[Lowfer] 1/24/13 DK7FC decodes and what collected them.....

[Michael Sapp]

Hi All:  Several decodes of DK7FC here last nite

       2013-01-24 07:00   DK7FC   0.137609   -34   0   JN49ik   1   WA3TTS   EN90xn   6636   298  
       2013-01-24 06:30   DK7FC   0.137609   -37   1   JN49ik   1   WA3TTS   EN90xn   6636   298  
       2013-01-24 04:00   DK7FC   0.137607   -37   1   JN49ik   1   WA3TTS   EN90xn   6636   298  
       2013-01-24 03:30   DK7FC   0.137608   -37   -2   JN49ik   1   WA3TTS   EN90xn   6636   298  
       2013-01-24 02:30   DK7FC   0.137610   -34   0   JN49ik   1   WA3TTS   EN90xn   6636   298  
       2013-01-24 00:30   DK7FC   0.137609   -32   1   JN49ik   1   WA3TTS   EN90xn   6636   298  
       2013-01-24 00:00   DK7FC   0.137609   -36   1   JN49ik   1   WA3TTS   EN90xn   6636   298  



Once again I had the termination ends of the NE and SW EWE antennas lifted from the termination resistors

and tied together.  Net effect is to have a single 70 foot long EWE antenna with isolated winding 11:1 transformers at both 

ends, and two runs of RG6 back to the shack.  The modified HD-1420 VLF converter is fed with a similar isolated winding hi-z

transformer (9:1 at present time).  


One point of interest is these antennas are only about 13 high and hang from and through trees.   The NE end of the

joined antennas hangs from a branch of an old white pine tree and is essentially parallel to it's resin-filled cellulose

attenuator trunk.......(I want to rearrange it to slope away from the tree trunk)

http://i1296.photobucket.com/albums/ag19/wa3tts/NEEWE_zps5797c15c.jpg


The horizontal portion of the wire from the NE transformer then heads SW to a fiberglass pole wedged in an apple tree, where the termination

box is visible (but wires lifted and tied together).

http://i1296.photobucket.com/albums/ag19/wa3tts/swewe_zpsb491dfdb.jpg


The SW portion of the antenna then heads to a wild cherry tree where the vertical portion drops at 

about a 20 degree angle to the transformer box at the base of the trunk  (just visible in photo)....

http://i1296.photobucket.com/albums/ag19/wa3tts/swewe_zpsb491dfdb.jpg


Certainly not the ideal situation, but I seem to be having some positive results with a small

suburban lot that measures 220 x 50 feet.


The EWEs ended up in the back of the lot in part because I have an HF groundplane antenna

with four elevated 65ft long radials in a bow tie type of arrangement---and in part because the

collective broadband noise is lowest at the back lot location.....which my LW/MW/SW

 Sony ICF2001 receiver readily confirms.


One final note is that the isolated winding 11:1 transformers are a recent upgrade. Previously

I had T77 trifilar transformers and 3-stack binocular T77 common mode chokes in place. They

were OK for the 600M band but were rather lossy at 137 kHz. For a test I placed the T77

transfomers and chokes back-to-back and fed 1mw or so from my Wavetek generator through

them on one lo-z port and then measured the throughput with my Boonton CA-91 50ohm

RF voltmeter from the other low-z port.  Losses at 137 kHz were 1 dB per transfomer & choke combination.

At 500 kHz losses were .6dB per transformer and choke combination.


The upgraded, isolated winding 11:1 transformer is shown below.....


http://i1296.photobucket.com/albums/ag19/wa3tts/IMG_2659_zps1fe1794c.jpg


This transformer evolved from experimenting with a BC-453 receiver and needing a high-z solution

to feed it's antenna post.  I quickly tried a basic W8JI BN73-02 binocular transformer to voltage feed the 

BC-453 and it responded well to the higher Z using my EWEs as the receive antennas.  I decided to

test the throughput loss at 200 kHz a week or so later and quickly realized I need more ferrite core

material to be efficient at the lower frequencies.  
    
    A few iterations later this 11:1 transformer came together.  Nothing really special about it other than 

using a first turn tubular primary winding---which is well known prior art---and some teflon plumbing tape

 wrap to insulate the tubing from the conductive BN73-02 material.  I found it was easier to allow the 

tubes to protrude slightly to make the necessary solder connections.  The 3T primary and 10T 

secondary windings were made with nominal tension per  winding pass, then teflon wrapped to

 keep the windings close together as well as to arrest any movement that might otherwise abraid

 the enamel insulation at the tubing ends.   A test of two of these transformers back to back

with the Wavetek generator and Boonton CA91 was quite rewarding..... 1dB per transformer

at 30 kHz, .5 dB per transformer at 60 kHz, and difficult to measure losses (~.1 dB)  at .137 kHz to 2 MHz

given the analog meter scale limitations of the Booton CA-91.  Realistically I think .1 to .2dB per transformer

from 137 kHz to 2 MHz is more believable given some prior experience with the CA-91 and some limited access I have to 

an Ailegent network analyer when measuring some prior transformer designs.


One final point is that the isolated winding  binocular core transformer designs also have inherently  good common mode choking capabilities.

My noise floor is noticeably lower overall.   


Also, with this transformer design, the ten turn secondary winding measures in at 3.7 mH with a Vichy DM4070 LCR meter and the primary 

measures .33 mH.


Well, thanks to all  for the bandwidth. Last few months of bench tinkering and LF listening have yielded some encouraging results, especially

given my rather adverse suburban noise environment.


73  Mike wa3tts