H field ferrite shielding
#1
Photo 
Hi,

This has been copied over from the internal forum, station hardware firmware antenna section, 32 hours without response on a subject that if done wrong, I think, would compromise your detector. Someone within the broader followers of Blitzortung may be able to assist. Smile

""Some very interesting posts on the various ways of shielding H field ferrites. It seems that copper foil and ribbon cable are evenly matched in popularity. If I need to shield my H field ferrite antennas, I will use ribbon cable, which will be easiest to obtain. I can see that you solder one edge of your ribbon cable and then attach that earth wire to your negative connector of the antenna connectors on the pcb, for both relevant channels/antennae.

What is not so clear is how the 2 edges of the ribbon cable relate to each other. Do you have to leave a space, similar to what is done with the copper foil or do you just wrap the unsoldered edge of the ribbon cable around your conduit and just terminate in adjacent to your soldered edge (lying beside it). I assume you don't solder the other edge to the first one or do you?? The photos I have seen, do not show how the 2 edges of the ribbon cable end up around your conduit.

regards,

Jeff Smile (nearly ready to mount on the roof!!!)""
Stations: 2041
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#2
(2015-01-21, 22:49)orion_jb2001 Wrote: Hi,

This has been copied over from the internal forum, station hardware firmware antenna section, 32 hours without response on a subject that if done wrong, I think, would compromise your detector. Someone within the broader followers of Blitzortung may be able to assist. Smile

""Some very interesting posts on the various ways of shielding H field ferrites. It seems that copper foil and ribbon cable are evenly matched in popularity. If I need to shield my H field ferrite antennas, I will use ribbon cable, which will be easiest to obtain. I can see that you solder one edge of your ribbon cable and then attach that earth wire to your negative connector of the antenna connectors on the pcb, for both relevant channels/antennae.

What is not so clear is how the 2 edges of the ribbon cable relate to each other. Do you have to leave a space, similar to what is done with the copper foil or do you just wrap the unsoldered edge of the ribbon cable around your conduit and just terminate in adjacent to your soldered edge (lying beside it). I assume you don't solder the other edge to the first one or do you?? The photos I have seen, do not show how the 2 edges of the ribbon cable end up around your conduit.

regards,

Jeff Smile (nearly ready to mount on the roof!!!)""
First... before even thinking about shielding... find the location with the lowest overall H field noise level at recommended gain settings, for example 10x10. You probably don't even need shielding, or it has little overall effect. "Noise" is effectively handled by the system, for the most part.
Second... shields should have a gap.... otherwise the H field won't get into the antenna. So the 'edges' should not touch or crossover lengthwise, a gap of a mm or so is probably sufficient, and the ends should be open.... Regardless of either ribbon or foil., ferrite or wire loop, coax or whatever. Otherwise you've placed your antenna in a Faraday Cage. All the shield does is (effectively) is 'short' some M components ,... some of them.
I'd say a major percentage of us don't use shielding... it certainly made no difference in my high H field noise environment... so I run 'unshielded' and apparently have an effective station, despite that.

Don't make this more complex then it needs to be! Smile relax... enjoy.... try 'naked antennas' in your chosen location for several days... you can shield later if you determine it's necessary. Probably won't be.

If you decide to shield without doing that, just leave the 'ends' separated by a mm or so, make sure the tube is open at both ends, and go for it....

You're talking about 'interference' with your station operation. We all live with it at different times and for different reasons... some more than others
... try this... http://www.wxforum.net/index.php?board=115.0
and most anything you'll run into, we region 3 operators (and others worldwide) have already chased down....
Interference discussed here... http://www.wxforum.net/index.php?topic=20439.0
Mike

Stations: 689, 791, 1439
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#3
Thanks for clarifying the gap for ribbon. Although clearly explained and recorded in photo with foil, I could not find a photo anywhere showing the edges of a finished ribbon shielded system showing such a gap, only a view from the top. May be that needs to be added to the official document.

As mentioned in my question ....'If I need to shield my H field ferrite antennas..."

Thanks for answering this public forum question. That is an important bit of information that may be others have overlooked.

Jeff
Stations: 2041
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#4
Exclamation 
Mike,

Just continuing to perfect the system. Am about to shield the H field ferrite antennas supplied from Egon, to assess difference in signal "cleanliness" and compare naked to shielded. My question, most if not all use copper foil on the outside of their conduit, can you use a copper tube, with a suitable gap and the ferrite antenna directly inside that copper tube, with then the copper tube inside your conduit?

Jeff

(2015-01-29, 03:37)orion_jb2001 Wrote: Mike,

Just continuing to perfect the system. Am about to shield the H field ferrite antennas supplied from Egon, to assess difference in signal "cleanliness" and compare naked to shielded. My question, most if not all use copper foil on the outside of their conduit, can you use a copper tube, with a suitable gap and the ferrite antenna directly inside that copper tube, with then the copper tube inside your conduit?

Jeff

I believe this from a previous Richo answer on shielding, answers my question;

""Solid metallic material near the antenna disturb the magnetic field, so there must be a distance between the antenna and the shield
I use 15-20mm optimally""

So having the ferrite antenna sitting inside the copper tubing would cause this disturbance to the magnetic field. Will wait for the copper foil to arrive next week to shield the H field, it was just that I am up on the roof today adjusting the length of my E field antenna so I was seeing if I could get the 2 mods down today. Smile

Jeff
Stations: 2041
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#5
Didn't one member take a length of copper pipe, slit it from end to end, open the diameter up a bit creating a gap, and slide the PVC pipe with ferrite in it, into the copper tube?

I think the report was finding a PVC pipe to hold the antenna that was the right diameter so the copper tube when stretch open into a "C" was leaving the right gap.

I ended up using copper foil that I got from a supply place for musicians, since it seems some of them put it inside the guitar sounding board to shield electronics mounted inside. A bit pricy but worked well and was easy to solder the ground to.

Dale

Jeff,
How long did you start out with for the Efield antenna and what did you decide to trim or extend it to?

Dale
Stations: 976, 1505
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#6
What Richo said about having the copper tubing too close to the ferrite makes sense. My ribbon cable arrived today and I am in the middle of earthing one side and setting up the new casings. I actually had some more tubing left over for the casing of the efield antenna and I am going to use that for my ferrites. It has an internal id of about 35mm, which will match Richo's optimum set up for H shielding.

The e field started out with a meter but have trimmed it back to 35cm. I found with the metre length when storms were close, I wasn't getting as many detections (overloading the signals I think) that I think I should have. Will now have to wait for some passing storms to see if it made a difference.

Jeff
Stations: 2041
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