Antenna grounding for end-fed antenna

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wbswetnam

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I have a 33' long sloper end-fed antenna. One end is 25' up in a tree (isolated from the tree limb itself by an egg insulator and 4' of rope, of course) and the other end is atop a 10' pvc mast where it connects to a 9:1 unun transformer (the one sold by EARCHI). This 9:1 unun does NOT have a terminal for a ground; just a bolt and nut to connect a random wire antenna and an SO-239 socket on the side.

The paperwork that comes with this little unit says that it can be used for power levels up to 150W but so far I have only used it pretty much for PSK31 and low power SSB (50W or less).

I am concerned with RF grounding for this antenna. I have an antenna tuner which has a lug on the back marked "Ground". Is this intended as an antenna RF ground, or a simple electrical ground? Not sure which it is... If I connect the coax coming from the end-fed to that antenna tuner, then a 2' coax from the tuner to the transceiver (a Kenwood TS480SAT) then a ground wire from the antenna tuner to an earth ground outside, is that an RF ground for the antenna? Is it unsafe for me to use this antenna for anything other than QRP levels (5W or less)? If I do need a counterpoise / RF ground, how do I do it with this antenna set up?

(For what 's worth, though, it does seemingly work. I've made numerous contacts with S. America on it in the last week on 10m!)
 

WA0CBW

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Single ended antennas need something to simulate the other half of the antenna. These antennas usually work better if they have an RF ground "plane." In the case of an end fed vertical antenna the RF ground "plane" is a number of radial wires stretched out from the base of the antenna. Since the end fed wire is in the air it still can benefit from an RF ground "plane" underneath the antenna. This RF ground "plane" should be connected to your station "single point ground" and also be connected to your "Electrical" safety ground. This RF ground could be a single wire strung out parallel and underneath your antenna wire. Your tuner and your station equipment should all be connected to your "single point ground." This is required per NEC code (see section 800; 810; and 820). Since your feeding your antenna at a voltage point the unun could be subjected to very high voltage levels depending on how much power you are running. A lightning surge suppressor should also be installed in the coax before it reaches the tuner and grounded to your single point ground.
BB
 

prcguy

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The coax is the counterpoise on the 9:1 balun end fed types and the feedline radiates and its length will affect performance. You can insert a 1:1 choke balun in the feedline to reduce the problem of RF in the shack but its placement will affect performance.

If you use an actual resonant 1/2 end fed wire with a very high ratio transformer (around 64:1) then counterpoise requirements are substantially reduced and performance will go way up. The PAR brand end feds operate this way and you can build a 100w 40/20/10m version with 66ft of wire and a transformer for a couple of $$ and it will work much better than the EARCHI thing. Plus you don't need an antenna tuner since the match is really good on the even harmonic bands these antennas operate on.

I use 66ft end fed with 64:1 transformer for portable operations on 40, 20 and 10m and it works basically the same as a center fed dipole of the same size. I did place a 1:1 choke balun in my 25ft RG-174 type feedline as a precaution because if you get too far from resonance the feedline will light up with some RF, otherwise its one of the best portable antennas I've found and also great for condo's, etc where a center fed antenna is impossible to install.
prcguy
 

wbswetnam

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The coax is the counterpoise on the 9:1 balun end fed types and the feedline radiates and its length will affect performance. You can insert a 1:1 choke balun in the feedline to reduce the problem of RF in the shack but its placement will affect performance.
How about if I place a 1:1 "ugly balun" (BUILD AN AIR WOUND 1:1 CHOKE BALUN FOR HF - THE UGLY BALUN!) on the coax just before it enters the shack (which means about 20' of coax between the ugly balun and the 9:1 unun)?
 

prcguy

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That will probably help but an ugly balun is somewhat narrow band and does not provide good choking across the whole HF band. It can be optimized for a specific band or two but you can make a really good 1:1 choke balun with a ferrite torrid and some coax.

One of the simpler versions is an FT-240-43 core available here: https://www.amidoncorp.com/ft-240-43/
Then wrap 10 turns of RG-58 coax around it like this: Pomiary ró

10 turns is usually good for 80 through 10m and 12 turns is a little better if your going to do 160m. You can simply wrap your feedline around the toroid core or put it in a box with connectors. You can use a smaller core like an FT-114A-43 which is a lot cheaper but you would have to use miniature coax like RG-174, LMR-100 or better yet Silver/Tefon RG-316. Those will easily handle 100w and will fit in a box about half the size of a pack of cigarettes.

