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Amateur Radio Hotspot VHF & UHF Digital Modes

By Rob Robinette K9OJ

I use a Micro-Node.com Nano-Spot, Chinese Jumbo Spot RTQ hotspot and Chinese MMDVM_HS_HAT_DUPLEX pi hat + pi2 for all my digital ham radio needs. All three can do everything Pi-Star can dish out including Yaesu System Fusion (YSF), DMR, D-STAR, P25, NXDN, YSF-to-DMR,  YSF-to-NXDN and YSF-to-P25. I'm using the Nano-Spot for YSF and P25, the Jumbo Spot for D-STAR and DMR and the MMDVM_HS_HAT_DUPLEX for YSF, DMR, D-STAR and P25. They all use the very easy to use but powerful Pi-Star software for configuration and control.

I got the Jumbo Sport RTQ from aliexpress.com for $115 (now $125) but it took about three weeks for delivery. Although it runs off a Pi Zero W it performs just as well running Pi-Star as the Nano-Spot with its more powerful quad core processor.

The Nano-Spot was $269 (now $299) from Micro-Node.com and took about a month for delivery due to high demand. The Nano-Spot comes in a nice case and has an external Wi-Fi antenna but the two hotspots are functionally almost identical. One problem with the Nano-Spot is it uses a Raspberry Pi clone  (probably the Orange Pi Zero Plus2) with a non-standard version of the Linux kernel. Its MMDVM firmware can be upgraded by following these directions. The Jumbo Spot uses a Pi Zero W with standard Linux and MMDVM_HS for easy upgrades.

I ordered the generic Chinese MMDVM_HS_HAT_DUPLEx pi hat from aliexpress.com for $65 and it took about three weeks for delivery. I paired it with a $35 pi 2 and open top pi case.

I had a heck of a time getting my digital radios to communicate with my hotspots so I created this webpage to hopefully help new hotspot users get up-and-running easier and quicker than I did.

Micro-Node.com's $299 Nano-Spot Hotspot

See my Nano-Spot Pi-Star settings

 

Jumbo Spot RTQ $125 Hotspot

The Nano-Spot and Jumbo Spot RTQ both have Wi-Fi, 70cm radio, OLED screen and support Pi-Star, YSF, D-STAR, DMR, P25, NXDN and YSF-to-DMR. See my Jumbo Spot Pi-Star settings.

Generic Chinese MMDVM_HS_Dual Pi Hat Hotspot/Repeater $65

Dual radios allow simultaneous reception and transmission. I paired it with an old $35 raspberry pi 2 with Pi-Star. See my MMDVM_HS_Dual Pi-Star settings.

 


Setting Up The Radios

For me setting up the radios to work with a hotspot was much more difficult than setting up the hotspot and Pi-Star software. Here's a rundown on what I had to do to get each radio setup:

For general troubleshooting I recommend you monitor your radio and hotspot transmissions on an SDR or analog radio so you can verify the hotspot is transmitting and your radio is transmitting in digital mode. If you have an SDR with computer output use it to monitor your radio and hotspot to compare their exact frequency. This can help you quickly dial in the correct Pi-Star RX and TX Offset.

The typical "CQ" call for all these digital modes is simply, "K9OJ is listening".

YSF   Yaesu System Fusion FT1DR

D-STAR   Kenwood TH-D74

DMR   Tytera MD-380

P25   Motorola XTS3000 Model II UHF

 

Pi-Star Settings

Nano-Spot Pi-Star Settings

Jumbo Spot Pi-Star Settings

MMDVM_HS_HAT_DUPLEX Pi-Star Settings

Tuning Your Hotspot's BER

 

Hotspot Info

Upgrade Nano-Spot MMDVM_HS Firmware

What YSF, D-STAR, DMR and P25 look and sound like on a waterfall display

Adding An OLED Display To A Hotspot

Adding A Nextion Display To A Hotspot

 

Motorola P25 Radio Info

Motorola XTS3000 Housing Swap

Modifying Motorola CPS Programming Software For Out-of-Band Frequencies

Motorola XTS2500 & XTS5000 Info


 


YSF

Yaesu System Fusion C4FM is super simple. Just program your hotspot frequency as simplex into the "A" VFO and hit the "Dx" button until "DN" (digital narrow) is displayed and you're all set. Pi-Star now supports YSF-to-DMR,  YSF-to-NXDN and YSF-to-P25 so you can access these modes with one Yaesu C4FM radio. You can now change YSF "rooms" using DTMF tones.

Yaesu FT1DR Hotspot Programming

The hotspot frequency is in row 1. A simplex frequency is all that's needed.

Troubleshooting YSF

Monitor Pi-Star's dashboard as you transmit and you should see activity in the "Local RF Activity" section. If you don't:

        Use an analog radio to monitor the hotspot and radio's transmissions. YSF has a white noise static sound to it. It does not sound "digital".

        Verify you're using VFO 1.

        Verify the radio transmit mode is showing "DN" (digital narrow) on the display.

        Check the radio and hotspot frequencies are the same.

        Make sure your radio is in simplex mode when using a hotspot. If you put your hotspot frequency in a repeater band your radio may automatically switch into repeater mode and transmit on the wrong frequency.

        Pi-Star's Admin/Live Logs display will give you more detail on what the hotspot is doing.

        Excessive "Loss" (shown on Pi-Star dashboard) means a network connectivity issue. If your radio transmissions to the hotspot show a high loss then the hotspot's connection to the internet has a problem. If only other other callsigns show high loss then they have a connection problem.

See this to adjust and tune your hotspot's RXOffset & TXOffset for lowest reception bit error rate (Local RF Activity BER). An incorrect setting can prevent your radio from decoding your hotspot's transmissions.

YSF Modulation

Notice the broad, thick, solid waterfall signal. YSF uses 12.5kHz of bandwidth like DMR & P25. YSF sounds very similar to P25 because they both use C4FM and sound like soft static.

YSF uses C4FM (Continuous 4-level Frequency Shift Keying & Frequency Modulation) digital modulation like P25 but the two standards are not compatible.

