Mobilinkd TNC4 User manual

TNC4 User Guide
Mobilinkd TNC4 User Guide
Rev A - 2023-02-05
Thank you for purchasing your ne Mobilinkd TNC4 Battery-po ered Bluetooth TNC.
This TNC is designed to suit all aspects of the Amateur Radio community. It is ready to plug in and go
ith easy to use and intuitive configuration soft are, and it is completely open for experimentation.
The schematics are published and all soft are used in the TNC is open source and available online.
Warning
Do not store your TNC where prolonged exposure to extreme temperatures can occur (such
as in the trunk or cabin of a car). It can cause permanent damage.
•hort term storage: -4° – 140°F (-20°C – 60°C)
•Long Term torage: 32° – 77°F (0°C – 25°C)
•Operating Temperature: -4°F – 131°F (-20°C – 55°C)
Regulatory Information
This is the stuff I am legally obligated to put in this document If I am obligated to put it in here, you
are obligated to read it. Enjoy!
United States of America
Contains FCC ID:A8TBM78ABCDEFGH
This device complies ith Part 15 of the FCC Rules. Operation is subject to the follo ing t o
conditions: (1) this device may not cause harmful interference, and (2) this device must accept any
interference received, including interference that may cause undesired operation
This equipment has been tested and found to comply ith the limits for a Class B digital device,
pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection
against harmful interference in a residential installation. This equipment generates, uses and can radiate
radio frequency energy, and if not installed and used in accordance ith the instructions, may cause
harmful interference to radio communications. Ho ever, there is no guarantee that interference ill not
occur in a particular installation. If this equipment does cause harmful interference to radio or
television reception, hich can be determined by turning the equipment off and on, the user is
encouraged to try to correct the interference by one or more of the follo ing measures:
• Reorient or relocate the receiving antenna.
• Increase the separation bet een the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from that to hich the receiver is
connected.
• Consult the dealer or an experienced radio/TV technician for help.
• Or, you know – you’re a licensed amateur radio operator. Figure it out!

TNC4 User Guide
Canada
Contains transmitter module IC: 12246A-BM78SPPS5M2
This device complies ith Industry Canada license-exempt RSS standard(s). Operation is subject to the
follo ing t o conditions: (1) this device may not cause interference, and (2) this device must accept
any interference, including interference that may cause undesired operation of the device.
Le présent appareil est conforme aux CNR d'Industrie Canada applicables aux appareils radio exempts
de licence. L'exploitation est autorisée aux deux conditions suivantes: (1) l'appareil ne doit pas produire
de brouillage, et (2) l'utilisateur de l'appareil doit accepter tout brouillage radioélectrique subi, même si
le brouillage est susceptible d'en compromettre le fonctionnement.
Under Industry Canada regulations, this radio transmitter may only operate using an antenna of a type
and maximum (or lesser) gain approved for the transmitter by Industry Canada. To reduce potential
radio interference to other users, the antenna type and its gain should be so chosen that the equivalent
isotropically radiated po er (e.i.r.p.) is not more than that necessary for successful communication.
Conformément à la réglementation d'Industrie Canada, le présent émetteur radio peut fonctionner avec
une antenne d'un type et d'un gain maximal (ou inférieur) approuvé pour l'émetteur par Industrie
Canada. Dans le but de réduire les risques de brouillage radioélectrique à l'intention des autres
utilisateurs, il faut choisir le type d'antenne et son gain de sorte que la puissance isotrope rayonnée
équivalente (p.i.r.e.) ne dépasse pas l'intensité nécessaire à l'établissement d'une communication
satisfaisante.
The TNC does not contain a user modifiable antenna – unless you have a soldering iron. Then all bets
are off. You’re an ham radio operator. Go wild.
Europe
The Microchip BM78 radio module inside the TNC4 has been fully tested to comply ith EC
requirements for CE marking. These tests include Health, Safety, EMC and Radio. Further testing of
the final product (the TNC4) as conducted to ensure compliance of the integrated product.
The TNC4 is RoHS compliant. Still, I would avoid eating the PCB if I were you.
Japan
Integration of this module into a final product does not require additional radio certification provided
installation instructions are follo ed and no modifications of the module are allo ed.
So, if you are in Japan, you cannot modify the Bluetooth module. You’ve been warned.