There are also big ferrite beads with a 1/2" hole and I believe three turns of RG-58 through a 31 mix bead will provide good choking for 80 through 10m.
prcguy

How about if I place a 1:1 "ugly balun" (BUILD AN AIR WOUND 1:1 CHOKE BALUN FOR HF - THE UGLY BALUN!) on the coax just before it enters the shack (which means about 20' of coax between the ugly balun and the 9:1 unun)?
 

wbswetnam

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There are also big ferrite beads with a 1/2" hole and I believe three turns of RG-58 through a 31 mix bead will provide good choking for 80 through 10m.
prcguy
Radio Shack sells a snap-on ferrite choke (cat # 273-105). Would it help if I put several of these directly on the RG8X just before it enters the shack?
 

prcguy

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You would need a lot of them for HF and a couple of those will cost more than a single FT-240-43 toroid that will do the job well. Most snap on chokes like the RS are a #43 mix ferrite and you need a lot of turns of wire or coax through the center to be effective at HF using a single core. I suppose if you had enough RS snap on cores to cover 2 or 3ft of coax it would probably be ok for HF.
prcguy


Radio Shack sells a snap-on ferrite choke (cat # 273-105). Would it help if I put several of these directly on the RG8X just before it enters the shack?
 

wbswetnam

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You would need a lot of them for HF and a couple of those will cost more than a single FT-240-43 toroid that will do the job well. Most snap on chokes like the RS are a #43 mix ferrite and you need a lot of turns of wire or coax through the center to be effective at HF using a single core. I suppose if you had enough RS snap on cores to cover 2 or 3ft of coax it would probably be ok for HF.
prcguy
How about if I use both the "ugly balun" (RF choke) AND several turns of the RG8X around a ferrite toroid after that before it goes into the house? Any harm in doing both?
 

prcguy

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You should be able to fit 10 turns of RG8X around an FT-240 size core and I don't see any point in adding an "ugly balun" in the same feedline. With just a little more effort you could replace the 9:1 EARCHI with a home made 64:1 transformer and 66ft of wire, which will give you some improvement you can really see.
prcguy

How about if I use both the "ugly balun" (RF choke) AND several turns of the RG8X around a ferrite toroid after that before it goes into the house? Any harm in doing both?
 

wbswetnam

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You should be able to fit 10 turns of RG8X around an FT-240 size core and I don't see any point in adding an "ugly balun" in the same feedline. With just a little more effort you could replace the 9:1 EARCHI with a home made 64:1 transformer and 66ft of wire, which will give you some improvement you can really see.
prcguy
Thx for the advice. I have some mix 31 ferrite toroid rings and snap-on beads on order, they should be here tomorrow.

On Sunday I made an "ugly balun" anyway. I had spare coax and a 4" diameter piece of pvc pipe and time on my hands so I thought "Why not? Sounds like a fun project", so I made one with 18' of RG8X. I hooked it up in line with the antenna feed line, and it totally skewed my SWR. I had the ugly balun on the ground (at the point where it enters the house) so I tried raising it up in the air about three feet, which helped some but not much. So much for the homemade RF choke experiment.

Obviously I will go with the toroids instead.
 

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The proper place for any RF choke is as close as possible to the antenna. If you don't place it properly, it's not going to work well, regardless of whether it is an "ugly balun" or a toroid or whatever.
 

wbswetnam

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The proper place for any RF choke is as close as possible to the antenna. If you don't place it properly, it's not going to work well, regardless of whether it is an "ugly balun" or a toroid or whatever.
I have read (or perhaps, read and misunderstood) that with an end-fed antenna, the feedline becomes the counterpoise when connected to a transformer (in my case, the 9:1 unun by EARCHI which does not have a ground connection, only an antenna terminal and a SO-239 socket). There must be some sort of counterpoise and the feedline is it. So it is not possible to allow some length of the feedline to be the counterpoise, but then choke off the RF just before it enters the house?

I'm starting to think I've completely botched this antenna project... how do I make a safe yet effective end-fed antenna?
 

wbswetnam

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I'm wondering what effect the unun may have at reducing the amount of dangerous RF that gets into the feedline and goes back into the house...? Even if RF is getting back into the feedline and all the back into the house, is this a dangerous situation as long as I run only 25W - 50W?
 

jonwienke

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I'm wondering what effect the unun may have at reducing the amount of dangerous RF that gets into the feedline and goes back into the house...?
The whole point of an RF choke is to block RF from following the feedline back to the transmitter.

Even if RF is getting back into the feedline and all the back into the house, is this a dangerous situation as long as I run only 25W - 50W?
Depends. 50W is supposedly the threshold at which burns and other injury can start happening, but I would prefer to prevent issues even if injury is unlikely. Even if it won't kill you, it's still not good for you, your transmitter or any other electronic equipment in the vicinity.