 


D-STAR

Programming my Kenwood TH-D74 for hotspot D-STAR was difficult with lots of little details that if you get wrong will keep you from communicating with the hotspot. You need to start with registering for D-STAR repeater access so you can use net-linked D-STAR repeaters.

You must enter your callsign into the radio's "Menu (Digital)-TX/RX" page. There is no "D-STAR ID" like DMR and P25 use.

D-STAR Callsign

Enter your callsign in the Menu (Digital)-TX/RX page. When using D-STAR my callsign goes out as "K9OJ/ROB" which is a common D-STAR technique.

 

D-STAR Memory Programming

The hotspot channels run from row 50 to 58.

When programming radio memories you must select the "DR" Digital Repeater mode.

You must also select a "Plus Shift" or "Minus Shift" with a 0MHz offset as shown above (I know, it's weird).

Memory 50 above, "Nano-TN" is the Tennessee-wide Reflector 077C. Notice the "URCALL" column "REF077CL" means "Link to Reflector 077 C module". The "C" must be in the 7th character spot and the "L" must be in the 8th spot.

At far right above, "RPT1" and "RPT2" is where we tell the radio about the hotspot. "K9OJ" is the hotspot callsign and should match what you have in Pi-Star under "General Configuration - Node Callsign". The "B" says to communicate with the "B" module and the "G" means connect through the hotspot's Gateway. The B & G must be in the 8th character spot (I have 3 spaces between my callsign and the B & G). If your hotspot uses VHF then you may need to use "C" instead of "B" (B=70cm, C=2m). RPT1 and RPT2 should match what you have in the Pi-Star D-STAR configuration section, "RPT1 Callsign" & "RPT2 Callsign".

To use the hotspot I select memory 50 (Reflector 077 module C) and transmit for a couple of seconds to get linked to the reflector. The radio will say "Linked to xxxxxx". This step isn't necessary if you have Pi-Star configured to connect to a default D-STAR reflector at startup. Then I change the channel to the talkgroup I want to speak with and transmit.

I use channel 51 (Unlink) to disconnect my hotspot from the reflector or talkgroup when I'm done. Channel 52 is the "parrot" or Echo talkgroup for testing the hotspot and radio. Channel 53 (Info) will make the hotspot tell you the link status. In the URCALL field the U, E and I must have 7 spaces in front of it so it is the 8th character.

Channel 54 is Reflector 001C world-wide. Channel 56 is the Morristown, Tennessee D-STAR repeater. Notice how there is a space between the repeater callsign "W4LDG" and the "CL" (Link to the C module) command because the CL must occupy the 7th & 8th character position in the URCALL column. For most repeaters the B module is a 70cm repeater and the C module is a 2 meter repeater.

Troubleshooting D-STAR

Monitor Pi-Star's dashboard when you transmit and you should see activity in the "Local RF Activity" section. If you don't:

        Use an analog radio to monitor the hotspot and radio's transmissions. D-STAR sounds like a typical digital transmission.

        Verify the D-STAR Callsign is set in the radio.

        Check the memory's Shift & Offset are set for 0 offset.

        Verify the memory's URCALL has the "B" or "C" in the 7th character position and the L, U, E or I in the 8th position.

        Check the memory's RPT1 and RPT2 has the "B" and "G" in the 8th character position.

        Verify the radio transmit mode is set to D-STAR.

        Check the radio and hotspot frequencies are the same.

        Make sure your radio is in simplex mode when using a hotspot. If you put your hotspot frequency in a repeater band your radio may automatically switch into repeater mode and transmit on the wrong frequency.

        If you cannot connect to a D-STAR reflector in Pi-Star verify your D-STAR registration is complete. After registering you have to get approved and then log in to complete your registration.

        Pi-Star's "Admin/Live Logs" display will give you more detail on what the hotspot is doing.

        Excessive "Loss" (shown on Pi-Star dashboard) means a network connectivity issue. If your radio transmissions to the hotspot show a high loss then the hotspot's connection to the internet has a problem. If only other other callsigns show high loss then they have a connection problem.

See this to adjust and tune your hotspot's RXOffset & TXOffset for lowest reception bit error rate (Local RF Activity BER). An incorrect setting can prevent your radio from decoding your hotspot's transmissions.

D-STAR Modulation

Notice the "shoulders" and solid waterfall signal. D-STAR is noticeably thinner on the waterfall display due to its 6.25kHz bandwidth. The other digital modes use 12.5kHz of bandwidth. D-STAR sounds like a "typical" digital signal.

D-STAR stands for Digital Smart Technologies for Amateur Radio. It was developed by the Japan Amateur Radio League and uses Gaussian Minimum Shift Keying (GMSK) digital modulation.


 


DMR

I really like my Tytera MD-380 DMR UHF radio but it wasn't easy getting it to work with the hotspot.

You have to set your DMR ID in the Pi-Star configuration page and in the radio. If you don't have a DMR ID you can register for your DMR ID here.

Programming memories into a DMR radio is a three step process. You first create "Digital Contacts", then put those digital contacts into "Channels", then put the Channels into a Zone. A Zone is just a grouping of channels.

DMR Memory Programming Digital Contacts

After setting your DMR ID in the radio's "General Setting" page, program your talkgroups in the "Digital Contacts" section. The "Call ID" is the talkgroup number.

 

DMR Memory Programming Channel Information

After entering your "Digital Contacts" above you can plug them into the "Contact Name" field of the "Channel Information" page. Note the "Channel Mode:Digital", "Color Code:1", "Repeater Slot (time slot):1" and "Privacy:None" fields.

I created "Nano-Local" talkgroup 9, "Nano-Echo" parrot, "Nano-USA" USA-wide talkgroup, "Nano-Unlink" talkgroup 4000, "Nano-Info" talkgroup 5000, "Nano-SE-REF" Southeast USA Reflector and "Nano-Texas" Texas-wide talkgroup channels.

DMR Memory Programming Zone Information

The last thing to do is to create a "Hotspot" zone and fill it with the channels you created above. A zone is simply a grouping of channels.

 

BrandMeister Controls in Pi-Star

You can change several DMR BrandMeister controls using Pi-Star's "Admin" dashboard.

