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RF Problems and the HF Vertical Antenna

Do not contact (N4ZOU) on April 24, 2005
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RF Problems and the HF Vertical Antenna

Are you having RF problems in the shack since you put up your HF vertical antenna? This is a common problem with an easy solution. RF energy traveling into your shack on the outside of the coax feed line causes this problem. The solution is adding an "ugly" 1:1 Balun in the coax to choke off the RF energy before it enters your shack.

So what's an "ugly" Balun? Nothing more than a few turns of the coax forming a coil. Don't scramble the turns; they must be side by side for the coax Balun to operate properly. 5 turns or more will be enough for 80-meters and up. Use caution not to coil the coax so tight that it causes the inside conductor to merge into the shield shorting it out. 4" PVC pipe coupler works well and it's cheap. Normally a 1:1 Balun would consist of multiple turns of three wires on a coil form and the simple coax Balun is also multiple turns of three wires when coiled, the center conductor, the inside of the coax shield, and the outside of the coax shield. Now your asking how this could possibly work. RF energy flows on the conductor and not in the conductor. This is the reason silver-plating or copper-clad steel works so well. The RF energy only penetrates the conductor slightly and for plated parts the RF flows entirely in the silver or copper plating and almost never in the conductor below it. In the case of coax this property separates the RF flowing inside the coax from the RF flowing on the outside of the coax.

We can use this problem to an advantage by careful placement of the "ugly" Balun. Most of us would think we would want that Balun at the base of the vertical and try and prevent all RF from flowing on the outside of the coax. In reality this is the worst place you could put it! Why? Simply use the outside of the coax as another radial. Putting the Balun at the base of the antenna would choke off the RF but the vertical element would simply put it there again. The Place to put the Balun would be 1/4-wavelength from the feed point of the vertical on the lowest band the antenna is capable of operating on. If your coax run is 1/2-wavelength or more you will want to place a Balun at each 1/4-wavelength point. You will also want to put a Balun on the feed line just before it enters the shack.

The formula for figuring out where the Balun should be placed is simple. 234 / frequency in MHz * the velocity factor of the coax = length in feet. An example is a Butternut HF6V 80 through 10 meter vertical. As the antenna is capable of operating on 80 meters simply input 234 divided by 3.5 times .75 would equal 50.14 feet assuming your using modern foam type coax with a velocity factor of .75. The HF6V uses a length of 75-ohm coax as a matching transformer. Simply ignore the velocity factor if different from the 50-ohm coax and measure 50.14 feet from the feed point of the vertical for the proper place to coil the coax forming the 1:1 Balun. If your feed line is shorter than a 1/4-wavelength on the lowest band the antenna is capable of operating on, place the Balun on the next highest band where the coax would be longer than 1/4-wavelength. This should cure RF problems associated with RF flowing into your shack on the outside of the verticals feed point.

N4ZOU

n4zou@yahoo.com

http://groups.yahoo.com/group/Butternut-antennas/

Member Comments:
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RF Problems and the HF Vertical Antenna  
by KG8JF on April 24, 2005 Mail this to a friend!
Does this methodology work for antennas like the Gap Titan and Eagle? Although both these models are coax fed and are basically resonant antennas, they are more like a dipole turned on its side and they don't use radials per se, but a small counterpoise at the base of the unit. I remember the Eagle used a bunch of ferrite beads slipped over the coax at the base of the antenna. I no longer use the Eagle but I remember that I had a lot of RF in the shack. It would arm the security system when I turned on the Amp.
 
RE: RF Problems and the HF Vertical Antenna  
by W8JI on April 24, 2005 Mail this to a friend!
There has been some stuff on my website about this for the past few years. See:

http://www.w8ji.com/verticals_and_baluns.htm

While the idea or suggestion of using a feedline choke on verticals wioth pror ground systems is a good one, there are a few incorrect statements in this E-ham article.

First, the velocity factor of the cable has nothing to do with where the choke "balun" is optimally placed.

That's because a choke balun wound with coax works on the shield ONLY, by creating a high impedance on the outside of the shield. It has no effect INSIDE the cable, and so the inside of the cable (and velocity factor) has no effect on the choke or best location for the balun.

