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Author Topic: RF Leak/Coax  (Read 3887 times)
YONU
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Posts: 67




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« on: January 16, 2013, 07:26:38 PM »

ok I have a quick question that I am sure one of the Elmers can answer I have a issue I am trying to sort out and I am not sure if it is RF Leakage or Coax or both.

if I run my Yaesu FT-757GX upto about 15w I am fine once I hit the 18-100w range odd stuff starts happening the laptop in the shack randomly reboots tvs in the house a good 50ft away start flicking USB drives on the media servers start disconnecting and reconnecting hell it even freezes up my usb CW interface. 

I know that it isn't the best but I currently have the vertical antenna connected to the rig with a single piece of RS RG58 as I haven't had a chance to go and pickup a better piece of cable

Thanks,
Reg
KK4NJC
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K6AER
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« Reply #1 on: January 16, 2013, 08:13:18 PM »

It's not the coax. Radiation directly from the antenna is your problem. distance is the only thing that wil help.
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YONU
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« Reply #2 on: January 16, 2013, 08:16:59 PM »

Well the antenna is 10ft over and 35ft above the shack I don't have it setup for a ground plane as the ham I purchased it from said I didn't need one would that help.

Thanks,
Reg
kk4NJC
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VA7CPC
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« Reply #3 on: January 16, 2013, 09:06:21 PM »

Well the antenna is 10ft over and 35ft above the shack I don't have it setup for a ground plane as the ham I purchased it from said I didn't need one would that help.

Thanks,
Reg
kk4NJC

I can't find the right smiley for "rolling on the floor laughing" . . .

It's a vertical, and therefore it needs radials!  The "other half of the antenna" is (right now) the shield on your coax, and you have "RF in the shack".

You _might_ improve the situation by putting a choke balun (lots of ferrite beads, or a coil of coax) on the coax near the rig.

.          charles
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YONU
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Posts: 67




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« Reply #4 on: January 16, 2013, 09:10:34 PM »

Thanks and yes I know I should have. Went with my thoughts to begin with you assume when someone has been a ham for 40yrs they knew what they were talking about.  Out of curiosity instead of building radials could I use the 100ft of chainlink around my property as the groundplane?

Thanks,
Reg
KK4NJC
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K8AXW
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« Reply #5 on: January 16, 2013, 09:52:58 PM »

YONU:  Sure you can be a ham for 40 years and not know what you're talking about!  I've been a ham for 58 years and I seldom know what I'm talking about!   Shocked

It would be interesting to know what your SWR is......

Sure, hook the shield of the coax up to the chainlink fence.  Some guys use the rain spout, fences.....whatever and it works.  By the same token, there are some guys that do this and it doesn't work!  You have to try.

Chainlink fences are kind of "iffy" though because of the questionable conductivity and connectivity of the links.  Like I said, "you have to try."

However, I'd start planning on burying some wire. 
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N6SBN
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« Reply #6 on: January 16, 2013, 10:05:06 PM »

  My lot is 35 X 70'.    I had huge amounts of RFI in my house when using a shortened dipole.  I switched to an S-9 vertical with radials on the roof.  I have much less SWR and  RFI than the shorty Dipoles.   Even so, I use less power.
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WB6BYU
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« Reply #7 on: January 16, 2013, 10:36:13 PM »

Without proper radials connected at the antenna, the same current flows on to the
outside of your coax as flows into the vertical radiator.  So your coax is PART OF THE
ANTENNA.  Now, when you bring one end of the antenna into the shack and near
computers and other electronic devices, is there any surprise that they act up when
saturated with RF?

A choke alone won't help - you need to give the RF current somewhere else to go.
Once you have added an effective set of radials (which can be simple wires running
down the roof as long as you have two or more resonant on each band) that may
be enough to avoid problems, but you can also add a feedline choke to reduce
common mode currents on the outside of the coax even further.