I recommend you register with BrandMeister and use their reflectors. I set Pi-Star's "DMR Master" to "BM_United_States_3108" (Atlanta).

To use the hotspot press the MD-380's Menu key to select the hotspot zone.

Turn the radio selector knob to select a reflector. I use BM-SE-REF as my default reflector. Then transmit for about two seconds to link to the reflector. The radio will say, "Linked to xxxxx".

Once linked turn the selector knob to select a talk group if you don't want to speak through the reflector.

DMR talkgroup 3147 is Tennessee-wide. 3148 is Texas-wide, 4639 is USA-wide and 91 is World-wide

We typically use Repeater Slot 1 (time slot 1) and Group Call (not Private Call) for most talk groups.

4xxx talk groups are actually reflectors which can be set as the default reflector.

Once you register with BrandMeister you can edit your hotspot's info for others to see.

You can manually select a new talkgroup on-the-fly in the Tytera MD-380 by hitting the radio's Menu key, selecting Contacts, keying in the talkgroup number (numbers only, no "TG"), then pressing the PTT button to connect.

Troubleshooting DMR

Monitor Pi-Star's dashboard when you transmit and you should see activity in the "Local RF Activity" section. If you don't:

        Use an analog radio to monitor the hotspot and radio's transmissions. DMR has a choppy "helicopter" sound to it.

        Verify the DMR ID is properly set

        Check the memory's Channel Mode is set to "Digital"

        Verify the memory's Contact Name is correct

        Check the memory's Color Code is set to 1

        Verify the memory's Repeater Slot (time slot) is correct (usually 1)

        Check the memory's Privacy is set to "None"

        Verify the memory and radio frequencies are the same.

        Make sure your radio is in simplex mode when using a hotspot. If you put your hotspot frequency in a repeater band your radio may automatically switch into repeater mode and transmit on the wrong frequency.

        Pi-Star's "Admin/Live Logs" display will give you more detail on what the hotspot is doing.

        Excessive "Loss" (shown on Pi-Star dashboard) means a network connectivity issue. If your radio transmissions to the hotspot show a high loss then the hotspot's connection to the internet has a problem. If only other other callsigns show high loss then they have a connection problem. You may be able to decrease your Loss % in DMR by increasing Pi-Star's Configuration / Expert / MMDVMHost / DMR Network / Jitter from 300 to 700.

See this to adjust and tune your hotspot's RXOffset & TXOffset for lowest reception bit error rate (Local RF Activity BER). An incorrect setting can prevent your radio from decoding your hotspot's transmissions.

DMR Modulation

Notice the bands in the waterfall signal. DMR uses12.5kHz of bandwidth and has a choppy, helicopter type sound to it.

DMR stands for Digital Mobile Radio and uses Four-state Frequency Shift Keying (4FSK) digital modulation with Time Division Multiple Access (TDMA) to create two time slots.



P25

Commercial P25 radios are very cool and I love the Motorola XTS3000 P25 radio I purchased on eBay. It's a heavy but rock-solid radio that thousands of police and firemen have relied upon for rugged reliable service. There are brand-new housings available for many Motorola P25 radios so you can completely refurbish their look. There are also brand-new batteries and accessories available. The XTS3000 Model I comes with no display or front panel buttons. The Model II has a display and six buttons and the Model III has a display and full keypad. I purchased a used Model II for $169. The XTS3000 comes in VHF, 700/800MHz and two UHF models. The UHF models put out around 4 watts on high and 1 watt on the low setting.

Motorola XTS3000 P25 UHF Radio

The first thing I did wrong was to purchase an XTS3000 UHF Range II with a frequency band of 450 to 520MHz. I didn't realize there were two UHF versions of the XTS3000. Luckily the radio will function just fine on 449.990MHz so that's where I set my hotspot frequency. If you go too far out of the radio's band the CPS programming software won't write the code plug to the radio so I can't use this radio for P25 repeaters. Fun fact: The XTS3000 uses the same antennas, microphones, batteries and charger as the newer XTS5000 but the programming cables and software are different.

The correct UHF radio version for hams would be "UHF Range 1" which covers 403 to 470MHz. Range 1 radios are also referred to as "R Split" radios. Range II radios cover 450- 520MHz and are called "S Split".  I was later able to extend my Range II radio's band down to 440MHz for use with ham repeaters, see Modifying Astro CPS for more info. Later I broke down and purchased a nice Range 1 R Split radio for ham use.

You'll also need a programming cable for the radio. The XTS3000 uses a "Ribless" cable. RIB stands for "radio interface box" and "RIBless" means you don't need a RIB. Ebay sells the cables for around $25 but make sure the seller mentions XTS3000 in the add because the XTS5000 RIBless cable will not work with the XTS3000. The cable clips to the left side of the radio and has either a serial or USB connector to connect to your computer. Mine has a 9-pin serial COM port connector and I use a USB-to-serial adapter with it. I had to set the USB-to-serial adapter for XON-XOFF flow control inside Windows's Device Manager to make it recognize the radio.

The next thing I did wrong was purchase an incorrect version of the Motorola CPS (Customer Programming Software). I ordered the current version which doesn't cover older radios like my XTS3000. After doing some research I found what I was looking for. You can download the Astro Saber and XTS3000 CPS programming software here. The software is no longer available from Motorola.

There is also an Astro 25 CPS version for the XTS2500 and XTS5000. There are also other versions of CPS for newer radios available on eBay so do some research before you buy programming software.

Astro Saber & XTS3000 CPS software only runs on 32 bit Windows 7 or XP. I used Windows 7 and used Window's Device Manager/Ports to see what COM port the USB-to-serial adapter was using and set the USB-to-serial adapter for XON-XOFF flow control. You have to set this COM port number in CPS to establish contact between the computer and radio.

Once I got the correct version of CPS and had the USB-to-serial adapter working it was time to program the radio. P25 radio memory is laid out very much like DMR with talkgroups, channels and zones.

The first thing you should do once you are hooked up is to read the radio data into CPS. Save the code plug if you want to be able to go back to the original programming. Once that is done you can edit and save the data and you'll be able to write it back to the radio.

