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From: Laurence KL7UK <hellozerohellozero@hotmail.com>
To: <rsgb_lf_group@blacksheep.org>
Date: Fri, 12 Aug 2011 09:25:29 -0800
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Subject: LF: screened room and the probe/mini
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"Now place the receiver and the rest of the local world with all its noise =
and QRM generators in a screened room and make the feed coaxial through a b=
ulkhead connector into teh screened room and see what happens.   All the QR=
M is contained within the screened room and cannot pass outside.    The ant=
enna is now a strange sort-of dipole with one end in free space=2C and the =
other connected to a solid mass made from the outside of the screened room.=
   It can't pick up any QRM from inside the screened room=2C and all it wil=
l now receive are signals generating an E-field between the probe and the s=
olid mass.  Perfect!
=20
The shack and the rest of the world is not in a screened room=2C so there l=
ies the problem. "
=20
=20
Andy notes -=20
=20
This is a very good prinicple and has served me very well in hotels=2C high=
 rises etc that tended to have a metallic rebar/frame content.... we dont h=
ave trees in a lot of the locations I find myself in**
=20
I found that often=2C by selecting a metal window frame=2C outside door or =
similar bonded to the structure appx 30-40dB common mode noise coming from =
the hotel room up the cable is eliminated. keep the strap from the coax sho=
rt  (small reactance needed) though if your listening on HF. Mine are max 0=
.3m long...
=20
Selecting the actual structure to %^&**# (nearly said it) is an art form an=
d its amazing the number of windows or doors are defacto half or fully touc=
hing the rebar/building frame. This as Andy says gives a defacto (sometimes=
 leaky) Faraday cage and if you can select the probe in a favorable positio=
n outside and  up over the edge of a building youll probably get fair resul=
ts. Ive used this solution in Singapore=2C China=2C Indonesia=2C Malaysia=
=2C Chile etc and got what I would call good results. Not ruffling my feath=
ers but received Eu on 500 and 137 on a PA0RDT from most of those locations=
 on a quiet/favorable day=2C and I would lay a hefty wager for these locati=
ons a 20/30m long wire suitably matched would have been worse....just inter=
cepting too much rubbish...
=20
Im guessing some of the UK brick houses built in the 40/50 and 60's with th=
e older window/outside frames will oblidge...
=20
Now a lot of Buildings in say Alaska/Oklahoma  are only wooden framed and t=
hus are fairly transparent to RF at LF/MF and HF - (use a portable radio on=
 SW with its whip and try to see what you can hear inside a metal framed/bo=
nded building=2C:-) )) - For instance in Alaska I have all sort of problems=
 from common mode and direct radiation noise - I found that a single or mor=
e earth rod where the coax comes in helps a tadge=2C but with common mode c=
hoke using peaky turns at the required freq helps a little more=2C sometime=
s=2C isolation transformers more as long as you can keep inthe intercap dow=
n and remind yourself they have to be phased properly on a toriod. But the =
best Ive found was to extend my ^%$# mat <nearly said it again>  (mulitple =
wires radiating away) from the shack window out to where the probe is in th=
e air as far as possible - and to keep these wires way way away from the el=
ectrical protection earth rods from the incoming supply which have their ow=
n noise and currents....
=20
I like the idea of remote power=2C optic cables=2C with small counterpoises=
 or balanced array=2C but for simplicity an PA0RDT/AMRAD or modified themes=
 are hard to beat for those poor souls like me that have to select a small =
quietish spot=2C dont have trees or real estate=2C or a nearly handy bonded=
 and rebar/metal framed building...
=20
If I build a new house Im going to get them to pull and staple 12 gauge sol=
id cable every metre up and over vertically the whole length of the buildin=
g and bond this to the @#%$# <nearly said it > rebar....
=20
Laurence KL7UK et al
=20
=20
=20
**Acacia trees for some reason are my tree of choice for hoisting up - Palm=
 trees for some reason arent so good. Im testing Pecan trees at this time :=
-))
=20



From: g3kevmal@talktalk.net
To: rsgb_lf_group@blacksheep.org
Date: Wed=2C 10 Aug 2011 17:08:37 +0100
Subject: Re: LF: Re: HB9ASB...





