HFU HF Underground
Loggings => DGPS => Topic started by: skeezix on July 13, 2017, 0313 UTC
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Another bad night. Thunderstorms rolled through in the wee hours (CDT).
Scotland is possible. Time is right and on a split channel.
Butt of Lewis Lt, Scotland
Wednesday, July 12, 2017 03:28:46
For Stevens
Wednesday, July 12, 2017 10:02:08
Wednesday, July 12, 2017 10:05:09
Wednesday, July 12, 2017 10:07:16
Wednesday, July 12, 2017 10:07:40
Wednesday, July 12, 2017 10:09:35
Wednesday, July 12, 2017 10:13:40
Wednesday, July 12, 2017 10:14:48
Wednesday, July 12, 2017 10:19:39
New Bern
Wednesday, July 12, 2017 09:00:12
Wednesday, July 12, 2017 09:03:30
Wednesday, July 12, 2017 09:06:46
Wednesday, July 12, 2017 09:09:00
Wednesday, July 12, 2017 09:13:23
Moriches
Wednesday, July 12, 2017 08:59:14
Hudson Falls
Wednesday, July 12, 2017 08:53:56
Wednesday, July 12, 2017 09:00:12
Wednesday, July 12, 2017 09:03:30
Wednesday, July 12, 2017 09:05:41
Wednesday, July 12, 2017 09:08:19
Wednesday, July 12, 2017 09:08:56
Wednesday, July 12, 2017 09:09:00
Wednesday, July 12, 2017 09:09:12
Wednesday, July 12, 2017 09:10:39
Youngstown
Wednesday, July 12, 2017 08:51:04
Wednesday, July 12, 2017 08:59:01
Wednesday, July 12, 2017 09:06:15
Wednesday, July 12, 2017 09:08:44
Wednesday, July 12, 2017 09:08:49
Wednesday, July 12, 2017 09:15:30
Wednesday, July 12, 2017 09:16:12
Wednesday, July 12, 2017 09:18:10
Wednesday, July 12, 2017 09:19:02
Count ID ref1 ref2 kHz Baud City Country Lat Lon km Deg
1 712 012 001 306.0 200 Perth, WE Australia -31.808 115.943 17,088 290
1 705 005 001 304.0 200 Cape Flattery QD Australia -14.976 145.301 13,621 282
1 611 622 623 304.0 200 Haozhi Gang China 32.017 121.717 10,743 331
1 444 684 694 295.5 100 Butt of Lewis Lt Scotland 58.526 -6.27 5,736 42
8 886 272 273 287.0 100 Fort Stevens, OR United States 46.208 -123.96 2,363 284
40 907 304 305 320.0 200 Richmond, BC Canada 49.114 -123.183 2,283 292
236 871 172 173 300.0 100 Appleton, WA United States 45.792 -121.332 2,168 282
5 771 196 197 294.0 100 New Bern, NC United States 35.181 -77.059 1,765 123
23 828 246 247 301.0 100 Angleton, TX United States 29.301 -95.484 1,756 187
1 803 006 007 293.0 100 Moriches, NY United States 40.794 -72.756 1,743 98
10 806 012 013 289.0 100 Driver, VA United States 36.963 -76.562 1,670 116
9 844 094 095 324.0 200 Hudson Falls, NY United States 43.272 -73.542 1,595 90
457 792 136 137 297.0 200 Bobo, MS United States 34.125 -90.696 1,233 168
9 839 118 119 322.0 100 Youngstown, NY United States 43.239 -78.972 1,170 95
10 918 310 311 286.0 200 Wiarton, ON Canada 44.75 -81.117 971 87
69 838 116 117 319.0 200 Detroit, MI United States 42.306 -83.103 883 106
131 836 112 113 292.0 200 Cheboygan, MI United States 45.656 -84.475 704 81
32248 777 218 219 304.0 200 Mequon, WI United States 43.202 -88.066 474 113
8045 831 102 103 298.0 100 Upper Keweenaw, MI United States 47.233 -88.628 446 55
30361 830 100 101 296.0 100 Wisconsin, Point WI United States 46.708 -92.025 219 30
(http://i.imgur.com/oUpw1je.png)
CURRENT DGPS ADVISORIES FOR 12 Jul 2017
Site Name Site Id BNM # OUTAGE MESSAGE
SCHEDULED / UNSCHEDULED OUTAGES
Level Island 891 0255-17
BROADCAST SITE IS UNUSABLE AS OF 07/12/2017 18:48 Z UNTIL FURTHER NOTICE.
Lincoln 764 0242-17
BROADCAST SITE IS UNUSABLE AS OF 06/22/2017 18:44 Z UNTIL FURTHER NOTICE.
