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Re: AIS reception feaseable with a Softrock RX?

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  • g8voip
    Hi James, Ben KD5BYB did contact me directly, and I think make a posting to confirm that he was receiving weather transmissions at 162.400MHz with his
    Message 1 of 15 , May 31, 2010
      Hi James,

      Ben KD5BYB did contact me directly, and I think make a posting to confirm that he was receiving weather transmissions at 162.400MHz with his unmodified VHF Ensemble, but did not have the means of measuring its performance.

      I am still a little way off getting around to modifying mine for 2m, completed the 6m evaluation, just starting the changes needed to get it running on 4m.

      My feeling is that the front end tuned circuits are broad enough that it is probably possible to tune it up around those frequencies without needing any changes, but I will check it out and make the results known on the forum.

      Not sure what to make of those sensitivity figures, probably as David confirmed yesterday, the transmissions are narrow band FM, so probably SINAD, but depends what the reference is, sounds a bit deaf for the usual 12dB SINAD.

      I might be able to make some SINAD measurements with the VHF Ensemble, but how meaningful they really are, not too sure as the FM performance of most of the SDR software is pretty poor and of course any measurement made is for the whole system, i.e. SDR hardware, sound card and SDR software, too many variables.

      73, Bob G8VOI

      --- In softrock40@yahoogroups.com, "savagejdc@..." <savagejdc@...> wrote:
      >
      > Bob,
      > That would be realy helpful. I shall have to look more closely at Ensemble. Please comment on whether you think any modifications are necessary to ensemble to get it working at those frequencies.
      >
      > Have been following HPDSR for a while and they have implemented multiple receivers too, but their price point is out of my league.
      >
      > According to this review https://milltechmarine.3dcartstores.com/customer_center/pbo_ais_test_jan.pdf , commercial AIS receivers seem to have a sensitivity of -107dB / -112dB. It doesn't say how this was measured and it wasn;t checked in the review.
      >
      > Regards,
      >
      > James
      >
      >
      >
      > --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@> wrote:
      > >
      > > Hi Keith and James,
      > >
      > > A couple of comments to add which might help, although I am not familiar with that particular AIS service you are talking about.
      > >
      > > As the two frequencies mentioned are only 50kHz apart, with a sound card sampling at 96kHz, both should be able to be received together.
      > >
      > > PowerSDR does have 'dual' VFO facilities, so both could be tuned correctly. I have never tried it, but there is there the facility to move sliders to output one VFO on the left speaker and the other VFO on the right. I guess you could manually feed these into your decoding program.
      > >
      > > It might be possible to use 'virtual cables' to do it within the PC itself, again not tried that out with two separate channels.
      > >
      > > One of the VHF Ensemble beta builders has reported operating his 2m version around those frequencies, but not too sure of the actual performance.
      > >
      > > I am currently evaluating one of the beta VHF RX Ensemble kits for Tony, just about to complete the 6m evaluation, then my intention is to modify it for the 70MHz (4m) version, and finally to the 2m one.
      > >
      > > When I evaluated the original v9.0 RX 2m plug in converter I also checked it at 137MHz for WX satellite reception, which worked very well. I have made a note of the 161.975 / 162.025MHz frequencies, so when I get around to doing the 2m evaluation in the next few days, I will do some testing at those frequencies and report back the results.
      > >
      > > 73, Bob G8VOI
      > >
      > >
      > >
      > >
      > >
      > >
      > >
      > > --- In softrock40@yahoogroups.com, "kwing175" <kwing175@> wrote:
      > > >
      > > > James,
      > > >
      > > > The responses I received to my original post lead me to belive that it is possible to modify softrock receivers to receive AIS signals. I have not tried.
      > > >
      > > > I am not sure that the V 9.0 will be able to tune in two separate frequencies at the same time. Is it possible to run two instances of an SDR program from one receiver? And, have each program tuned in to a different frequency?
      > > >
      > > > The next question in my mind is how do I input two signal streams into the AIS software?
      > > >
      > > > Work commitments have prevented me from exploring this application of SDR. I am still very interested though. Please keep the group posted with your progress.
      > > >
      > > > Regards,
      > > > Keith
      > > >
      > > > --- In softrock40@yahoogroups.com, "savagejdc@" <savagejdc@> wrote:
      > > > >
      > > > > I have been thinking along similar lines. Has anyone made any progress on this? What I haven't worked out is whether the AIS frequencies can be tuned to using the VHF kit on a V 9.0 kit ie 161.975 Mhz and 162.025 Mhz, or whether the softrock or the VHF kit would need to be modified. Can anyone confirm this?
      > > > >
      > > > > Am I correct in thinking that with a 96K audiocard it should be possible to receive both of the AIS channels at the same time? ISTR that the bandwidth of each is 12.5Khz.
      > > > > If that is the case then I wonder if it would be feasible to decode both data streams at the same time.
      > > > >
      > > > > Rgds,
      > > > >
      > > > > James
      > > > >
      > > > >
      > > > > --- In softrock40@yahoogroups.com, "kwing175" <kwing175@> wrote:
      > > > > >
      > > > > > First off let me say I am not an electronics whiz, nor am I a software whiz. However,I immensely enjoy this group and appreciate everyone's effort in keeping it alive. Thanks.
      > > > > >
      > > > > > Tony was kind enough to supply me with a pre-built SoftRock Lite II about a year ago. Subsequently I purchased a V9.0 kit. Then work got in the way of fun. The kit sits waiting for my attention.
      > > > > >
      > > > > > OK, I've had something on my mind while lurking in the background. Here is the idea/question: The Marine Automatic Information Syestem (AIS) operates on two channels- 161.975 Mhz (Marine VHF ch 87) and 162.025 Mhz (Marine VHF ch 88). The system transmits in digital mode GMSK. Can a SoftRock reciever (which one?) and SDR software (which package?) be set up to receive these frequencies and receive this signal mode? Any guidance or instruction will be greatly appreciated.
      > > > > >
      > > > > > At one I time modified an old scanner with a discriminator tap as discribed on this web site; http://www.discriminator.nl/index-en.html. I then input the signal to Shipplotter Software, http://www.coaa.co.uk/shipplotter.htm. The result is a PC based system to track marine vessel movements.
      > > > > >
      > > > > > For additional explanation of AIS see: http://www.bosunsmate.org/ais/
      > > > > > For free software that decodes AIS information see: http://www.navmonpc.com/ and http://www.sping.com/seaclear/
      > > > > >
      > > > > > Thanks in advance,
      > > > > > Keith
      > > > > >
      > > > >
      > > >
      > >
      >
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