TNC4 User Guide
Korea
I think Korea requires that I provide a user manual in Korean. I don’t (yet) speak, read or write the
language. Sorry. Give Google Translate a try:
Taiwan
注意 !
依據 低功率電波輻射性電機管理辦法
第十二條 經型式認證合格之低功率射頻電機， 經許 可，
公司、商號或使用者均不得擅自變更頻率、加大功率或 變更原設計
之特性及功能。
第十四條 低功率射頻電機之使用不得影響飛航安全及 干擾合法通信；
經發現有干擾現象時，應立即停用，並改善至無干擾時 方得繼續使用。
前項合法通信，指依電信規定作業之無線電信。
低功率射頻電機須忍受合法通信或工業、科學及醫療用 電波輻射性
電機設備之干擾。

TNC4 User Guide
C ina
The BM78/BM78 ROM module has received certification of conformity in accordance ith the China
MIIT Notice 2014-01 of State Radio Regulation Committee (SRRC) certification scheme. Integration
of this module into a final product does not require additional radio certification, provided installation
instructions are follo ed and no modifications of the module are allo ed. Refer to SRRC certificate
available in the BM78 product page for expiry date.
The BM78 module is labeled ith its o n CMIIT ID as follo s: CMIIT ID: 2015DJ7133
PLEASE NOTE: The TNC4 does not meet CMIIT equipment marking requirements at this time.
UK
Hereby, Microchip Technology Inc. declares that the radio equipment type BM78/BM78 ROM module
is in compliance ith the Radio Equipment Regulations 2017. The full text of the UKCA declaration of
conformity for this product is available (under Documents > Certifications) at:
• https:// .microchip.com/en-us/product/BM78
PLEASE NOTE: The TNC4 does not meet KCA equipment marking requirements at this time.
Brexit McBrexitface.

TNC4 User Guide
Overview
This guide ill introduce you to the key features of the TNC, its connectors, s itches and indicator
LEDs. Most of this manual illustrates the configuration and operation of the TNC using an Android
device and Android soft are. Ho ever, the TNC ill ork ith any operating system and soft are
that can talk to a KISS TNC over Bluetooth SPP (Serial Port Profile), Bluetooth LE using our custom
service, or via USB CDC (serial port emulation).
KISS TNC
The TNC4 is a KISS TNC, hich means that it is purely a modem and not really a terminal node
controller. A more accurate description of the TNC4 and all KISS devices is a KISS modem. The
TNC4 does not manipulate the packets it receives in any manner. It cannot, by itself, digipeat (relay)
packets or do any store and for ard operations associated ith an intelligent TNC. This is an
important point that can be a source of some confusion. A KISS TNC simply encodes and decodes
digital information as audio that can be transmitted over the air by a radio on a voice channel.
The TNC4 is capable of 1200 baud AFSK communication. This is suitable for APRS and packet data
over a standard voice channel.
The TNC4 is capable of 9600 baud packet (GFSK/GMSK). This mode requires a radio that is designed
to handle this mode. The radio must provide flat, unfiltered audio output (discriminator output) and
direct access to the modulator.
The TNC4 is also capable of M17 packet date mode (4-FSK). Like the 9600 baud mode, this mode
requires a radio that provides flat, unfiltered audio output (discriminator output) and direct access to the
modulator.
T e Mobilinkd TNC System
The Mobilinkd TNC System is comprised of three physical components: A radio, the Mobilinkd TNC,
and a computer, tablet or smart phone that supports Bluetooth SPP or LE-TNC. The TNC connects to
the radio ith a cable and talks to the smartphone or computer via Bluetooth connection.
The TNC4 is also able to talk to the phone, tablet or computer via USB serial port emulation.

