB hub. This is usually due to the missing drivers for the USB 3.0 controller. The USB 3.0 drivers may not work with the USB1.1 or USB2.0 devices (like the described USB HUB). In such case the driver should be installed.

The device manager should then recognize the HUB:

If the optional CAT interface is installed, it should be shown in the device manager:

Now it’s time to get additional modules working: USB to Serial interface and USB Sound card.

Serial port interface module

When there is a requirement for an additional CAT module that can be connected to any of the USB ports (USB1 to USB3) I designed stand-alone module. Here is the schematic diagram of the serial port module. Bill of materials is almost identical to the serial port modeul placed on base board. Here are gerber files for the CAT board. Here is BOM for crytical components for the CAT module.



CAT/serial interface module – Assembly process

There is nothing special about assembly. Components are placed on both sides:

In the case when RS232 voltage levels are not needed, it is not necessary to solder the integrated circuit IC5 for voltage level shifting. The radio station FT817 has TTL logic levels on serial port. In this case, two bridges are required instead of RS232 driver: between the pins 12 and 13 and between the pins 11 and 14 on the IC5. This is shown in assembly drawing with red markings.

Testing the CAT module

When all components are soldered, check that there is no short circuit on the supply (between terminals 1 and 4 on P1 – see schematic). The module can now be connected to the hub base board in one of the free ports: USB1 / P1 or USB2 / P2. The installation procedure is started after that for the FTDI FT232. When installation is sucessfully finished, the interface is shown in the system as a new serial (COM) interface. It can be checked in the control panel – device manager. The circuit nžeeds additional check whether the ISOW7841 converter works. At the P6 connector, the voltage between the terminals 5 (+ Viso) and 6 (GNDISO) is measured and must be 5V or 3,3V, depending on the bridge R26. Keep load to this isolated power source low. In practice the current should not exceed few mA.

Configuration

It turns out that control lines must be inverted to properly control the PTT and CW signals via open collector NPN transistor. It is quite straightforward to reprogram the FT232RL using the FTPROG application. This software utility allows changing the configuration including inverton of the control signals, which is an elegant solution and does not require additional components in the circuit. The procedure is described in the FTPROG manual, in section 5.5.

Inverting the polarity is simple: First, the FT232xx interface circuit should be connected to the USB port and the FTPROG program is started. A connected interface appears in the list on the left. In the list, we find the FT EEPROM option and the Invert RS232 signals section below. On the right side, check Invert RTS # and Invert DTR # tick boxes. Finally click on the “program” icon in the toolbar (small lightning arrow) to store the changes in the internal eeprom of the device. Same application is used to change the function of other signals, including four GPIO lines D0 to D3.

USB Sound Card

The last add-on module described here is the USB audio interface. The basis for the sound card is well known PCM2900C. During the investigation for most suitable single chip slution I have noticed this controller in many similar applications. PCM2900C is a USB stereo codec manufactured by Texas Instruments. It doesn’t require any specific driver for use on USB. A generic system sound drivers and HID device driver are sufficient. The codec itself provides independently adjustable sampling parameters on the recording channels (audio input) and playback channels (audio output). Sampling is 16-bit with the highest rate of 48kHz. For applications in radio stations, the dynamic range is more important than the sampling rate, which is 89dB for ADC and 93dB at the DAC output. The interface is shown to the system as a stereo player and stereo audio input device with identifiers VID = 0x08BB and PID = 0x29C0. It is found in the system settings as “USB AUDIO CODEC”. Additionally there is also a HID interface with three signals, two for volume Up/Down control and one for silencing (“Mute”). When the keys are used (e.g. on the front panel of the housing), they can control the volume settings in the hosting operating system. This is useful if the computer and the station are somewhat distant and it is not convinient to use the volume icon with the mouse. The amplitude of the input analog voltages must not exceed 60% of the supply voltage (3,3V). Also, the DAC can generate alternating voltages with amplitudes up to 60% of the supply voltage. Since the power is single-ended, the center of the analog inputs and outputs is set to the center of the supply voltage (driven from PCM2900C). This voltage is available for use in analogue preamplifiers and filters on each analogue channels.

Low Pass Audio Filter

All four inputs and outputs have external active low pass filters with an upper frequency limit of 12 kHz, which is equal to the maximum bandwidth of the channel when connected to the radio station. A spice simulator was used for designing as it is the fastest and easiest way to check whether a certain idea works and what the component values are for the first practical approximation of the end circuit. This dramatically speeds up the first experiments and reduces the amount of initial errors. One of the best tools for simulation is the LT-Spice. It is my favourite with built-in schematic drawing editor and post-processor for analysis of results. LT-Spice is free and available on the website of the Linear Technology.