Programming the XTS3000

One of the most common gotcha's of P25 radio programming is forgetting to set your DMR ID in the radio's ID field. Yes, use your DMR ID for P25. For my XTS3000 the ID went into the "Astro System 1/Genera/Individual ID" field. If you don't have a DMR ID you can register for your DMR ID here.

DMR ID In CPS

In CPS software click on "Expand All" at the bottom of the page, then double-click on "Astro System - 1" in the left window and enter your DMR ID.

 

Setup Channels or "Conventional Personalities"

In the CPS software double-click on "Conventional Personality - 1" in the left window. "Conventional Personality" means "non-trunking channel". Set the transmit and receive frequencies.

 

Set "RX Voice/Signal Type" to "ASTRO" for digital.

 

I set the Transmit Power Level to Low for hotspot use and High for repeaters.

 

Select "293" for the "Network ID" and "C4FM" for "Digital Modulator Type".

 

"Strapped" means the talkgroup can't be changed by using the radio buttons.

 

You have to do the above steps for each talkgroup channel.

Setup Your Talkgroups

I programmed the following talkgroups: TG10100 world-wide, TG10200 USA, TG9999 is Unlink, TG00010 is Parrot.

 

Setup Your Hotspot Zone

I named my zone "HOT" for hotspot.

 

I added the talkgroups to the hotspot zone. A zone is simply a grouping of channels.

Other popular talkgroups include North America TAC1 10201, Canada 302 and Europe 10300.

When you get everything set be sure and save the radio file then "write" the file to the radio. Just connect the radio and turn it on, then click the "Write to Device" button in CPS. The XTS3000 shows "1 CPQ" during data transfer. The radio will reset when finished.

On the radio select the zone, then channel and you're ready to transmit to your hotspot. For my radio Zone 1, Channel 3 is the parrot or echo radio test talkgroup. Anything you transmit to this talkgroup will be sent back to you so you can verify everything works and hear the quality of your audio. Use this to determine how close to hold the radio or mic for best audio.

I like to use the three-position "A B C" switch to select the zone. You do this in the CPS "Controls/Switches" page. You have to put "Zone Select" in both the Conventional and Trunked selections for it to work properly.

Troubleshooting P25

Monitor Pi-Star's dashboard when you transmit and you should see activity in the "Local RF Activity" section. If you don't:

        Use an analog radio to monitor the hotspot and radio's transmissions. P25 has a soft white noise static sound to it. It does not sound "digital".

        Verify the P25 (DMR) ID is set in the radio.

        Check the channel's TX Voice/Signal Type is set to Astro.

        Make sure the channel's Digital Modulator Type is set to C4FM.

        Verify the channel's Network ID is set to 293 for both transmit and receive.

        Check the hotspot and radio frequencies are the same.

        Make sure your radio is in simplex mode when using a hotspot. If you put your hotspot frequency in a repeater band your radio may automatically switch into repeater mode and transmit on the wrong frequency.

        Pi-Star's "Admin/Live Logs" display will give you more detail on what the hotspot is doing.

        Excessive "Loss" (shown on Pi-Star dashboard) means a network connectivity issue. If your radio transmissions to the hotspot show a high loss then the hotspot's connection to the internet has a problem. If only other other callsigns show high loss then they have a connection problem.

See this to adjust and tune your hotspot's RXOffset & TXOffset for lowest reception bit error rate (Local RF Activity BER). An incorrect setting can prevent your radio from decoding your hotspot's transmissions.

P25 Modulation

Looks and sounds very similar to YSF because they both use C4FM modulation. P25 uses 12.5kHz of bandwidth like YSF and sounds like soft static.

P25, sometimes called APCO 25 or Pop 25, is short for "Project 25" and uses C4FM (Continuous 4-level Frequency Shift Keying & Frequency Modulation) digital modulation like YSF but the two standards are not compatible.


 


Nano-Spot Pi-Star Settings

See Toshen Golias' excellent webpage for more info on configuring Pi-Star.

My only problem with the Nano-Spot is it uses a non-Raspberry Pi Foundation processor board. It's most likely an Orange Pi Zero Plus2 (Chinese Pi clone) with an Allwiner H3 processor @ 1.2GHz, 8GB EMMC flash, 512MB RAM with built in Wi-Fi and Bluetooth which matches the Nano-Spot's published specs. The Orange Pi boards have limited support and the Nano-Spot comes with an older version of the Linux kernel. Note the "Kernel 3.4.113-sun8i" in the configuration above compared to the 4.9.35+ in the Jumbo Spot configuration below. Kernel updates are my main concern with this processor board.

 


My Jumbo Spot Pi-Star Settings for D-STAR and DMR

My Jumbo Spot liked a TX & RX offset of +400.

I'm very impressed with my $115 (now $125) Jumbo Spot RTQ from aliexpress.com. I have ordered many things from aliexpress and haven't had any problems. "RTQ" stand for "ready to QSO" because it comes with a case, antenna, OLED display and Pi-Star loaded 8GB MicroSD Card. You will have to supply a 2.5ma or higher rated power supply with a standard Android phone style micro USB plug. You can just plug it in and it will come up in "Auto AP" mode. Look for a "Pi-Star" Wi-Fi source on your computer and join it, sign in with a password of "raspberry". You can then use a browser to edit the Pi-Star Wi-Fi settings then reboot and the Jumbo Spot should join your Wi-Fi net.

The Jumbo Spot does everything Pi-Star can dish out: Yaesu System Fusion, D-STAR, DMR, P25, NXDN and YSF-to-DMR. It took about three weeks for delivery from China but I had to wait longer than that for my American assembled Nano-Spot. Although The Jumbo Spot's computer is a Pi Zero W it performs really well and uses standard raspberry pi Linux and MMDVM_HS modem for easy kernel, operating system and MMDVM firmware upgrades.

Jumbo Spots typically use a 500Hz TX and RX offset so I simply added 500Hz to my desired hotspot frequency. I played around with it and found 400Hz was best for my Jumbo Spot and radios. I'm currently running YSF and P25 on my Nano-Spot and DMR and D-STAR on the Jumbo Spot.

To open the case you remove the antenna then pry apart the upper cover enough to get the tabs clear and pull it off.