5 turns 4" in diameter, the article's suggested size, is only about 2 microhenries. 2 microhenries on 80 meters is only about 50 ohms, and that would almost certainly make an inconsequential change in common mode current on 80 meters. In other words, it isn't a good common mode choke (or balun) at all until you get up around 15 MHz. Heck, it's only 500 ohms at 35MHz!

As for choke placement, 1/4 wl away from the base of a vertical is the worse place for the choke. Here's why...

When the cable sheild is "grounded" or partially grounded at the base of the antenna a distance 1/4 wl away has a HIGH common mode impedance (this has nothing to do with things happening INSIDE the cable, like SWR or velocity factor). The impedance could be thousands of ohms. Adding 50 ohms or even 500 ohms would only make a small difference.

The CORRECT place for a feedline choke would be at the base of the antenna, and in rough cases a second choke some distance away from the vertical. If you wanted to do something 1/4 wl away from the antenna WITHOUT a choke at the antenna base it should be a GROUND, not a choke balun!

Even 1/4 wl groundplanes with four radials can benefit from use of a feedline choke, but it belongs at the feedpoint.

73 Tom
 
RE: RF Problems and the HF Vertical Antenna  
by KD4AC on April 24, 2005 Mail this to a friend!
On the GAP Titan, the "counterpoise" was only supposed to affect 40 and 10 meters. Adjusting the length of the longer section of counterpoise adjusted the center frequency of 40M and adjusting the smaller wire adjusted 10M. Since GAP antennas are supposed to be vertical dipoles, I wouldn't think a balun would be needed, but I don't think it would hurt either. I miss my Titan. It worked very well for me on 40 through 10M. It received well on 80M, but was less than fair when it came to transmitting. Although, to be fair, I didn't do much transmitting on 80M with it anyway. Anyway, I guess I'll have to take this article into consideration as I install my BigIR vertical.
 
RE: RF Problems and the HF Vertical Antenna  
by N3JWN on April 24, 2005 Mail this to a friend!
I found that 6-8 turns on 6" diameter old plastic bleach bottle will work just fine as close to the base of the antenna as posible it works have fun but be safe thanks!! Dick / n3jwn
 
RF Problems and the HF Vertical Antenna  
by K4IA on April 24, 2005 Mail this to a friend!
My vertical RFI problem (had it with an R7000 and a Gap Titan) came because the coax ran horizontally for some distance away from the antenna and picked up RF from the antenna itself. Best to run the coax vertically below the antenna as soon and as far as you can to keep this from happening. Then add a line isolator (choke) type balun at the shack end of things.
 
RF Problems and the HF Vertical Antenna  
by N4LQ on April 24, 2005 Mail this to a friend!
If your $500 vertical produces RFI and has poor radiation, the best cure is to form the entire vertical into a coil then cram it into the garbage can. When finished, erect a 30 ft mast of PVC pipe or something and hang up a multi-band inverted vee. In most cases you will find a big improvement in signal strengths.

 
RE: RF Problems and the HF Vertical Antenna  
by K4RAF on April 24, 2005 Mail this to a friend!
I have used 9 turns when making & using a choke. 4T then 3T then 2T on anything around 4" in diameter. I had used round plastic motor oil containers. Works better than doing an engineering study. I have never believed in baluns for HF, although I have used sleeve baluns on VHF/UHF. You would be better off using balanced line to feed it than using a balun.
 
RE: RF Problems and the HF Vertical Antenna  
by KD4AC on April 24, 2005 Mail this to a friend!
"If your $500 vertical produces RFI and has poor radiation, the best cure is to form the entire vertical into a coil then cram it into the garbage can."

Wrong. The best thing you can do is make sure you have a proper ground plane. If a proper ground plane is installed, there won't be a poor radiation issue.
 
RE: RF Problems and the HF Vertical Antenna  
by N4LQ on April 24, 2005 Mail this to a friend!
Yes the ground plane is important. Make sure you install a good one after you dispose of the vertical. Then put the inverted vee over the ground plane.
 