Lincoln 764 0234-17
BROADCAST SITE WILL BE UNUSABLE FROM 07/13/2017 16:00 Z TO 07/13/2017 18:00 Z.
Annapolis 847 0254-17
BROADCAST SITE IS UNUSABLE AS OF 07/12/2017 13:02 Z UNTIL FURTHER NOTICE.
Tampa (Macdill) 827 0227-17
BROADCAST SITE STATUS IS UNCONFIRMED DUE TO NETWORK OUTAGE AS OF 06/13/2017 08:20 Z UNTIL FURTHER NOTICE.
GENERAL INFORMATION
Reedy Point 870 0204-17
DGPS BROADCAST SITE WILL PERMANENTLY CEASE BROADCASTING CORRECTIONS ON 31 JULY 2017 AT 1400Z
Note: The Louisville, KY DGPS Beacon (290 KHZ, Site ID 869) was terminated as of 1200Z (0800 EDT) May 31, 2017.
The Millers Ferry, AL (320 KHz, Site ID 865), Rock Island, IL (311 KHz, Site ID 863), and St. Paul, MN (317KHz, Site ID 864) DGPS beacon signals were terminated as of 1200Z (0800 EDT) June 30, 2017.
AFE822x v2.0 SDR with 43' Wellbrook ALA100LN loop oriented E-W
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Another bad night. Thunderstorms rolled through in the wee hours (CDT).
Scotland is possible. Time is right and on a split channel.
Yeah, tough to tell with just one log.
Annapolis 847 0254-17
BROADCAST SITE IS UNUSABLE AS OF 07/12/2017 13:02 Z UNTIL FURTHER NOTICE.
Annapolis is coming in loud and clear here. Whether the DGPS data is usable or not is another question. I've been researching magnetic loop antennas again, to see if I can possibly null out the local pests like Annapolis. I can probably get rid of the ground wave, but might still have to deal with a sky wave, especially at night?
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Annapolis is coming in loud and clear here. Whether the DGPS data is usable or not is another question. I've been researching magnetic loop antennas again, to see if I can possibly null out the local pests like Annapolis. I can probably get rid of the ground wave, but might still have to deal with a sky wave, especially at night?
Not sure how to get rid of both ground wave & sky wave, since they'd have different phases & different angles.
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In investigating the nulling ability of my NDB loop - which is currently a 7.5" ferrite rod on a rotator - I did a study related to obtaining the best possible null on daytime NDBs within a few hundred km of me, all of which would be via presumed groundwave propagation. With the ferrite rod in the horizontal position, symmetrical nulls were obtained at azimuths off the ends of the rods as expected. These nulls were typically about 25 dB in depth best as I could figger. I was aware that at MW and LF at least, the wavefront should experience some tilt do to the imperfect ground plane over which it is propagating, and that nulls could possibly be deepened by tilting the rod. I began to tilt the rod off of the horizontal axis to see if I could deepen the null somewhat, and I found that for the vast majority of daytime NDBs, the null could be deepened - in general - to about 30 dB. To do this, I had to tilt the rod to an angle of about 5 -10 degrees above horizontal.
I extended this endeavor to find the typical tilt required to obtain the best null on presumed single hop NDBs at night, and if IIRC, I examined a number of reliable NDBs in QC, ON, SK, GA, and TX. I expected to find the presumed sky-wave signals arriving from much higher angles than for groundwave. Instead, I found that the deepest nulls tended to be found with the rod tilted in the range of 10 - 15 degrees above horizontal. Not all that much difference noted in arrival angle for groundwave and skywave. At least for skywave at ranges of 1500 km and better...
A lot of the mechanism of LW propagation still remains a mystery to me but I have found a couple of things that have helped me.
1) I am for the most part a visual DXer (CW in the SDR ). Being able to depress a strong NDB by even 10-15 dB in a pileup is usually enough to help ID a weaker NDB on the same offset. It is rare that I waste the time to try to nuke an interfering beacon completely; just knocking it down a bit usually helps a lot. I don't know know how this will translate to DGPS performance.
2) I do not worry about the few extra dB nulling ability that can be had by tilting the loop off of the horizontal axis. In a quick opening, there isn't that much time to mess with the loop positioning in 2 axes. The untilted loop has given adequate nulling performance.
3) There are, though, a couple of scenarios in which care and planning are very helpful when using the directional properties of a loop. This last season I was able to log an A1A NDB in Cape Verde through a pair of A2A beacons in ON and MN by judiciously nulling their carriers a/r. It took 3 weeks of effort (and some code) to get the log, but I doubt I could have done this without the loop.
4) "The worst antenna that you can build is the one that you over-think and do not actually build."
Of course, YMMV, but that's when we go back to the drawing board...