TNC4 User Guide
TNC Switc es, Connectors and Indicators
The Mobilinkd TNC4 has three s itches, t o connectors and t o indicators. Each of these is sho n in
the image and described belo .
S1 – Po er button. Press for 2 seconds to turn on. RGB LED ill flash yello , the slo ly blink blue.
Press for 2 seconds to turn off. The RGB LED ill fade from bright yello to off.
S2 recessed reset s itch. To reset the TNC, carefully insert the tip of a pen into the hole and gently
depress the s itch.
S3 recessed DFU (device firm are update) button. This is used hen updating the device firm are.
To enter firm are update mode, connect the TNC to a USB host, ensure the TNC is turned on, then
carefully insert the tip of a pen into the hole and gently depress the s itch.
SB – USB-C connector for charging/po er/USB serial port.
TRRS – 3.5mm TRRS audio connector for Radio.
1. Tip = Speaker (audio input to TNC)
2. Ring 1 = PTT (Simplex PTT mode)
3. Ring 2 = Mic (and PTT in Multiplexed PTT mode)
4. Sleeve = GND/Common
RGB LED – This is a mult-function indicator. The blue LED flashes slo ly hen disconnected,
flashes a double-blip hen connected via Bluetooth, or flashes a triple-blip hen connected via USB.
The LED sho s red hen transmitting and green hen receiving data.
Red LED – Charge indicator. On hen connected to USB and charging, other ise off.

TNC4 User Guide
Before First Use
The battery ill not be fully charged hen you receive the TNC. It is al ays best to plug in a USB-C
cable and charge the battery before first use. When the red LED turns off, the battery is charged. The
battery ill typically last for 48 hours of continuous use.
TNC Cable
The TNC must be connected to the radio via a cable. Mobilinkd sells cables for a ide range of hand-
held radios, as ell as data cables for mobile and base radios ith TNC ports.
The cable connects four signals:
1. Audio in (this is the speaker or data out on the radio)
2. Audio out (this is mic or data in on the radio)
3. PTT signal
4. Common (GND)
On some hand-held radios, the PTT signal is multiplexed onto the audio output. In this case, the
dedicated PTT signal is not used. The radio must have its VOX setting turned off.
The TNC is expected to operate properly ithout a ferrite bead on the cable. Ho ever, some radios
emit excessive RF through the speaker-mic port, especially hen the antenna is poorly matched or
damaged. In this case, a ferrite bead may be necessary.
Radio Settings
Each radio is different, so having a comprehensive list of optimal settings in a document like this is not
possible. Ho ever, it is important to understand hat radio settings impact the performance of the
TNC and its ability to decode packets.
The squelch should be left open on the radio hen connected to the TNC. The TNC4 ill detect the
presence of data on the audio signal (it uses DCD or Data Carrier Detection). With a closed squelch,
part of a packet preamble ill be missed before the squelch on the radio opens. This ill prevent
decoding of packets.
The “Battery Saver” option should be disabled. This should have no impact on the life of the battery
hen the radio is run ith an open squelch.
If you have an inexpensive Chinese radio (Baofeng, Wouxun, and many others) ith a “Dual Receive”
feature, this must also be disabled. This essentially operates the receiver as a scanner, s itching the
receiver bet een t o frequencies. In general, with these radios, every setting that can be turned of
should be turned off. That is especially true for any squelch tail elimination settings.
Please allo me to editorialize for a moment. The quality of the radio ill directly impact the ability of
the TNC to decode packets. Do not connect the TNC4 to a cheap radio and expect miracles. The
system is only as strong as its eakest link.

TNC4 User Guide
Connecting the TNC
Connect the TNC to the HT ith both the TNC and the
radio turned off.
Plug the 3.5mm connector into the TNC. Plug the
radio connector (these styles vary) into the radio's
Speaker/Mic connector.
Connecting/Pairing
Detailed instructions for pairing the TNC on Android are belo . Instructions for iOS are omitted
because this happens more seamlessly ith BLE.
1. Press S1 briefly to turn on TNC. The blue LED ill flash slo ly.
2. Ensure Bluetooth is enabled on other device.
3. On other device, scan for Bluetooth devices. You should see “TNC4 Mobilinkd”.
4. Connect to “TNC4 Mobilinkd”. The pairing should happen automatically.
Pairing wit an Android Device
1. Install the Mobilinkd Configuration App for Android (available on Google Play.)
2. Open the Mobilinkd app.
3. Press S1 briefly to turn on TNC. The blue LED ill pulse slo ly.
4. Open the app menu and select “Bluetooth settings”
5. In the Bluetooth settings menu, select “Pair ne device”
6. When you see “TNC4 Mobilinkd” under “Available devices”, select it.
7. After a fe seconds, you should see the TNC appear under “Currently connected”.
8. Hit the back button to go back the the Mobilinkd app.