RF Problems and the HF Vertical Antenna  
by W1DUD on April 24, 2005 Mail this to a friend!
.....It's only boring if you don't have HF privliges....."73" the DUD
 
RE: RF Problems and the HF Vertical Antenna  
by VE7ALQ on April 24, 2005 Mail this to a friend!
I have a Fortran program which runs under Linux "G77"
ftp://ftp.yehudi.ca/ham-radio/r.f
This program allows you to enter the length of a short
whip, the frequency in Megacycles for the (base loaded)
whip and it gives you the Radiation Resistance Rr in
Ohms. Using this Program I was able to calculate

1.8 mHz 23 feet 0.67 ohms
2.182 mHz 23 feet 1.00 ohms
4.0 mHz 23 feet 3.44 ohms
7.0 mHz 23 feet 10.19 ohms
10.1 mHz 23 feet 21. ohms

The figure 23 feet was chosen because
(1) It is the length of my Bencher/ButterNut HF6V
(2) Marine whips are 23 feet long (hence 2.182 mHz)

So you see that you have to have a very good ground
or ground plane if you are go radiate with efficiency
below 40 meters (7.0 mHz) The Marine whip works
(1) Salt Water makes an excellent ground.
(2) 2.182 mHz lays out a vicious ground wave.
(3) Range of the ground wave enhanced by salt water.

For line isolators, I buy http://www.radioworks.com
I put one near the feedline of the antenna, and
another one in the shack just after my equipment.
 
RE: RF Problems and the HF Vertical Antenna  
by W4JLE on April 24, 2005 Mail this to a friend!
Use what you want as a form for the balun, what is important if you want to cover 80 and up is the length of the coax you wind around the form.

18 to 21 feet is what you need.

By the way, those knocking a virtical have never properly installed one. Most folks put one up and make comparisons with their NVIS dipole. Joe 50 miles down the road tells them the s-meter isn't deflecting as far as on the dipole and they dump it and quote the old saw about it radiating equally poor in all directions.

As antennas follow the laws of reciprosity, forget about what Joe says and do A/B testing on a DX station.

Find someone in the DX window and you will see that the low angle of radiation compared to a dipole comes into it's own. IF YOU HEAR THEM BETTER, they hear you better. Listen to the BIG signal G3WXX - Tom puts in the US nightly around 3.795 he runs phased virticals ( 4 square) and most nights sounds like a local.



 
RF Problems and the HF Vertical Antenna  
by KI4CRA on April 24, 2005 Mail this to a friend!
I have both the Gap Challenger and the Titan. The Titan is a recent addition to the shack, it works so well that I have decided to sell my Challenger and the tilt-over mount. Having said that, I have had the Challenger up for 18 months now, with NO RF comming into the shack what so ever. The Titan is the same, NO RF into the shack. I don't knw if distance makes a difference or not. The Challenger is a good 50'from the shack and the Titan is approximately 75' from the shack. I recently put a second set of guys on my Titan, and just to be on the safe side made a 6" choke approximately 3-5" from where the coax exits the antenna. Does it help? Only time will tell, so far I have noticed no difference either way.
What I have discovered with my disability and in this wonderful hobby of ours, that what does or doesn't work for one may work for another and vice versa. So it is in our hobby, what works for one may not work for another and vice versa. These are just my obsevations, I could be wrong, have been wrong before and will be wrong again such is life. 73 all and hope to catch you on the air.
Mark
AI4HO
 
RE: RF Problems and the HF Vertical Antenna  
by KD4AC on April 24, 2005 Mail this to a friend!
"Make sure you install a good one after you dispose of the vertical. Then put the inverted vee over the ground plane."

You go ahead and do that. I'll stick with my BigIR vertical.
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 24, 2005 Mail this to a friend!
.

If I have to ad baluns or Rf Chokes to prevent RFI, I would go back to the drawing board and find what to do to solve the problem.

Adding baluns and such is not correcting the problem, but covering the problem up and it still exists.

Like a bleached blonde and all the makeup and just her belly button showing, doesn't make me feel the want of her. Trying to be something she is not.