So it is not possible to allow some length of the feedline to be the counterpoise, but then choke off the RF just before it enters the house?
I'd avoid any antenna design that requires RF to go back down the feedline, for the reasons outlined above.
 

wbswetnam

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What I'm gathering from this is that verticals and other end-fed antennas are an unsafe design and are only appropriate for QRP work. Is this correct?
 

prcguy

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The only real problem antenna mentioned here is the 9:1 balun end fed types. A ground plane vertical, or half wave vertical dipole or half wave end fed with choke balun or most any other antenna will not have significant feedline radiation unless the designer screwed up.

The RF exposure limits are accumulative over a specified period of time and most of the HF band is not a big problem. Even if you can feel a tingle on the coax it doesn't mean its a dangerous level.
prcguy


What I'm gathering from this is that verticals and other end-fed antennas are an unsafe design and are only appropriate for QRP work. Is this correct?
 

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There are some 9:1 baluns which have a ground post to which you electrically attach a ground rod. This is also a good place to attach some counterpoise wires. They can be random pieces of scrap wire from old antenna projects (most of us do keep those odd lengths of wire in a box somewhere) for added help in keeping the RF off the equipment.

They aren't really necessary but they do help out. Spread them out, run them along the building foundation, drape them down the support, behind the bushes, etc. In your case they should be attached in some fashion as close to the shell of the SO-239 connector. Then the ugly balun which should help out.

Verticals and end fed wires are perfect for small spaces and postage stamp lots and properly designed through trial and error are just as safe as a dipole at 100 feet. It's just the RF feedback you have to engineer out of the setup.
 

Ed_Seedhouse

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What I'm gathering from this is that verticals and other end-fed antennas are an unsafe design and are only appropriate for QRP work. Is this correct?
Not really, no. For example verticals were used in most of the old high power A.M. broadcast band radio transmissions. They wouldn't have used them if they weren't "safe". Of course all these vertical had a large field of radials to act as a counterpoise. A well designed vertical antenna is perfectly safe and may be fed with high power, but the kicker is "well designed" and if well designed is it well implemented?

EVERY transmitting system requires a counterpoise. If there is no counterpoise there is no radiation. In practice there is always a counterpoise even if it is the radio chassis or the feed line. A well designed counterpoise avoids using these and almost always results in safer as well as more efficient operations. The more efficient the counterpoise the more efficient the transmitter/antenna system.
 

nanZor

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I have a 33' long sloper end-fed antenna. One end is 25' up in a tree (isolated from the tree limb itself by an egg insulator and 4' of rope, of course) and the other end is atop a 10' pvc mast where it connects to a 9:1 unun transformer (the one sold by EARCHI). This 9:1 unun does NOT have a terminal for a ground; just a bolt and nut to connect a random wire antenna and an SO-239 socket on the side.
It appears that the newer Earchi 9:1's do include a separate ground lug for counterpoise, etc.

In any case, the coax serves double-duty as a transmission line and a counterpoise. I'd put a 1:1 common mode choke, like an MFJ-915 on say a 30 foot jumper, and then run the output of the choke back to the shack.

This would more or less emulate a 30 foot counterpoise wire, although when on the ground, it is detuned anyway. You may also want to slightly lengthen / shorten the 33' wire.

One option without having the ground lug on the matchbox, and if you bring the matchbox close to the ground, is to just run counterpoise wires from the shell of the coax out along the ground. Still, I'd use a 1:1 choke, but in this case, instead of putting it right at the feedpoint, make it do double duty as if it were a single counterpoise by placing the choke further down the line. Add individual counterpoise wires near the feedpoint shell if you wish.

If NO choke is available, then you may want to try the "remote counterpoise" of just running quarter-wave wires around the baseboards of the shack attached to the rig's ground. Yep, a problem on 80m, but might tame the system a little bit when the entire feedline is also the counterpoise.
 
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Xicaque

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That will probably help but an ugly balun is somewhat narrow band and does not provide good choking across the whole HF band. It can be optimized for a specific band or two but you can make a really good 1:1 choke balun with a ferrite torrid and some coax.

One of the simpler versions is an FT-240-43 core available here: https://www.amidoncorp.com/ft-240-43/
Then wrap 10 turns of RG-58 coax around it like this: Pomiary ró

10 turns is usually good for 80 through 10m and 12 turns is a little better if your going to do 160m. You can simply wrap your feedline around the toroid core or put it in a box with connectors. You can use a smaller core like an FT-114A-43 which is a lot cheaper but you would have to use miniature coax like RG-174, LMR-100 or better yet Silver/Tefon RG-316. Those will easily handle 100w and will fit in a box about half the size of a pack of cigarettes.

There are also big ferrite beads with a 1/2" hole and I believe three turns of RG-58 through a 31 mix bead will provide good choking for 80 through 10m.
prcguy
PRCGUY,

your second link is not working. Do you have another sample to share as I am having similar issues as the OP. Thanks!!
 
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