=20

----- Original Message -----=20
From: Andy Talbot=20
To: rsgb_lf_group@blacksheep.org=20
Sent: Wednesday=2C August 10=2C 2011 4:30 PM
Subject: Re: LF: Re: HB9ASB...


I'm surprised so many seem to misunderstand how high impedance E-field prob=
es work.  There is too much hearsay and false comments being peddled.   Sto=
p thinking of the feeder as 'part' of the antenna as if it were all one ent=
ity and consider each stage.... And forget that thing called Ground complet=
ely.
=20
It starts with a high input-impedance amplifier which must have two connect=
ions - ignore any common reference for now=2C it just has two input pins.  =
A voltage is imposed across these from any antenna with two ports=2C  like =
a short dipole.   This input voltage is buffered=2C amplified=2C  and sent =
to the two output pins from which it travels down a feeder - balanced=2C co=
ax=2C or whatever -  and into your receiver.   So far we haven't made any c=
onnection between input and output=2C and they could (and ideally would) be=
 independent and isolated from eachother
=20
However=2C they're not.   One input connection is usually common with one o=
utput - usually the  0V DC supply pin and the reference  (and please note=
=2C I am not referring to this as ground=3B ground is taboo=2C a dirty word=
=2C  and will not be mentioned)    Which means the other hot-side input pin=
 now has a voltage imposed on it with respect to the reference.  This will =
probably come from a probe antenna which is coupling to the E-field of a ra=
diated signal.   Now=2C bear in mind any antenna must have two output ports=
=2C so where is the other side?   As the reference input pin is connected t=
o the output reference pin=2C any other connection to this point will form =
the other 'half' of the high impedance short dipole antenna.
=20
Now=2C the feeder dropping down from the amplifier / probe assembly (or acr=
oss=2C or up and over=2C or buried in the soil [see=2C still didn't say the=
 taboo word] ) is connected to the input reference pin by virtue of the amp=
lifiers internally linking them=2C and must therefore form the other half o=
f the dipole.   This is bad.   We have a hi-Z dipole=2C with one short elem=
ent in the air where it should be=2C and the other element being one conduc=
tor of a probably long length of feeder with its end connected to we know-n=
ot-what.
=20
So what do we now have?  A long assymetric dipole plus amplifier assembly=
=2C stretching from some arbitrary shack connection up into free space.   T=
he voltage at the not-middle of this is the stuff that is amplified and fed=
 to the receiver.    So=2C as the bulk of the dipole is close to the shack =
expect the majority of signal received to be locally generated noise.  =20
=20
That is the case for a completely unscreened and un-earthed (still didn't u=
se the word :-)  system.  Picking up any locally generated E-fields at high=
 levels onto the dipole. =20
=20
Now place the receiver and the rest of the local world with all its noise a=
nd QRM generators in a screened room and make the feed coaxial through a bu=
lkhead connector into teh screened room and see what happens.   All the QRM=
 is contained within the screened room and cannot pass outside.    The ante=
nna is now a strange sort-of dipole with one end in free space=2C and the o=
ther connected to a solid mass made from the outside of the screened room. =
  It can't pick up any QRM from inside the screened room=2C and all it will=
 now receive are signals generating an E-field between the probe and the so=
lid mass.  Perfect!
=20
The shack and the rest of the world is not in a screened room=2C so there l=
ies the problem.   However much you don't want it to be=2C with this setup =
the feeder will always form the majority of the antenna because there is no=
thing else there that can be the other half of the dipole.   And if the bot=
tom end of the dipole intrudes into the rest of the world=2C it will pick u=
p stuff it shouldn't
=20
Andy
=20
So the FEEDER does form the majority part of this type of antenna=2C simply=
 one side of a very poor asymetrical dipole.
It would appear this is not the antenna for a noisy urban environment
The long element of the dipole is picking up every possible noise and ampli=
fying it and feeding all this noise plus signal to the RX=2C the minute Pro=
be element is insignificant.=20
This has been my observation all along.
