PSN-L Email List Message
Subject: Re: Digging in...
From: ian ian@...........
Date: Sat, 13 Aug 2005 08:20:28 +0100
this all sounds terribly professional. In my last house, I drilled a
hole in the top of the property's boundary wall and hammered the
geophone spike into it. Then I screwed the geophone back on to its
spike. I covered this with 2 plastic containers, one bigger than the
other, and put a rock on top to make sure it didn't blow away. This
sufficed to protect it from something like the 180" of rain/year that we
got. I then had about 50 ft of external co-ax connecting to the
filter/amplifier, via a lightning arrestor. I had to get it away from
the house as our 2 screaming kids would have made things impossible!
This seemed to work fine. I was able to listen in to tantrums of the
local volcano 20 miles away, as well as its companions around the state
(Hawaii). I too was in a cul-de-sac street with the main road about 200
feet away. I picked up the local traffic on the main road during the
day. The only other noise source, which I discovered when I dismantled
it to re-locate, was the presence of Gecko eggs inside the plastic
So, whilst you are waiting for the concrete to cure, you could try
something "rough and ready" like the above.
Dennis Wieck wrote:
> ChrisAtUpw@....... wrote:
>> Hi Dennis,
>> Is it a timber house or one with brick/stone walls?
> Its brick
>> How many stories?
>> Are they the 4.5 Hz geophones?
>> So long as you stay away from the foundations, you should not get
>> too much house noise. I suggest that you try putting the geophone
>> under the house with the three legs pushed firmly into the soil and
>> see what results you get. Look for significant changes in the
>> background noise between no wind and strong wind conditions and keep
>> some recordings for reference. Also look out for spikes and
>> interference signals, traffic or other noise over 24 hrs.
> The good news is I am 200 yards from the nearest road ( except for
> what comes in my driveway)
>> I connected my geophones up to the amplifier in a portable radio and
>> listened with headphones. OK, these signals aren't the seismic ones,
>> but you can often recognise noise sources by ear easier than trying
>> to figure them out from the traces. I start to hear fast cars on the
>> main road at about 1 km. There is a slightly depressed water drain on
>> the main road about 100 yards away which gives thump signals
>> occasionally with passing lorries..... Check for slamming doors and
>> windows, fridge start/stop, cooking loads, central heating timing,
>> wind noise.....
>> If the under house installation is OK, you can scoop out several
>> inches of the topsoil and lay a 3 ft square concrete base in a wood
>> frame. You need to cover it with polythene to keep it 'wet' for maybe
>> a month to 'cure' fully. You use a 50:50 cement and sand mixture, no
>> gravel. Professional installations use a vibrator to remove air
>> bubbles from the wet mix after it is poured. You can get a lot out
>> with a stick. Cement can be quite corrosive in contact with metal,
>> but you can use special paints. You will have to leave adequate space
>> for the thermal / draft screening box if you are definitely going to
>> use a SG horizontal; maybe a longer slab?
>> The second option would to build a small vault probably dug in
>> the ground 3 or
>> 4 feet deep. ( Most likely I would not be able to get to bedrock).
>> I have seen
>> several of this type on the web. I live pretty much in the country
>> on about 5
>> acres. Most of the land is pretty hilly with a lot of trees.
>> You would have to make it water proof / adequately drained / dry
>> inside. See various websites for ways of doing this.
>> http://www.guralp.net/services/stations/eskdalemuir/ is a
>> professional example in soil which saturates with water. See also
>> I have seen references saying that you need to be relatively far
>> from trees etc or the wind moving them will affect the sensors. If
>> I do this I would have further to run the cables back to the
>> house. Is it better to have the longer run from the sensors to
>> the boards or to have the A/D output have the longer runs?
>> Trees may give broad band noise, but this may be more serious for
>> the longer period instruments. Aim to keep your sensors at a distance
>> equal to the height of the trees, minimum. This is very roughly the
>> expected extent of the roots.
> This is about impossible on my lot. Even the under the house spot
> would not meet this but would probably be the closest.
>> Exposed houses will also experience wind noise.
>> You have the problem of long cable runs and probably some
>> lightning protection required for installations away from the house.
> I am used to this. I am a ham and have dealt with tower and coax to
> my radios grounding.
>> Some soils have such poor electrical conductivity / are so dry that
>> the effective 'electrical ground surface' is several feet below
>> ground level. All your house electrical wiring is effectively
>> sticking out above the electrical ground! If lightning is a severe
>> local hazard, you can use intermittently charged batteries and a
>> length of fibre optic cable to isolate the digital signals. There are
>> several websites with advice on this for various states. You can bury
>> cables in plastic water pipe. Pipe end fittings designed for water
>> tanks are readily available.
> Is there a problem with moderate ( probably less than 100 ft) runs
> between the geophones and the amp/filter/A/D or do I need to remote
> them ( that adds to the waterproof question)?
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