Thursday, November 21, 2024

Southern Cape ZS1I SVXLink Reflector Changes and Modifications (Part 1)


Want to know more about the Southern Cape ZS1I SVXReflector?  Click HERE

Awhile back I posted the following in an article: 

"Some time ago I was looking for a UHF Motorola Radio to be used with a SVXLink node.  I put out a request for such a radio and Mark ZS4OIL responded that he has such a radio.  I was unsuccessful in all my efforts to buy the radio from him.  He refused to accept anything even the costs to send the radio to me.  Mark donated a UHF Motorola GM300 radio  to me.   I received the radio this morning.  This radio will be used as a link radio for the ZS1I SVXLink Reflector that is currently connected via VHF to the ZS Link Network here in the Southern Cape.

Mark I would like to thank you for your generosity, great amateur radio spirit and for donating this radio, to be used to extend the ZS Link Network in the Southern Cape.  Highly appreciated and once again a big thank you!!

I will later post images where this radio is connected to the network and operational."

Herewith a few images of the radio attached to the  ZS1I SVXLink Reflector.  Click on images for larger view.



As the title of this topic indicate I made a few changes to the Motorola GM300 UHF Radio and the ZS1I SVXReflector.

Radio Changes:

1.  I programmed two frequencies  =  433.550 Mhz and 433.500 Mhz

2.  The COS Modification was done as illustrated in the image below

3.  RX CTCSS of 88.5 Hz programmed

4.  Remote hook switch modification for RX CTCSS was done

5.  Added Ext. Speaker wire to the 16 pin expanded accessory connector at the back of the radio


These modifications are necessary when using these older type of Motorola radios that does not have the newer logic boards installed.  With the newer Motorola's you can program some of  the output pins on the 16 pin expanded accessory connector.  The radio is now ready to be connected to the SVXLink Reflector Node.

SVXLink Reflector Changes:

1.  During the initial setup I decided to use the GPIOD value for the type of squelch detector.  It was setup in the SVXLink.Conf file under  SQL_DET in the RX1 section.  In the TX1 section PTT_TYPE was set as GPIOD.  Testing the setup without CTCSS worked flawlessly but adding the CTCSS to the mix resulted in either the Motorola or Modified Node not being happy.  Now this modification is not the first I have done relating to this radio.  No matter what I tried it would work fine but when I added CTCSS both units would go completely crazy with all sorts of issues.  I suspect that the modified IRLP Board might have something to do with this.  Be as it may there is always a plan B.

2.  If I do not need to use CTCSS the radio and the node works fine without any issues.  However I found that there are some commercial break-thru in my area and that adding CTCSS is a must.  Now do I replace the current radio or modified IRLP Board with a newer radio and build a new interface board.  This could be used as plan B but I decided to use another type of squelch detector that would allow for the use of CTCSS.  The beauty of SVXLink is that there are many options available.  Possible values are:  VOX (not recommended), CTCSS, SERIAL, EVDEV, SIGLEV, PTY, GPIOD, HIDRAW or a combination of CTCSS and GPIOD.  I decided to set SQL_DET=CTCSS in the Rx1 section and PTT_TYPE=GPIOD  in the Tx1 section.

This is not as easy as just replacing GPIOD with CTCSS for RX1.  To use the CTCSS value one need to make several other changes to the SVXLink.Conf file.  It took me a few days to get the "combinations" correct in order for CTCSS to function properly. 

COS (Carrier Operated Squelch) and CTCSS is used to open receiver control in SVXLink

Let's look at how to enable COS and CTCSS to open the Motorola's receiver in SVXLink Reflector. But first before we look at the method I used to detect the carrier operated squelch the general rule in the construction of a radio link or repeater link in this part of the world is to only use COS and not VOX. A  sub-tone or better known in amateur radio circles as CTCSS must be activated.  CTCSS will not allow the receiver to open due to interference that may occur in the area of the installed radio device. This is a very important when a Radio or Repeater is connected to ANY VOIP- or Radio Network.  With the COS modification already done as per image in the Radio Changes section above we now need to set the SQL_DET parameter in the SVXLink.Conf file under [Rx1].  We also need to make a few other changes that relates to the use of CTCSS.

I chose not to use flat unfiltered audio or setting jumper JU551.  I decided to use SVXLink to receive the incoming CTCSS tone and open the transmitter on receiving the correct CTCSS tone. SVXLink can decode the sub-tone and use it to inform that the COS is active, and that the transmitter will then go into TX.  Sounds easy? Well it is if you know what settings to change to make it work   I made the following changes in SVXLink.Conf under the following heading:

[Rx 1]

(I changed the following and it worked for my setup.)

SQL_DET=CTCSS
SQL_START_DELAY=0
SQL_DELAY=0
SQL_HANGTIME=0
SQL_EXTENDED_HANGTIME=1000
SQL_EXTENDED_HANGTIME_THRESH=15
SQL_TIMEOUT=300
CTCSS_MODE=2
CTCSS_FQ=88.5:1
CTCSS_SNR_OFFSET=0
CTCSS_OPEN_THRESH=12
CTCSS_CLOSE_THRESH=5
CTCSS_BPF_LOW=60
CTCSS_BPF_HIGH=270
DEEMPHASIS=0
PREAMP=0
PEAK_METER=0
DTMF_DEC_TYPE=INTERNAL
DTMF_MUTING=1
DTMF_HANTIME=100

As I mainly use DTMF to do switching between networks the above setup is working with the SVXLink Reflector currently in use.  With regards to transmit (PTT) side of things I use the following setup in SVXLink.Conf file under [Tx1].  This setup is working well and thus far I have not experienced any problems.

[Tx 1]

(I changed the following and it is working for the setup I use.)

PTT_TYPE=GPIOD
PTT_GPIOD_CHIP=gpiochip0
PTT_GPIOD_LINE=17
TX_DELAY=3
PREEMPHASIS=0
 
The GPIOD method is based on the gpiod library and this method is used with the Raspberry Pi and my modified IRLP Board. 

It is important that when "playing" around with the above configuration variables that you consult the SVXLink doc file called SVXLINK.CONF available HERE

To sum up:
 
1.  The necessary Radio Changes and Modifications were made.
2.  Changes were made to the SVXLink Reflector
3.  The changes result in:
  • Opening the squelch in SVXLink when the sub-tone is received
  • PTT activated once the squelch opens
  • Close the squelch when the sub-tone is no longer present
  • Close the squelch also when there is no signal at GPIOD anymore and deactivate the PTT
  • Setting the TXDelay to 3 is working for my setup.  This value might need to be increased to between 500 and 800ms in some cases.  FM radios (Mobile and handheld) need time to open the squelch after a signal appears.  The greater the distance and the weaker the signal, you will need more milliseconds to turn the transmitter on and starting the audio transmission.
     

The use of CTCSS for squelch detect and GPIOD as PTT type is working well with my "unusual" self constructed node. I  have pointed you in the direction of how to use the above setup to get your SVXLink Reflector working with this setup.  I trust that this article will be of use to others.

ED.  In Part 2 I will be explaining how to use the ZS1I SVXLink Reflector and will also provide the benefits of the reflector in general to radio amateurs and the ZS Linked Network.

Can one see Auroras (Southern Lights) in South Africa?

Aurora Australis (Southern Lights) over Simons Town. Picture: Hassaan Tanvir During a recent discussion on the "Sonsak Span Amateur Rad...