A common practice in choosing a filter topology for AD and DA converters with a high(er) dynamic range are the MFB (Multiple Feedback) filters. This filter offers exceptional stop band rejection over other filter topologies. Load at the output of the simulated filter represents the transformer primary.

This design is an inverting signal path, 2nd-order, low-pass filter that offers numerous advantages over most widely used Sallen-Key filters:

No gain for the noninverting current noise and/or DC bias current. Figure above shows the non-inverting input grounded, which is great for reducing noise but less than ideal for DC precision. Adding a resistor equal to the DC impedance looking out the inverting node achieves bias current cancellation; adding a capacitor across this resistor reduces the noise contribution for the resistor and the op amp bias current noise. If the amplifier is a JFET or CMOS type, this bias current cancellation will not work and the noninverting input should simply be set to ground or a desired reference voltage. The in-band signal gain is set by – (R1/R3). As will be shown, R3 also sets the Q of the filter while having no influence over ω0.

More on this topic can be found in the Application Report “Design Methodology for MFB Filters in ADC Interface Applications” by Michael Steffes.

The operational amlifier for the filter should have following features:

Low Quiescent Current: 75 μA/ch

Supply Range: down to 3,3V

Low Input Voltage Noise Density

Rail-to-Rail Input and Output

Gain Bandwidth at least 1 MHz

Low Input Bias Current

Low Offset Voltage

Unity-Gain Stable

Optionally Internal RF and EMI Filter

OpAmp with such features will provide roboust and low-noise audio system with high dynamic response required for operation with modern digital modes. I searched through the filters on the manufacturers web pages and the “ideal” candidate seems to be TLV600x.

The circuit from the schematic above is available in this file for LT-spice simulation.

The result of simzulation:

The filter with the calculated/simulated components was implemented as a protoype and connected it to a sine wave generated by PCM2900C with ampliutude 100mVpp. At the output the actual effective value of the voltage (RMS) was measured.

For the representation purposes, the output RMS voltge was divided by 1mV and the dB ratio was used in the diagram below. The measurements of the implemented filter prototype:

Output signal was measured without the transformer. The isolation transformer for galvanic isolation of audio signals has transfer characteristics, which is just the opposite of the measured results above: the transfer ratio drops at lower frequencies. Both characteristics compenaste into flat output, which is desired for the digital modes and provides nice response for voice audio.

Sound card complete design

To squeeze as much performance as possible from PCM2900C it needs as much clean power as possible. It is provided with the TPS7A4901, which is a linear regulator with a low drop and a very small output noise in the range below 20μVRMS. The key to achieve this is choice of proper capacitors. Ceramics works best in the price-performance ratio. For a capacitance of 10uF ceramic capacitors can be quite large, but there is no need for high voltage ratings since all voltages remains under 5,5V. In addition, the TPS7A4901 has overcurrent and overvoltage protection.

To isolate audio signals galvanically, two audio transformers are provided. The audio transformer is really big device compared to other components. It could be replaced by isolator at the digital, USB side, but this would then introduce other issues with isolated DC/DC converter and all noise it would generate. Therefore, I decided to go with old and proven audio transformers. The complete schematics for the audi interface is shown in the following diagram:

The diagram above shows three keys (connector P8). They are used for the volume control functions in the operating system, because the PCM2900C is composite device consisting of sound and HID (Human Interface Device) USB device. These three keys can control the sound level and mute the sound as shown in following Table:

Table 3 – The function of the three volume control buttons

Button Function HID0 Volume Up HID1 Volume Down HID2 Mute

Sound card Assembly

Here are the gerber files for sound card. The assembly drawing of the printed circuit board of the sound card is shown in the following figures:

The components are placed on both sides of the printed circuit board. Start soldering with the passive and smaller components. Capacitors and resistors are mostly the size 0603, with the exception of 10uF capacitors that are size 1206. The layout can fit smaller 0805 as well, depending on what do you have have at your disposal. A complete list of components for the USB sound card is in this table:

