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Thread: DX: What's Possible? Primer for new DXers

  1. #1
    Join Date
    Jul 2008
    Location
    Middle Tennessee
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    Default DX: What's Possible? Primer for new DXers

    Being the most common kind of propagation, if you understand the characteristics of tropo everything else will fall in place.

    Tropo typically builds slowly, can last a long time, and provides steady-ish signals. Fades are more consistent, shallow (ie the signal doesn't just go from full strength to completely dead in a very short period of time), and often consistent (ie signal for 5 seconds, fade for 2 seconds, repeat). Also, tropo does not form instantly, it typically builds over minutes or hours. Ducts are typically well known, with signals building in strength and lengthening in distance before the band is completely immersed in tropo. It is also typically geographically sensitive, limited in distance by terrain and weather characteristics, so I can be completely sure if I identify a station in the mountains of Colorado that faded up suddenly, it cannot possibly be tropo.

    E-Skip is characterized by strong, suddenly appearing signals in a more concentrated area typically 700-1200 miles distant. It is not geographically sensitive and can "pick" any area on the compass to reflect. Fades are deep, so if you are receiving that station from Colorado at full local-quality, and all of the sudden it drops to nothing and comes right back after 1 second, all the context clues indicate you are experiencing E Skip. In my case, I often hear E Skip into areas that are possible by tropo, for example, Louisiana in Saturday's opening. I knew it was not tropo because there was no indication of tropo being active prior to the opening, it was in the middle of the day (not the time when tropo often builds) and the fading and signal characteristics screamed E-Skip (the signals appeared suddenly).

    I hope this helps,
    Last edited by Mike-CT; 12-10-2013 at 10:39 AM.
    Bryce Foster - K4NBF (formerly KG6VSW)
    Hermitage, TN EM66
    www.k4nbf.com

    Tuners:
    Elad FDM-S2 SDR
    Sony XDR-F1HD

    Antennas:
    Innovanntenna 10 Element FM beam (primary) @35 ft
    Winegard HD-6065 (phase) @25 ft with Bolin Phase Box
    Tennadyne T2 V/UHF log periodic @ 30 ft

  2. #2
    Join Date
    Jul 2005
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    Pleasant View, TN EM66
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    Default DX: what's possible?

    As we're outside the peak DX season it might be a good time to reiterate what's plausible DX and what isn't. I know we have quite a few long-time members for which this will be old hat, but we also have quite a few newer members who may not know.

    - There are two common types of DX:
    - Sporadic-E
    - Tropospheric

    - Sporadic-E:
    Most common from late spring through mid-summer, with a second weaker peak around Christmas.
    Most common in mid- to late morning, with a second peak around 4pm local time.
    However, it can happen at any time of day and/or year.

    ALWAYS starts on lower frequencies and moves up. CB "skip talk" first, then TV RF channel 2, then 88MHz FM, then 108MHz FM.
    Sporadic-E only rarely affects TV channels above 6. (I've been DXing for over 20 years and have only seen channel 7 skip *once*)
    The highest frequency ever affected is 222MHz. TV DX on UHF channels **is not** sporadic-E. TV DX on channels 7-13 is almost certainly not sporadic-E.

    Sporadic-E has a "skip zone". Distances of *less than* about 700 miles are rare. Distances of less than 500 miles are nearly impossible.
    There is also a maximum distance, commonly about 1,300 miles. "Double-hop" openings are possible which can extend this to 2,500 miles or more. However, these are also very rare.

    - Tropospheric:
    Most common during warm months, rare when it's cold.
    Most common around sunrise; weakest during the day.

    Can and often does affect higher frequencies. UHF tropospheric DX is common.
    UHF TV DX *is* tropospheric. VHF channels 7-13 DX is almost certainly tropospheric.

    There is no skip zone -- no minimum distance. DX of *less* than 500 miles is almost certainly tropospheric.
    Distances of more than 500 miles are rare. Most of us will never see any tropospheric DX of more than 700 miles.

