2m SSB without a SSB rig (seriously)

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KK4YWN, Dec 24, 2014.

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  1. KK4YWN

    KK4YWN Ham Member QRZ Page

    This might seem totally wacky at first, but bear with me a bit as this is experimental stuff and i know you folk like to experiment.

    The project: A SSB echolink node (don't stop reading its not as bad as you think!). I'm using a Raspberry Pi computer, a cheap USB audio card, and a homebrewed audio interface. To the best of my knowledge, only one other SSB node exists (on HF).

    The raspberry pi has accessible general purpose inputs/outputs (GPIO) that make interfacing simple. I used a 4n25 optocoupler and a 200ohm resistor to handle PTT duties. If you have a radio that can output a squelch-controlled signal you can turn the circuit around and feed the output to a GPIO input. So, with SQ and PTT properly isolated, we simply need to isolate speaker/mic into the sound card. One popular interface can be found for about $15 and its cheaper than buying the parts and building it yourself. But be warned: it functions, but not well. There will be common mode on the mic line. A few hundred ohms resistance helps.

    Using svxlink software as the core, the raspberry pi hums along nicely. It can bridge RF to the echolink network, bridge RF to RF, bridge local audio to anything, and even handle remote t/rx work and voter systems. Its good stuff.

    Why do this?
    I needed a project.
    Promote SSB use on 2m (and find someone to talk to!).
    Bring new hams to SSB domain.

    Results:
    Excellent. Really. Weak signals get into the VOS (voice operated squelch) with better SNR than the radio produces. I've no idea what audio processing is in-play, but connecting to my radio via echolink actually improves my ability to copy known weak stations. This doesn't mean they're instantly 100% copy, but there is a very noticeable and welcome improvement. RF-side stations report good audio/modulation. However, because of common mode currents on the mic line, close-in stations can detect hum. Besides this, remote stations report fine audio from echolink connected operators. Echolink-connected operators are amazed at the distances the station can cover with a modest beam and 25watts.

    Observations:
    The 600:600 audio transformers used for isolation are not good. I'm moving to another solution soon.
    There was a great deal of hesitation from my local SSB buddies about bringing this online. However, since bringing it online, it has become a major source of entertainment in our area. Its very well received now (no pun intended).
    There exists some bizarre condition that allows very weak signal reception with great clarity. The mechanism for this is totally unknown, but it requires a stronger signal source. When John (N4JS) is in QSO with my station, and I am connected via echolink, I can often hear other stations between johns words. The other station is exceptionally clear and noise-free, but only exists in the echolink node. It can not be heard in the receiver and it can not be heard unless john is transmitting. Other stations may produce similar results, but john happens to be closest to me, and if he has room-noise in his audio, its enough to wipe-out the other station. There must be some sort of mixing that the software is able to dig out and amplify, but for the life of me I have no idea how this works.
    The RF stations must be willing to chase the drift of my station since it can't be retuned remotely. So far they've been really good about this.
    Linking two echolink nodes together draws a crowd. Good operating practice becomes a must.

    Overall, this has been a really fun project and its brought a lot of life to our favorite SSB frequency. The system has proven itself capable, and has been a well spring of new ideas. If you have the means to experiment, I would love to hear about your experience.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Great experiment, but wouldn't interest me at all since using any kind of networking utility (Echolink) means contacts don't count for awards or contest points or really anything other than filling a log with contacts.:p

    Plus, 2m beams are really small and easy to erect high above ground so they can be very effective. And running high power on 2m (even a kilowatt or more) isn't complicated nor likely to interfere with neighbors' electronic appliances, so almost anyone can do it with little risk.

    Good example of making use of technology, though!:eek:
     
  3. KK4YWN

    KK4YWN Ham Member QRZ Page

    What counts toward awards/contests besides direct contact? I assume repeaters and satellites do. Am I incorrect? I ask because several other related projects have presented themselves, and maximizing their usability would be beneficial. My meager link currently satisfies its design goals, but it sure did open up new lanes of thought about 2m ssb operation.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Repeater contacts don't count for any award or contest points anywhere I know of.

    There are some special "satellite" awards, but satellite contacts don't count in any actual contest. They can count for Field Day, which isn't really a contest. Sat contacts do not count for the standard awards like VUCC, WAS, WAC, DXCC, WAZ, etc.
     
  5. KK4YWN

    KK4YWN Ham Member QRZ Page

    Thank you. That info helps guide the next couple of projects.

    I'll keep the current project focused on ssb promotion and general rag-chewing. For both, it has been a great deal of fun.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'll bet it has! I've enjoyed 2m SSB since building my first 2m transverter in 1968. Back then, 2m below 147 MHz was about 70% AM and 30% SSB-CW. FM was in its infancy but gaining ground rapidly on the high end of the band.

    By about 1973, it was maybe 20% AM and 80% SSB-CW down there, and FM on the high end was becoming very popular.

    You can never go too far improving a 2m SSB station until maybe you get to...
    [​IMG]
     
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, I mentioned there are satellite awards...but they're not the same as the regular ones. Satellites are repeaters.

    I think FD is the only "sorta" contest where satellite contacts count (although it's not really a contest per ARRL rules). They don't count in any of the VHF contests.

    EME, on the other hand, counts for all the awards and contests.

    Echolink, which uses the internet as its backbone, doesn't count for anything I know of. I've used it a few times when it was a new thing many years ago, and that wasn't too exciting. I think repeaters should count "more" than Echolink does, since at least repeaters are amateur built, owned and operated and don't rely on any public resource.
     
  9. KK4YWN

    KK4YWN Ham Member QRZ Page

    the echolink client isn't very exciting. but i understand why it appeals to some hams. a buddy of mine uses it to link his rig to other linked rigs, then accesses it using his HT. so he's able to walk around the house with his HT and make contacts with people using the echolink network in a similar fashion.

    a few nights ago he bridged his node with my node and talked ssb on his HT... OK to NC. funny stuff.

    the linking is what makes echolink attractive. the hills/valleys out here make point-to-point a bit of a rich mans hobby. but linking a few strategically placed transceivers gives the peanut-whistle stations a chance to make contacts. eventually, they'll grow tired of using the link and the latency that goes along with it (slightly less than a second).

    i see it as an enabler: providing accessibility that otherwise wouldn't exist. its also a great source of laughs when its busy.
     
  10. WA9SVD

    WA9SVD Ham Member QRZ Page

    You're trying to make us jealous, aren't you?:rolleyes:
     
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