Mobile antennas for NVIS at 80 meters

Discussion in 'Mobile Radio Systems' started by N0IOP, Oct 9, 2019.

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  1. WA4SIX

    WA4SIX Ham Member QRZ Page

    Please don't argue with Alan. He is right all of the time.

    AK5B likes this.
  2. KN4DQE

    KN4DQE Ham Member QRZ Page

    Excellent video about military NVIS applications.....including mobile.
  3. KN4DQE

    KN4DQE Ham Member QRZ Page

    And a follow up - which is also good. Check about 25 min for mobile, taken directly from the military.
  4. W4GO

    W4GO Ham Member QRZ Page

    This thread is quite a shouting match. Maybe citing a specific but representative case would be of value.

    I browsed through the comments from this year's VA QSO Party on looking for remarks about varying signal strength that I could corroborate with my own log and recollections.

    In his comments, Dave, WN4AFP, operating as fixed QRP in Greenville, SC, describes working my 200 W mobile station. (Dave is an experienced contester whom I have worked many times on contest roves.) I’ve excerpted the relevant part of his comment with my notes added in brackets:

    "... However, I ran into W4GO/m, Matt and I had to follow him around on Sunday [17 March, 2019] afternoon on 80m if I could. After getting home from church, I saw the spotter page and everyone was running on 80m. This was going to be a challenging finish. After calling Matt for 2 hours without a response, he finally heard me [I logged this QSO at 17:59 UTC] and I worked him in 16 counties [total for both Sat. and Sun.]. 80m finally opened up for the last few hours and it was a big boost to my score. ..."

    Piecing together the timeline from Dave's account and my own log, and also incorporating distance measurements from Google Earth, we have this sequence of events:
    • At about 11:59 EDT = 15:59 UTC, WN4AFP first attempted to work me on 80 m SSB. I was in Lynchburg, VA, 251 mi from WN4AFP. Dave continued to call, with no response, over the next two hours. I was exclusively “running” (i.e., calling CQ) during this contest, as opposed to “searching-and-pouncing.” Dave evidently copied my 200 W transmissions, but I heard no trace of his QRP (5 W or less) signal.
    • During this two-hour period, I traversed five counties and logged 165 QSOs, all on 80 m SSB. Most QSOs were with VA stations, but MD, DE, NC, PA, NJ, NY and OH were also logged. I recall that there were several quiet spells with few callers and low noise floor during which Dave likely could have gotten through with good propagation.
    • Most of the stations that I worked in this period submitted logs in the low (5 W to 100 W) or high (> 100 W) category. However N4RP and KF4KKF were two QRP stations that I worked, with difficulty, in this two-hour span. They were both in Northern VA, approximately 100 mi to 120 mi from this part of my route.
    • At 13:59 EDT = 17:59 UTC, I heard and worked WN4AFP for the first time that day. I recall that I copied him with extreme difficulty. My location was in Prince Edward County (PRE), 273 mi from WN4AFP.
    • About 16:00 EDT = 20:00 UTC: Interpreting Dave's phrase "last few hours" to mean roughly four hours from the contest end, he observed a substantial improvement in 80 m conditions to VA starting around this time, perhaps give or take an hour.
    • Following our first QSO of the day in PRE, I activated 11 more nearby counties. WN4AFP worked me in four of those, each time on 80 m SSB, with our last QSO at 18:19 EDT = 22:19 UTC, in my last county of the contest. Our distance varied from 273 to 327 mi over this part of my route. Dave was never particularly loud, but he at least managed to be heard over varying degrees of local RFI and competing callers, which is significant for a QRP station.
    In short, this is a corroborated account of a period of at least two hours, from noon (possibly beginning earlier) to 14:00 local time, in which stronger stations within about a 400 mi radius were heard, but at least one weaker station was not. After this higher-loss period, the weaker station was workable from 14:00 to 18:19 local time (and possibly later).

    While I don’t have documented S-meter readings, the stations that remained workable during the above fade-out were generally received with weaker signals than later in the afternoon and early evening. For a station at ca. 300 mi, a swing between roughly S7 to S9+10 dB on my rig’s meter might have been typical (this varies quite a bit from one station to another, however).

    The above is a fairly mild example of the signal deterioration that I see on regional 80 m signals when mobile. Sometimes conditions degrade more severely.

    These are just my observations -- and in the above example, those of WN4AFP as well. Draw your own conclusions.

    (Note the March date of the Virginia QSO Party, which comprises most of my daytime 80 m mobile activity. My experience roving in the Maryland-DC QSO Party in August is that summer brings deeper fade-outs during the day, compounded by higher noise. Also, one should assume different behavior from 80 m propagation during solar maximum. The foregoing observations come from the current, deep solar minimum.)
    KS1G and KX4O like this.
  5. KX4O

    KX4O Ham Member QRZ Page

    A lot of us in the MF/HF antenna and propagation biz have taken a renewed interest in this thread. Can you please provide the primary source for your statement above?
  6. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    To the original poster, if you aren't aware of who K0BG is, go read his site, it's a compendium of mobile HF operating. Amazing collection of information. The Cebik of mobile operations IMO.
  7. KX4O

    KX4O Ham Member QRZ Page

    Oh yes... we are well aware of his site and his assumptions on NVIS.

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