=20
G3KEV
=20
  		 	   		  =

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<body class=3D'hmmessage'><div dir=3D'ltr'>
<DIV>"<EM>Now place the receiver and the rest of the local world with all i=
ts noise and QRM generators in a screened room and make the feed coaxial th=
rough a bulkhead connector into teh screened room&nbsp=3Band see what happe=
ns.&nbsp=3B&nbsp=3B <STRONG><FONT color=3D#c00000>All the QRM is contained =
within the screened room and cannot pass outside.</FONT></STRONG>&nbsp=3B&n=
bsp=3B&nbsp=3B The antenna is now a strange sort-of dipole with one end in =
free space=2C and the other connected to a solid mass made from the outside=
 of the screened room.&nbsp=3B&nbsp=3B It can't pick up any QRM from inside=
 the screened room=2C and all it will now receive are signals generating an=
 E-field between the probe and the solid mass.&nbsp=3B Perfect!</EM></DIV>
<DIV><EM>&nbsp=3B</EM></DIV>
<DIV><EM>The shack and the rest of the world&nbsp=3Bis not in a screened ro=
om=2C so there&nbsp=3Blies the problem.&nbsp=3B"</EM></DIV>
<DIV>&nbsp=3B</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>Andy notes - </DIV>
<DIV>&nbsp=3B</DIV>
<DIV>This is a very good prinicple and has served me very well in hotels=2C=
 high rises etc that tended to have a metallic rebar/frame content.... we d=
ont have trees in a lot of the locations I find myself in**</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>I found that often=2C by selecting a metal window frame=2C outside doo=
r or similar bonded to the structure appx 30-40dB common mode noise coming =
from the hotel room up the cable is eliminated. keep the strap from the coa=
x short&nbsp=3B (small reactance needed) though if your listening on HF. Mi=
ne are max 0.3m long...</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>Selecting the actual structure to %^&amp=3B**# (nearly said it) is an =
art form and its amazing the number of windows or doors are defacto half or=
 fully touching the rebar/building frame. This as Andy says gives a defacto=
 (sometimes leaky) Faraday cage and if you can select the probe in a favora=
ble position outside and&nbsp=3B up over the edge of a building youll proba=
bly get fair results. Ive used this solution in Singapore=2C China=2C Indon=
esia=2C Malaysia=2C Chile etc and got what I would call good results. Not r=
uffling my feathers but received Eu on 500 and 137 on a PA0RDT from most of=
 those locations on a quiet/favorable day=2C and I would lay a hefty wager =
for these locations a 20/30m long wire suitably matched would have been wor=
se....just intercepting too much rubbish...</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>Im guessing some of the UK brick houses built in the 40/50 and 60's wi=
th the older window/outside frames will oblidge...</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>Now a lot of Buildings in say Alaska/Oklahoma &nbsp=3Bare only wooden =
framed and thus are fairly transparent to RF at LF/MF and HF - (use a porta=
ble radio on SW with its whip and try to see what you can hear inside a met=
al framed/bonded building=2C:-) )) - For instance in Alaska I have all sort=
 of problems from common mode and direct radiation noise - I found that a s=
ingle or more earth rod where the coax comes in helps a tadge=2C but with c=
ommon mode choke using peaky turns at the required freq helps a little more=
=2C sometimes=2C isolation transformers more as long as you can keep inthe =
intercap down and remind yourself they have to be phased properly on a tori=
od. But the best Ive found was to extend my ^%$# mat &lt=3Bnearly said it a=
gain&gt=3B &nbsp=3B(mulitple wires radiating&nbsp=3Baway)&nbsp=3Bfrom the s=
hack window out to where the probe is in the air as far as possible - and t=
o keep these wires way way away from the electrical protection earth rods f=
