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7963Re: [wsjtgroup] 6m vs. 2m

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  • Bill VanAlstyne W5WVO
    Nov 30, 2010
      Ben’s response on m/s below 30 MHz is interesting. I would expect that path lengths would be comparatively shorter there than at 50 MHz and above. I think any experimentation on 10 meters would be quite interesting.
      Regarding JTMS – good question. Joe K1JT included JTMS in WSJT9 so experimentation could continue by those who wanted to do it. I know that nobody (including Joe) has been pushing this, and I think it is kind of languishing. In the formal testing we did prior to the WSJT9 beta release, JTMS did not show itself to be significantly better than the improved WSJT9 version of FSK441. Joe felt that in order to justify replacing a successful m/s mode (FSK441) with a new, incompatible mode (JTMS), JTMS would have to prove itself to provide a really significant improvement over FSK441. Since this didn’t happen (and we have statistically significant data that demonstrates that fact), the newly enhanced FSK441 (which is fully backward-compatible to the FSK441 version in WSJT7) was set up as the main m/s mode in the new release.
      Anybody that wants to continue testing with JTMS, however, is encouraged to do so. If you do any testing, it would be most useful to create a scientifically rigorous testing model whose output can be statistically analyzed against FSK441. One suggestion for a test model is as follows:
      (a) Two stations about 1,000 miles apart, each with two identical transceivers, would be linked to independently running parallel instances of WSJT9. The ideal distance between the stations should be determined such that a large number of pings, but no tropo or sporadic-E, could be expected on the band of choice. The entire test protocol could be run on both 6 meters and on 2 meters at different times, either by the same stations or by different stations appropriately configured as described here.
      (b) Transmissions would be made by one of the stations, reception (and recording through WSJT) would be made by the other station. Having just one station do the transmitting and one do the receiving cancels out any effect of differences in local noise level between two different stations. If the transmitting rig can take the duty cycle, WSJT can be optionally set up to transmit during both 1st and 2nd sequences for testing purposes. I know the Elecraft K3 can do this, for example, because I did it for an hour while monitoring the PA deck temperature, which stayed within acceptable limits. Otherwise, less robust transmitters can be set up to transmit either 1st or 2nd sequence, with the alternate time sequence being dead space whose only purpose would be to allow the transmitters to cool.
      (c) One transmitting transceiver would run JTMS, the other FSK441. Each setup would transmit the same beacon message “[callsign]/B [6-character grid]” on both modes at the same time. Each transceiver, whether receiving or transmitting,  would be connected to the same antenna with appropriate combiners where necessary. Using separate antennas for each transmitter and/or receiver would introduce unacceptable levels of variation.
      (d) If an Elecraft K3 transceiver with dual receivers is used on the receiving end, then only one transceiver would be required at that end, as the receivers in the K3 are completely identical and phase-locked, and they would be listening to the same time period and the same pings to a high degree of precision. The K3’s tight IF roofing filter allows use of frequencies 5 kHz apart without receive degradation even in the presence of extremely strong signals. (I’ve verified this using a very strong [but clean] local signal for test purposes. With the K3, I found I was actually able to decode weak pings on a frequency only 3 kHz from the strong signal. Using a Kenwood TS-2000, by comparison, I found I could not get within 20 kHz of the same strong signal and decode anything at all.) The K3 Line Out stereo output jack carries the mono audio output of each receiver. A splitter cable would be required to route the audio to two identical sound cards linked to two instances of WSJT9.
      As can be intuited, the point of this test architecture is to equalize all variables except the software being used for encoding and decoding. Everything else – transmitters, receivers, antennas, sound cards, and most important, the time sequences and their unique individual meteor pings – would be the same for both modes. We could then see how each mode performs on the same meteor ping, as well as having macro-level data for the whole test period (at least an hour, two hours if 50% duty cycle) that can be analyzed using standard statistical methods.
      Unfortunately, my K3 is not yet equipped with the KRX3 second receiver, and I only have one K3. I would recommend a K3/KRX3 for the receiving end of the test because of its phase-locked dual-receive capability and high dynamic range. I would want to keep the two test frequencies as close together as possible to minimize frequency-related differences in propagation. (Unfortunately, such differences cannot be entirely eliminated, since it is impossible in practical terms to use the same frequency at the same time for two different transmissions from the same station and antenna along the same path.)
      On the transmitting end, it’s not as important to have any particular radio used, as long as they are both the same and set up in exactly the same way.
      If anybody has equipment as described above and would like to take part in such an experiment, please let me know and I’ll try to coordinate it. Equipment pooling (borrowing) might be necessary.
      If there is insufficient interest in doing this kind of rigorous testing, then JTMS could end up being abandoned. “Could”, not “will”. That is ultimately up to Joe.
      Bill W5WVO
      From: Sebastian
      Sent: Wednesday, December 01, 2010 01:35
      Subject: Re: [wsjtgroup] 6m vs 2m

      Great information Bill!

      Something that I have wondered about meteor scatter is what you mentioned about 2 meters vs 6 meters. I do agree that it is 'easier' to make meteor scatter contacts on 6 meters than on 2 meters.

      However, why don't we also attempt meteor scatter on 10 meters? At this time, 10 meters is also pretty much dead, are there any technical reasons why 10 meters isn't used for meteor scatter?

      Also, has there been any testing done with JTMS the 'experimental' mode in v9?

      73 de Sebastian, W4AS

      > One last word on 2 meters vs 6 meters. It's
      important to understand that
      > meteor scatter, like all modes of
      ionospheric propagation, depends on the
      > relationship between ionization
      intensity and wavelength. The shorter the
      > wavelength, the more intense
      the ionization must be in order to refract or
      > reflect radio waves.
      Meteors can produce extremely intense ionization, in
      > many cases intense
      enough to reflect 2-meter radio waves back to earth. The
      > problem is,
      this high ionization intensity degrades quickly to levels that
      > WILL NOT
      support propagation at 2 meters, but that WILL support propagation
      > at 6
      meters. This is why 2-meter meteor pings are (on average) so much
      shorter than 6-meter pings, and why (again, on average) you hear fewer pings
      > on 2 meters overall. Meteor scatter is easiest to work on 6 meters,
      > to work on 2 meters, and extremely difficult to work above 2
      meters. The
      > shorter the wavelength, the weaker and shorter is the
      > reflection, and the more antenna gain and power you need
      to make up for
      > that.
      > Now, if I could just raise MY
      antenna system another 20 or 30 feet, I might
      > be able to work Curt
      (1,340 miles). Many tries, no success as yet. :-)
      > Bill
      > DM65qh

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