TNC4 User Guide
Pairing with iO
Open the Mobilinkd Config App for iOS.
Press the blue “refresh” button to scan for devices.
Select the TNC4 from the list.
iOS ill first ask if you ould like to connect. Select “Connect”.
iOS ill then ask if you ould like to pair ith the device. Select “Pair”.
Pairing with Windows
Detailed instructions for using the TNC4 ith Windo s is beyond the scope of this document.
Ho ever, it is important to note that Windo s ill occasionally ask for a pass ord hen pairing ith
the TNC4. If this happens, use the pairing code “123456”. We have no idea hy this happens. If you
have a support contract ith Microsoft, you are elcome to ask them about it. No other operating
system has ever been reported to do this.
Connecting with Linux
Every Linux variant is a bit different about ho pairing is handled. This seems to happen fairly
seemlessly. The TNC4 uss the default RFCOMM channel for SPP (channel 1).
# rfcomm bind 0 <MAC ADDRESS>
This ill create the TTY port /dev/rfcomm0, hich can be used like a normal serial port.

TNC4 User Guide
Configuring the TNC
This section describes the configuration process using the Mobilinkd Config App for Android. The
Mobilinkd Config App for iOS ill be very similar, except the connection and pairing is slightly
different (a little less intrusive).
This section assumes that you have follo ed the “Pairing ith an Android Device” section above and
have the Mobilinkd TNC config application running. The TNC and radio should be connected, the
TNC should be on, and the radio should still be off at this point.
1. Push the “Connect” button to connect the Mobilinkd TNC Bluetooth device. You ill see the
device name and firm are version displayed.
The image on the right sho s the main menu for the Mobilinkd Config app. This menu is the starting
point to launch the various screens sho n in the documentation belo . When you are done ith a
certain activity, press the “Close” button to go back to this screen.
Most of this guide assumes you ill be using the TNC4 for APRS and ill be using it for 1200 baud
AFSK, hich is the common standard for APRS, and is the most idely used mode for VHF packet
radio.
If you ish to use the TNC4 at 9600 baud, please refer to the section on 9600 baud operation.

TNC4 User Guide
Configuring t e Power Settings
You can check the battery level and configure the po er settings from the
“Po er Settings” dialog. The TNC4 is fully charged hen it reads
approximately 4.2V (4200mV). The nominal battery voltage is 3.7V. Avoid
operating the TNC belo 3.4V, other ise erratic behavior may occur.
The TNC may be configured to automatically turn itself on hen USB po er
is present, and automatically turn itself off hen USB po er is not present.
This is often desirable hen using the TNC in a vehicle. These settings are
controlled independent of one another.
•To po er on hen USB po er is present, select the “Po er on ith
USB Po er” option.
•To po er off hen USB po er is removed, select the “Po er off ith
USB Po er” option.
The TNC4 ill still po er on via the Po er button hen USB po er is not
present and “Po er off ith USB Po er” is enabled.
Please be a are: It is a frequent source of confusion for users hen they have removed a TNC
normally used in a vehicle and have forgotten that these setting are enabled. The TNC ill turn itself
on and off hen connected/disconnected from USB po er.

TNC4 User Guide
Modem ettings
The modem settings screen is used to change the modem type and to
configure certain modem-specific settings.
When changing the modem type, it is important to go back and reset
the Audio Input settings and Audio Output settings as these can be
different for each modem.
The Passall option allo s passing corrupted packets. This should
normally be off. It is sometimes useful for diagnostics and for eak
signal ork. But it may cause packet soft are to misbehave hen
corrupted packets are received.
The TX and RX polarity settings are used for M17 to adjust the
polarity of the modem to the radio.
Other options ill appear and be greyed-out (unselectable) because
they do not apply to the TNC4.
A note for iOS users: the Modem Setting screen ill sho fe er
options because the TNC2 is not supported on iOS, and some of
these options only apply to the TNC2.

