Hello Tom,

I also had this problem and never completely solved it, but  I did have 
considerable success in reducing the level of interference.

I began by thinking that the computer and A/D was probably the common 
point of seismic noise generation.  Most likely by rectification by 
overloading at the first amplification of seismic signal.  So, try to 
get the RF off the input lines from seismometers into the computer and A/D.

First I wrapped my (about 12 foot long) shielded cable running from 
seismometer to A/D (Saum built outboard device) through a torroid as 
many times as could be wrapped in the about 1 1/2 inch I.D. of the 
torroid.  I did the same with the cable from A/D to computer, leaving 
the A/D isolated between torroids.  This helped.

Next I went into the Saum device and put a 0.01 mmf capacitor between 
the input terminal and ground.  That helped a lot more without reducing 
the seismic signal noticeably.  I expect that with Larry's A/D, you 
would need to do this for each channel (only if it is not already 
provided by Larry).

Before doing any soldering, I suggest trying various configurations 
using components clipped in with short alligator leads.

In summary and retrospect, I think that I had an RF common mode current 
that was developed on the seismic cables when I transmitted.  By common 
mode, I mean that the current was running on the shield of the wire 
between A/D and seismometer.   This resulted in the A/D being positive 
when the seismometer was negative (alternating).

Good Luck on curing the problem,

Roger

On 02-21-2010 12:00 AM, psn-l-digest-request@.............. wrote:
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 1                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Ham radio interference
> From:    Thomas Dick
> Date:    Sat, 20 Feb 2010 11:00:30 -0600
>
> Anyone got some suggestions; experiencing interference while
> transmitting ---
>                                 my ham radio setup; FT101, FT757 and Icon 207
>                                 low band filtering, torroids on in power
> and grounds -- ground uses 6 ft copper coated rods
> ...                            only about 20 ft from a lake
> antennas; vertical for 2 meters at 60 feet, ground plane for ten meters
> at 80 feet, 160 meter, 80-40 inverted V
>
> my seismic epuipment; two 20 sec Lehmans, AS1 with magnetic induction,
> Larry Cochrane Amp, AD converter(in metal cases and grounded outside
> again with a separate 6 rod), 4.5 HZ geophones .. with isolation and
> battery backup.
>
>
> When I transmit on any band. drifting of the base line display occurs
> and spikes appear. I used to run 400 watts on 29.6 mHz (a repeater) but
> abandoned that after 25 yrs when I couldn't cure this problem. I
> recently put up the 80-40 meter antenna and have a 1:1.2 SWR.... still
> the interference is there! Any suggestions?
>
>    
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