It has nothing to do with your choice of coax.
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WB6DGN
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« Reply #8 on: January 17, 2013, 01:26:43 AM »

What I know about HF and especially HF antennas you could put in your eye and net even feel it.  That said, I will repeat what I learned when I bought a GAP Titan antenna some years ago.
I was told that that antenna did not require radials as it was essentially a half wave, center fed vertical and, for the lower bands, had a "counterpoise" that helped at those frequencies. 
You didn't say what antenna you had but, if its a GAP Titan, that would explain the comments about the radials.
Now, everyone, DON'T SHOOT THE MESSENGER!  Much of this information came directly from GAP as I called them several times with numerous questions about the antenna.
Whether this works as they explained, I have NO idea (nor do I really care as, I found out, HF is not my "thing").  I'm merely repeating it here to account for the OP's seller's comments.
Tom
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WB2WIK
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« Reply #9 on: January 17, 2013, 08:11:08 AM »

What, exactly, is the antenna in question here?  If it's homebrew, a good description would help.

If it's something commercially made, what's the brand and model number?
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YONU
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Posts: 67




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« Reply #10 on: January 17, 2013, 08:12:59 AM »

Sorry it is an imax 2000
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AC2EU
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« Reply #11 on: January 17, 2013, 08:22:49 AM »

You and your radios are unfortunately part of your antenna system! Waaaaay too much RF in the shack!!   Shocked

Other than doing it properly with radials as suggested, you may eliminate some or all of the RF by earth grounding the coax before it enters the shack which should be done for safety purposed anyway.
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WB6BYU
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« Reply #12 on: January 17, 2013, 08:29:21 AM »

Quote from: YONU
Sorry it is an imax 2000


I'm sorry, too.  That makes it more difficult to decouple the coax so it doesn't
act like part of the antenna.
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W9GB
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Posts: 2623




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« Reply #13 on: January 17, 2013, 08:32:31 AM »

Quote from: KK4NJC
When I operate my Yaesu FT-757GX HF transceiver into an Solarcon IMAX 2000 vertical antenna odd stuff starts happening in the radio shack.
My laptop randomly reboots, TVs in the house start flicking, USB drives on the media servers start disconnecting/reconnecting, and it even freezes up my USB CW interface.
Reg --

You are making a number of NOOB (new amateur, Novice) mistakes and likely do not understand (or appreciate) proper antenna system installations.
Where are the 3 amateurs that signed your amateur test in North Carolina, for some Elmer guidance or help??

1.  Your reported problems (RFI) are COMMON MODE RF issues.  Vertical antennas are prone to this issue.  
Choke UNUN may reduce this, but does not address antenna issue.

http://www.balundesigns.com/servlet/the-1-dsh-1-Isolation-fdsh-Choke-Baluns-cln-Feedline-Isolation-%22Choke%22-baluns/Categories

2.  The Solarcon IMAX 2000 is a cheap CB antenna (27 MHz, 11 meters), that has some limitations and design flaws, but could be used on 10 meters with some changes/additions.  The antenna has a RADIAL KIT -- Do you have that?
Personally, I am not a fan of the antenna or its construction.

MANY used IMAX 2000 antennas being sold or given away are BROKEN (see eHam.net Reviews).
http://www.eham.net/reviews/detail/1376

IMAX 2000 Exposed
http://www.video-observer.com/imax/imax2000.htm

3. You can build a simple 10 meter or 40/15-meter dipole for $10 to $15 in materials.
WHY have you not taken this easier, proven route for your HF antenna?

4. How to Build a Technician Class Dipole for 10 meters.
http://www.hamuniverse.com/10metertechniciandipole.html
« Last Edit: January 17, 2013, 08:48:51 AM by W9GB » Logged
YONU
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Posts: 67




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« Reply #14 on: January 17, 2013, 08:37:53 AM »

I have a dipole up the I got the vertical at the adviae of a couple of local hams
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