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Author Topic: RF burn from carrier adj knob TS-430S  (Read 15602 times)
GSFITZSR
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Posts: 9




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« on: May 08, 2012, 12:13:34 PM »

I'm getting a significant burn if I adjust the output of my unit while keying. It will burn my fingers anytime I go above 30W while holding the carrier knob. I get the same burn if I touch any screw on my antenna tuner case/lid. This seems only to happen on 80M and slightly on 40M down to nothing on 15M.

My setup is TS430S transceiver and a end-fed antenna from MapleLeaf Studios (62ft. wire length). I'm using a MFJ auto-tuner and the coax is 40ft. to the antenna. I'm on the second floor of my home with the antenna tied to the roof about 25ft. in the air. The other end is up in a tree about 40ft. Transceiver, MFJ auto-tuner and power strip are grounded together but not to any earth ground. Running off one 12VDC gel cel.

Thanks for advice in advance.

Greg
KS5PWJ
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G0GQK
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« Reply #1 on: May 08, 2012, 01:26:18 PM »

I knew as soon as I started to read your posting that you would be using either an end fed wire or a vertical antenna. This is a problem which occurs, or can occur using an antenna of this type. Sometimes it can be cured sometimes it can't, but you need to improve your earthing, and do you have radials with your end fed? This can cure the problem.

You can try putting about 6 turns of loops about 12" on your coax. If you were using a computer in the shack you would find that the screen was affected with "things" moving. Others will be along soon who will also give you some advice

Mel G0GQK
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W5DXP
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« Reply #2 on: May 08, 2012, 02:11:36 PM »

The default counterpoise for an end-fed antenna is the outside of the coax braid. You might try a common mode choke on the feedline. 17T of small coax on an FT-240-43 toroid seems to work well on 80m and 40m according to this web page:

http://www.karinya.net/g3txq/chokes/
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GSFITZSR
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« Reply #3 on: May 08, 2012, 02:16:40 PM »

Mel,

Thanks for the input.

No I do not have any ground radials or grounds of any sort on the antenna. There is a ground attachment post on the balun but instructions said it was not necessary, but could be used if needed. The antenna maker said the coax feed line would be the counterpoise.

I did a test by making a choke balun. I took a 100' RG8X line and wrapped about 20' of one end around a 4" dia plastic jar then connected it to the antenna balun. I still get the RF burn after doing this.

What do you suggest for radials since the feed point is 25' off the ground?

Thanks,
KF5PWJ
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WX7G
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« Reply #4 on: May 08, 2012, 02:51:07 PM »

Connecting a 62' counterpoise wire to the GND terminal on the tuner should cool things off.

Another possible solution is an MFJ-931 "artificial ground" or an MFJ-934 "tuner and artificial ground."
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WA9UAA
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« Reply #5 on: May 08, 2012, 02:51:37 PM »

Hi Greg,
The antenna is being voltage fed on those bands where the rig is biting you. The fix is a counterpoise of 1/4 wavelength ( 234/f  = length in feet) of wire attached to the ground lug of the tuner for each of the offending bands. These wires will move the high voltage point away from the rig and it will appear at the end of the counterpoise wires. These ends should be well taped (insulated) to protect from electric shock. The wires can be run outside or inside the radio shack but must be well insulated. Ideally they should be run away from the antenna as they will become part of the antenna system. If the angular difference is greater than 90 deg. no problem.

Alternatively, the W3EDP antenna with a radiator of 84 feet and a counterpoise of 17 feet for the low bands and one of 6 and 1/2 feet for the upper bands is a possible solution. These lengths are more easily matched and worth your time to try.

73,
Rob WA9UAA
http://www.mds975.co.uk/Images/amateur_radio/w3edp.gif
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GSFITZSR
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« Reply #6 on: May 09, 2012, 09:00:39 AM »

Regarding the 62' counterpoise. It must be connected at the receiver and not the ground lug of the antenna balun?

From the receiver I can run out a window and down to the ground, along my home foundation. This would put it more or less parallel to the antenna. Or, I can run out the window to the ground and perpendicular to the antenna across my yard. I will bury it later once I find the solution that works best.

I will look into the artificial ground.

Rob, If I had 84' to hang your suggested antenna I would consider it.

Thanks again.
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AG6WT
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« Reply #7 on: May 09, 2012, 09:15:46 AM »

2nd the recommendation for the artificial ground (AG). It was specifically designed to address this sort of problem. It is essentially a tuner for your counterpoise so that the current goes there instead of in your rig (and your hand!). Hook up the AG to the ground lug of your tuner and a counterpoise to the output of the AG. Adjust the AG to maximize the current when transmitting.
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W9GB
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« Reply #8 on: May 09, 2012, 12:37:45 PM »

Quote
What do you suggest for radials since the feed point is 25' off the ground?
It is electrically impossible to end-feed a 1/2-wavelength antenna without a good counterpoise at the feedpoint and have a totally "cold" feedline. -- W8JI
http://www.w8ji.com/end-fed_1_2_wave_matching_system_end%20feed.htm

The End Fed Half Wave Antenna (EFHA) by Steve Yates, AA5TB
http://www.aa5tb.com/efha.html

« Last Edit: May 09, 2012, 12:40:47 PM by W9GB » Logged
WB6BYU
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Posts: 13580




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« Reply #9 on: May 09, 2012, 12:44:05 PM »

The antenna appears to be designed to use the coax as the ground system
of the antenna.  That means that, of course, there will be RF on the coax,
and on your rig.  That's a feature of this particular design, not a bug:
it counts on the coax shield being part of the overall antenna.  Since the coax
is connected to the chassis of the rig, when you touch the rig you become
part of the antenna as well.