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Thanks for the real world data, jFarley. It seems that ignoring the arrival angle may be indeed be good enough, at least for first efforts. In the case of DGPS, since we typically run for hours at a time, I could always experiment with trying to more carefully null out the offending pest, and see if there's any difference in decoding. My plan is to pick one frequency with a desirable target, say Alaska or Hawaii, and null out the station that generally eliminates any chance of hearing it.
Did you happen to write up anything on this 7.5" ferrite rod antenna? I seem to remember you mentioning it before. I have several long ferrite rods in the workshop (somewhere...).
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I have, and if you go to the Equipment forum and search "ferrite rod" a couple of topics will pop up. This will partially detail what I have been using.
That being said, a couple of notes about ferrite loops for LW NDBs...
In the past season, I have used 2 antennas for NDB DXing. For wideband unattended SDR Recording, I have been using an active whip antenna similar to the DX Engineering Z1501, now discontinued. I have found this to be quite sensitive for such a compact antenna and have been able to get logs from HI to GRL and down to CHL at 8200 km. While I primarily used this for unattended recording, it being wideband makes it very simple to use for active scanning during live sessions. It is non-directional.
The main goto antenna for live DXing was the ferrite rod loop. Being very directional, it was easy to exploit its azimuthal discrimination properties for flushing out weak signals. It is also a bit more sensitive than the active whip; it seemed to add up to 200 km in range to logs during daytime groundwave reception. The directional properties were very useful for both signal discrimination AND local QRN suppression.
A ferrite rod loop has a serious flaw which will show up in unattended long term reception. The ferrite R61 required for best Q at LW frequencies has a nasty temp coefficient which will result in the resonant frequency of the loop shifting upwards as the temperature drops during the overnight hours. For typical temperature excursions overnite, the resonant freq may shift upwards by 5 kHz or more for a given capacitance. This will probably be unacceptable for targeted reception at a particular frequency as you seem to desire for DGPS.
I have tried to get a handle on this via the software I use to control the loop. Prior versions of the software had the ability to let the user create multiple Calibration Curves in a Calibration Table. Each curve defines the resonant frequency of the loop versus the number of steps of the stepper motor drive train (there are about 4600 steps to fully traverse the tuning capacitor) and is most accurate at the temperature at which the loop was calibrated. As the season progressed - and the temps dropped - I would create new Calibration Tables, and prior to use, I would select the appropriate curve for the current ambient temperature. This helped a lot, but tuning errors of a few kHz were still seen.
Last season, I added a temp sensor to the loop head which could be polled by the controller software, and created new Calibration Curves as the season progressed. When the program demanded a resonant frequency for the ferrite loop, the software would compute a stepper position for the currently polled temperature using a pair of bounding Calibration Curves in the table if this was possible. I was able to decrease tuning errors to approximately 1-2 kHz, but given the fact that this tank was running at a fully loaded Q of better than 250 (necessary for a good Effective Height), loss of sensitivity due to mistuning was still unacceptable.
My bottom line here is that the compact ferrite loop has proven to be an excellent performer for live DXing, a scenario in which the user can always tweak the resonant frequency for peak reception. It has some limited use for overnight recording, but here I have to kind of guess at how the temp will drop in the wee hours and set its tuning so that resonance will slide through resonance at the time I would expect to hear a particular NDB.
My code has the ability to scan through a prepared list of particular NDBs, and tune the loop (and spin the rotator to the NDB az); I have not really been able to exploit this all that successfully so far. I have come to the conclusion that I am not going to get there with ferrite. I am in the process of building a new loop - an air core loop - with increased sensitivity and better temperature stability due to the absence of ferrite. Here's a pic of the work in progress:
(http://i1049.photobucket.com/albums/s387/jFarley44/IMG_0780_zpsfp94smkg.jpg) (http://s1049.photobucket.com/user/jFarley44/media/IMG_0780_zpsfp94smkg.jpg.html)
This seems to be giving promising results while undergoing testing down in the basement.
I hope to have this fully deployed in a couple of weeks, and will post details then.
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Oops; a couple of notes about the image.
The lower box houses a homebrew rotator. It is programmed via a filtered and scaled PWM output pin in the main loop interface processor. It will position the loop at any az between 0 and 360 degrees, with 70 degrees of overtravel at both ends of the range. Positioning accuracy is better than 2 degrees.
The upper box houses the interface processor, tuning mechanism, and variable capacitor.
The loop per se is about 28" across, and has 30 turns of 20 AWG wire, with a 2 turn pickup loop. This loop does not appear to need an amplifier. I have observed Qs of around 120 - 150, but I may knock this down a bit when I get it outside.
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I have, and if you go to the Equipment forum and search "ferrite rod" a couple of topics will pop up. This will partially detail what I have been using.
Thanks, I found them. Now to (re?) digest them, and decide what I want to try to do ;D