Description Identifier Size Quantity Value X7R Ceramic capacitor C1, C3 0603 2 4u7 X7R Ceramic capacitor C2, C4 0603 2 100n X7R Ceramic capacitor C6 0603 1 10nF X7R Ceramic capacitor C7, C8 1206 2 10uF/6V X7R Ceramic capacitor C9 0603 1 100n X7R Ceramic capacitor C10 0603 1 10n X7R Ceramic capacitor C11, C12, C24, C25, C26, C27 0603 6 1u X7R Ceramic capacitor C13, C16, C28, C29 0603 4 330p X7R Ceramic capacitor C14, C18 0603 2 18p X7R Ceramic capacitor C15, C17, C20, C21, C22, C30, C31, C32, C33 1206 9 10u X7R Ceramic capacitor C19, C23, C34, C35 0603 4 1n8 Schottky Diode D1 SOD-323 1 NSR1020MW2T1G Ultra low noise regulator IC6 TSSOP8 1 TPS7A4901DGNT USB sound CODEC IC7 DB28 1 PCM2900C LinCMOS Rail-To-Rail OpAmp IC8 TSSOP14 1 TLV2264A RF filter L4 0805 1 BLM11P600S Male header P1 HDR1X4M 1 4 pins Header P2, P3 HDR2X2 2 DNP Header P4 HDR1X4 1 DNP Header dual row P8 HDR2X3 1 DNP Resistor R10 0603 1 22k Resistor R11 0603 1 39k Resistor R12, R13, R14, R15, R16, R17 0603 6 1k5 Resistor R18 0603 1 2E2 Resistor R19, R20, R21, R22, R25, R28, R29, R30, R32 0603 9 12K Resistor R23, R26, R31, R33 0603 4 3K9 Resistor R24, R27, R34, R35 0603 4 100 Resistor R36 0603 1 1M Resistor R37, R38 0603 2 22E Transformer T1, T2 SM-LP-5001 2 Bourns! Test point TP3 En_pin_TP 1 Test point TP4 En_pin_TP 1 Test point TP5 En_pin_TP 1 Test point TP6 En_pin_TP 1 Test point TP7 En_pin_TP 1 Quartz Y1 SMU4 1 12MHz

Here is the BOM for crytical components for Sound Card.

Here is photocopy of the assembly drawing with marked components values: scan20180103235210002813

When PCB is assembled it is necessary to route the audio signal from selected channel through the transformer. There are two locations where audio signal is disconnected. First, select the input and output channel by placing the jumper on P2 and P3 headers. Second spot is near the P4 pads. The traces from the transformers are not directly connected to the pads of header P4. For normal operation, it is necessary to connect oval pads with adjoining pads to the P4 connector, as shown in assembly drawing (BOT side) with red markings.

Test the Audio Interface

After assembling the sound card module, first check that there is no short circuit at the power supply. Check the shorts with an ohm-meter on the C7 and C8 capacitors. Next connect the sound card to the hub. It should be recognised as a USB audio interface (USB Audio CODEC). Next check the supply voltages. The voltage across C8 must be 5V, ± 500mV, and across C7 3.3V ± 100mV. Also check the voltage for the midpoint of the audio filters +VAcom across the capacitor C25, which must be close to 1.65V.

Now make some sound measurements with signal generator and an oscilloscope. Apply a sinus signal of approximately 10mVpp, frequency of 1kHz to pins 1 and 3 of the connector P2, and check that the computer is recording it. In the control panel, find a USB sound card and select “listen” under the advanced properties.

At the audio output side, connect the oscilloscope to the pins 1 and 3 of the connector P3 and play some sound using this USB sound card. Some of the free signal generatoers can be used. SigJenny is a nice, free tool for generating continuous or burst signals from a PC sound card. Also AF Signal Function Generator which is nice, but no waveform display. Finally check the HID USB device (keys) if the audio controls are operational by shorting the pins on header P8 (1-2, 3-4 and 5-6).

Housing

The standard aluminum case from Hammond was chosen for the housing. It is alluminium cast, low cost housingwith the part number 1590G.It is available from digikey, farnell, mouser, TME, RS Components or Conrad. The outer dimensions of the housing are 100x50x24mm. The case lid carries the main board with the hub. To mount the main PCB on the lid, it is necessary to make four holes according to the following drawing:

It is also necessary to remove the small wall on the lid where the connectors are as shown in the following photo:

To avoid short circiuit by metal housing use plastic spacers. They can be printed with the 3D printer and attached to the PCB with dual sided adhesive tape:

The thickness should be between 1 to 1.5 mm. Here is the STL file for the spacers.

The box part of the housing should have slots for the connectors. Drawing above shows the dimensions of all slots. Depending on the connection configuration (using the RJ45 connector or cable via the cable gland), and depending on the need for additional USB output, these slots and bores should be machined to your specific needs. The machining process is fairly simple in both cases, with hand machining with saw and file or by using the CNC milling machine. It is necessary to cut up to three holes perpendicularly to the box wall.