The best place to put a radial wire is at the feedpoint - the manufacturer
provided a ground lug on the "matching device", just in case you wanted to
use it.  Probably for just this very reason.  Once you do that, it should reduce
the common mode current on the coax, then some combination of common
mode chokes, ferrite cores, changing the coax length, and/or adding further
radial wires at the rig end should reduce the voltage at the rig to where you
no longer get zapped.


A "radial wire" or "counterpoise" is NOT the same as a "ground wire".  The latter
connects the rig or antenna to a good RF ground, and needs to be short to be
effective.  A tuned radial needs to be 1/4 wave long and NOT grounded anywhere
along the length - it is resonant, like an antenna.  In fact, in this case, it is the
other half of the antenna that the manufacturer didn't sell you.


True, you can use an "artificial ground", but that costs twice what you paid for
the antenna, and requires you to readjust it each time you change bands.  The
whole point in getting such an antenna and an auto-tuner was to avoid needing
to do that in the first place, right?  At this point it's just throwing good money
after bad.
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GSFITZSR
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Posts: 9




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« Reply #10 on: May 09, 2012, 01:24:04 PM »

Update:

I added a 62' piece of 12AWG to my transceiver ground post and ran this out the window, down 15' then across my lawn. This made no difference. I still get zapped when I touch the gain knob on 80M around 50W when keying. I'm going to move the ground wire to the balun ground post at the feed point.
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HB9PJT
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« Reply #11 on: May 09, 2012, 01:56:26 PM »

I would put that wire to the coax shield at the antenna feed box instead at the TRX.

73, Peter - HB9PJT
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W9GB
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Posts: 2659




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« Reply #12 on: May 09, 2012, 02:51:36 PM »

I have read Bruce Beckett's, NU0R (MapleLeaf Studios) eBay claims .. No ground needed ...
Sorry, I don't agree.  
The antenna wants and needs a low impedence current return path.
I have posted 3 different sources that agree with that statement.


Here is a great web page by M0JHA that mirrors your setup.
Note his comments ... To use and operate properly.
http://www.m0jha.com/about111.html
« Last Edit: May 09, 2012, 03:02:11 PM by W9GB » Logged
WB6THE
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Posts: 129




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« Reply #13 on: May 09, 2012, 04:12:25 PM »

Hey Greg...
Without getting all technical....
All antennas of ANY kind are some variation of a dipole antenna.
Dipole antennas have two "halves". Both halves radiate energy.
Both halves are equally RF "hot".
What is happening to you is that your radio is trying to be the "other half"
of a dipole. This "other half" has no place to go so it builds up RF voltage
which you feel as biting you or warming up your fingers. And it
can make the radio do many strange things, too.

When I was in the Navy I used to come home on leave and buy 50 or 100
feet of wire, throw it over the roof and stick the end in the transceiver antenna
connection and the very same thing happened to me. I had a Crooks Radiometer
which was my 'mascott' and that gadget would ionize the gas remaining inside
it the nicest color of deep violet! You can have QSOs on that but its not right!

Now, even your coax might be trying to work as the "second half". The second half
(also called an opposite half might also be called a "counterpoise). One end is not
so-called "ground" to RF energy.

It may be that the most simple way to fix the problem is to attach a length of wire
to the chassis (ground) which is about 1/4 wavelength of the frequency you are
trying to operate on. Might be a bit less or a bit more length. Connecting to a water
pipe probably won't even help.

If you already have that so-called second half connection then its either too long or
too short. Even the length of the coax will cause what you are experiencing to vary.
What works good on one frequency might not work well on another frequency or band.

So, what others are telling you is true. Rig up a counterpoise wire or maybe a few
wires of length related to a quarter wavelength of your operating frequencies/bands.

You're running and end-fed antenna, so does it have a matching box that you need to
adjust and a short counterpoise wire is running from it? Add a foot or two to that wire.

The "other half" concept is for sure what is biting you!

The truth is out there!

73
Alan
WB6THE

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GSFITZSR
Member

Posts: 9




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« Reply #14 on: May 09, 2012, 05:58:11 PM »

Alan, the balun of this end fed unit is sealed, no adjustments needed.

Update 2: Removed the 62' wire from the transceiver and moved it to the ground lug on the antenna balun. Ran the wire down to the ground about 25' then across the yard. No difference, still get zapped on 80M.

To clarify the installation: I was incorrect about the OAL of the antenna. It's 72 feet from end to end, not 62 feet. I used a 100' piece of RG8x coax to connect to my transceiver with 20' of one end wrapped around a 4" plastic bottle to create a choke, then connected to the antenna balun. The coax runs across my roof then to a balcony through a window, connected to my antenna tuner then the TS-430. Ground wire (62') was connected to the transceiver ground lug, then to the antenna balun ground lug. The antenna is 25' high on the balun end and 40+ feet high on the other end (in a tree).

I will add to the ground wire to make the OAL 72' and try again.

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