Topic: Antenna build

[ho66es]

I managed to get a selection of green boards and am building a system. The main part I needed to assemble was an antenna.

I went down this road



however I seem to have more wire than I should have left over, I did follow instructions, the hooks are 1m apart on each cross arm, however the length around is 2.85m or so.

Simple maths tells me 8x2.85 is 22.8m and 9x2.85 25.65m, what degree of precision is required? should I add an extra turn or should I dismantle and move the hooks further out and try to get 25m in 8 turns exactly?

thanks in advance for any help

[b.e.wilson]

It's not that big a deal. If the area of the loop is slightly bigger than what you have there, the signal will be slightly stronger and the amps will be turned down just a bit. The system is designed to do a good job compensating for these sorts of variables.

A bigger concern with unshielded loops is the pattern distortion if the loops are situated "unsymmetrically" near metal. If you have much metal nearby, say to one side of the loops, the pattern can distort enough that you will loose the advantage of having orthogonal loops, which are the sharp nulls off the normal to the plane of the loop. Having those nulls makes it convenient to see some direction to the stroke's location, and can be used to "null out" a nearby noise source.

So mounting location is more important than the amount of wire in the loop, which is true for almost every antenna ever made.

[ho66es]

It's not that big a deal. If the area of the loop is slightly bigger than what you have there, the signal will be slightly stronger and the amps will be turned down just a bit. The system is designed to do a good job compensating for these sorts of variables.

A bigger concern with unshielded loops is the pattern distortion if the loops are situated "unsymmetrically" near metal. If you have much metal nearby, say to one side of the loops, the pattern can distort enough that you will loose the advantage of having orthogonal loops, which are the sharp nulls off the normal to the plane of the loop. Having those nulls makes it convenient to see some direction to the stroke's location, and can be used to "null out" a nearby noise source.

So mounting location is more important than the amount of wire in the loop, which is true for almost every antenna ever made.

many thanks for response. So at this stage I would be as well taking it apart, moving hooks as far out as possible and re stringing? I think I have more than enough wire for that.

Also I should look at shielding if possible, or waterproofing and mounting in garden. Hmm waterproofing and mounting in garden would get about 10m away from metal at extreme, indoors more like 2m from metal. If I could think of a convenient way of shielding this construction I would, guessing I would need copper foil or tape of some sort.

[b.e.wilson]

For waterproofing, just tape the connections.

If you really want to take it apart, you would need to for the purpose of painting the wood, but not for expanding the area of the loop. Once apart for painting, you can assemble it as you wish.

Indoors vs. outdoors: I always opt for outdoors; stronger signals out there.

Shielding is harder, but as you are careful about bunching the wires together, it shouldn't be too difficult to apply sticky metal foil. Just make sure it has a slit in it so a complete circuit is not created around the circumference of the loop (that is, a break in the shield as you follow the direction of the wires).

[ho66es]

For waterproofing, just tape the connections.

If you really want to take it apart, you would need to for the purpose of painting the wood, but not for expanding the area of the loop. Once apart for painting, you can assemble it as you wish.

Indoors vs. outdoors: I always opt for outdoors; stronger signals out there.

Shielding is harder, but as you are careful about bunching the wires together, it shouldn't be too difficult to apply sticky metal foil. Just make sure it has a slit in it so a complete circuit is not created around the circumference of the loop (that is, a break in the shield as you follow the direction of the wires).

ok just ordered 30m x 50mm emi copper foil tape, should be enough to shield each antenna, do I keep shields seperate from each other? and does the size of gap between ends of shield matter or should it be as small as possible?

if I use openwrt on a TP-Link TL-WR703N I have, I can mount behind garage and use powerlan to connect to main lan so thats the outdoor bit sorted

sorry to be a pain asking all these questions just want to get it right 1st time

[miraculon]

I also made loop antennas for my system Red. This antenna has nine turns.

I used non-metallic conduit instead of the frame method. (It was very difficult to make; getting the wire turns through the conduit required Teflon wire and pulling lubricant)

The foil goes all the way around the wires/conduit. In the case of the loop antenna I just have a break at the junction boxes. The top one has a wire connecting the two halves, the bottom is a true break. One side is grounded to the antenna connector on the amplifier board.

http://www.wxforum.net/index.php?topic=19736.msg190932#msg190932



Greg H.

[ho66es]

I also made loop antennas for my system Red. This antenna has nine turns.

I used non-metallic conduit instead of the frame method. (It was very difficult to make; getting the wire turns through the conduit required Teflon wire and pulling lubricant)

The foil goes all the way around the wires/conduit. In the case of the loop antenna I just have a break at the junction boxes. The top one has a wire connecting the two halves, the bottom is a true break. One side is grounded to the antenna connector on the amplifier board.
Greg H.

thanks for that, ok will go for 9 turns, I have enough wire for that and will shield it when copper tape arrives.

[ho66es]

Ok done a bit more work

Shielding and wiring termination


overall pic


I bought a roll of 60mm wide copper tape and applied it (loads left). wiring completely covered bar a small gap at base, earth/shield is only wired to one end of each loop, tested with meter to other end  at almost 0 ohms so it appears to be a continuous shield.

Now to get tracker running on openwrt, seems to work in windows but thats not where I want to run it. Just need to figure the commandline syntax for linux

[robo]

Hi ho66es,

you have twisted the wires between the antenna and the amplifier. As far as I know the wires between the antenna and the amplifier should not be twisted and they should be as short as possible.

cu Robo

[b.e.wilson]

Yep, by twisting the wire (or by having long leads) you've added capacitance in series with an inductor, and it will start resonating. Add enough capacitance and it will resonate (oscillate) in the 10-50 KHz bandpass window--all you'll see is a sine wave.

What's the yellow/green wire? Never mind, it's grounding the shield. Not strictly necessary, but safe.

[ho66es]

Hi ho66es,

you have twisted the wires between the antenna and the amplifier. As far as I know the wires between the antenna and the amplifier should not be twisted and they should be as short as possible.

cu Robo

Yep, by twisting the wire (or by having long leads) you've added capacitance in series with an inductor, and it will start resonating. Add enough capacitance and it will resonate (oscillate) in the 10-50 KHz bandpass window--all you'll see is a sine wave.

What's the yellow/green wire? Never mind, it's grounding the shield. Not strictly necessary, but safe.

ty for that, modified as shown



testing with two boards

IMG_20140912_171904


and

IMG_20140912_171909


both produce similar results but the second doesn't allows 38400 only 4800

windows software


this is all just lying around house at moment, needs serious tidying and moving etc

anyone running on openwrt out there care to share commandline they use (with username and pwd xx'd out)

[robo]

Hi ho66es,

looks good now.

I'm running the XLT tracker on openwrt, but I set it up and then forgot it.

Maybe the following thread will help (mostly in German): http://www.wetter-board.de/board323-spezialthemen/board287-blitzentladung-aufzeichnung/board385-blitzortung-deutsch/52689-tracker-auf-router-mit-openwrt/

At http://tracker.blitzortung.org/green/ you should find what you need.

cu Robo

[ho66es]

Hi ho66es,

looks good now.

I'm running the XLT tracker on openwrt, but I set it up and then forgot it.
cu Robo

thanks for the tips

Capture00


url I think I used was http://www.wetter-board.de/board351-archivraum/board419-blitzortung-archiv/board386-blitzortung-english/56819-openwrt-on-tp-link-tl-mr3020-with-additional-hardware-mods/

now to get it tidied up and stowed away and running