Or like our lawyers making laws that don't work so make more to cover and try again and not solving the problems. They make the problems.

You make your problems.

Arrrgh.

.:
 
RF Problems and the HF Vertical Antenna  
by N0AH on April 24, 2005 Mail this to a friend!
I lost you at Hello-
 
RF Problems and the HF Vertical Antenna  
by N4OKG on April 24, 2005 Mail this to a friend!
I've been using a Butternut HF6V with 160 at my present location for about 6 years and have experienced absolutely no RF in the shack. As for propagation, I've worked Australia on PSK with 35 watts. Perhaps the 50-odd feet distance from the shack, the dozen 26 foot buried radials and the station ground has something to do with it. I avoid using a tuner and usually operate in a frequency range near resonance (under 2:1 VSWR). I had similar results with a roof-mounted Butternut at another location a few years back.

73, Al N4OKG
 
RE: RF Problems and the HF Vertical Antenna  
by N5AX on April 24, 2005 Mail this to a friend!
I agree with disposal.
Please use the "recycle" can for the vert.
 
RF Problems and the HF Vertical Antenna  
by W1DUD on April 24, 2005 Mail this to a friend!
....Dud is the right name for you. I have priviledgges, I just not stupid enough to waste my time taking a test to get them..???? On 11 meters?..
 
RE: RF Problems and the HF Vertical Antenna  
by AA4PB on April 24, 2005 Mail this to a friend!
If your vertical has RF flowing down the shield and into the shack, that is an indication that you do not have an effective RF ground (radials) at the base of the vertical. While the choke may keep RF out of the shack, it won't decrease the loss in the grounding system or improve the radiation from the antenna. It would be much better to fix the problem than to cover it up with a band aid.
 
RE: RF Problems and the HF Vertical Antenna  
by N3ZKP on April 24, 2005 Mail this to a friend!
I also run a Butternut HF6-V and have no rf problems in the shack. Of course I have an excellent ground plane for the antenna to work against. It is 23,000 square feet of corrugated steel roof on the 2nd story of an office building in downtown Baltimore.

Properly installed a vertical is an excellent DX antenna. If they weren't, the majority of the DXpeditions wouldn'e be using them. For local use a dipole is better, although I use mine for both state and regional MARS nets and have no problem being heard anywhere up and down the Atlantic coast and into the deep south on those nets.

People who trash verticals are generally too cheap and/or too lazy to install them properly.

Lon
 
RE: RF Problems and the HF Vertical Antenna  
by W8JI on April 24, 2005 Mail this to a friend!
A 1/4 wl groundplane mounted 1/2 wl above ground has issues with RF on the coax. It has very good efficiency!

On the other hand a GAP antenna has very poor lowband efficiency because of the very poor ground that is laid right on lossy dirt. (Of course the coax inside used as a loading stub doesn't help!) The GAP has RF on the coax problems for the same reasons as the R7 and other antennas....the groundplane is very small.

In the R7 efficiency is reasonably high because the poor counterpoise is normally well up in the air away from lossy earth. In the GAP, the ground wires are generally laid on lossy dirt, and so the counterpoise system dissipate a lot of power.

The problem is if you fix the GAP groundplane the SWR goes up, because the antenna is designed to "match" with a very marginal (poor) ground.

While a choke on the feedline isn't required with a large ground system, it doesn't always mean efficiency is poor. It does when the small ground system is very near lossy earth!

73, Tom
 
RF Problems and the HF Vertical Antenna  
by N0AH on April 24, 2005 Mail this to a friend!
I had a Gap Titan. My Cushcraft MA5V beat the crap out of it.

It is always nice to have Tom, W8JI, join any of these forums. He always adds a warm touch of reality. Thanks Tom.

I just saw the QST review on antenna analyzers and the newer MFJ 269 did very well with a couple of exceptions. Can't seem to figure out a 50 ohm load.

But it looks like if you really want to see what your vertical is up to, you might want to invest into one. It has a lot of features the other analyzers lacked. RF problems and the HF vertical antenna? That manual of the 269 analyzer is here to help!!!!!!

