(2017-04-22, 14:54)Max_Headroom Wrote: Gentlemen & members!


Judging from my question, it will be evident I have a very dim view of antenna theory, so pls be gentle...


I live on the top floor of a high rise with a great view of my city.
I plan to place both the ferrite antennas & E-probe on the balconny.

However, living as I do, I assume there is plenty of sources of interference coming from lower floors.


Question: is it possible to build a shielding around the probe in the (potentially) offending sectors?



Regards/M

(2017-10-15, 17:42)KY5G Wrote: Crap....  it just occurred to me that I am too ignorant of the basics in this particular subject to converse intelligently about shield theory, design, optimization for H-filed ferrite antennas.
It would appear I have just added a couple thousand pages of reading to my list...  

(2017-10-15, 17:42)KY5G Wrote: Based on the Pesky Project gallery pics/text, and the current shipping ferrite core diameter of approx 10mm (actual core, not as wrapped and heatshrink added), the spacing between the outside of the core and the shield should be approx. 10mm x 10 (stated multiple) = 100mm

1) Is 100 mm correct?

2) Would a round shield housing offer any benefit over a square housing?  Obviously, square is easier to construct/prototype, but I'm asking about performance...

3) The gap distance shown is 2-4 mm...  That's a pretty big range...  What is the theory behind sizing the gap?  Would it be based on the frequency and polarization of the "noise" vs. "desired" signal?
3a) Does the gap function as an admission aperture?

4) How should the gap be oriented?  Does it matter? Say a ferrite that is long axis oriented E/W to generally receive N/S signals....  Gap Up? Down? North? South?

4a) Would there be any benefit (on horizontally oriented ferrites rcving vert polarized sigs) to having TWO gaps oriented in the 2 cardinal directions the ferrite favors?  (Of course, you'd need to bong GND to both halves, or bond the halves together at both ends on the "far side".

5) When using the third ferrite oriented vertically, which would favor receiving horizontally polarized signals, how would you orient the gap? How many gaps?  1, 2, 4?  Intuitively, I'm lead toward 4 as a minimum... oriented N,S,E,W...  Or 6, oriented every 60 degrees.... Or 8, every 45....  How many gaps before the shield is rendered less than useful.

Crap....  it just occurred to me that I am too ignorant of the basics in this particular subject to converse intelligently about shield theory, design, optimization for H-filed ferrite antennas.
It would appear I have just added a couple thousand pages of reading to my list...  

(2017-10-15, 21:11)Cutty Wrote: First, shielding does NOTHING for Magnetic components... it's only an attempt to minimize an Electric component. I ran for a couple of years with NO shielding, since my junk is all Magnetic,
with very little E noise.  The Pesky was tried for one specific electric troublemaker, and it worked, where other approaches and types did not.

1. 10 X Diameter of the Core is the WIDTH of a Side... The Antenna is centered inside, so there would be 37.5MM from core center to side. Don't ask me why. There's probably some math to compute, but this is what the Engineers told us to use on that ECM COMM gadget.
2  Any thin gap width would probably work. My notes specified 2-4mm for the project we were working on at the time... some engineer said it., and it was in the L and S communications bands.
3. All kinds of shielding approaches.... First Question:  If you don't have electrical interference being picked up by the H field antenna's you probably don't need any????
4. Gap runs along axis of rod.
4a. Not on a ferrite core... nothing works for me for H polarized in my environment,. 
5.  Only need one gap if you need any shielding at all. the gap is to keep from 'shorting' the shield, and possibly degrading reception.

Re: "Crap" ... How do you reckon the rest of us learned anything?    Ask away!  
If we don't know the answer, we'll invent something, maybe.
Confusion and lack of knowledge is easily fixed,...

(2017-10-16, 22:05)KY5G Wrote:

(2017-10-15, 21:11)Cutty Wrote: First, shielding does NOTHING for Magnetic components... it's only an attempt to minimize an Electric component. I ran for a couple of years with NO shielding, since my junk is all Magnetic,
with very little E noise.  The Pesky was tried for one specific electric troublemaker, and it worked, where other approaches and types did not.