 


MMDVM_HS_HAT_DUPLEX Pi-Star Settings For YSF, D-STAR, DMR and P25

Generic Chinese MMDVM_HS_HAT_DUPLEX Radio/Modem

Dual UHF radios, MMDVM, OLED, Nextion and STLink solder pads.

I purchased this generic Chinese MMDVM_HS_HAT_DUPLEX Radio/Modem from aliexpress.com for $65 and paired it with a raspberry pi 2 and it works great. It came with MMDVM 1.3.3 firmware installed and it's been upgraded to 1.3.7 (as of June 2018). This dual-radio MMDVM_HS_HAT_DUPLEX radio/modem can act as a repeater and transmit on the output frequency simultaneously what it receives on the input frequency. It will also allow you to use both DMR timeslots simultaneously.

My board came with two female SMA connectors that I had to solder to the board and two UHF antennas. The female pi hat connectors came soldered in place. The board also came with two sets of male jumpers that can be used on boards like the pi Zero that come with no 40 pin hat connectors. My pi 2, like the pi 3, has the male 40 pin connector already in place so I didn't have to use the jumpers but it's nice that they include them.

This board fits on top of a pi 2 or 3 but not a pi 1. Just press the board in place, install Pi-Star and you're ready to go.

Be sure and separate your RX and TX frequencies by at least 5MHz to reduce interference between the transmitter and receiver.

One major difference with a dual radio board like this compared to a simplex hotspot is you have to program the correct DMR time slot when programming your radio's code plug. A simplex board will send both timeslots' transmissions using a single timeslot but this board will send TS1 input out TS1, and TS2 input out TS2. It took me a while to figure out why I wasn't hearing any DMR traffic (my MD-380 radio was monitoring the wrong time slot).

The MMDVM_HS_HAT_DUPLEX worked fine out of the box on YSM, D-STAR and P25 but I had to set a TXOffset and RXOffset of 1210 (+1.210kHz) to get DMR working.

A $6 OLED screen can be easily added to this MMDVM_HS_HAT_DUPLEX board. I added a Nextion display to the board.

I installed 90 degree SMA connectors so I could point the two antennas away from one another (see photo below). This exploits the signal null of the transmitting antenna to reduce interference between the transmitter and receiver.

Antennas vertical and pointed in opposite directions to minimize interference. Shown here during Nextion display testing.



Tuning Your Hotspot's BER

Many hotspots require the transmit and receive frequencies to be adjusted for best reception. Pi-Star's Dashboard "Local RF Activity BER" (bit error rate) displays your hotspot's reception error rate. We can minimize the BER by adjusting Pi-Star's Configuration/Expert/MMDVMHost/Modem/RXOffset setting. RXOffset adjusts the hotspot's receive frequency in Hertz. It can be a negative or positive value. Many MMDVM boards come with a sticker that lists a starting RXOffset & TXOffset settings. Use the sticker setting as the starting RX and TXOffset values.

If you have an SDR waterfall display or a frequency counter you can use it to monitor your hotspot transmission to see where it is actually transmitting. Adjust the Configuration/Expert/MMDVMHost/Modem/TXOffset setting so that your hotspot is transmitting exactly on frequency. Then set the RXOffset to the same value. This is typically a very good starting point for BER fine tuning.

RXOffset adjusts the hotspot's receive frequency in Hz. It can compensate for an out-of-alignment hotspot receiver or an out-of-alignment radio transmitter--you can set your hotspot receive frequency to exactly match your radio's transmit frequency. RXOffset affects the BER (reception Bit Error Rate) shown on the Pi-Star Dashboard.

TXOffset adjusts the hotspot's transmit frequency in Hz. It can compensate for an out-of-alignment hotspot transmitter or an out-of-alignment radio receiver. TXOffset affects the BER of your radio--not the BER shown on the dashboard. If your radio displays BER you can change TXOffset to tune for lowest radio BER.

Pi-Star Configuration / Expert / MMDVMHost / Modem / RXOffset

RXOffset of 1340 was set by BER fine tuning, TXOffset was set using an SDR waterfall display. The difference between the two is probably due to my MD-380 DMR radio being slightly out of alignment.

Keep in mind RXOffset and TXOffset are applied to all digital modes so if you use multiple radios and/or modes with your hotspot they will all be affected. You'll have to tune for the best overall signal and BER for all your radios.

If the Dashboard BER is higher than about 1% then I recommend you tune RXOffset to reduce it to a minimum.

An RXOffset of -22 (22Hz shift down) on my Nano-Spot worked best for my radios but one Nano-Spot user had to use a setting of 1200 to get his MD-380 to decode DMR from his hotspot. Most likely his MD-380 receiver is way out of alignment.

The Chinese Jumbo Spot comes with a sticker that shows the TXOffset and RXOffset need to be set at 500 (+500Hz) right off the bat. After fine tuning I ended up with 400 for both RX and TXOffset.

My generic Chinese MMDVM_HS_HAT_DUPLEX board works best with an RXOffset of 1340 and TXOffset of 1220.

Hotspot Can't Receive DMR Transmission

This is a fairly common problem with a new hotspot. If your RXOffset is far enough off the hotspot will not decode your radio's DMR signal. Look for a sticker on the modem board or documentation that gives a starting TX and RXOffset. If you can't find one then just start adjusting RXOffset in steps of 100. Try 100, -100, 200, -200, 300, -300, 400, -400 . . ." until your hotspot begins to decode the digital signal and it shows up on the Pi-Star Dashboard. Then set your TXOffset to match. I like to use an SDR waterfall display to adjust the TXOffset so the hotspot transmits exactly on the set frequency.

BER Fine Tuning

DMR seems to be more sensitive to frequency and BER so I like to use it when tuning the BER. If you don't use DMR then just use the digital radio you use most with your hotspot.

Set your radio to its lowest power setting to make your hotspot more sensitive to RXOffset adjustments.

I like to use two browser windows to speed BER tuning. One window is open to the Configuration/Expert/MMDVMHost page and one is open to the Dashboard page showing BER.

Set your radio to the parrot channel if available (DMR private call to talk group 9990) and transmit, you should always give your callsign when transmitting, "K9OJ echo test".