    =====

    To recap...

    - FM radio DX of more than 1,300 miles is VERY rare.
    - TV DX of more than 500 miles is VERY rare.
    - If very long haul DX does happen it is VERY likely someone else will notice it.
    - The broadcasting industry changes quickly. Don't assume Radio-Locator is right. They may not be.
    Doug Smith W9WI
    Pleasant View, TN EM66
    http://www.w9wi.com

  3. #3
    Join Date
    Dec 2010
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    Poughkeepsie, NY
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    Default

    Doug and Danny... You've provided a very valuable and concise summary. I would say that the 1300 miles max skip distance is kind of conservative. Geometrically, 1500 miles provides a pretty good upper limit. On FM, 38 (4%) of my E-skip loggings are over 1400 miles (of which 3 or 4 might be double hop), and 11% are above 1300 miles. On DTV, 2 out of 15 (13%) are over 1300 miles, and 1 is less than 500 miles. Low VHF TV lends itself to shorter skip distances than FM. The maximum distance assumes a clear shot to the horizon... any horizon blockage is going to shorten your maximum distance.

    Now if we can only get some DX (skip or tropo!) Real dry spell going here.
    Chris - Poughkeepsie, NY
    DTV DXer since April 2009
    DTV DX screenshots at: http://www.flickr.com/photos/dtvdxer/sets
    DTV DX Videos at: http://www.youtube.com/user/dtvdxer

  4. #4
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    Maybe we should also add that DTV E-skip is not easy. A reception could consist of just a few seconds of decode, which can easily be missed if you are not focused on it. Also if your receiving location is not properly located in relation to the other few DTV lowband stations out there, you may never even see any DTV TV signals by E skip because the distances involved wouldn't be right. DTV Es with a dipole for an antenna? Very unlikely.

    * Nobody yet has received double hop lowband (Ch 2-6) DTV TV Es.
    * Nobody yet has received single hop highband TV (Ch 7-13) DTV Es.
    Mike B.
    Enfield, CT
    -72 30' W/41 59' N
    FN31RX

    Online since 1999 and still going at
    mikesdx.com

    Archives: The Original Mike's TV/FM Page with Tuner Mods and Lots of Old Stuff

  5. #5
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    Keep the ideas coming; I think at some point we should assemble them into a "meta-post".

    I think we want to keep it brief. Yes, 1,600-mile Es is *possible* but the chances a new DXer will encounter it are VERY slim. Yes, Boston<=>Miami DTV tropo is *possible* but if you're not Roy you probably won't see it .
    Doug Smith W9WI
    Pleasant View, TN EM66
    http://www.w9wi.com

  6. #6
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    Mar 2006
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    My own experience with the diurnal occurrence of Es is very much like the graph that Pat has posted. I find Summer Es is most common around 1500-1900 local solar time (to most of us in the US, about 4:30-8:30 PM), with Es not rare from 0930-1500, and again from 1900-2030.
    When it's summer, and you're thinking dinner, you should be thinking skip.

    One thing I and other DXers have noticed is that Es that is either off-hours (2300-0700 local time) or off season (September to November or February to April) is far more likely to be from the far north (e.g. Canada) than typical Es.

    What is very true is that the distribution can vary greatly from year-to-year (some years there is no morning Es, others, mostly morning Es).

    DTV Es with a dipole should be quite possible if there are lowband DTVs in the "sweet circle" (1400-2100 km DX) and the dipole is removed from sources of VHF RFI (e.g., outdoors in a park).

    One barrier to DTV Es from greater than 2400 km is that the propagation paths that would support such a great distance often incur more multipath and fading - both of which will thwart a DTV decode. VHF high DTV Es, on the other hand, is only unprecedented because of the sheer rarity of Es above 174 MHz itself. I predict that when there is a good Es opening on those frequencies, more DXers will log a highband DTV than would have logged an analog TV by highband Es in the past - thanks to PSIP.