1. 10 X Diameter of the Core is the WIDTH of a Side... The Antenna is centered inside, so there would be 5MM from core center to side. Don't ask me why. There's probably some math to compute, but this is what the Engineers told us to use on that ECM COMM gadget.
2  Any thin gap width would probably work. My notes specified 2-4mm for the project we were working on at the time... some engineer said it., and it was in the L and S communications bands.
3. All kinds of shielding approaches.... First Question:  If you don't have electrical interference being picked up by the H field antenna's you probably don't need any????
4. Gap runs along axis of rod.
4a. Not on a ferrite core... nothing works for me for H polarized in my environment,. 
5.  Only need one gap if you need any shielding at all. the gap is to keep from 'shorting' the shield, and possibly degrading reception.

Re: "Crap" ... How do you reckon the rest of us learned anything?    Ask away!  
If we don't know the answer, we'll invent something, maybe.
Confusion and lack of knowledge is easily fixed,...

FIRST - Absolutely understand.  I am considering the shielding to control for the many, many numerous electrical annoyances in my vicinity.  I am rapidly clearing MY property of them, but there are many in the 1 mile radius too.  (Note: I counted 75 SMPS inside my house when I started.... nuts.  I realize that impulse noise is the real killer, but dang!  Had/have a bunch of those too.)

1.  OK....  The math for the figures you just gave me doesn't work out right....  The prototype was 75mm width on a 7.5mm core....  (75mm - 7.5mm)/2 = 33.75mm minimum free space between surface of core and closest approach of square tube surround.  Not sure where the 5mm spacing comes in...  Since it doesn't seem to be a critical dimension, I am going to use non-conductive tubing with an outside diameter closest to 100mm or so...  That will put the copper shield approx. 45 mm spacing from the 10mm core.

2. Gap spacing....  Yeah, I did some research on aperture size, shape, and spacing as it applies to shielding effectiveness...  It would appear that the gap is for electrical purposes only if one considers the frequencies
that we are talking about...  The cutoff frequency is somewhere in the high teens/low 20's GIGAHERTZ, and the wavelength at 4mm is something like 74 GHz...  E-field radio ain't getting through...

3. Don't KNOW if I will or not... But I plan to put this H-field 3-axis antenna up near the top of a 38 foot mast, and even if I DON'T have trouble today (and I likely will.... it's noisy here), I may have it down the road and don't want to have to pull it down to add the shielding.

4. Understand now what it is ans why it's there...  Under our general circumstances, only one continuous gap/aperature is required and orientation makes little difference at the frequencies under consideration... especially since I ALSO have all 4 LPF installed.

5. Right...

"Crap" ----  Thank you!  You are very kind.

Note: I intend to test the addition of screen "caps" top and bottom, but will leave gaps as required and bond the caps to the cylinder shield as required to shield but not short the element reception...  Don't think the end-firing area is likely much of a concern, but you never know....  Will be doing the testing at 8 foot level to avoid pulling the mast with my GPS antenna and third leg of 80m delta loop hoist rope/pully attached.

Also considering adding the "CSS Thingy" wrap and disc(s) too...  why not try it....  1) Un-shielded, 2) Shielded 3) Shielded, just CSS thingy wrap 4) Shielded, just CSS disc(s), and finally 5) Shielded, BOTH CSS Thingy wrap AND disc(s).  Something to do anyway...  and a spreadsheet of empirical data to share.

73,

(2017-10-16, 23:34)Cutty Wrote: You're correct....   the 5mm is a typo... should be 37.5 mm from rod center.... The width of a 'side' would be 10 times the core's diameter, and the core is centered insite the 'box' axially.  So a 10 mm core would have 100mm sides.. Windings don't count. just Core material.

...and a thought occurred to me.. this assumes a round rod... I have to assume, don't know, that if we were using a 'rectangular' or 'flattened' ferrite core we'd reference the widest portion.... hmmm...

(2017-10-17, 05:44)RichoAnd Wrote: Why not use ribbon cable as shown in my original recommendation
https://forum.blitzortung.org/showthread.php?tid=447&pid=4401#pid4401
10-15mm from windings to shield is enough

See also page 22 of the RED manual

/Richo