Monitor the Dashboard BER. I like to write it down when testing. Transmit two or three times to make sure you're getting a representative BER value. Be sure and transmit with the radio held in the exact same position to make the BER values consistent.

Start by using an RXOffset increment of 100. Set the RXOffset setting to 100 (or add 100 to a previously set value) and transmit three times and note the BER. If BER increased then try going negative with an RXOffset setting of -100.

If nothing much changes try again with another step of 100.

As you're changing the RXOffset you'll find the BER starts to decrease and then increase when you go too far. When that happens back up using smaller steps of 20, then 10, then 1s until you find the minimum BER. You should shoot for something under 1%.

The last time I tuned a hotspot BER my RXOffset went like this:

100 BER 1.7%, 200 1.7%, 300 1.1%, 400 0.3%, 500 1.3%,  450 0.7%, 425 0.5%, 400 0.2%, 350, 0.6%, 375 0.5%, 385 0.5%, 395 0.3%, 397 0.3%, 410 0.4%, 405 0.3%, 402 0.3% and 400 was consistently lowest.

Now check your other radios and verify their BER is reasonable. If not then tune the BER using that radio and then split the difference between the other radios for the best average BER.

 


Upgrade Nano-Spot MMDVM_HS Firmware

My Nano-Spot was delivered with the old 1.0.0 version of MMDVM firmware. I was able to upgrade it to the current 1.3.6 version using the following procedure:

Use Configuration/Expert/Tools: SSH Access to enter the following commands:

cd /home/pi-star/MMDVM_HS/scripts

rpi-rw

sudo su

nano install_fw_rpi.sh

# Modify the following line in the script to the version you want to install. Here I'm upgrading to version 1.3.3:

FW_VERSION="v1.0.0" to FW_VERSION="v1.3.6"

# Change the last line to EXACTLY this:

eval sudo $STM32FLASH -v -w zumspot_rpi_fw.bin -g 0x0 -R -i 3,-2,2:-3,2 /dev/ttyAMA0

# Save the edits: ctrl-o

# Exit: ctrl-x

# Run the script:

./install_fw_rpi.sh

When the script finishes:

halt

cycle the power and verify the upgrade went through (version is shown on the Pi-Star dashboard)

Note: The Nano-Spot uses an Allwiner H3 (sun8i) quad core (4x Cortex-A7) processor. The board is most likely an Orange Pi Zero Plus2 (Chinese Pi clone) which is roughly equivalent to a Pi 3. The Orange Pi Zero Plus2 has good hardware specs but little community support and is probably why the Nano-Spot comes with such an old Linux kernel. This does not bode well for the Nano-Spot's long term future and operating system upgrades.

 


Ham VHF and UHF Digital Modes Modulation Video

How the digital modes look and sound on a waterfall display. YSF & P25 sound like white-noise static. DMR has a choppy helicopter type sound and D-STAR sounds like a "typical digital" signal. The DMR section has two transmissions, the first is my handi-talkie and the second is the hotspot echoing my transmission. The hotspot's transmission 1.2kHz start tone was an artifact of the MMDVM firmware which has been eliminated with firmware 1.3.6.

 


Adding An OLED Display To A Hotspot

It's pretty simple to add an OLED display to your MMDVM modem board so you can track activity and callsigns. You connect the display to the modem then set Pi-Star's display settings.

I purchased a generic Chinese OLED display from aliexpress.com for $5.

You can connect the display to either the modem card or the raspberry pi but since most modem cards use the raspberry pi's GPIO pins it's easiest to connect the display directly to the modem card.

I had to solder a 4-pin header into my MMDVM_HS_HAT_DUPLEX modem's OLED display solder pads. This allowed the use of the included push-on wire bundle to connect the display to the modem board.

4-Pin Header

Connect the OLED display wires to your modem card like this:

        Red to 5vO or 3vO (5 or 3.3 volts Out)

        Black to GND (ground)

        Purple to SCL

        Orange to SDA

        Only these four connections are necessary.

MMDVM Modem Board's OLED Connector

Solder a 4-pin header to the OLED solder pads and connect the display. Only these four connections are necessary.

With many modem boards you can solder the OLED display pins directly to the modem board solder pads. Be sure and verify the pins line up correctly. My Chinese OLED pins didn't line up with the modem board's OLED solder pads so I had to use a header and wires to connect the display.

In Pi-Star's main configuration page select the following settings:

Pi-Star Display Settings For OLED Display

Select "MMDVM Display Type: OLED", "Port: Modem" and "Nextion Layout: G4KLX".

If you connect your OLED display to your MMDVM modem card (not to the raspberry pi) then you must select "Modem" for the "Port:" setting.

If you connect your OLED display to the raspberry pi GPIO pins then you must select "ttyAMA0" for the "Port:" setting.

With these settings the display should now show callsigns and operating info.

If your display doesn't work you can change Pi-Star's Configuration/Expert/MMDVMHost/OLED/Type to 3 or 6.

Many people use standoffs to mount the display to the raspberry pi's case.

 


Adding A Nextion Display To A Hotspot

Nextion displays come in larger sizes than OLED and they are customizable using the free Nextion Editor to create your own custom .tft screen configuration layout files.

Note that you are not required to use the Nextion Editor, there are ready-to-go .tft files you can load into your display to get you up and running quickly.

It's pretty simple to add a Nextion display to your MMDVM modem board. You connect the display to the modem, load a .tft display config file using a MicroSD card and then set Pi-Star's display settings.

I added a 3.2 inch Nextion display to my MMDVM_HS_HAT_DUPLEX modem card + Pi2 hotspot. I purchased the NX4024T032 Nextion display on Amazon for $34.

The little MicroUSB connector board that comes with the Nextion display is for testing only. You can connect the display's black and red wires to the MicroUSB board to power it up and test it before connecting it to a modem or raspberry pi. The MicroUSB connector board is not needed for the install on the hotspot.

You can connect the display to either the modem card or the raspberry pi but since most modem cards use the raspberry pi's GPIO pins it's easiest to connect the display directly to the modem card.

