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Author Topic: Long wire with ATU as HF antenna  (Read 870 times)
ALPARD
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Posts: 111




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« on: September 13, 2019, 03:59:24 AM »

My ATU has a post at the back for long wire. I think it is for random length of wire and then there is a post for earth on the ATU too.
So, according to the ATU manual, it is used for long wire HF antenna.

But will this antenna not radiate in the shack, when transmit?

It is a wire coming into the shack from outside and then to ATU and then HF rig. How would it not radiate? If it radiates, then RF will be in the shack causing some problems? I suspect so. What do you think? Or what are your experience on this if you had used / are using long wire and earth as your HF antenna.

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K8AC
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Posts: 1912




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« Reply #1 on: September 13, 2019, 04:35:17 AM »

When my friends and I started as Novices in the late 1950s, that's the antenna configuration that all of us used, and yes, it caused some problems in the shack.  Depending upon the band, antenna length and power you were running, you might get an "RF bite" from metal in your station.  Fortunately, we were all running less than 50 watts INPUT and so we could live with the problem.  And, there were no other electronic devices in the house to interfere with.  A couple of manufacturers made small tuners that operated ONLY with single wire antennas.  There were no SWR meters - you "tuned the antenna" by maximizing the glow of an NE2 neon bulb on the front panel of the tuner.  Somehow, we were able to work just about all states with this meager configuration.

73, Floyd - K8AC
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W5DXP
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« Reply #2 on: September 13, 2019, 05:10:44 AM »

Strange as it may seem, when there is maximum RF-in-the-shack, i.e. maximum voltage, there is minimum current and therefore minimum radiation inside the shack. If you have a good RF ground for the shack and your "random" length antenna is 1/2WL, the maximum radiation will occur 1/4WL from the tuner. Unfortunately, your tuner may match relatively high current situations easier than low current situations.
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My antenna says, "What makes me happy is when the tuner is adjusted for maximum available current through my radiation resistance!" 73, Cecil, w5dxp.com
W9IQ
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Posts: 3531




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« Reply #3 on: September 13, 2019, 05:28:47 AM »

True enough, Cecil but the difficulty is determining if the voltage in the shack is "maximum".

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
WA7ARK
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Posts: 740




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« Reply #4 on: September 13, 2019, 06:01:00 AM »

Think about the metal box that the tuner is in; what is that metal chassis box connected to?

One connection is the shield of the short coax jumper between the ham rig and the tuner. Hopefully, the other is a thru-wall connection to an outside ham-only ground rod?

What is the ham rig connected to? Power Supply? Computer?

What is happening in the power supply? Does it have a three wire AC line cord plugged into a house outlet? If so, then there is a direct connection from the tuner chassis via the green wire in the line cord to the house in-wall wiring, which goes to the electrical service panel, and is connected to a ground rod and the electric utility ground system.

If the rig is connected to a computer (most are nowadays for digital modes), then there is also a ground connection from rig to computer (USB or serial cable). The computer is grounded to the house AC distribution system as well, and is also connected to modems, printers, networks, and possibly a phone line.

Now imagine that the tuner is pushing an AMP or two of RF current into the long-wire antenna. Kirchoff's Current Law requires that the same amount of RF current flows off the tuner chassis. Where does that return current go?

It divides. Some goes along the coax shield back toward the rig, where it splits again if there is a computer, heading for the house ground. If there is a thru-wall connection to an outside ham-only ground rod, you can hope that most of the return current heads for it; leaving only a little bit flowing through your rig, power supply, computer and the house wiring...

Really bad crap happens if you do not have the short thru-wall connection to an outside ham-only ground rod, both for transmit and receive! Not only will you likely get RF burns, you will almost certainly crash the computer and possibly lock-up a digital radio. On receive, you have created a situation where the off-air signals you are trying to receive will be mixed with all of the RFI produced by every switching power supply in your house!

Running a long-wire to the back of an in-shack tuner is about the worst antenna installation a ham can do!!!! That has not much to do with the way it radiates. It has everything to do with the mayhem it creates during transmit and receive.

The only way I would run a "random longwire" type of antenna is to locate it out as far from the ham station as my lot will allow, put a system of near/on/in ground radials (just as you would use for any Marconi vertical antenna) right under where you feed it, put a WX-resistant remote automatic tuner right at the feed-point with the ground screw on the tuner connected to the radial field, using coax between the station and the tuner, with several ferrite common-mode chokes along the coax.

