GRBAlpha - How to use digipeater or DNxD - 13. Frequency settings for digipeater or DNxD

The uplink or downlink frequency of GRBAlpha is 435.025MHz. There WAS 145MHz for uplink , but it is not work because of some trouble.

As I wrote in "GRBAlpha - How to use digipeater or DNxD - 05. My antenna, transceiver, and tracking system", I memorize 5 sets of frequencies with 5kHz step for transmitting and receiving just like when we use ground repeaters. The frequency pairs are like as :(uplink/downlink) 437.015/437.035, 437.020/437.030, 437.025/437.025, 437.030/437.020, 437.035/437.015. According to checking the frequency and direction with Gpredict, I change the memory channel starting from the pair of "437.015/437.035(uplink/downlink)", and I control my rotetor manually. 

GRBAlpha - How to use digipeater or DNxD - 12. To use DNxD

DNxD is the "Delayed Needronix Digipeater".

A normal digipeater responds immediately after you transmit your message to a repeater like as I mentioned in this blog just before. (See "GRBAlpha - How to use digipeater or DNxD - 11. To use digipeater".)

DNxD is different from that. "Delayed" in the name means you can set the delay time that your message will be transmitted after you send it.

It is very easy to use DNxD system. You only add "@xxx " ("@", 3 digits, and a space; "xxx" are 3 digits how many minutes you want to transmit your message after you upload it.) in the beginning part of your message.

When you want to send your message after 90 minutes, prepare your message like as "JI1IZR>CQ:@090 Hello from Japan, my GL is PM95pi". 

GRBAlpha replies "OM9GRB-8>JI1IZR:Your message will be retransmitted in 090 minutes, thank you for using Delayed Needronix Digipeater (DNxD)!" when GRBAlpha catches your message.

After 90 minites, GRBAlpha will transmit a message like as "JI1IZR>CQ,OM9GRB-8:@090 Hello from Japan, my GL is PM95pi". This message will be transmitted 3 times with 1 minute interval.

I recommend you that you include your Grid Square Locator in your DNxD message as a receiver of your message can caluculate how long delay he/she needs to set in his/her DNxD message in the response message for yours.

Please notice that the DNxD keeps only 1 message. If someone has already uploaded a message in DNxD, you will get a response from GRBAlpha like as "OM9GRB-8>CQ:Delayed Needronix Digipeater (DNxD) is busy for next 001min(s). Try later." 
when you transmit your DNxD message.

Even when DNxD is busy, you can use normal digipeater on GRBAlpha.

GRBAlpha - How to use digipeater or DNxD - 11. To use digipeater

When we use a digipeater, we usually set a via station. So you may think you have to set "via OM9GRB" when you use GRBAlpha digipeater. But you need not to set "via" in the case of GRBAlpha.

You only have to transmit your message like as "JI1IZR>CQ:Hello from JAPAN, my GL is PM95pi" in AX.25 format on 437.025MHz (+-doppler) while GRBAlpha is in your visible site. When GRBlpha catches your signal, it responses like as "JI1IZR>CQ,OM9GRB-7:Hello from JAPAN, my GL is PM95pi" at once after you transmission. The response is only one time.

When you want to set a destination station, for example "JA1AAA", prepare your message like as "JI1IZR>JA1AAA:Hello DE JI1IZR". In this case, GRBAlpha responses like as "JI1IZR>JA1AAA,OM9GRB-7:Hello DE JI1IZR".

Please do not try to transmit several times in a short period. Listen for a while after you transmit your message. Someone may catch your message and try to respond to you. If you cannnot get any response from GRBAlpha, I recommend you to check your settings as I mentioned in this blog before.

GRBAlpha - How to use digipeater or DNxD - 10. About sampling rate

When you use a software modem like Direwolf or Soundmodem, you may have difficulty to decode signals. As I mentioned in the Section "06. RF & AF input level", you need the signal level as more than S2. Even when you get this level, you do not have enough result. In this case, try to check your settings about sampling rate.

In case of Windows system, you have to check the system sampling rate at first. Open the control panel of sound on your PC, then check  the detail property of microphone, line-input, line-out, and speaker. You will find the sampling rate there like "16bits, 48000Hz".