TNC4 User Guide
Configuring Receive (RX/Input) Volume
The radio's volume level must be properly adjusted for optimal packet
decoding. Press the “Audio Input Settings” button.
1. Turn the radio on. If the squelch is set to be open (as you did
hen follo ing the instructions above), you should see the input
volume level on the audio meter.
2. The TNC has the ability to amplify lo -level audio inputs
typical of mobile radio data ports. For almost all hand-held
radios, the input gain level should be set to 0.
3. Adjust the volume on the radio until the volume meter lights up
the right-most level indicator.*
4. If you cannot turn up the volume high enough on the radio to
light up the right-most indicator, increase the input gain level.
5. The input t ist should typically be set to 6dB hen using an
audio signal (hand-held speaker output, 1200 baud data output)
and 0dB hen using correlator output (9600 baud data
output).**
6. You can press the “Auto-adjust button” if you are daring. This is best used hen connecting to
a mobile radio hen the input gain and input t ist need to be adjusted.
7. Press the Close button to return to the main menu.
* If your radio uses the volume knob for on/off, it may be helpful to mark on the radio and knob ith
the optimal volume setting so it can be set quickly after turning on the radio.
** The input t ist level controls various filter parameters in demodulator. Adjusting the input t ist
may change the ability (for better or orse) of the demodulator to decode packets.
When s itching bet een 1200 baud and 9600 baud operation, it is important to re-adjust the audio input
settings. The same is true hen s itching radios.

TNC4 User Guide
Configuring Transmit and (TX/Output) Volume
Select the “Audio Output Settings” button on the main menu to open the
audio output settings.
Modern ham radios use t o different signaling methods for the Push-to-
Talk (PTT) signal, hich causes the radio to transmit.
Most base stations, mobile rigs (anything that uses a MiniDIN-6 data
connector) and any radios ith a Ken ood-style connector use a
separate PTT line to trigger PTT. This form of PTT signaling is called
“simplex” since there is one signal on the line.
Many HTs (Yaesu, Icom, Alinco and others) use the Mic+ line for both
audio and PTT signaling. This form of PTT signaling is called
“multiplex” since there are multiple signals on the same line.
If you don't kno hich one yours uses, trial and error orks to figure it
out. Press the Transmit button on the bottom to transmit a test signal.
You should see the TX indicator on the radio light up.
Transmit (TX/Output) Volume
Configuring the transmit gain requires a second radio and, ithout expensive monitoring equipment,
ill be a bit subjective. The default volume level (64) is a reasonable starting point. It may not be
necessary to adjust the volume level at all. I recommend lo ering the level.
This exercise is best done ith the TNC/radio connected to a dummy load or at very lo po er. Both
radios should be set for simplex on an open frequency so as not to interfere ith others. Do not adjust
the radio's output volume while tuned to the primary APRS frequency.
To adjust the radio volume, select 2200Hz tone button, then press the Transmit button.
While monitoring the tone on the second radio, adjust the Output Volume slider until you do not hear
the volume increasing any more. Then back off the volume by 10%.
You cannot adjust the output volume unless the Transmit button is selected. This is by design, to
prevent accidentally changing the output volume.
Troubleshooting: If you do not hear the any audio or the TX indicator on your radio does not light up,
verify that the PTT Style selected above is correct. Disable TX, then change the PTT Style selection
and try again.
Output Twist
Output t ist controls the level of the Mark and Space (1200Hz and 2200Hz) tones relative to one
another. Levels belo 50 reduce the level of the 2200Hz tone, hile levels above 50 reduce the
1200Hz tone. The output t ist should typically left at 50 unless you are using a transmitter that does
not do proper pre-emphasis of the audio signal. This setting has no affect hen running 9600 baud.
When s itching bet een 1200 baud and 9600 baud operation, it is important to re-adjust the audio output
settings. The same is true hen s itching radios.