This will prevent RF from traveling along the coax shield as a common-mode current to get into the station. It will also minimize RFI from all of the digital gadgets in your house from coupling to the shack-end of your coax and traveling toward your antenna as a common-mode current.

btw, the second worst installation a ham can do in today's modern house-full of switching-power supplies everywhere reality is to bring open-wire feed-line to an in-shack antenna tuner, but that is another post....
 
« Last Edit: September 13, 2019, 06:19:24 AM by WA7ARK » Logged

Mike, WA7ARK
G3RZP
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Posts: 1318




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« Reply #5 on: September 13, 2019, 08:57:45 AM »

The W3EDP (83 foot length of wire)works quite well: no ground connection, just a counterpoise. But it really needs a tuner with no galvanic connection to the coax: a link coupled tuner is best. Of course, being a 1930s antenna, it isn't digital, so some will turn their noses up at it!
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WA7ARK
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« Reply #6 on: September 13, 2019, 09:37:11 AM »

The W3EDP (83 foot length of wire)works quite well: no ground connection, just a counterpoise. But it really needs a tuner with no galvanic connection to the coax: a link coupled tuner is best. Of course, being a 1930s antenna, it isn't digital, so some will turn their noses up at it!

Ok, I will bite. The link has two ends. One end of the link is hooked to the 83ft wire. What is the other end of the link connected to?

What frequencies it this supposed to work on?
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Mike, WA7ARK
G3RZP
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« Reply #7 on: September 13, 2019, 10:01:05 AM »

The link is connected to the coax. The link is galvanically isolated from the parallel tuned circuit: one end of the tuned circuit is connected to the 83 foot long wire and the other end to the counterpoise. There are three lengths of counterpoise for 80, 40, 20 and 10 - there was no 15 metres until after WW2.

Search early to mid 1930s QSTs for the W3EDP.
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K0ZN
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Posts: 1862




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« Reply #8 on: September 13, 2019, 10:51:10 AM »

This issue is not exactly black and white. I'm not going to get drawn into some theoretical debate with some of the "experts" on here, but I can tell you what I have experienced and had success with (which is what you asked). Keep in mind:  "YOUR results may vary!"  To Wit:

At my previous QTH I had a direct fed random wire about 120' long for quite a while. It was fed by my Alpha linear which easily put out 1,500 watts. My tranceiver was in the middle of the operating table, the linear was to the right and the Tuner (Ameritron ATR-30) sat about 6 feet away on an elevated shelf up by a window where the antenna came in. I had Zero problems with RF in the shack. What I DID have was a very extensive ground system which consisted of about 7 "radials" in a crow's foot configuration laid under the antenna and a couple of ground rods about 6 ft. from the tuner. I also bonded/connected, literally, EVERYTHING in the house multiple places: copper water pipes, HVAC Ducts, and a few random "radials" hung in the basement ceiling. NEVER had a problem with RF at Legal Limit. In my experience the biggest "problem" with directly fed wires is that they are often pretty noisy.... but they are very frequency flexible. The key to the directly fed "random" wire (for transmitting) is an EXTENSIVE, low impedance RF ground system. If you can't or won't make an extensive RF ground system, then at other than QRP, you might have issues. There is no free lunch here!

At this QTH I have run a 200 ft. directly fed long wire for use on 160, 80 and 40.....worked great in terms of getting out on the lower bands. I don't have the extensive in-shack ground here I had at the other QTH, so yes, at Legal Limit there was some RF in the shack. If I kept the power down to a couple of hundred watts it was a non-event. I use a field strength meter to get an idea of what is going on RF wise in the shack.

My Go-To antenna for the last 15 years has been a "doublet" aka Center Fed Zepp fed with 450 ohm Ladder Line. Works ALL HF frequencies well (Ham and SWL, which is why I love it). It is an efficient radiator. I run Legal Limit into that antenna for the last 15 years. NO PROBLEMS with RF in the shack. None. My Johnson KW Matchbox sits right next to my Icom tranceiver on the operating table. NEVER had a problem. I don't know where balanced parallel line gets a bad rep for RF in the shack.  > IF <  your antenna system and transmission line are properly installed (no sharp bends, kept away from other metallic conductors, etc.) and is TRULY balanced, Ladderline/Open Wire line, etc. does not cause problems. The key is a BALANCED system....balanced mechanically and electrically symmetrical, both sides of the antenna the same distance from ground or objects, etc. Possibly part of my success with the ladderline over the years is because I use the Johnson KW Matchbox which is one of the best Balanced tuners ever made and it has link coupling. I would not attempt to predict what an UN-balanced tuner using a balun, etc. may or may not do in the way of assuring phase balance in the output.

My take is that at lower powers and with a balanced system you are not going to have problems. Throw in unbalance and an inappropriate tuner and all bets are possibly off, at least at high power.

