[RFI] Shielded vs unshielded loops - difference

[David Cole]

Tom,

THank you for sharing that build!  Do you by chance have any PC boards
for the RX?
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On Fri, 2014-03-28 at 22:08 -0600, Tom Thompson wrote:
> Several of you have shown interest in the loop  antenna.  I have updated 
> my web page to show more details.  If you have it cached, you may have 
> to refresh it.  The URL is: 
> http://tomthompson.com/radio/ReceivingLoop/loop.html
> 
> Let me know if some of it is unclear.
> 
> Tom   W0IVJ
> 
> On 3/28/2014 1:53 PM, Tom Thompson wrote:
> > Hi Ken,
> >
> > One thing to keep in mind when you choose a loop is the antenna 
> > factor.  I believe your RFI is mainly on 80m.  A small (10")  loop 
> > that is not tuned will have a terrible antenna factor on 80 m. You may 
> > not even hear the noise from your house.  Also, your receiver probably 
> > does not have a very good attenuator in the front end. When you get 
> > close to the noise, you can detune the loop and get some attenuation.  
> > You need to keep the signal right at the noise level in the null for 
> > the AGC NOT to work if the S-meter is not very good.  When the AGC is 
> > NOT working, you can listen to the strength of the signal through the 
> > speaker.  Again, remember the null is looking through the loop with 
> > the feed at the bottom.  Also, I always put a choke balun right at the 
> > loop so I don't get false readings from picking up signals on the coax 
> > when the signal gets strong.
> >
> > When you start your hunt, find the direction of the noise by nulling 
> > the loop.  You now have an ambiguity in direction.  Peak the noise by 
> > turning the loop edgewise and walk in one direction. Keep rotating the 
> > loop back and forth looking for the peak signal to get stronger.  If 
> > the peak is getting weaker, walk in the other direction.  When you get 
> > very close to the RFI, use the null feature of the loop and attenuate 
> > the signal by switching in an attenuator or detuning the loop.
> >
> > I have been able to trace a grow light almost to the room in the house 
> > by not getting on the residential property.  Once I find the house and 
> > if the RFI is on a timer, I will position myself in front of the house 
> > and wait for the noise to appear to make sure I have the right house.
> >
> > If you get this far, email me and I'll tell you how I approach the 
> > grower.  That is sometimes tricky and could be dangerous so I do not 
> > want to generalize here.
> >
> > Tom   W0IVJ
> >
> > On 3/28/2014 1:17 PM, Kenneth G. Gordon wrote:
> >> "The unshielded loop will...respond to electrostatically induced noise."
> >>
> >> While:
> >>
> >> "The shielded loop , on the other hand,  is almost insensitive to
> >> electrostatically induced noise."
> >>
> >> In other words, the shielded loop is NOT a good choice to DF the 
> >> types of
> >> noise we are most often bothered by, while the un-shielded loop is
> >> specifically sensitive to such noise.
> >>
> >> So, my use of my NM-20B, with its shielded loop, was counter-productive.
> >>
> >> Kenneth G. Gordon W7EKB
> >>
> >> "Courage is being scared to death but saddling up anyway."--- John   
> >> Wayne
> >>
> >> _______________________________________________
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> >> RFI at contesting.com
> >> http://lists.contesting.com/mailman/listinfo/rfi
> >>
> >
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> >
> 
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