The sampling rate should be "48000Hz" at least in case of 9600bps. My Ham friends, JA0CAW and JA5BLZ, pointed me it out.

Additonally, I recommend you to set the sampling rate of Direwolf or Soundmodem as more than 48000Hz.

In case of Soundmodem, set the "TX SampleRate" and the "RX SampleRate" as "48000", or more, in the "Settings" window of "Sound Card" that I mentioned in the Section "07. Settings of soundmodem".

In case of Direwolf, add "ARATE 48000" in the "direwolf.conf" file like as:

#############################################################
#                                                                                                                      #
#                               FIRST AUDIO DEVICE PROPERTIES                          #
#                                        (Channel 0 + 1 if in stereo)                                   #
#                                                                                                                     #
#############################################################
ARATE 48000

GRBAlpha - How to use digipeater or DNxD - 09. About terminal software

Now you may catch and decode the signal from GRBAlpha. If you cannot, please check your connection, levels, etc., that I have already mentioned. After you succeed to decode, your next step is transmitting your message.

Because Direwolf or Soundmodem themselves do not have the function to send messages, you have to prepare a terminal software for transmitting.  UISS, Tunaterm, Teraterm or other terminal softwares, that have the function to connect to Direwolf or Soundmodem through No.8000, 8001 port, are enough for this purpose. I also built a simple JAVA applicaiton that has the function only to send messages. You can get this from here. This file includes a manual. Please check it before you use it. This application needs "Open-jdk8" or "Open-jdk11", so you have to install one of them in your PC.

GRBAlpha - How to use digipeater or DNxD - 08. Settings of Direwolf

"Direwolf" works on Linux or Windows. You can get information from here: https://github.com/wb2osz/direwolf
You can download windows version from here: https://github.com/wb2osz/direwolf/releases
In case of Ubuntu, you can install it from "Ubuntu Software".
Direwolf is designed especially for APRS, but we can use it as a software TNC.

The settings of Direwolf are very simple. You only modify "direwolf.conf" file.

First, I explain in case of Linux.

After you install "Direwolf", you may have a file named as "direwolf.conf" at your home directory of your Linux PC.
If you cannnot find it, you can download an original file from here.
After you download the "direwolf.conf" file, save it in your home directory. Then open it with a text-editor.

To use 9600bps, you must find:
MODEM 1200
#MODEM 9600
The "#" means comment-out. The above setting means you use 1200bps and disable 9600bps.
If you want to use 9600bps for GRBAlpha, change them to:
#MODEM 1200
MODEM 9600

To enable to use your PTT, you have to modify:
PTT /dev/ttyUSB0 RTS
so as to suit your equipment settings.
For example, change "ttyUSB0" to "ttyUSB1", or "RTS" to "RTS -DTR", etc.
Before you use PTT setting above, you should set the permission for normal user on /dev/ttyUSB0. You must run a command in the terminal window like as:
sudo chmod o+wr /dev/ttyUSB0

Next, I explain in case of Windows.

After you install "Direwolf", you will find "direwolf.conf" file in your folder you installed "Direwolf". Then open it with notepad or other text-editor.

To use 9600bps, the setting is the same as Linux case above-mentioned.

To enble to use your PTT, you have to modify:
#PTT COM1 RTS
Delete "#" and modify to suit your equipment settings.
For example, change "COM1" to "COM2", or "RTS" to "RTS -DTR", etc.

About detail of settings, please read "User-Guide.pdf" file from here: https://github.com/wb2osz/direwolf/blob/master/doc/User-Guide.pdf

After modified your settings, you have to restart "Direwolf".

GRBAlpha - How to use digipeater or DNxD - 07. Settings of soundmodem

I use "Direwolf" because my PC for HAM activity is working on Linux now. But as many people use Windows, I explain the setting of "Soundmodem" for GRBAlpha first.

"Soundmodem" is develped by UZ7HO. I used my Windows10 tablet PC with "Soundmodem" as a TNC for 1200bps uplink or downlink. You must use "High-Speed Soundmodem" for 9600bps of GRBAlpha. You can get the information and download from here: http://uz7.ho.ua/packetradio.htm

I explain here only about the additional settings other than default settings.

For select "G3RUH", choose "Modems" in the "Settings" menu.

