Topic: Savannah Georgia

[avogodro]

screenshot

[avogodro]

i had more screen shots and pics but the 512kb limit prevented any more pics to be uploaded until i could downsize them.

[robo]

Hi Nick,

I am trying to setup my station and i am having a hard time receiving strikes.  I have not had time to procure 40pin hdd ribbon cable.  I used 22ga solid copper wire to wind around the ferrite rod antennas and soldered the two ends together with a wire that is connected to the ground point on the amplifier board.  Is this something that shields the antennas too much?  I did not get any hits from a very active storm that was less than 50 miles away and a storm that was right overhead practically  i only got about 10 hits.  I have some pics of my setup.

The way you shielded your ferrites is not correct.  There must be a gap in the shielding along the rod.  I cannot tell you the reason, maybe a ham can tell you.  Please remove this shielding.  You can try without shielding.  I'm an electronics technician for digital technique, no idea about this analog stuff.

cu Robo

[JonathanW]

Nick,
The shield cannot be continuous around the ferrite antennas - there must be a break in it.  It sounds like you basically wound an additional shorted coil around the outside of the ferrites, which could, indeed, prevent reception.

If you look at how the project document suggests making shields, there is a break all along the length of the ferrite.  The same goes with copper foil - there's a gap along the length.

Best,
Jonathan

[miraculon]

The continuous wire forms a transformer with the inner winding (actual magnet wire on the ferrite) as the "primary" and this larger wire forming the secondary. It becomes a shorted secondary transformer. This reduces the inductance from the much higher desired value, to only "leakage inductance" remaining. This will be quite small and not be effective.

As mentioned, there are several techniques to forming a shield with a break in it. The split foil is what I did with mine. The Blitzortung guys recommend using ribbon cable with one end of all the wires soldered together and open on the far end.

Here is a closeup of the copper foil tape with the split. You might want to consider just eliminating the larger black wire and go without the shield. With RED, some of the "founding fathers" of Blitzortung say the shield isn't required. (my pictures are from a "green" unit).

[dfroula]

Your additional winding is shielding the antenna from the desired signals, as well as noise. You need a longitudinal gap in the shield to allow the distant RF signal to reach the ferrite antenna.

Here's another image showing the PVC ferrite antenna enclosure shielded with aluminum foil tape, with the gap to avoid the shorted turn.

The shield gap allows far-field RF currents to flow on the inside of the shield, where they are coupled to the ferrite antenna windings. The shield will still allow near-field, capacitively-coupled, electrostatic noise to be drained away to ground, while allowing lightning signals to be coupled to the ferrite antenna.

The shield has no effect on near-field inductively (magnetically) coupled local noise.

Don
WD9DMP

[avogodro]

Awesome information.  Thank you for all of the replies.   And thank you for taking it easy on me.  I will get some copper/aluminum tape to make the appropriate changes to my setup.  I may try it without shielding to see if there is a change.  When i get the copper/aluminum tape where do i solder the ground wire on it? close to the longitudinal gap or does it matter?

also is the metal tape easier than the proposed hdd ribbon cable or is it a better option?  Just curious.

Again thank you guys for the help and explanations.
Nick
KK4ANB

[miraculon]

It doesn't matter. I soldered my wire close to the "box" end of the PVC so that the wire would be shorter. Just make sure you don't have a wire strand touching the other side of the gap or you will be right back where you started....

Greg H.

[dfroula]

In my case, the width of the aluminum tape I used was not sufficient to wrap entirely around the PVC tube (minus the gap), so I needed to overlap two layers. The adhesive keeps the two layers from making good electrical contact. Also, it is next to impossible to solder a copper wire to aluminum with standard soldering techniques.

To get around these issues, I drilled a small hole at one end of the aluminum tape-covered tube about 1/2" from the gap and 1" from the tube end, where it fits into the junction box. I stripped about 2" of insulation from a solid length of 24AWG wire and passed the exposed wire through the hole from the inside of the tube. I bent the exposed wire into a repeating "S" shape and bent the S so it bridged the two layers of foil tape (NOT across the gap, but across where the two foil layers overlap). I then used another short piece of aluminum tape over the "S" to secure the wire across the layers. I used a small dental tool to press the tape around the S curves to keep the wire in good contact with the tape shield.

The other end of the shield ground wire is connected with the grounded end of the ferrite antenna and the black and drain wires of a short piece of shielded microphone cable. The other end of the microphone cable has the black and drain wires connected to the grounded side of the amplifier input.

The ungrounded side of the ferrite antenna is connected to the red wire of the microphone cable. The red wire on the other end of the microphone cable is connected to the ungrounded amplifier input terminal.

Don
WD9DMP

Awesome information.  Thank you for all of the replies.   And thank you for taking it easy on me.  I will get some copper/aluminum tape to make the appropriate changes to my setup.  I may try it without shielding to see if there is a change.  When i get the copper/aluminum tape where do i solder the ground wire on it? close to the longitudinal gap or does it matter?

also is the metal tape easier than the proposed hdd ribbon cable or is it a better option?  Just curious.

Again thank you guys for the help and explanations.
Nick
KK4ANB

[miraculon]

A couple of caveats about this:

The adhesive keeps the two layers from making good electrical contact.

• Make sure that your adhesive really isn't conductive. I have used conductive adhesive metal tapes for EMC work.
• Don't let a sharp corner of the aluminum tape dig into the "other" side of the lapped joint. This will cause a short.

Copper tape is solderable and the PVC takes the heat OK during the soldering process. It is costly and somewhat hard to find, however. There is no reason that the aluminum tape shouldn't work for you like it did for Don.

Greg H.

[JonathanW]

A couple of caveats about this:

The adhesive keeps the two layers from making good electrical contact.

• Make sure that your adhesive really isn't conductive. I have used conductive adhesive metal tapes for EMC work.
• Don't let a sharp corner of the aluminum tape dig into the "other" side of the lapped joint. This will cause a short.

Copper tape is solderable and the PVC takes the heat OK during the soldering process. It is costly and somewhat hard to find, however. There is no reason that the aluminum tape shouldn't work for you like it did for Don.

Greg H.

http://www.mcmaster.com/#copper-foil-tape/=syov17

[avogodro]

I will try the copper tape as that sounds a bit easier. THANK you for the in depth explanation of the aluminum foil method.  I may have to use this if I dont find any copper tape.

would this work as well?
copper tape in ebay:
i shouldnt need more than 6 feet.  Unless i really screw up a few times.

http://www.ebay.com/itm/6-FEET-X-50mm-Copper-Foil-Tape-EMI-Shielding-for-Guitars-Pedals-6-ft-X-2-/321372045317?pt=Guitar_Accessories&hash=item4ad3444005#ht_707wt_916

[miraculon]

I bought Cu tape from this place on eBay. I can't remember if it had conductive adhesive or not. I think that you will have a wide gap with 50mm, IIRC. You might need to overlap and make sure it has conductive adhesive. When I did my ferrite shields, I set the gap and let the Cu tapes overlap where ever it was.

If it is not conductive, you will need to tack-solder along the overlap. I made a solder connection every few inches on my 1m loops. The adhesive on the Cu tape I used was somewhat conductive, but while I was building it I decided to make sure it had good continuity. Seam soldering probably isn't necessary.

Greg H.

[steel_edges]

I just received this tape I purchased on ebay:

http://www.ebay.com/itm/121374054062?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Seems to be pretty high quality stuff.  The discoloration is only on the outside wrap not the whole roll and the adhesive is conductive.

George