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eHam Forums => Elmers => Topic started by: YONU on January 16, 2013, 07:26:38 PM



Title: RF Leak/Coax
Post by: YONU 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


Title: RE: RF Leak/Coax
Post by: K6AER 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.


Title: RE: RF Leak/Coax
Post by: YONU 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


Title: RE: RF Leak/Coax
Post by: VA7CPC 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


Title: RE: RF Leak/Coax
Post by: YONU 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


Title: RE: RF Leak/Coax
Post by: K8AXW 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!   :o

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. 


Title: RE: RF Leak/Coax
Post by: N6SBN 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.


Title: RE: RF Leak/Coax
Post by: WB6BYU 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.


Title: RE: RF Leak/Coax
Post by: WB6DGN 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


Title: RE: RF Leak/Coax
Post by: WB2WIK 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?


Title: RE: RF Leak/Coax
Post by: YONU on January 17, 2013, 08:12:59 AM
Sorry it is an imax 2000


Title: RE: RF Leak/Coax
Post by: AC2EU 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!!   :o

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.


Title: RE: RF Leak/Coax
Post by: WB6BYU 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.


Title: RE: RF Leak/Coax
Post by: W9GB 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


Title: RE: RF Leak/Coax
Post by: YONU 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


Title: RE: RF Leak/Coax
Post by: W9GB on January 17, 2013, 08:52:31 AM
Quote from: KK4NJC
I have a dipole up.  I got the IMAX 2000 vertical as advice from a couple of local hams.
LOTS of Bad Advice out there, especially from the former CB/pirate operators looking to sell their bad purchases ($$$) to a new operator.

SO, now you know a couple of amateurs to not ask for advice in future (not Elmers).
===
You have a dipole.  HEIGHT is a key requirement for antennas !!


Title: RE: RF Leak/Coax
Post by: AC2EU on January 17, 2013, 08:57:01 AM
I have a dipole up the I got the vertical at the adviae of a couple of local hams

It happens.
You will get lots of "shoot from the hip advice" as you continue in the hobby. The best thing you can do is research the advice before you act on it. Some will be good, some will be what happened to you...

When I started a few years back, a seasoned ham of 30 or so years experience suggested that I put up a G5RV !!!!  ???  ::)  After looking into it , I decided that it wasn't for me!  ;D


Title: RE: RF Leak/Coax
Post by: YONU on January 17, 2013, 08:58:55 AM
I just went and tried the dipole and I get the same result on and stuff acting up I only have the dipole up about 15ft at moment since I was tuning it.


Title: RE: RF Leak/Coax
Post by: WB2WIK on January 17, 2013, 10:30:08 AM
I have a dipole up the I got the vertical at the adviae of a couple of local hams

I would suspect those local hams were also fairly new.

Any old-time hams in your area with a lot of antenna expertise?


Title: RE: RF Leak/Coax
Post by: YONU on January 17, 2013, 10:40:29 AM
Yeah the one that sold it to me he is going on 50yrs now


Title: RE: RF Leak/Coax
Post by: W9GB on January 17, 2013, 10:44:15 AM
Quote from: KK4NJC
I just went and tried the dipole and I get the same result on and stuff acting up I only have the dipole up about 15 feet, at moment since I was tuning it.

1.  Get the antenna UP, away from the operating position.

2.  Get a Choke balun at that dipole feed point.

3.  You said you were using some RG-58/U coaxial cable (unknown source).
Coaxial cable needs to be GOOD QUALITY (shielding) -- stay with KNOWN brands with properly installed PL-259 connectors.  SHOP at the major amateur radio stores.
AVOID the olde CB shops, truck stops, and garage sellers easily found in SE USA, at this point.

4.  Pick up telephone and talk to Pres Jones, N8UG at The Wireman in Landrum, SC.  
I have known Pres for over 30 years -- this is the person you ask for advice from --
for your DIY antenna supplies. (coax cable, antenna wire, insulators, rope)

http://www.thewireman.com/

Quote
Yeah the one that sold it to me he is going on 50yrs now
Birth age means nothing.  Passing an amateur radio FCC license since 2000 only means you can memorize multiple choice questions and answers.
Selling an IMAX 2000 to you tells me he was likely into CB (maybe since 1970s CB craze) and only became an amateur after 2000, when the FCC dropped Morse Code requirement.

Quote from: AC2EU
When I started a few years back, a seasoned ham of 30 or so years experience suggested that I put up a G5RV !!!
After looking into it , I decided that it wasn't for me!  
In early 1970s, I got some good advice and bad advice about antennas.
Using SOLID Copperweld wire for my simple Novice antenna was BAD advice.  #14 AWG Stranded copper wire would have been a better recommendation.

w9gb


Title: RE: RF Leak/Coax
Post by: AC2EU on January 17, 2013, 11:08:22 AM
I just went and tried the dipole and I get the same result on and stuff acting up I only have the dipole up about 15ft at moment since I was tuning it.