I had to solder a 4-pin header into my MMDVM_HS_HAT_DUPLEX modem's Nextion display solder pads. This allows connection using the display's push-on wire connectors.

4-Pin Header

Connect the Nextion display wires to your modem card like this:

        Red to 5vO (5 volts Out)

        Yellow to TXD (transmit data)  Note: This is labeled RXD (receive data) on the Nextion display circuit board.

        Blue to RXD (receive data)  Note: This is labeled TXD (transmit data) on the Nextion display circuit board.

        Black to GND (ground)

MMDVM_HS_HAT_DUPLEX Nextion, OLED and STLink Solder Pads

I soldered a 4 pin header to the Nextion solder pads to allow the use of the Nextion display's push-on connectors. Note the OLED solder pads at left between the antennas and the STLink pads at top center.

 

Testing the Nextion display.

I used the NX4823T032-L2.tft file from the MMDVMHost github website to configure my 3.2 inch Nextion display. Note the "32" in the file name means 3.2 inch display. Be sure and download the file that matches your screen size. This file uses the ON7LDS layout which displays the hotspot's IP address.

You also have the option of downloading the free Nextion Editor to create your own custom .tft screen configuration files.

To get the .tft file into the Nextion display you need to use a MicroSD card formatted in FAT32 with the .tft file as the only file on the card.

Power down and insert the MicroSD card with the .tft file into the Nextion display's MicroSD card slot (not the raspberry pi's SD card slot).

Upon power up the Nextion display will load the .tft file and configure itself. The Nextion screen will display the status of the .tft update. On my first try I got a "model mismatch" error because I used a .tft file for a 3.5 inch display, not a 3.2 inch like I needed. Once the update is complete you can power down and remove the MicroSD card.

In Pi-Star's main configuration page select the following settings:

Pi-Star Display Settings For Nextion Display

Select "MMDVM Display Type: Nextion", "Port: Modem" if you connect the Nextion display to the MMDVM modem board and I used an ON7LDS .tft file so I selected "Nextion Layout: ON7LDS".

If you connect your Nextion display to your MMDVM modem card (not to the raspberry pi) then you must select "Modem" for the "Port:" setting.

If you connect your Nextion display to the raspberry pi GPIO pins then you must select "ttyAMA0" for the "Port:" setting.

I selected a tty port by mistake and the hotspot could not transmit and receive due to my setting error.

With these settings the display should now show callsigns and operating info.

Many people use standoffs to mount the screen to the raspberry pi's case. I mounted my display to the bottom of the pi's case.



Open Source Hardware Licensing

There's been a lot of discussion about MMDVM ripping off ZUMspot and Chinese hotspot manufacturers ripping off everyone. The ZUMspot and MMDVM_HS_HAT creators use this Open Source Hardware license. This license is about sharing a design for the benefit of humanity and allows anyone to build your hardware. The creators of ZUMspot and MMDVM_HS_HAT include a non-commercial clause that simply states:

A commercial use is one primarily intended for commercial advantage or monetary compensation.

You would have to prove the guy in China selling these boards is doing it primarily for monetary compensation. He's legal as long as he says his primary purpose is to make this hardware available to as many Hams as possible at a good price. The license doesn't even prevent him from making a profit.

The primary purpose of the Open Source Hardware license is to prevent someone from taking credit for your design, not to restrict the manufacture of the hardware.

There is no "genuine" ZUMspot or HS_HAT versus a "clone" because they were released as Open Source Hardware. By using the Open Source Hardware license the creators gave approval for anyone to build these boards. With this license there are no clones or pirates. I appreciate all the hard work that went into creating these MMDVM boards and I love that the creators gave the design away using the Open Source Hardware license so Hams around the world could benefit. If the ZUMspot and MMDVM creators were worried about other people "ripping them off" by building their hardware they should have patented the design. Please don't give away your design and then bitch about someone using it.

I use the Open Source Hardware license without a non-commercial clause for some of my designs because the important thing is to get the hardware to the users.

 


Modifying Motorola Astro CPS Software To Allow Out-Of-Band (OOB) Frequencies

As I mentioned above I accidentally purchased a UHF Range II (S Split) Motorola XTS3000 with band coverage of 450 - 520MHz (outside of the 70cm Ham band). The UHF Range 1 (R Split) radios with band coverage of 403 - 470 MHz are preferred for Ham use but the 450 - 520MHz radios can be programmed down to 440MHz using a modified Astro CPS program. Standard Astro CPS will allow a slight out-of-band programming like I did for my hotspot at 449.900MHz. CPS will let you know you're out of band but it will still allow you to upload it to the radio. If you try to program a frequency too far out of band CPS will display an error message and not upload the code plug to your radio.

I followed the guidance at this website to modify the AstroPort.exe (Saber and XTS3000 Astro CPS) file to allow programming of XTS3000 450 - 520MHz radios to accept frequencies from 440 - 520MHz. This will allow you to program 70cm repeaters in the 440 - 450MHz range. I believe this is a valid modification for Amateur Radio use. Output power will probably be reduced and performance isn't guaranteed when transmitting out-of-band but my radio performs really well.

While I was at it I also modified Astro CPS for Range I (403 - 470MHz) UHF radios to allow 403 - 477MHz frequencies.

You can download Saber and XTS3000 CPS with the modified "AstroPort.exe" file here. After installing the Saber and XTS3000 CPS program simply replace the original "AstroPort.exe" file with the modified file. The modified file and instructions are in the zip file in a folder called "Modded_AstroCPS".

Astro 25 CPS software for the XTS2500 and XTS5000 can also be modded to allow out-of-band frequencies following the guidance at this website.



XTS3000 Housing Swap

I like the look of the firemen yellow Motorola radios so I bought a new Motorola OEM yellow housing for my XTS3000 on eBay and swapped the chassis, control module and "Motorola" placards (front and rear) into the yellow case. There are many YouTube videos that detail the swap but this one is the best. Referencing this video and the pdf linked to below will get you most of the way through the swap. The chassis swap is easy with the OEM Motorola chassis removal tool (eBay) but getting the control module out can be a pain.

It took me a couple of hours to do the swap because I had trouble getting the knobs and knob inserts off and getting the control module out. I also did a ton of Googling and YouTubing to make sure I was doing it right.