FYI: the "worst" length for a random wire in terms of RF in the shack is a length that is 1/4 wave or an odd multiple of 1/4 wave; that puts the maximum current right in the shack.

This is a Hobby!  Give whatever you want a try. If it works good, you will have fun. If it doesn't you learned something! Install the best practical RF ground system you can. Good luck.

73,  K0ZN

« Last Edit: September 13, 2019, 10:58:58 AM by K0ZN » Logged
WA7ARK
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Posts: 740




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« Reply #9 on: September 13, 2019, 11:43:59 AM »

The link is connected to the coax. The link is galvanically isolated from the parallel tuned circuit: one end of the tuned circuit is connected to the 83 foot long wire and the other end to the counterpoise. There are three lengths of counterpoise for 80, 40, 20 and 10 - there was no 15 metres until after WW2.

Search early to mid 1930s QSTs for the W3EDP.

Ok, I had visions of a in-shack tuner where the link connected directly to the 83ft wire.

The W3EDP requires a "counterpoise", which is a fancy name for a floating ground, capacitively-coupled to the dirt below it. That might work as long as the counterpoise is outside. Same principle as a non-resonat Marconi antenna with elevated radials. Both require a tuner.

In the modern world, I would shy away from this antenna unless the tuner was remoted away from the shack, and  I could use
common mode choke(s) on the coax feedline, preferably with the coax shield also bonded to a ground rod just before the coax comes into the shack's outside wall.
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Mike, WA7ARK
KJ6TSX
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« Reply #10 on: September 13, 2019, 05:08:30 PM »

I am new to using ladder line so please excuse my ignorance <GRIN>
I am considering installing a doublet antenna, my plan is the run 450 ohm ladder line from the antenna down a metal mast, across the asphalt shingle roof, down the side of the stucco building through the wall to the back of my MFJ 989D antenna tuner.
Do we see any problems with this installation??

Thanks
George KJ6TSX
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WA7ARK
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Posts: 740




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« Reply #11 on: September 13, 2019, 05:41:41 PM »

...I am considering installing a doublet antenna, my plan is the run 450 ohm ladder line from the antenna down a metal mast, across the asphalt shingle roof, down the side of the stucco building through the wall to the back of my MFJ 989D antenna tuner.
Do we see any problems with this installation??
...
Not sure if you want my opinion or not (or if your post was "tongue-in-cheek?)

Running OpenWireLine/LadderLine close to a metal mast is problematic.
Running it across a wet asphalt shingle roof is problematic.
Running it near stucco (with chicken wire lath under the stucco) is problematic.
Running it through an outside wall all the way into the shack is problematic.

I sure as hell do not want ladder line carrying a few hundred to few thousand Volts of RF only inches away from the USB cable that runs between my IC7300 and my Dell Desktop Computer I use for digital modes... Balance is never good enough to pull that off! The OWL/LL radiates, and picks up radiated RFI.

Open Wire Line and Ladder line worked fine in 1937. It is a huge mistake to use it today..

If you absolutely, just gotta try it, then run coax from from the tuner to a balun outside the shack wall. Use a voltage balun, and ground the center tap on the balun secondary to a ground rod. Just maybe, that will leave the RF from the feedline outside so that it doesn't bother your computer, and that will also block the RFI from all the switching power supplies inside your house from getting to the antenna.

Well-shielded coax solves all these problems, except one. The OWL/LL might have a couple of db lower loss. However, you do not win if using OWL/LL degrades your receive noise level by several db!
« Last Edit: September 13, 2019, 05:49:05 PM by WA7ARK » Logged

Mike, WA7ARK
W5DXP
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« Reply #12 on: September 13, 2019, 07:28:58 PM »

Open Wire Line and Ladder line worked fine in 1937. It is a huge mistake to use it today.

Mike, I run this twinlead length selection contraption in the shack about 4 ft from my XCVR and PC with no problems even at 500w. 300 ohm line has the fields more confined than open-wire or 450 ohm ladder line.

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My antenna says, "What makes me happy is when the tuner is adjusted for maximum available current through my radiation resistance!" 73, Cecil, w5dxp.com
WB6BYU
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« Reply #13 on: September 13, 2019, 07:33:56 PM »

Quote from: ALPARD

...But will this antenna not radiate in the shack, when transmit?




Probably not as much as you might think.

Current flow is what is responsible for most radiation from a wire.  If the wire has a relatively
high impedance (meaning low current and high voltage) then the wire between the tuner and
the outside actually isn't going to radiate that much RF.