TNC4 User Guide
Configuring t e KISS Parameters
These parameters are best left at their default values:
TX Delay – 33
Persistence – 64
Slot Time – 10
TX Tail – 2
TX Delay represents the amount of time in 10s of milliseconds that the
TNC ill key the radio and transmit the preamble before sending the
packet.
Persistence is part of the CSMA backoff represents the odds (out of 256)
that the TNC ill transmit ithin its slot time hen no carrier is detected.
Slot Time is also part the the CSMA protocol; it is the delay in 10s of
milliseconds that the TNC aits before checking hether it can transmit.
TX Tail is the amount of time in 10s of milliseconds the TNC keys the
transmitter after the packet is sent. It must al ays be 2.
Full Duplex – ignore carrier detect and the CSMA parameters and trasmit ithout aiting for a clear
channel. The assumption is that hile running duplex, the TX channel is al ays clear.
Please see http://www.ka9q.net/papers/kiss.html for a more in depth discussion of these KISS
parameters.

TNC4 User Guide
Firmware Update
The firm are of the TNC can be updated, but this can only be done via USB.
The TNC firm are is updated using STM32CubeProgammer from STMicroelectronics. This is a
cross-platform programmer for Linux, OS X and Windo s.
You can find this tool from the Mobilinkd Do nload site at http:// .mobilinkd.com/do nloads/ or
from STMicroelectronics at https:// .st.com/en/development-tools/stm32cubeprog.html
Firm are update instructions ill be posted ith the firm are file.
The TNC enters firm are update mode by pressing the DFU button on the side hen the TNC is
plugged into a USB connection. Be arned: the only indication that the TNC is in DFU mode is that
there is no blue LED indicator hen in this mode, and the po er s itch does not ork. If you do not
use the firm are update tool to program the TNC, you must press the reset button to recover.
Recommendations For Use with APR droid
This assumes that you kno have follo ed the “Connecting/Pairing” and “Configuring the TNC” steps
above. This is a good first-time setup and should be customized to your needs once you are familiar
ith APRS and APRSdroid.
You are encouraged to do nload the APRSdroid soft are from Google Play. You can also find the
soft are at http://aprsdroid.org/. Detailed APRSdroid configuration documentation can be found on
the APRSdroid GitHub site: https://github.com/ge0rg/aprsdroid/ iki/Settings.
Before starting, turn the radio off to avoid accidentally transmitting bad APRS data.
1. Ensure the TNC is on and paired ith the Android device. Make sure the Mobilinkd Config
app is disconnected and that you have exited the app. Leaving the Mobilinkd Config app
connected ill prevent APRSdroid from connecting to the TNC.
2. Start APRSdroid.
3. Go into Menu|Preferences
1. Set your callsign
2. Set your SSID. SSID 7 is common for hand-held radios.
3. Under APRS digi path”, enter “WIDE1-1,WIDE2-1”
4. Set your APRS symbol. If you don't kno hich one to use, choose /[ for no . That ill put
a “jogger” symbol on the map for your position.
5. Personalize the comment field.
6. Go into “Location Settings”
1. Under “Location Source”, select “Periodic GPS/Net ork Position”. (You may ish to
change this later.)
2. Under “GPS Precision”, select “Lo ”. If this device connects to a mobile phone
net ork, select “Use net ork position”.
3. You may ish to update the “Minimum update time” and “Minimum update distance.”

TNC4 User Guide
7. Go into “Connection Preferences”
1. Under “Connection Protocol”, select “TNC (KISS)”.
2. Under “Connection Type”, select “Bluetooth SPP”.
3. Under “TNC Bluetooth Device”, select “TNC4 Mobilinkd”
4. Return to the main screen.
5. There are three vie s: Hub, Map, and Log. Ensure you are in Log vie .
6. Select “Start Tracking”.
7. The blue LED should start blinking more slo ly (t o brief blinks every 2 seconds).
8. You should see a green line in the APRSdroid log here it sent a position report to the TNC.
If you receive an error “java.io.IOException” in the log hen trying to connect, verify that the TNC is
on and that it is flashing slo ly (no established connection). If the TNC is flashing slo ly ith a
double-pulse, it is connected to another app.
Sending your First Packet
1. Turn on the Radio and ensure its volume level is set properly.
2. Tune the radio to your primary APRS frequency .
3. Press S1 briefly to turn on the TNC. The blue LED ill pulse slo ly.
4. Start APRSdroid and select “Start Tracking”. The LED ill flash slo ly hen connected. This
ill immediately beacon your position.
When testing the TNC, it is best to ensure that a digipeater is nearby or that you have another
APRS/packet radio to test ith. A hand-held radio ill typically need line of sight to a digipeater
ithin 3-5km (2-3 miles) in order to have the signal digipeated.
Listen to the audio on the local APRS frequency. If at least some of the
signals are clear and free from static or audio distortion, the TNC
should be able to decode those APRS packets.
Some adjustment of the audio level may be required to get optimum
packet decoding. Every radio model is different and the volume levels
necessary may vary considerably. Even after follo ing RX audio
configuration steps above, the volume level may need to be adjusted to
get the optimal performance out of the system.

