Messages

481

Equipment / Re: This might be the start of something big

« on: August 15, 2017, 1206 UTC »

The response curves, especially the bottom one, seem to indicate that your loop is operating at a significantly high Q.  I speculated, based on some previous attempts here, that the loaded Q down at LF might be low.  I must have been using a bum amp or screwed up something else, because the Q suggested by the curves is definitely not low.  It is significantly higher, and I came up with values similar to what you calculated, which blows me away...

The shape of the response is very similar to what I have routinely seen with the ferrite loop I use, which routinely measures out at 200-300 Q midband LF.  If true, this suggests a very high effective height for your loop.

I also generally note the sharper response on the low side of the peak.

482

Equipment / Re: This might be the start of something big

« on: August 14, 2017, 1406 UTC »

If you could actually measure the Q from a screenshot, that would be cool and helpful.

Measuring the Q of a resonant loop which is operational and under power can be problematic.  I use this technique which seems to jive with both theory and alternative measurements with a scope and signal genny.

I tune the loop to a vacant frequency F, and observe the resonant peak in the SDR's FFT window, scaling both the amplitude and frequency display to get the best rendering of the peak.  Generally, you are seeing the noise peak up to expose the resonance curve.  I like to have this peak at 20 dBm higher than the noise outside of the resonance range.  This may not be possible for lower Q loops.  If necessary, I couple in a wideband noise generator to give me the desired peak height. 

I measure the bandwidths of the response at the following power points around the frequency F:

BW3 at -3 dBm if possible - this is usually tricky and error prone for higher Q loops
BW7 at -7 dBm
BW12 at -12 dBm
BW18 at -18 dBm.

Given these, apparent Q can be computed from each measurement:

Q= F / BW3
Q = 2F / BW7
Q = 4F / BW12
Q = 8F / BW18

I generally take the loop Q to be an average of 3 or 4 measurements.  This method has worked for me well while evaluating loop designs.

483

Equipment / Re: This might be the start of something big

« on: August 14, 2017, 1341 UTC »

Just stuck my head in the door of the Electromagnetics Lounge, but the coffee wasn't ready yet.  Will be back...

In the meantime, the most important thing I look for in a loop design is the Effective Height, which is a measure of its signal collecting ability.  This is 2 * PI * N * A * Q / lambda, and if I have the following correct:

N = 9T
A ~ 9 M^2 For a loop with 10 foot sides
lambda = 1000M for 300 kHZ

then the He for the loop would be approximately 0.5 * Q Meters.

Knowing what the actual Q is would give a rough idea of what to expect from this loop in resonant mode.

I see that you are using the amp/supply from the HF loop.  This uses back to back tuning diodes such as NTE618.  These devices, IIRC, have a guaranteed minimum Q of ~ 100 at 1000 kHz.  In a tuning diode, the Q (at a given bias) is generally a close to linear  function of frequency.  My recollections of trying this type of tuning with the ferrite loop seemed to validate this, and that the diode Qs seemd to be significantly lower at NDB frequencies.  Even so, if the diode Qs were around 30, the the He would compute out to be around 15M, which would not be too shabby.

If you could actually measure the Q from a screenshot, that would be cool and helpful.

484

Equipment / Re: Some random things I've observed about QRM/etc. by sitting outside

« on: August 14, 2017, 1304 UTC »

Keeping noise out of LF antennas here is a never ending endeavor.  Cupla things I have learned.

The biggest thing I watch is keeping ground loops out of the system, which can generate mysterious noise from time to time.  An active antenna which may have multiple grounds - power for the antenna amp and an RF ground represented possibly by the coax shield - is something I avoid.  I try to keep the power ground as the "reference", and break up other grounds if possible.  The addition of an RF isolating transformer in the signal return path has worked wonders for me.  I also have a USB digital path out to the site, and I use a USB isolator  from time to time as required.

Many NDB DXers use a common mode choke(s), with at least one out at the antenna.  Here, a ground rod rod near the loop my be required.

485

MW Loggings / Re: 1620 WDHP U.S. Virgin Islands

« on: August 14, 2017, 1212 UTC »

Congratulations!

486

DGPS / Re: DGPS Logs 12-13 Aug 2017

« on: August 13, 2017, 1826 UTC »

There was an early opening to the NW last night; several new  for the season in SK, AB, BC, and MT logged around 0715 +/-.

487

Equipment / Re: This might be the start of something big

« on: August 12, 2017, 1530 UTC »

Nice!

When it's up in the tree, are you going to rotate the entire tree?  If so, Fanco makes a nice ultra heavy duty rotator which will do the job.  I assume you already have the required 480V 3 phase service to your shack?

488

General Radio Discussion / Re: Very sad news

« on: August 11, 2017, 1445 UTC »

Here is a bit more about his background:

https://www.hfunderground.com/board/index.php/topic,19471.0.html

489

General Radio Discussion / Re: Very sad news

« on: August 11, 2017, 1327 UTC »

137 Guests, 3 Users
Users active in past 15 minutes:
Josh, Rafman, PirateSWL






ummmmm

 Really Josh!?! This is what you post regarding the death of Chris Crosby?!? You must be saying my post is fake and a lie. How heartless and ignorant can you be??? Rafman was a well respected member here on HFU and I for one am offended by your ignorant comment.

https://www.afterlife.co/us/obituary-south-hill-christopher-crosby-4866103

We have lost a dear member of our community, and I think we would all appreciate it if this exchange goes no further.  Full stop.

If you follow the Forum Stats [More Stats] link you will see that the account tied to Rafman has been logged in far longer than any other HFU member.  There have been times when it was logged on for days at a time.  Most likely, this will remain the situation until some family member shuts things down.

