Author Topic: E-Field antenna predicament  (Read 1643 times)

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Offline miraculon

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E-Field antenna predicament
« on: June 05, 2014, 07:54:32 PM »
Using my "natural radio" VLF receiver with Stanton headphones with an HPF, I found a quiet location in the garage. It is inside and below the roof line. I have a place on my GPS mast that I could mount the E-Field antenna on, but it will be very close to the power wires that run over my garage.

After building the E-Field amp and preamp, it seems immune to the noise. The HPF in the amplifier must be very effective. I believe that I have lower harmonics of 60Hz and maybe the filters will take care of the close field.

Should I locate the antenna in the known quiet location, or risk noise pickup in the more "ideal" outdoor location.

Here is the outdoor mast that the GPS lives on. I could mount the E-Field on the unused portion of the mast at the top. Note the 220V wire (twisted ones) along with cable/phone lines below. It is probably only about 5-6 ft from the mast to the power lines.



Also, is the jury still out on whether to ground the E-Field preamp? I remember my Hobby-Boards lightning detector which was a simple Darlington transistor pair interfaced to a counter. The very first thunderstorm was almost totally missed by the detector. I found that I had a poor ground due to being grounded to the vent stack and sewer lines (iron pipe, not PVC).

I added a bonding wire from the vent stack line to the cold water pipe and it worked like a champ.

I am waiting on boxes and STP Cat5, but I will be packaging the amp and antenna soon. Appreciate any comments/guidance.

Greg H.



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Offline Cutty Sark Sailor

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Re: E-Field antenna predicament
« Reply #1 on: June 05, 2014, 08:15:54 PM »
Nope, jury is not out... do not ground the preamp. The air capacity probe to earth is important. Greg, I'm surrounded by M component noise, as you well know. I ran the E field right here next to the computers under test, with little or no noise that prevented testing. I immediately decided to mast my probe, since I'd already determined I had little E field problems. Works fine... I'd say try a 'high' mount temporarily, if you can do that. Duct tape is handy for lots of things  :-P

Also remember these things are sensitive... and they want them to be used <500Km ... My best settings are almost always <½ my H field, with thresholds at 90mv  and the darn things still reach 1200-1500mi.  So back the gains down... I'll get 500 mi strikes at a 1x2 with my 15" probe... the noise may not be the factor you expect.

Also, you may find that higher gain on 1st amp may not be as efficient as lower than 2nd! I have.  It's also easier to change quickly, since all three channels' gain is controlled by the one amp on the preamp board, and the channel C setting sets all three. I'd start the thing out at 4x4 with threshold at 90, alternate channel mapping, and remember C threshold will be lowest of the highest settings of amp 1 or amp 2 channel c.  So if you can't get it to 90, and have turned on alternate channel mapping, go back and force all channels on, set amp1 channel c for 90mv, which now becomes the 'minimum high' for both channel c's. Now, on amp 2 you can adjust the threshold higher, but not lower than 90mv.  Regardless of what your 'settings' numbers show you, the actual setting will be reflected on the 'signals' page.

Mike
 


Offline Knickohr

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Re: E-Field antenna predicament
« Reply #2 on: June 06, 2014, 06:21:14 AM »
I'm wondering, how you can use such short E without high gains  :shock:

I use an 2000mm copper tube (diameter 12mm) and the signals are just OK with nearly max. gains  :roll:

Thomas

Offline Cutty Sark Sailor

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Re: E-Field antenna predicament
« Reply #3 on: June 06, 2014, 08:25:57 AM »
I'm wondering, how you can use such short E without high gains  :shock:

I use an 2000mm copper tube (diameter 12mm) and the signals are just OK with nearly max. gains  :roll:

Thomas
http://forum.blitzortung.org/showthread.php?mode=linear&tid=517&pid=4844#pid4844
and the probe connects to the inboard terminal, not the outer which is ground. Do not connect
any other ground to the system, period, except the ground at the controller board.
May sure you haven't re-engineered any part of the system. If you do that, no one can help.
The probe mounts vertically outside and away from structures, at least 6 feet off the ground.
It connects with good coax cable to the amp, which connects with shortest possible shielded CAT5/6
to amplifier 2 on the controller.
Beyond that, check your components for correct values, but most of all, solder connections.
2 meters is too much probe.
Now look at http://www.wxforum.net/index.php?topic=22710.0
 


Offline JonathanW

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Re: E-Field antenna predicament
« Reply #4 on: June 06, 2014, 09:34:16 AM »
I'm wondering, how you can use such short E without high gains  :shock:

I use an 2000mm copper tube (diameter 12mm) and the signals are just OK with nearly max. gains  :roll:

Thomas

I was running into a problem that I solved by making sure the led was lit on the pre-amp (I think someone else here had a problem with a solder bridge on the pre-amp, and the led would probably have not been lit in his case, either).

Offline 92merc

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Re: E-Field antenna predicament
« Reply #5 on: June 06, 2014, 11:24:29 AM »
I'm still waiting on my E Field parts to arrive.  But I had bought a surge suppressor for the coax, that would need to be grounded.  I believe that would only ground the shield.  But would that be bad?
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Offline Cutty Sark Sailor

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Re: E-Field antenna predicament
« Reply #6 on: June 06, 2014, 11:32:34 AM »
I'm still waiting on my E Field parts to arrive.  But I had bought a surge suppressor for the coax, that would need to be grounded.  I believe that would only ground the shield.  But would that be bad?
No ground other than the one on the controller. The coax characteristic is an integral part of the high pass filter. The amp operates on a split rail, virtual ground. The virtual ground in the preamp is actually established by the forward voltage drop of the power led, about 2.5 v above "ground". The probe is in a manner of speaking, one plate of an air dielectric capacitor with earth as the other plate. Stick to the cookbook and all should be well. If a bolt has your name on it, it's gotcha anyway.
 


Offline JonathanW

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Re: E-Field antenna predicament
« Reply #7 on: June 06, 2014, 11:43:09 AM »
I'm still waiting on my E Field parts to arrive.  But I had bought a surge suppressor for the coax, that would need to be grounded.  I believe that would only ground the shield.  But would that be bad?
No ground other than the one on the controller. The coax characteristic is an integral part of the high pass filter. The amp operates on a split rail, virtual ground. The virtual ground in the preamp is actually established by the forward voltage drop of the power led, about 2.5 v above "ground". The probe is in a manner of speaking, one plate of an air dielectric capacitor with earth as the other plate. Stick to the cookbook and all should be well. If a bolt has your name on it, it's gotcha anyway.

It helps to view the "preamp" and wire/probe as a single unit (kind of like a typical short whip for 2 meters, that includes a matching transformer inside).  The thing is, the amp itself should probably also be viewed as part of the same unit.  The closest I'd consider some sort of lightning protection to the probe would be on the shielded ethernet connection between the controller and the amp, and even there, the cable is being used in a non-differential mode to transfer analog signals.  So you risk some attenuation/modification of the signal.

The preamp has integral protection diodes in the connection to the wire/probe.

When I install my station in its permanent home, the entire station (including the controller) will be placed some distance from my house.  The station itself will be grounded on the spot (including the enclosure for the amps and controller) using the controller/power supply ground.  If I go with a wired ethernet connection to the station and not wireless/solar, it will be with shielded cat5e, coax for power, and some nice copper ground strap alongside to prevent problems with ground potential rise from nearby hits and tie the ground to the house single-point ground.

The only place I'm considering surge/lightning protection is in the data/power line connection between the house and the station.

I'm not particularly worried about a direct strike to the station, but I have a bunch of 75-100' trees around that could lead to substantial rise in local ground potential if they attract a strike.  I'd rather not burn out buried cable.

« Last Edit: June 06, 2014, 12:27:19 PM by n0ym »