You will see "Modems settings" window. Select "FSK G3RUH 9600bd" at "Mode" of "Modem type ch: A" and "Modem type ch: B", and click "Ok".

Then you have to restart High-Speed Soundmodem. You will see "FSK G3RUH 9600bd" on the top.

Additionally, you have to enable "KISS Server Port" for using my application, "GRBAlphaMessenger". I will explain this application later.

For enable it, choose "Devices" in the "Settings" menu.

You will see "Settings" window. Check in the check box on the right of "KISS Server Port 8100". And choose your COM port for PTT, because you can transmit packet data with some tranceivers, like FT-847, only when you activate to PTT port of rear "PKT" connector. In this case, of course, you have to use some PTT adapter for your PC, and connect the adapter to PTT port of your tranceiver.

Then restart High Speed Soundmodem.

GRBAlpha - How to use digipeater or DNxD - 06. RF & AF input level

GRBAlpha satellites has very high transmitting power as 1w according to :

https://www.om3ksi.sk/en/2021/03/18/information-for-radio-amateur-enthusiasts/

When I catch the signal from GRBAlpha, the S meter of my FT-847 with the internal pre-amp enble, indicates up to level 7. You have to get more than level 2 or 3 to decode this GFSK signal, I think. This is in the opposite side of the recent digital communication like FT8, etc. So you may need multi-elements antennas with adequate gain.

On the other side, the input level from the tranceiver to PC should be lower rather than 1200bps. For example, I show you my setting of my PC below.

Please look at the upper right side on this screenshot. You can see a microphone icon and the level. When I listen to 1200bps signals, I set the level a little more than this. Too high input level causes distortion of the signal and misdecoding. I found an uploaded video on Youtube that someone received GRBAlpha signal with RTL-SDR. So many signal sounds were heard but only a little decoded. The sounds from the video was too loud and had much distortion. I think one of the reason for little decoding may be the AF input level.

GRBAlpha - How to use digipeater or DNxD - 05. My antenna, transceiver, and tracking system

For an example, I will introduce my antenna and tranceiver.

My antenna is 15 ele yagi horizontal polarized antenna. 15 ele is more than adequate. I somtimes saw my rig's S meter up to 5. Too strong signal sometimes causes misdecode of software TNC. I will explain about the PC's input and output level later. The reason why I set my antenna as horizontal polarized is that I want to avoid effects from some ground stations like mobile. Of course, the frequency for satellites is not permitted for grounds, but, as you know, some ignore this rule. 

I normally use Yeasu FT-847. It has the output line for 9600bps named as "RX9600" at the "PKT" connector in the rear panel. And I set "PKT RATE" as "9600" in the menu No.23 of FT-847. I sometimes use Icom IC-821 while my FT-847 has some trouble. It also has the output line for 9600bps named "DISK" at the "Accessory" socket in its rea panel. Of course, I set "9600 bps mode" on in the "Set mode with [M/S]".

I use the "Gpredict" for my tracking because I use Linux PC. But I do not control automatically the rotator or rig frequency. I manually control both. I memorize 5 sets of frequencies with 5kHz step for transmitting and receiving just like when you use repeaters. The frequency pairs are like as :(uplink/downlink) 437.015/437.035, 437.020/437.030, 437.025/437.025, 437.030/437.020, 437.035/437.015. According to checking the frequency and direction with Gpredict, I change the memory channel starting from the pair of "437.015/437.035(uplink/downlink)", and I control my rotetor manually. If you control the frequency automatically with your PC, you can perhaps control only downlink frequency. In this case, you can make uplink only around the TCA.

GRBAlpha - How to use digipeater or DNxD - 04. Difference of Signals

I explained a littel about the 9600bps signal sound of GRBAlpha in the former article.

Seeing is believing, I show you here the spectrum figures of the two kinds of sounds in that article. These are screenshots of Audacity on Linux.

The first one is the sound from the "RX9600" output line of rear "PKT" connetctor of my Yaesu FT-847.

The second one is the sound from my handy TRX.

You will find the latter one is deleted low and high area of sound. These deleted parts are very important to decode G3RUH packet. So you need discriminator output on your TRX when you want to decode GRBAlpha signal.