Refer to this excellent pdf for chassis removal and reassembly: Batdude's Guide to the XTS3000 & XTS5000.

You must use the Motorola chassis removal tool to get the chassis out of the old case shell without cracking the case. The tool also aids in reassembly. I got my tool on ebay. Just search for "Motorola XTS3000 chassis tool".

From Old Scratched Up Black Case to New Fireman Yellow

You must release the Flex ribbon connector that connects the control module to the chassis as you remove the chassis from the case.

The trick for removing the knobs is to push up on one side of the knob with both your thumbs one one side of the knob and fingers on the other side to start that side of the knob up, then push up on the other side of the knob to get it to start up. When you get both sides up a little the knob will slide off.

Below the channel selector knob lives a little "light tube" used to illuminate the channel markings. This light tube is clear plastic and very easy to lose. Watch for it as you remove the channel selector knob and knob insert.

Both of my knobs came off and left the knob insert on the control shaft. If the knob insert stays on the knob shaft you need to use a small jeweler's screwdriver to gently push outward on two little tabs that latch onto the control shaft. Looking down into the insert you'll see the two latch tabs. Move the two tabs just a little outward with the screwdriver while pulling up on the insert will get it to slide off. If you damage the inserts they won't latch onto the shaft and the knob won't be secure. Replacement inserts are available but both of mine were undamaged and reusable.

The volume knob insert has an o-ring that may stick inside the insert or may be left on the control shaft. Don't lose it. Remove it from the insert.

When you remove the radio chassis the control module remains in the case. The control module includes the antenna connector and both knob controls. To remove the control module start with removing the single screw that holds the speaker in place and removing the spring bar the screw holds down. Gently slide the two "Flex" ribbons up out of their slots on both sides of the radio to free them. Make sure the speaker is loose so it can move out of the way when the control module comes loose. When looking into the radio case you want to release the control module's top left locking tab. Insert a small, thin flat-blade jeweler's screwdriver between the control module tab (white) and the case and gently pry the tab until it unlatches. In the disassembly/assembly YouTube video the guy struggles to release the right module tab. It's much easier to release the left tab. Releasing the left also makes it much easier to get the control module out.

There is a small hole in the case to help you push out the front "Motorola" placard. I used a thin pick to push the placard out enough to get a fingernail under it. Use gentle pressure to peel it off and it won't warp or bend. The small rear placard came off with the use of just a fingernail. Warming the placards before removal with a hair dryer can make it easier to get them off without damage. A little general purpose glue will hold them in place on the new shell.

For reassembly remember to remove the new case's inside viewport protective film and try not to get fingerprints on it or the actual display module. Leave the outside protective film on until the radio is fully reassembled.

Insert the control module and simply push it up and snap it into place. Look at the knob and antenna connectors to make sure the module is fully in place and centered. Inspect both control module locking tabs to make sure they are fully engaged.

Gently slide the two Flex ribbons into their slots on both sides of the case.

Install the speaker holding spring bar into place and screw it down.

Install the knob inserts and knobs. Put the volume knob o-ring on the control shaft first, then install the insert & knob. The control shafts are keyed to line up with knob insert slots. The knobs have indentions that must line up with the shape of the knob insert.

Place the front panel button panel into the new case.

You must make sure the chassis o-ring stays in its groove as you insert the chassis into the new case.

Don't forget to install the speaker screw, install the button pad or to remove the new case's window inside protective film.

Keep the radio display-up when inserting the chassis to keep the display module from coming out of place.

Attach the Flex ribbon to the chassis and gently slide the chassis up into the case as you close it but don't close it all the way.

Use the Motorola chassis removal tool as shown in Batdude's pdf to help snap the chassis fully into the case without damage to the case or o-ring.

In the end the swap went well with no damage and no lost or extra parts. The biggest bonus is the radio looks brand-spankin' new with a new, scratch free display.

 


Motorola XTS2500 & XTS5000 Info

I purchased a VHF XTS5000 P25 radio (136 - 174MHz $130), Ribless programming cable ($27) and Astro 25 CPS programming software ($25); all from eBay. The XTS5000 is one generation newer than the XTS3000 but it is very similar. The XTS2500 & XTS5000 use the same batteries and speaker mics as the XTS3000 but the programming cable and CPS software are different. Make sure the programming cable you get specifically mentions the model radio you have. The XTS2500 & XTS5000 use "Astro 25 CPS" programming software.

The XTS2500 and XTS5000 come in the same lineup as the XTS3000. There are Model I (no display or front buttons), Model II (display + 6 buttons) and Model III (display + full keypad). All models come in VHF, 700/800MHz and two UHF versions. Like the XTS3000 UHF Range I (R Split) covers 403 - 470MHz and UHF Range II (S Split) covers 450 - 520MHz. Since most P25 repeaters and hotspots use UHF, the UHF Range 1 (R Split) radios are best for ham use but they're kind of rare and much more expensive than the XTS3000, especially the desirable Model III with full keypad.



MFJ-1278 to TNC-2 Modification

Have an old MFJ-1278 modem lying around? See this to turn it into a stand-alone TNC-2 modem and APRS digipeater.

 


Mini Cooper Ham Radio and Antenna Install


WARNING

Tube receivers, transmitters and amplifiers have large capacitors that store enough electricity to kill even when unplugged. If you go into a tube chassis you MUST verify it is unplugged and no voltage remains in the capacitors before working inside it. See Amplifier Safety for more info.

 

Current QSL Card

 

Old QSL Card

The C-141 had two 400 watt HF transceivers, two auto-tuners and one antenna so we had "dual watch" but could only transmit on one radio at a time. The tuners were in a pressurized 7psi container to prevent arcing at high altitude (very low air pressure). The antenna is the "bullet nose spike" on the T-tail. Here's an  Avaition Radio Fundamentals presentation I used to teach C-141 pilots about their plane's radios. We had pretty good reception at forty thousand feet.

 

MajorValve says watch yourself inside that tube chassis.

 

By BrainlessTales.com

Comments and corrections are always welcome at robinette at comcast dot net.

 


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