TNC4 User Guide
Recommendations For Use with aprs.fi
The aprs.fi app for iOS is available from the Apple App Store. It is the first app on iOS to support the
Mobilinkd TNC4.
Connect the TNC4 to your radio ith the appropriate TNC cable. Tune the radio to the local APRS
frequency. A comprehensive list of frequencies in use can be found on Wikipedia.
https://en. ikipedia.org/ iki/Automatic_Packet_Reporting_System#Technical_information
Using aprs.fi ith the Mobilinkd TNC4 is quite straight-for ard.
From the main map screen, select the “More” button.
After that, click on the TNC menu option.
Touch “Search for available TNCs”. After you have connected to your TNC once, you can just select
“Connect TNC” ithout needing to search for it again.

TNC4 User Guide
When the TNC4 is turned on, it should appear in the search screen under “BLE TNCs discovered”.
Select the TNC4.
You should see that the TNC screen appears and sho s that it is connected.
Select the Beacon icon on the bottom.
In the Beacon screen, you can disable Beacon via net ork and enable Beacon via TNC.
Set your station ID and your APRS station symbol (there are many to chose from).
You can set a comment that ill be sent every time a beacon is sent.
While testing, it may help to lo er the Minimum Transmit Interval, but it is al ays a good idea to set
this back to the default hen you are done.
And as you scroll to the bottom of that screen, you can select “Beacon No ” to send your first beacon.

TNC4 User Guide
9600 Baud Operation
The TNC4 supports 9600 baud GFSK operation. This is a much more challenging mode, as it requires
a radio hich supports this mode and ill require some additional tools to properly adjust the TNC to
the radio.
Supported Radios
Amateur radios hich have a standard MiniDIN-6 data port and hich advertise support for 9600 baud
operation should ork. 9600 baud cannot be used on radios that only support voice operation (pre-
emphasized and de-emphasized audio). There are no HTs kno n to support 9600 baud that do not
already have their o n TNCs built in, and these generally do not support operating at 9600 baud ith
an external TNC.
Help ith other radios can be found at the Mobilind group.io email list: https://groups.io/g/mobilinkd
Modem Settings
To use 9600 baud, select the 9600 baud modem in the modem settings screen. When changing the
modem type, it is important to re-adjust the input and output audio levels, and it also may make sense
to adjust the TX Delay in the KISS settings.
KISS Settings
The TX Delay can often be adjusted quite a bit lo er for 9600 baud than for 1200 baud. We have seen
TX Delay settings as lo as 12 ork at 9600 baud. This ill depend a lot on your radio and the remote
stations you connect to.
Audio Input Settings
Use the auto-adjust feature to start the adjustment process. Do this after changing the modem type in
the modem settings. The further the detected t ist is from 0, the greater the receive impairment is
likely to be. There is rarely a benefit to adjusting the t ist from the TNC’s suggested setting.
The audio input gain may benefit from t eaking hile testing ith remote systems. We are still
actively refining the automatic gain setting algorithm, but this seem to vary enough ith just the fe
radios e are testing ith that this ill likely to benefit from manual adjustment.
To adjust the input gain using a reference transmitter (one hose output deviation is properly
calibrated), transmit a scrambled string of 1s or 0s and adjust the audio input gain until the audio level
is just in the red.
Audio Output Settings
The audio output settings can be difficult to calibrate properly, but e can get very close using an RTL
SDR and a dummy load. These are t o inexpensive pieces of equipment that every amateur radio
operator that is engaging in this level of experimentation and operation should o n.
The steps belo assumes that the TNC is connected to the transceiver and po ered on.