Until then, let's keep the memories of our friend positive, in spite of our communal loss.

490

General Radio Discussion / Re: Very sad news

« on: August 09, 2017, 2346 UTC »

Very sad news.  RIP, rafman.

491

Longwave Loggings / Re: Summer NDB Logs

« on: August 09, 2017, 1456 UTC »

Logs from Downers Grove, Illinois

I start my statistical season in August, so clicking off some reliables to get things going. All from live sessions.


2017-08-09  0433  201.0  GL    La Grande Riviere, QC, CAN  1528 Km
2017-08-07  0503  201.0  YKX  Kirkland Lake, ON, CAN  963 Km
2017-08-09  0434  207.0  YNE  Norway House, MB, CAN  1541 Km
2017-08-07  0507  208.0  YSK  Sanikiluaq, NU, CAN  1760 Km
2017-08-09  0411  212.0  YGX  Gillam, MB, CAN  1693 Km
2017-08-07  0511  218.0  YUY  Rouyn, QC, CAN  1010 Km
2017-08-09  0511  224.0  DN   Dauphin, MB, CAN  1385 Km
2017-08-07  0517  227.0  GW   De Kalb County, Auburn, IN, USA  262 Km
2017-08-09  0438  236.0  OW   Ramsayville, ON, CAN  1083 Km
2017-08-07  0521  239.0  HKF   Middletown, OH, USA  396 Km
2017-08-09  0413  244.0  TH    Thompson, MB, CAN  1718 Km
2017-08-07  0217  245.0  YZE  Gore Bay, ON, CAN  636 Km
2017-08-09  0508  250.0  FO    Flin Flon, MB, CAN  1753 Km
2017-08-09  0510  257.0  XE   Saskatoon, SK, CAN  1827 Km
2017-08-09  0441  264.0  ZPB  Sachigo Lake, ON, CAN  1385 Km
2017-08-09  0442  269.0  UDE  Delta, MB, CAN  1222 Km
2017-08-09  0422  272.0  ZMR  Montreal, QC, CAN  1197 Km
2017-08-09  0448  275.0  AV   St Andrews (Winnipeg), MB, CAN  1155 Km
2017-08-07  0229  283.0  PT   Pelee Island, ON, CAN  443 Km
2017-08-09  0424  287.0  ZWG  Medicine Rock (Winnipeg), MB, CAN  1156 Km
2017-08-09  0443  289.0  YLQ  La Tuque, QC, CAN  1359 Km
2017-08-09  0426  290.0  QR   Regina, SK, CAN  1587 Km
2017-08-07  0219  326.0  VV    Wiarton, ON, CAN  642 Km
2017-08-09  0429  329.0  YEK  Arviat, NU, CAN  2190 Km
2017-08-07  0220  332.0  QT   Thunder Bay, ON, CAN  741 Km
2017-08-09  0501  336.0  BV   Champlain, QC, CAN  1446 Km
2017-08-09  0453  338.0  YPX   Puvirnituq, QC, CAN  2165 Km
2017-08-08  0451  344.0  YGV   Havre St Pierre, QC, CAN  2099 Km
2017-08-08  0442  400.0  CI     Sault Ste. Marie, MI, USA  578 Km
2017-08-08  0443  400.0  FN    Fort Collins / Loveland, CO, USA  1427 Km
2017-08-08  0440  403.0  ZTO  Woodhill / Brampton (Toronto), ON, CAN  715 Km
2017-08-07  0215  404.0  ZR   Sarnia, ON, CAN  497 Km
2017-08-08  0438  408.0  SN   Saint Catharines, ON, CAN  735 Km
2017-08-08  0436  411.0  SDA  Shenandoah, IA, USA  624 Km
2017-08-08  0435  414.0  GRN  Gordon, NE, USA  1171 Km
2017-08-08  0434  415.0  CBC  West End (Cayman Brac), , CYM  2576 Km with new   -400 410 offsets
2017-08-08  0432  415.0  DJD  Canton, GA, USA  892 Km
2017-08-08  0430  417.0  SLP  Shelby, NC, USA  914 Km
2017-08-08  0429  420.0  TU   Tupelo, MS, USA  847 Km
2017-08-08  0426  421.0  VLY  Mc Kinney, TX, USA  1211 Km
2017-08-08  0424  423.0  PCW  Port Clinton, OH, USA  431 Km
2017-08-08  0422  425.0  PFL  Fort Sill, OK, USA  1204 Km
2017-08-08  0420  426.0  IZS  Montezuma, GA, USA  1107 Km
2017-08-07  0213  517.0  FN   Clinton, IA, USA  194 Km

NDBs this report 44   New NDBs 0

492

North American Shortwave Pirate / Re: Captain Morgan Shortwave 6950.5 AM 0054 UTC 8/6/17

« on: August 06, 2017, 2120 UTC »

Just trace audio here.   

493

North American Shortwave Pirate / Re: UNID 6940 AM/USB 0103 UTC 8/6/17

« on: August 06, 2017, 2118 UTC »

Fair signal here in an SDR recording.  TY!

494

North American Shortwave Pirate / Re: Radio Free Whatever 6945 USB 2350 UTC 8-5-17

« on: August 06, 2017, 2117 UTC »

Generally excellent reception here with great audio.  Enjoying the show now, and thanks RFW!

495

Longwave Loggings / Re: Summer NDB Logs

« on: August 02, 2017, 1210 UTC »

CLEs are monthly events organized by the ndblist Yahoo group, and the subscription link is on their home page:

https://groups.yahoo.com/neo/groups/ndblist/info

Logs which are posted here are harvested by the editors and are used to update the RNA>signals page:

http://www.classaxe.com/dx/ndb/rna/

If you DX NDBs, this is the place to be!