Need suggestions to reduce signal pick up of coax cable.

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I started an AM receive antenna installation by laying out 200ft of RG6  
coax. It's good coax with braid plus foil shield.
  The coax is on the ground, I shorted the end and connected the other  
end to my radio, there are no ground connections.
  The coax has 3 to 6 S units on my local radio stations.
I want my coax to pick up as little signal as possible, because I want  
to install directional antenna on it.

  Next, I tried grounding the far end to a 5ft copper rod,
this increased signal strength.

  Then I grounded the shield just before it enter the house,
this increased signal strength.

Removing the far end ground and having just the ground near the radio  
didn't help.

  I tried 3 different Chokes on the Coax at the radio, one monster choke  
is a very large potcore that I wound 15 turns of coax on, it has 25kohms  
of reactance at 1MHz.
  The chokes didn't help.

  I wound a 1:1 Isolation transformer installed at the radio.
That didn't help.

  I could invest in some Quad shield cable, but nope.
I already have over 1000ft of RG6.

  The quietest so far is just the coax, no grounds.
The chokes and transformer didn't seem to hurt, but they didn't help either.

  I also changed the short at the far end to a 75 ohm resistor.
That didn't help.

Anyone have recommendations on how to quiet the coax?

                           Mikek





Re: Need suggestions to reduce signal pick up of coax cable.
On a sunny day (Sat, 9 Jun 2018 07:31:35 -0500) it happened amdx

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First thing:
 What sort of noise do you get with that co-axe?.
 If it is the usual MW RF impulse noise, better find the source.
 put a second antenna near the noise source, and use one of those noise subtracter circuits:
  http://www.vk5tm.com/homebrew/noisecancel/noisecancel.php

2) Is the grounding of the coax at the receiver, so the receiver's input circuit, correct?
   This is easy to check, short the co-axe at the receiver side, and the noise should disappear,
   if not then the receiver's input circuit is shit.
   Best circuit is likely just a single turn and then an LC, note the galvanic isolation

             --------- FET gate
   ===--    |     |  
    |   | |(      |/ Ctune
    |    )|(     ===
    |___| |(     /|
           |______|
                  |
                 ///  

3) In any case it is better to have a preamplifier at the antenna side, and a less sensitive RF input stage in the receiver.
  
  

Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 8:20 AM, snipped-for-privacy@nospam.org wrote:
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  I had to check, I did not use the word noise, I'm receiving radio  
signals on my coax.
  How do I quiet it?


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  When I installed my active mini whip I had terrible noise, I have  
already conquered electrical impulse noise.
  Mostly outdoor lighting with sensors.
                                    Mikek


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Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 8:23 AM, amdx wrote:
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How did you shield the chokes and transformers?
Can we assume that when you put  shorting connector right at
the receiver, the interference went to zero?
And with the inductive gizmos connected and the shorting connector
at the INPUT to the inductive gizmos?
What happened with the short and connecting the coax shield to the
radio ground?

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Re: Need suggestions to reduce signal pick up of coax cable.
On Saturday, June 9, 2018 at 11:24:07 AM UTC-4, amdx wrote:
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Hmm, I'm not a radio guy, but isn't ground part of the antenna you'll
hang on the end?  If so, then why is picking up radio signals when  
you ground it, bad?  

George H.  
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Re: Need suggestions to reduce signal pick up of coax cable.

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I have the MiniWhip sold by someone in Leningrad on eBay.  It's VERY
sensitive to grounding and ground loops:
"Grounding of MiniWhip and other active whip antennas"
<http://www.pa3fwm.nl/technotes/tn09d.html
I had to move the MiniWhip to various location on my hillside before I
found a usable location.  I current theory (pun intended) is that I'm
dealing with ground currents delivered by the electrical breaker box
ground rods on various houses.  My ideal location turned out to be as
far away as possible from any of these ground rods.  However, I don't
know if this is genuine or coincidence.  