rom the incoming supply which have their own noise and currents....</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>I like the idea of remote power=2C optic cables=2C with small counterp=
oises or balanced array=2C but for simplicity an PA0RDT/AMRAD or modified t=
hemes are hard to beat for those poor souls like me that have to select a s=
mall quietish spot=2C dont have trees or real estate=2C or a nearly handy&n=
bsp=3Bbonded and rebar/metal framed building...</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>If I build a new house Im going to get them to pull and staple 12 gaug=
e solid cable every metre up and over vertically the whole length of the bu=
ilding and bond this to the @#%$# &lt=3Bnearly said it &gt=3B rebar....</DI=
V>
<DIV>&nbsp=3B</DIV>
<DIV>Laurence KL7UK et al</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>**Acacia trees for some reason are my tree of choice for hoisting up -=
 Palm trees for some reason arent so good. Im testing Pecan trees at this t=
ime :-))<BR>&nbsp=3B</DIV>
<DIV>

<HR id=3DstopSpelling>
From: g3kevmal@talktalk.net<BR>To: rsgb_lf_group@blacksheep.org<BR>Date: We=
d=2C 10 Aug 2011 17:08:37 +0100<BR>Subject: Re: LF: Re: HB9ASB...<BR><BR>
<META name=3DGenerator content=3D"Microsoft SafeHTML">
<STYLE>
</STYLE>

<DIV><FONT face=3DArial></FONT>&nbsp=3B</DIV>
<BLOCKQUOTE style=3D"BORDER-LEFT: #000000 2px solid=3B PADDING-LEFT: 5px=3B=
 PADDING-RIGHT: 0px=3B MARGIN-LEFT: 5px=3B MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV style=3D"FONT: 10pt arial=3B BACKGROUND: #e4e4e4=3B font-color: black"=
><B>From:</B> <A title=3Dandy.g4jnt@gmail.com href=3D"mailto:andy.g4jnt@gma=
il.com">Andy Talbot</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A title=3Drsgb_lf_group@blacksh=
eep.org href=3D"mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blackshe=
ep.org</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday=2C August 10=2C 2011=
 4:30 PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: LF: Re: HB9ASB...</DIV>
<DIV><BR></DIV>
<DIV>I'm surprised so many seem to misunderstand how high impedance E-field=
 probes work.&nbsp=3B&nbsp=3BThere is&nbsp=3Btoo much hearsay and false com=
ments being peddled.&nbsp=3B &nbsp=3BStop thinking of the feeder as 'part' =
of the antenna as if it were all one entity and consider&nbsp=3Beach stage.=
... And forget that thing called Ground completely.</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>It starts with a&nbsp=3Bhigh input-impedance amplifier which&nbsp=3Bmu=
st have&nbsp=3Btwo connections - ignore any&nbsp=3Bcommon reference for now=
=2C it just has two input pins.&nbsp=3B A voltage is imposed across these f=
rom any antenna with two ports=2C &nbsp=3Blike a short dipole.&nbsp=3B&nbsp=
=3B This input voltage is buffered=2C amplified=2C&nbsp=3B and sent to the =
two output pins from which it travels down a feeder - balanced=2C coax=2C o=
r whatever - &nbsp=3Band into your receiver.&nbsp=3B&nbsp=3B So far we have=
n't made any connection between input and output=2C and they could (and ide=
ally would) be independent and isolated from eachother</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>However=2C they're not.&nbsp=3B&nbsp=3B One input connection is usuall=
y common with one output - usually the &nbsp=3B0V DC supply pin and the ref=
erence &nbsp=3B(and please note=2C I&nbsp=3Bam not referring to this&nbsp=
=3Bas ground=3B ground is taboo=2C a dirty word=2C &nbsp=3Band will not be =
mentioned)&nbsp=3B&nbsp=3B&nbsp=3B&nbsp=3BWhich&nbsp=3Bmeans the other hot-=
side input pin now has a voltage imposed on it with respect to the referenc=
e.&nbsp=3B This will probably come from a probe antenna which is coupling t=
o the E-field of a radiated signal.&nbsp=3B&nbsp=3B Now=2C bear in mind any=
