Some months ago I purchased a Geotech Instruments  Helicorder RV-301B with 
the accompanying amplifier AR-320B.  It works just  fine when I drive it 
using one channel from one of Larry's older amp/filter  boards.  The input is 
from a Lehman-type horizontal  detector utilizing a coil with 8k resistance. 
(hz1 detector).   

I normally have the Lehman hz1 output going  into a second, newer version 
of Larry's amp/filter A/D boards, and  then on to WinSDR.  
 
Here is my problem:  I want to split the output  from hz1 using a Y 
connector to both the WinSDR display and the helicorder so I  can record analog and 
digital simultaneously.  When I do this, the  helicorder stylus goes dead 
and the CRT display from the amp/filter/AD board  displays rhythmic amplitude 
spiking.  There appeared to be an  impedance mismatch, so  an EE designed a 
buffer amplifier for me with  two outputs.  Unfortunately, when using the 
buffer amp, the helicorder  stylus still is inoperative and the spiking again 
shows up on the CRT display  from the amp/filter/AD board, just as before.
 
I am at a loss at what to try next.  The  Geotech Instrument people say 
they are too busy to give me any advice.  I  am wondering if any of you using 
the RV301B helicorder has tried to use a split  signal such as I described?  
I would appreciate any suggestions from the  PSN family.
Thanks and regards,
 
Al Hrubetz
Dallas, Texas
 
  





Some months ago I purchased a Geotech Ins=
truments=20
Helicorder RV-301B with the accompanying amplifier AR-320B.  It works=
 just=20
fine when I drive it using one channel from one of Larry's older amp/filte=
r=20
boards.  The input is from a Lehman-type horizontal=20
detector utilizing a coil with 8k resistance. (hz1 detector). =
=20
  
 
I normally have the Lehman hz1 outpu=
t going=20
into a second, newer version of Larry's amp/filter A/D boards,=
 and=20
then on to WinSDR.  
 
Here is my problem:  I want to split the=
 output=20
from hz1 using a Y connector to both the WinSDR display and the helicorder=
 so I=20
can record analog and digital simultaneously.  When I do this, the=20
helicorder stylus goes dead and the CRT display from the amp/filter/AD boa=
rd=20
displays rhythmic amplitude spiking.  There appeared to be =
an=20
impedance mismatch, so  an EE designed a buffer amplifier for me=
 with=20
two outputs.  Unfortunately, when using the buffer amp, the helicorde=
r=20
stylus still is inoperative and the spiking again shows up on the CRT disp=
lay=20
from the amp/filter/AD board, just as before.
 
I am at a loss at what to try next. =
 The=20
Geotech Instrument people say they are too busy to give me any advice.&nbs=
p; I=20
am wondering if any of you using the RV301B helicorder has tried to use a=
 split=20
signal such as I described?  I would appreciate any suggestions from=
 the=20
PSN family.
Thanks and regards,
 
Al Hrubetz
Dallas, Texas