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What kind of lighting?  LED or incandescent?  117VAC LED bulbs are
sometimes rather noisy.  What happens when you turn off the outdoor
lights?



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Need suggestions to reduce signal pick up of coax cable.
On Saturday, June 9, 2018 at 1:23:08 PM UTC-10, Jeff Liebermann wrote:
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As someone else already mentioned, use two 200 foot coax cables to
form a differential signal and a common mode rejection. If both coax outer
shields get the same noise, than a differential stage on the receiver
can be designed to reject common mode noise. The two inner wires will then
have the signal you want as a differential input. The common mode rejection
will be one goal.

Re: Need suggestions to reduce signal pick up of coax cable.
On Saturday, June 9, 2018 at 10:31:44 PM UTC+10, amdx wrote:
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Semi-rigid coax - where the outer conductor is thin tube of solid copper - is probably the nicest, but 200 feet wouldn't be cheap

http://www.farnell.com/datasheets/1700823.pdf

covers RG402. 200feet is 61 metres, and for that much it's $A11.84 per metre in Australia.

Solder-on connectors aren't cheap either.

It's going to be cheaper in the US - Newark will sell you a 50 metre spool for $US184.14

--  
Bill Sloman, Sydney


Re: Need suggestions to reduce signal pick up of coax cable.
On Saturday, June 9, 2018 at 8:31:44 AM UTC-4, amdx wrote:
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er.

Don't know, but just a thought, try installing a common mode choke.  At FM  
frequencies this can be a few turns of the coax on a 2 liter coke bottle.  
Normally this deals with issues created by a balanced antenna on an unbalan
ced line, but really it has to do with currents on the outside of the coax.
  The fact that grounding your shield at the remote end increased the noise
 makes me think this could be your problem.  

Rick C.

Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 9:12 AM, snipped-for-privacy@gmail.com wrote:
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I addressed that here,
"I tried 3 different Chokes on the Coax at the radio, one monster choke
is a very large potcore that I wound 15 turns of coax on, it has 25kohms
of reactance at 1MHz.
   The chokes didn't help."
  They were all CMCs.

  The fact that grounding your shield at the remote end increased the  
noise makes me think this could be your problem.
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Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 7:31 AM, amdx wrote:
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Does the signal go away if you disconnect the center conductor at the radio?


Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 9:19 AM, John S wrote:
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    I'll try that later today.
                       Mikek

Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 10:32 AM, amdx wrote:
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  JohhnyBgood, could you repost, on both of my computers your post is empty.
                         Mikek

Re: Need suggestions to reduce signal pick up of coax cable.
On Sat, 09 Jun 2018 07:31:35 -0500, amdx wrote:

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 JOOI, did you try touching the tip (or screen - it shouldn't matter  
which in this case) of the co-axial plug to the screen/ground of the  
receiver?s co-axial aerial socket? The interference could simply be due  
to ground currents in the receiver's input circuit leaking into its input  
filter.

 If you just connect that co-ax to the centre pin on the aerial socket as  
an end fed long wire aerial, you're likely going to see S9 plus 30dB or  
higher signals on the Medium Wave band (I've assumed you mean the MW  
broadcast band with your AM reference). Trying to attenuate a 30dB over S9  
signal down to the S1 level, assuming 6dB per S point, corresponds to a  
total attenuation factor of 78dB. That level of attenuation is tricky  
enough to achieve in the best of circumstance and no mean feat at that!

 Considering your project (200 feet of co-ax *and* a directional aerial  
for the MW band), I guess you must be well clear of any conurbations and  
out in open country. Even though you might not be so troubled by QRM as  
most of us unfortunates usually are, QRN is likely to be the limiting  
factor in this case. That S6 level of unwanted leakage from local MW  
broadcast stations is likely to be drowned out by the QRN from a decent  
MW antenna array anyway. You may be worrying about nothing if those  
interfering signals from such an antenna array are going to appear as S9  
plus 30dB or higher anyway.