 antenna must have two output ports=2C so where is the other side?&nbsp=3B&=
nbsp=3B As the reference input pin is connected to the output reference pin=
=2C any other connection to this point will form the other 'half' of the hi=
gh impedance short dipole antenna.</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>Now=2C the feeder dropping down from the amplifier / probe assembly&nb=
sp=3B(or across=2C or up and over=2C or buried in the soil [see=2C still di=
dn't say the taboo word]&nbsp=3B) is connected to the input reference pin b=
y virtue of the amplifiers internally linking them=2C and must therefore fo=
rm the other half of the dipole.&nbsp=3B&nbsp=3B This is bad.&nbsp=3B&nbsp=
=3B We have a hi-Z dipole=2C with one short element in the air where it sho=
uld be=2C and the other element being one conductor of a probably long leng=
th of feeder with its end connected to we know-not-what.</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>So what do we now have?&nbsp=3B A long assymetric dipole plus amplifie=
r assembly=2C stretching from some arbitrary shack connection up into free =
space.&nbsp=3B&nbsp=3B The voltage at the not-middle of this is the&nbsp=3B=
stuff that is amplified and fed to the receiver.&nbsp=3B&nbsp=3B&nbsp=3B So=
=2C as the bulk of the dipole is close to the shack expect the majority of =
signal received to be locally generated noise.&nbsp=3B&nbsp=3B </DIV>
<DIV>&nbsp=3B</DIV>
<DIV>That is the case for a completely unscreened and un-earthed (still did=
n't use the word :-)&nbsp=3B system.&nbsp=3B Picking up any locally generat=
ed E-fields at high levels onto the dipole.&nbsp=3B </DIV>
<DIV>&nbsp=3B</DIV>
<DIV>Now place the receiver and the rest of the local world with all its no=
ise and QRM generators in a screened room and make the feed coaxial through=
 a bulkhead connector into teh screened room&nbsp=3Band see what happens.&n=
bsp=3B&nbsp=3B All the QRM is contained within the screened room and cannot=
 pass outside.&nbsp=3B&nbsp=3B&nbsp=3B The antenna is now a strange sort-of=
 dipole with one end in free space=2C and the other connected to a solid ma=
ss made from the outside of the screened room.&nbsp=3B&nbsp=3B It can't pic=
k up any QRM from inside the screened room=2C and all it will now receive a=
re signals generating an E-field between the probe and the solid mass.&nbsp=
=3B Perfect!</DIV>
<DIV>&nbsp=3B</DIV>
<DIV>The shack and the rest of the world&nbsp=3Bis not in a screened room=
=2C so there&nbsp=3Blies the problem.&nbsp=3B&nbsp=3B However much you don'=
t want it to be=2C with this setup&nbsp=3Bthe <STRONG>feeder will always fo=
rm the majority of the antenna because there is nothing else there that can=
 be</STRONG> the other half of the dipole.&nbsp=3B&nbsp=3B And if the botto=
m end of the dipole intrudes into the rest of the world=2C it will pick up =
stuff it shouldn't</DIV>
<DIV>&nbsp=3B</DIV>
<DIV><FONT face=3DArial>Andy</FONT></DIV>
<DIV><FONT face=3DArial></FONT>&nbsp=3B</DIV>
<DIV><FONT face=3DArial>So the FEEDER does form the majority part of this t=
ype of antenna=2C simply one side of a very poor asymetrical dipole.</FONT>=
</DIV>
<DIV><FONT face=3DArial>It would appear this is not the antenna for a noisy=
 urban environment</FONT></DIV>
<DIV><FONT face=3DArial>The long element of the dipole is picking up every =
possible noise and amplifying it and feeding all this noise plus signal to =
the RX=2C the minute&nbsp=3BProbe element is insignificant.&nbsp=3B</FONT><=
/DIV>
<DIV><FONT face=3DArial>This has been my observation all along.</FONT></DIV=
>
<DIV><FONT face=3DArial></FONT>&nbsp=3B</DIV>
<DIV><FONT face=3DArial>G3KEV</FONT></DIV>
<DIV><FONT face=3DArial></FONT>&nbsp=3B</DIV>
<DIV><FONT face=3DArial></FONT>&nbsp=3B</DIV></BLOCKQUOTE></DIV> 		 	   		 =
 </div></body>
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