If you have a resonant dipole you should be able to use it without a tuner. If you have problems at the resonant frequency, I would suspect that you have connection or coax problems. One of the things I see a lot with other hams' installations are badly soldered pl 239 connectors.
Earth grounding the coax before it enters the shack is still a good idea no matter what the problem turns out to be.

You are going to have to do some troubleshooting...


Title: RE: RF Leak/Coax
Post by: YONU on January 17, 2013, 11:42:08 AM
well I will go resolder the 239 to earch ground the coax can I simply solder a wire to the 239 outside or do I need to get a grounding block


Title: RE: RF Leak/Coax
Post by: YONU on January 17, 2013, 12:58:05 PM
ok I just redid the 239 on the Dipole and that helped some,  when I said 50 I mean as in 50yrs as a HAM, I put a choke Balun on the Dipole I can tell if that helped or not.  As to getting it away from the shack there is only so far I can move it atleast not without major cable runs in excess of 200ft


Title: RE: RF Leak/Coax
Post by: G8HQP on January 18, 2013, 08:41:49 AM
When someone tries to sell you an antenna never believe what he says, especially if:
1. the antenna is second-hand, or
2. the antenna is new, or
3. he says it doesn't need a balun/ground/counterpoise.

Most antennas need one of the items mentioned in point 3. If not given it they will use your feed cable and shack equipment as a balun/ground/counterpoise. About the only exception is a dummy load masquerading as an antenna, which will 'work' quite happily and give low SWR with no assistance.


Title: RE: RF Leak/Coax
Post by: YONU on January 18, 2013, 08:54:07 AM
I actually took it down myself so let me ask this he had to mounted to a Aluminum mast drove in the ground with a ground wire on the mast could that be why he said it didn't need radials?  (Sorry I am very bad for giving folks the benefit of the doubt)


Title: RE: RF Leak/Coax
Post by: N1UK on January 18, 2013, 11:16:00 AM
Quote
I actually took it down myself so let me ask this he had to mounted to a Aluminum mast drove in the ground with a ground wire on the mast could that be why he said it didn't need radials?  (Sorry I am very bad for giving folks the benefit of the doubt)


It may well have worked for him. He has a different setup and a different length of feedline etc etc.

I hear that a lot of locals use the Antron vertical on 10m. Have you looked at that.

There is a lot of incorrect and half information on the local repeaters. You need to listen and filter it carefully.

Looks like lots of good advice here though.

Mark N1UK


Title: RE: RF Leak/Coax
Post by: YONU on January 18, 2013, 11:44:31 AM
Well that makes sense and yeah I am learning about filtering the info



Title: RE: RF Leak/Coax
Post by: WB6BYU on January 18, 2013, 12:11:11 PM
Quote from: N1UK

It may well have worked for him. He has a different setup and a different length of feedline etc etc.



Mark has a good point to remember.  What "works" for one ham may not "work" for another
if their situations, operating habits, or expectations are different.

This is especially true for common mode current problems, because the severity of the
problem depends on the length of feedline, what is connected to the station at the other
end, the operating frequency, and, in the case of interference, the sensitivity of the
other equipment to stray RF pickup.

For example, if his mast was 1/4 wavelength long (about 9 feet), it would provide a good
RF ground if it were insulated from the ground at the base, but would be a poor ground
if the base were actually connected to ground.  With a half wave mast (about 17') the
opposite is true.  The same goes for the length of coax and what is connected to it at
the shack end:  if that presents a high impedance, common mode currents will be small.
With a low impedance, they can be higher.  This can change based on such things as
plugging in a set of headphones with the wrong length cord.


I also have to add that the number of years being a ham (or class of license) does not
necessarily imply a good understanding of technical issues.  Unfortunately, many hams
get stuck in their ways as they age, and their misconceptions get solidified to where
they no longer search for the truth, and can't recognize or accept it if they happen to
bump into it by accident.

You can also see, on these forums as in other places, that often hams giving advice
assume that the other person is interested in the same aspects of the hobby.  You'll
get different answers about 80m antennas from an active DXer or a rag chewer, for
example, because they have different needs for radiation patterns.  That's not to say
that either is wrong, but rather that you need to gauge how well their operating
style matches yours to tell which is more appropriate to your needs.



Title: RE: RF Leak/Coax
Post by: VE1CZ on January 21, 2013, 07:16:17 PM
I have been using a Imax 2000 for a few years now and no problems with RFI.It is mounted on a tripod on the garage roof on a mast about 12 feet.I hang my 80 meter inverted v and a 40 meter delta loop below that, as well as a coaxial choke at the base of the antenna with absolutely not RFI issues,but the antenna is mounted about 50 feet away from the house and very close to the sat.dish,works for me!