    Es from distances less than 1300 km are far more common on CB, 10m, VHF-low mobile and 6m than they are on TV or FM, not only because of the increased bending with lower frequency, but because the simpler antennas used in these services send more RF (signal) above the horizon and into the ionosphere than the antennas used by TV and FM broadcasters, who focus the RF at the horizon for maximum local coverage.

    There is a distinct difference in the behavior of Continental tropospheric propagation (i.e., over land) and Marine tropospheric propagation (i.e., over water, which includes large freshwater lakes, as well as seas). Continental tropo is best in the late summer, and rare in the afternoon. It tends to improve gradually after sunset, and is best from midnight to about 2 hours after sunrise, but may continue into the morning (I have heard many reports from DXers of very long DX around noon, or 1030 solar time, just before the tropo dies out). Both off-hour and off-season Continental tropo are far more common than off-hour/season Es or Marine tropo.

    Continental tropo is hampered by local terrain far more than Es.

    Continental tropo often (but not always) affects lowband TV and FM broadcast, as well as highband and UHF.

    Marine tropo is best when warm, humid air gets pushed over cool water. It is best in the spring (Gulf of Mexico) or the late spring and early summer (Atlantic Ocean and Great Lakes), and is best from afternoon to mid-evening (1200-2100 local solar time). It can often be exploited with very modest antennas very close to the surface.

    Under usual Marine tropo conditions, conditions deteriorate significantly with any distance from the beach. I found tropo DX to be far better on the Lake Michigan beach at Manistique than it was at a cabin on Indian Lake (only about 5km inland over flat terrain from Lake Michigan)

    In my own observations, Tropo over Lake Michigan had little or no effect on lowband VHF.

    While it may be noted that Marine and Continental tropo usually occur at different times, co-incidence of the two modes has happened on occasion. Fernando Garcia in Nuevo Leon, Jim Pizzi in New Mexico, Pat Dyer in Texas and John Combs on Florida are DXers who were successful with very-long-haul "hybrid" tropo DX.

    All tropo is severely hampered, if not obliterated, by any significant wind.
    Comparing Sporadic-E skip to skip on the AM and shortwave bands is like comparing apples and oranges.

    Comparing tropo to skip is like comparing apples and bacon cheeseburgers.

  7. #7
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    I am always fascinated by E skip openings that break out of nowhere at 3 or 4 AM. They are very rare but I've experienced some when in years past, I would leave the radio on at low volume all night while sleeping in an attempt to hear meteor skip. I've been jarred awake on more than one occasion by those rogue Es openings. Also on another subject, any RF noise on low band VHF will definitely thwart your efforts to get any digital TV stations. I know because I have had no luck with digital Es and I have a lot of noise on VHF from the neighbor's computers and other devices.

  8. #8
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    Guys,

    I found Bryce's post and moved it over to this thread.

    Since threads seem to get cluttered with posts that don't directly relate to it, I've removed a bunch of posts, including mine, to try to keep it on topic. I hope nobody minds.

    I don't know how Bryce's post ended up first. vBulletin has to be responsible for that.

    Once we have all the info we need, I'll close the thread.
    Mike B.
    Enfield, CT
    -72 30' W/41 59' N
    FN31RX

    Online since 1999 and still going at
    mikesdx.com

    Archives: The Original Mike's TV/FM Page with Tuner Mods and Lots of Old Stuff

  9. #9
    pjdyer Guest

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    See May 28. 1990 in this http://www.qsl.net/wa5iyx/fmdx-ra.htm for some wee-hour FM Es samples.

    73, Pat - WA5IYX

  10. #10
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    Maybe that one can be re-posted.
    Mike B.
    Enfield, CT
    -72 30' W/41 59' N
    FN31RX

    Online since 1999 and still going at
    mikesdx.com

    Archives: The Original Mike's TV/FM Page with Tuner Mods and Lots of Old Stuff

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