But radiation isn't what causes "RF in the shack" anyway.  It's due to common mode current on
the outside of your coax - basically, the shield of your coax (and anything attached to it) become
part of your antenna
, and if that connects to your rig, which connects to the computer and
the AC wiring in your house, you now have RF everywhere that is far more of a problem than
that due to the radiation from the wire.


I've used a lot of end-fed wire antennas over the years, typically with a tuner in the shack.  They
certainly can work well.  And they can be quirky, too, in all sorts of ways.  It actually isn't as
simple as it might seem to get a good installation.

Here is what I do to make it work out:

First, RF problems increase with your power level.  Generally (but not always) you don't have many
problems running QRP, and the problems often are manageable at 100W.  But issues increase rather
rapidly above that point.  If you are running an amp, especially connected to a computer, then you
probably want to take a different approach.

Second, you must have a ground system connected to the chassis of the tuner.  This needs to be
intentional, designed to serve the purpose, not something accidental (which is what you get if you
don't plan it).  The details depending on several factors, such as the antenna length.  It doesn't have
to be a direct connection to an earth ground rod (though that isn't a bad idea when available) - it could
be a set of radials / "counterpoises", or a car body, or a metal roof, etc.  But it must have a relatively
low impedance at the operating frequency.

I like to use antennas that are close to a half wave on the lowest frequency I plan to use.  I know, many
hams will complain that many autotuners won't match them, but I haven't had any issues with my
manual tuners.  If I want to change bands quickly, I build a fixed-tuned circuit for each band with a
big switch to select them:  that way I just switch to the band I want, without any additional adjustment.
The high impedance of a wire that is a multiple of 1/2 wavelength (or a multiple thereof) means that
the current is low at the feedpoint, and it doesn't require as elaborate of a ground system for good
performance.  If I have problems, a single quarter wave radial wire for the problem band strung around
the room or wherever it fits is often sufficient to clean up any problems.

On the other hand, when the tuner is mounted outside with a good ground system, then an autotuner
with an intermediate-length wire (to avoid the half wave resonances) makes more sense.


You certainly don't want to make the wire too short:  at 1/4 wavelength or less the current has to be
much higher to radiate much power, requiring a very good ground system.  I find such an antenna to
be more problematic than a high impedance feed.  

Not that it can't work, however:  my first antenna for 75m SSB was a quarter wave wire plugged into
the back of my radio, without a tuner, and a 12' ground wire to a metal water pipe.  No, it wasn't ideal,
but it allowed me to make contacts.  A 3/4 wave wire actually can make a pretty good 40m antenna,
and may not need a tuner if the length is adjusted for resonance, though it also benefits from a good
ground system.

I've had more problems with "RF in the shack" when the coax between the rig and the tuner is made
longer than when it is just a couple of feet.  That may have been specific to a particular installation
(second floor in a barn).   It is easier to confine the RF to a good ground system (and keep it off the
coax) than with a poor one:  common mode chokes on the coax only help if you also have provided
an alternative path for the RF to take.

And a lot of your results will depend on how RF-sensitive your station is.  I don't use a computer with
my radio (there is never space for both on the desk at the same time).  Most of the issues I've had
have  been with a particular keyer, which tends to keep sending after I let go of the paddles when
there is RF floating about, in spite of ferrites on the cables.  (Adding bypass capacitors to the keyer
might help, too.)


So, yes, and end-fed wire to a tuner in the shack can be an effective antenna.  Or it can be a real
mess if you approach it in too haphazard of a fashion.


This is a hobby, and every ham has a different assortment of priorities, capabilities and limitations.
If the best you can manage in a temporary installation is a wire over a tree coming in through the
window, you usually can make it work, particularly for QRP operators.  Or when you're in a huge
storm and everything blows down, leaving you with that zinc moss strip running along the peak of
the roof as your only outdoor antenna.  Or when a wire under the eaves is what will escape the
attention of the HOA snoops.

On the other hand, if you have a shack full of electronics connected to your rig that isn't designed
for high levels of RF, then you may have a lot more problems, particularly if you plan to run high
power.  It isn't a solution for everyone.
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KF4ZGZ
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« Reply #14 on: September 14, 2019, 03:02:54 AM »

The W3EDP is a zepp antenna ..... kinda got a "built in" counterpoise.
It's on my list of " build and play with someday" antennas.

To the OP ..... depending on how your shack is situated, there may be little if any rf.
A previous residence shack was set up so my tuner was less than 1 foot from the window.
RF was never a problem.
Current house ...... I have several feet before exiting the shack/house, so I do have to be careful.

But typically, some tuners can be grounded and it alleviates MOST rf issues.
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Matt
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