[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [IRCA] [ultralightdx] Oregon Cliff (Rockwork 4) Ultralight DU's for 7-17...Wild!



Thanks for your thoughtful analysis Mark. I might add that the advantage of live DXing of being able to phase antennas may also becoming overtaken by technology.

The AFEDRI Dual Channel SDR (AFE822x SDR-Net) allows diversity reception (two SDRs set to the same center frequency and same bandwidth, coherently synchronized), and those two channels may be combined in software to be phased with each other, assuming each channel is fed with a separate antenna. The same thing could presumably done with recordings after the fact. The company provides only hardware; they say that the software to do this includes HDSDR + SDR_Control (SDR-Control is provided by Afedri), PowerSDR_mrx and Linrad, though I have no personal experience with any of this. Someday... (check http://afedri-sdr.com/index.php/ordering-information for details)

The X2 option for RFSpace's NetSDR provides similar functionality, but doesn't seem to be widely available. I believe Gnuradio supports it, but I don't know whether phasing the two channels is addressed, or whether that will be the user's contribution to the mix. Simon Brown is (perhaps) working towards providing phasing capability for the X2 in his SDR-Console, but he seems to have a lot on his plate.

A very few radio stations now provide online audio archives of their recent broadcasts, and I've ID'd Radio Sport from New Zealand as well as Taiwan Fisheries broadcasts using this method and recorded SDR files. Now, THAT'S DXer friendly.

best wishes,

Nick



I am a firm believer in "both kinds of DX": live and after-the-fact capture analysis.

Whenever possible you should use a mix of the old-school and new-school methods.

Advantages of live DXing:
* You can use webstream, remote-receiver, and shortwave parallels.
* You can use high-Q tuned antennas rather than broadband. In two situations this is the way to go. One would be when you have very weak signal conditions and not enough space for a broadband antenna of sufficient sensitivity. The other would be when you are in an urban situation where any broadband antenna of sufficient gain to hear DX is going to present locals at such high levels that the receiver will create spurious signals. * You can use a phasing unit to target the specific "pest" affecting the frequency on which you're actively DXing at the time. It takes a very good antenna system (e.g. physically-large array) to deliver much better than a 25 dB null in a broadband sense. But narrow bandwidth nulls of better than 40 dB are easily had with a Quantum Phaser (or similar) and a pair of different-pick-up antennas (e.g. loop vs. whip, loops at right angle), or with two similar-pick-up antennas spaced at least 50m / 164 ft. apart.

Advantage of after-the-fact capture analysis (Perseus, Excalibur, etc.)
* During a "hot" opening, a single top-of-hour capture gets you a whole medium-wave band worth of ID's. This would take much more time to accomplish with live DX sessions. Optimum conditions may have gone away by the time you're even halfway through the band doing it live. At US/Canada East Coast beach sites around local sunset, two top-of-hour captures (+/- 3 min.) can get you an amazing amount of choice DX. Same is true for West Coast around local dawn. And, if it's auroral, admittedly a fairly rare occurrence in recent years, you'll be busy all night on tops-of-hour as well as on the half-hours for the Venezuelans. * You can repeatedly replay a given target, trying AM, synchro AM, USB, and LSB modes; various IF bandwidths; notch filters et al. On live DXing you have less time to figure out the optimum receiver settings.

Since you typically won't have webstreams and shortwave to assist you on after-the-fact analysis of medium wave capture files, use the periods BETWEEN the tops-of-hour (:00+/-3) and bottoms-of-hour (:30+/-2) captures to do live DX, making sure to avail yourself of things that are only feasible when DXing the old-school way. You can still have TotalRecorder (or your other favorite audio recording tool) running during the live DX activity since you won't want proof of a breathtakingly rare catch passing you by. What you find out during the between-captures live DX will feed into antenna-aiming etc. decisions you may want to make before the next capture session.


_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://montreal.kotalampi.com/mailman/listinfo/irca

Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers

For more information: http://www.ircaonline.org

To Post a message: irca@xxxxxxxxxxxxxxxx