The housing can have additional feet for attaching to the radio with velcro tape.

Here is STL file for the feet shown above.

Here are STEP files for both parts of the housing just in case someone would like to make them out of plastic with the 3D printer.

Connect the FT817 radio

The main idea during the interface design was to have one cable to the interface (USB) and one cable to the radio. The problem is the FT817 has 3 different connectors for CAT, PTT and CW key. The cable from this interface to the radio should therefore be some kind of compromise.

Following Figure shows the layout of the connectors on the main printed circuit board (the USB hub).

There is RJ45 connector on the USB hub and when using the standard UTP network cable with four twisted pairs there are two possible configurations of the wires connection to the RJ45: Type “A” and Type “B”. The colors of the standard “UTP” network cable with both types are marked on the Figure above. The bottom right drawing shows where the signals must be connected on the sound card, additional CAT module and serial interface placed on the base board.

At the radio side there are three connectors: 8 pin accessory, 6 pin data and 3,5mm audio for the keyer. Both possible types of the network cable color schemes are shown.

The list and arrangement of connections and internal connections is summarized in following Table:

No. Signal Twisted pair

P5 (RJ45)

Serial port on HUB

additional CAT module Sound card

»A« »B« 1 KEY ze or 8 P6 – 2 2 Noga ZE OR 7 P9 – 1 3 RXD or ze 6 P6 – 3 4 TXD MO MO 5 P6 – 4 5 GND mo mo 4 P6 – 7 P6 – 6 P4 – 1,3 6 Data in OR ZE 3 P4 – 4 7 PTT rj rj 2 P6 – 1 8 Data out RJ RJ 1 P4 – 2

When all internal connections are properly connected according to the scheme above, the interface should look something like this:

The final step is to prepare the cable as shown in the figure above. The network cable goes first into the 6 pin DATA connector, followed by 8 pin Accessory connector and finally the 3,5mm keyer connector. At the end there is optional foot switch. The whole cable looks like this:

The foot switch above is more “hand switch”. It was soldered that way just for testing purposes.

One final step is to test the interface.

Final test and first QSO

Currently the most popular digital mode is FT8, so the decision to test the interface was not at all difficult. I already had a WSJT-X installed on my computer. I connected the interface to the computer and other end to the FT817 as described in the previous chapter.

First I set up everything necessary to work with the radio on FT8 mode. The settings in the WSTJ-X program are available through the F2 key. I set the serial interface rate at 9600 baud at the station, which is quite enough for reading at 1s refresh rate. The PTT method could be “CAT”, but I wanted to test the operation of both serial interfaces. Therefore I chose “RTS” because this signal is connected to the PTT signal. For CAT and the PTT I have chosen the appropriate “COM” interface. One final configuration is audio interface. Under the audio settings, I selected “USB AUDIO Codec” for input and output. All settings are shown in following figure:

When the WSJT-X settings were appropriate, I turned on the radio and selected the 40m frequency band. The program set the proper frequency on my FT817 and the waterfall started displaying the received signals. There was one small, but important final adjustment neccessary. At the station, I switched to the lowest transmit power (1W) and switched the LCD indicator to the “ALC”. Then I activated “Tune” in the WSJT-X, which started broadcasting a constant tone. With the volume control, I set the “ALC” indicator to one bar below the maximum value. With this, all the settings were completed.

Finally, the most exciting part of the experiment remains: broadcasting “CQ S54MTB JN75“. I tried on 40m band (7,074MHz) in one tinz empty space inside the waterfall. After a few calls, I made the first QSO with Nikolay R1BEO from the KP50 locator. He gave me a report -12dB, I returned -5dB. Then I looked at the PSK-Reporter website, to check the reception of my signals. I was quite excited when I realized that the signal went from Kazakhstan to Florida. And the excitement was even bigger when I realized that in the awe, I forgot to switch to higher power and transmitted with only 1W.

Here are some additional photos of the interface and the modules…

There are some new revisions available after assembling first boards

1. USB Hub

The optocouplers are too high and comes in the way of audio transformers. I moved them lower on the board for clearance (new gerber files USB Hub rev1.1):

2. CAT card

There are two additional jumpers available for easier soldering when TTL levels are required (new gerber files CAT card Rev1.1)

3. Sound card

Sound card has some improvements: additional test points on all inputs and outputs, two additional GND pads for easier testing and little shorter PCB for easier mounting on top of the main hub board (New gerber files Sound card rev1.1):

Working with FT817, listening with FT991: