RE: LF: RE: Vlf ot Penguins and awesomes - More

[Laurence KL7 L <hellozerohellozero@hotmail.com>]

Edgar/Jim -- Ive come up with an initial transformer design of 25T pri (1 ohm 1 mH) and around 170 turns sec - typically their LNA are around 520 ohm Z input but my simple  bi polar is appx 50 ohm. As ever the primary needs to be low R as possible therefore  fairly thick as can be wound on a pot core and the secondary around #30 =

I note their design appears to be Z primary 1 ohm and input Z to amp 520 so 24/528T 16:1 ratio well n the AWESOME anyway - thanks again

Will give it a go.....as ever the difference in near field E probe to B/Mag  is amazing -cant hear the 8kHzdog fence pulser on the Eprobe (still my best VLF DX antennna here) but its a good 599 on the 1mH/1Ohm 10m sided 5T loop....

I wish I had paid for attention to Dr Piggott nearly 40 years ago!

Laurence KL7L  WE2XPQ

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From: hvanesce@comcast.net
To: rsgb_lf_group@blacksheep.org
Date: Mon, 8 Feb 2016 14:09:55 -0500
Subject: RE: LF: RE: Vlf ot Penguins and awesomes

Edgar,

 

Excellent find, thanks for posting, hope it answers Laurence’s questions.

 

A comment regarding the summary (last paragraph) on .pdf page 32, original document page 27: prototype transformer C_s can deviate considerably from initial design value especially if a simplified model for C_s is used in the design or design spec for the magnet wire is not controlled for insulation type and winding/layering method. If a transformer modeling tool is not available, the old Radiotron Engineer’s Handbook has some helpful models.  

 

Note Paschal’s comment in a related context (C_a of loop) in paragraph 1,  .pdf pg 40, original document pg 35:

“...it is difficult to calculate the value of C_a    …easier to build and measure”.

In the case of the matching transformer, using a transformer model that has a reasonable approximation for C_s could save a fair amount of test/rewind time on the way to a VLF receiver with sensitivity of 0.5uV/m-Hz^1/2 (measured, Fig 8.5, .pdf pg 78)          

 

Of interest in context of C_s:

Item 4,  .pdf page 44, original document page 40; and last paragraph, same page

Item 2 (packing density),  .pdf page 47, original document page 43

Item 4,  .pdf page 47, original document page 43

Paragraph 2 (Litz wire tradeoffs), .pdf page 49, original document page 45

Last paragraph on .pdf page 52, original document page 56 (in the context of high-impedance preamps):  “C_s forms a tuned circuit… (therefore) low-impedance amplifiers are a much better practical solution”

 

I wonder if page 38 of the original document is blank. It’s not included in the .pdf document (which is why the offset between .pdf page number and original document page number changes after original document page 37)

 

Thanks for posting the link; hope it answers Laurence’s questions; I had been looking for this article off and on since seeing a reference to it some years ago.

 

73,

 

Jim AA5BW

 

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of edgar
Sent: Sunday, February 7, 2016 6:38 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: Vlf ot Penguins and awesomes

 

Hi Laurence,

You probably have this, but in case you do not.

http://traktoria.org/files/radio/antenna/VLF/the_design_of_broad-band_vlf_receivers_with_air-core_loop_antennas.pdf

It may not answer your questions.

Regards, Edgar
Moonah, Tasmania.