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Author Topic: 2m Digital Net  (Read 3169 times)
N4QAD
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Posts: 16




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« on: August 14, 2017, 06:58:19 AM »

I am looking for the best mode for 2m Digital Net.
SSB has been ruled out because of radio cost issues.
We plan on using one of our existing repeaters.

The problem I am finding is what mode gives you reliability & speed on FM digital.
I keep doing searches on the different protocols and I'm having a lot of issues finding details on how they work, if they are using checksums, or any kind of error checking or best use case scenerios.
I'm seeing a fair amount of MT63-2KL.  Why is that?
Do we just use 8PSK1200F because it is the fastest and with 2M your not digging down in the weeds to pull a signal and bandwidth is not an issue?

Does it matter where the waterfall is centered?  I see 1Khz and 1.5Khz on other websites.  Is there a default on FLdigi?

I appreciate any help.

Thanks,

Nick Zircher


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KJ4HVL
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Posts: 74




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« Reply #1 on: August 14, 2017, 11:08:03 AM »

What kind of range are you looking for? Note that some FM digital modes are wider than the bandpass of your nearby repeater (9600BPS modes, and GMSK) and not function reliably or at all. Others may be miffed if you are spitting out modem tones on their assumed to be voice-only repeater.

1200Bps AX.25 is a good starting point, though range won't be much beyond voice range. Since it is the backbone of APRS lots of people have modems that can decode it. Other weak signal so called "sound-card" modes are probably not going to get a lot of replies since nobody uses them with FM. Since FM is a full carrier mode, your spectral power density is wasted in weak signal modes (the main reason why most people use SSB for weak signal modes is that all the power goes into the current tone, instead of being spread out across the tx bandwidth).
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KC9NVP
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Posts: 208




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« Reply #2 on: August 14, 2017, 12:19:08 PM »

Well there are four different types of FM digital, Fusion, D-Star, DMR (all taking analog voice and converting into digital mode).  The fourth mode uses an interface (sound card, signalink, or some other interface) to your laptop and radio to convert the digital signals into audio sounds for transmit over basic FM radios using software program such as fldigi (can be found for free on the internet).

Our Miami County Ohio club, W8FW runs a digital net each Sunday night at 7pm on our repeater using fldigi set to MT63-2KL and seems to works fine.  Some members are using base radios, other HTs and a couple using other interfaces besides USB Signalink (search for signalink on the internet and you will find several sources to purchase it from or you could wire up your own interface, schematic can also be found on the internet).  We even have used it a few times during ARES drills.

Good Luck,


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KC3RN
Member

Posts: 200




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« Reply #3 on: August 24, 2017, 03:52:56 AM »

My local club hosts a 2m digital net on Monday evenings.  I'm actually one of the back-up net control ops, when our primary net control op is otherwise occupied.  We use MT63-2KL, because that is the standard mode as established by the western PA ARES group.  It may change based on your location, but I think MT63 has become pretty much the standard.  To address your specific questions:

"Does it matter where the waterfall is centered?" - Yes.  All stations need to be centered on the same freq for reliable decodes.  1500 is the standard we use.  That keeps the entire signal within the proper audio bandpass.

Is there a default on FLdigi? - Not unless you save the configuration.  Also note that we run FLMSG along with FLDIGI.  That allows you to send/receive the proper ICS forms.  We usually start with the ICS-214 (roster).  Net control starts the roster, then each station adds their call and re-transmits.  The continues until each station that has checked in has added their callsign.

We have a number of regular check-ins that are running Rigblasters or SignaLinks, but most stations (including myself) are using acoustic coupling.  We do that for a couple of reasons.  First, it's easy to generate interest and participation.  Anyone with a laptop and HT can participate.  Second, in an emergency situation, more operators are likely to have access to that gear, rather than a portable rig with a "real" interface.

All this is done over analog FM using the club repeater system.  D-star, C4FM, etc, are all digital voice modes, and aren't necessary for digital data operation.
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N4QAD
Member

Posts: 16




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« Reply #4 on: August 25, 2017, 12:51:10 PM »

That is an awesome idea with the Roster.  Thanks everyone for your replies.
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W4KYR
Member

Posts: 1608




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« Reply #5 on: August 25, 2017, 01:56:57 PM »

Quote
I am looking for the best mode for 2m Digital Net.
SSB has been ruled out because of radio cost issues.
We plan on using one of our existing repeaters.


They used to run RTTY with a repeater on 2 meters. Does anyone still do that anymore?



http://forums.qrz.com/index.php?threads/rtty-on-fm.252389/#post-1964500

Quote
Many years ago, FM RTTY on VHF was quite common. The 146.10/.70 was commonly used for RTTY repeaters, and most were home to RTTY bulletin boards.
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The internet and cellphone networks are great until they go down, what then? Find out here. 
https://www.eham.net/ehamforum/smf/index.php/topic,111948.0.html

Using Windows 98 For Packet...
N4QAD
Member

Posts: 16




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« Reply #6 on: November 29, 2017, 06:19:50 AM »

Update:
After doing this net for a few months now it has been working great.
We have been using MT63-2KL on a 70cm fusion repeater.
We started using FLmsg and using the netlog for everyone checking into the net.
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