 I suspect the problem is less to do with a deficiency of the co-ax and  
more to do with a deficiency of receiver's input screening, hence my  
suggestion above.

--  
Johnny B Good

Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 10:59 AM, Johnny B Good wrote:
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  If I understand--- I have taken the coax loose and connected just the  
shield to the shield connection of the radio.
  No signal.
  Connecting the coax shield to the center pin of the radio does give  
plenty of signal, but I think that's not a problem.


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Naw, highest signal is about an S 9, plus a few db.

Trying to attenuate a 30dB over S9
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  I guess you must be well clear of any conurbations and
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  Not seeing nearly as much noise as you.
I just put two very large CMCs on the power cord of the radio, An Icom  
71A btw. This did reduce the signal pick up.
So, now with the power cord CMC and a short at the far end of the coax,
  I have 5 S units on 590kHz, but 1260kHz and 1430kHz only have 0.5 S  
units, that is a huge reduction.
  This leads me to think I need to run my radio from a battery.

590kHz has been the highest signal with every iteration. Both transmit
from the same location, 590kHz at 1700watts and 1430kHz at 5000watts.

  You may be worrying about nothing if those
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  Now with my Power cord CMC and the coax shorted at the far end. I can
get 14 stations 9 are 1 S unit or below 4 stations below 3 S units and
590 is 5.5 S units.
  I'm going to spend some effort getting the coax below any leaves and in
contact with actual as much dirt as I can.

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   ?

               Mikek



Re: Need suggestions to reduce signal pick up of coax cable.
On 09/06/2018 20:42, amdx wrote:
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What noise level do you get if you attach a 75R dummy load at the  
antenna end?

Is there any change if you touch earth to coax earth to antenna earth?

If you use an attenuator, does the noise level drop more that the  
attenuator value?

I'm wondering if there is some strong signal you're inadvertently  
picking up.

--  
Mike Perkins
Video Solutions Ltd
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Re: Need suggestions to reduce signal pick up of coax cable.
On 6/9/2018 2:55 PM, Mike Perkins wrote:
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The 75 ohm termination causes an extra 2 S units increase from 980kHz to  
1480kHz, from 870 down the signals are about the same.
This is verses the Short.

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   None that I have noticed.

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Re: Need suggestions to reduce signal pick up of coax cable.
On Saturday, June 9, 2018 at 8:31:44 AM UTC-4, amdx wrote:

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How much would 200' of aluminum foil cost you?
You could just foil-wrap the whole run.  And depending on the width of the foil, you could probably get 3x or 4x the length by cutting the foil in strips first.

Would be messy to install.

Also, are you concerned about lightning damage?  (i.e., a lightning strike being conducted into your house/receiver?   Something to consider?


Re: Need suggestions to reduce signal pick up of coax cable.

<snip>

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Lightning surge protectors handle nearby strikes.

https://www.universal-radio.com/catalog/protect/5611.html

Your insurance agent handles direct strikes, provided you survive.

73,

--  
Don Kuenz, KB7RPU


Re: Need suggestions to reduce signal pick up of coax cable.
I haven't read the replies yet but the first thing that comes to mind is to
 find or wind baluns and use 2 lines of coax cut to the same length. Like a
 home brew LVDS. Of course the shields are connected directly and you might
 even want to strip it to the shield in a few places in the run and clamp t
hem together - electrically of course but the right clamp is probably what  
you'll need. This will further reduce pickup, making more sure that it is c
ommon mode even if it comes to ground gradients.  

I think the way you described what you're getting with the current setup is
 the shield is picking up the signal inductively. Even if you leave one end
 open it is still RF so that doesn't necessarily mean shit.  

Now I will read the rest and either find out that I am an asshole or (EEK !
) that I am right. You did say you had a bunch of RG-6, and I am a firm pro
ponent of using what you got.

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