I always put 6 turns of coax at the rig and near the antenna's feedpoint for lightning protection. It might be an old wive's tale, but I sleep beter at night. For RFI, I think it came from the same book but anything is worth a try when you have a thorn in your side.

As for RFI, you have near field problems and far field problems. Both effected by the power you are running, he angle of radiation, and the shielding of what is being interfered by.

Neighbor problems are their's. Solve 99% of them, and the remaining 1% becomes a 100% again. Been there, done that. Never again. If you use a vertical, or beam, your going to get complaints proportional to your power and proximenty to your neighbors.

Don't think that by changing to a beam, your problems will go away. They'll just be a little bit different and perhaps improve with tower height. But crank up your Alpha 99, and wait for the knocks at the door. Neighbors can bite. Or they can be cool. I've had both. And at some QTH's, none. I liked the none the best.

RF problems and the HF vertical? Run at or below 100 watts and use CW. You'll cut down the problems and take all that money you were going to spend on RFI solutions and buy that MFJ 269 antenna analyzer instead. Peace man-

Take the Ricky Willaims attitude! Relax, Don't Worry! Be Happy!
 
RE: RF Problems and the HF Vertical Antenna  
by NS6Y_ on April 25, 2005 Mail this to a friend!
Broadcast verticals have something like 300 radials, that should give you an idea of how to cope with lossy ground, there's so much metal there's less loss than otherwise.

If you want a decent antenna analyzer get a Palstar or an AEA, or build a 'Tenna Dipper kit, or give Elecraft 6 months or a year and they'll have a good one out for all of us. There's also one coming out soon called the Antenna Smith that makes my AEA look like an ugly duckling, I can hardly wait to see that baby come onto the market!

Do NOT get an MFJ!
 
RE: RF Problems and the HF Vertical Antenna  
by N3HKN on April 25, 2005 Mail this to a friend!
Is the coil really a Bal-Un? Or is it a simple choke? What happens to the RF that it blocks? Some claim that it magically goes back up the feedline to radiate. I believe that it is lost in heating the choke.

I have had a GAP challenger for years and it is outstanding on 40 meters which is the band that the three counterpoise wires,laying on the ground, are used for. Well outstanding is a typical claim since I have no other antenna to compare it to and thus it must either be the best or the worst. Since I do not want to look dumb for spending almost $300 I say it is outstanding. On 20 it is no better than a 3ft square magnetic loop (1/2" copper pipe) in the attic. Granted the loop has a dipole like pattern so that is an advantage for it.

I have my GAP wires laying on top of the ground, "integrated" with the grass and held down with coat hanger wires (hooks). I found that if I press down on a wire to force it close to the earth the impeadance of the antenna changes.

I am going to get a Hustler 6BTV and lay out as many wires as I can. Problem is that plastic coat hangers seem to be the norm so that may be the limiting factor. I would never bury radials. The more intimate the contact with the lossy earth the more loss you have in that half of the "dipole". If I could I would elevate the vertical and use just a few elevated radials thus we have the inverted V of other messages but with the feed point only a few feet above ground.

Why make this complicated. A vertical is a dipole bent 90 degrees at the feedpoint. To lay one half of the bent dipole on the ground does not appear to be the best choice. But if you have to then provide as much metal in that half as you can so the "vertical" thinks that it is close to a balanced antenna. A 1:1 real BalUn at the feedpoint looks like a good thing to do also since they are needed with dipoles to properly match to unbalanced coax.
 
RF Problems and the HF Vertical Antenna  
by K4IQT on April 25, 2005 Mail this to a friend!
Interesting set of comments here, a few of which are actually based on scientific fact.

W8JI, who has "been there, done that", told you rightly (no surprise). A properly-sized choke balun placed close to the feedpoint last summer worked just fine on my 6BTV, completely curing a minor issue with RF in the shack.

73,
Terry K4IQT
 
RE: RF Problems and the HF Vertical Antenna  
by K4CMD on April 25, 2005 Mail this to a friend!
It's a simple RF choke. It's described (and photographed) in the ARRL Antenna Handbook, and I've used them at the antenna and rig ends of my coax for years. No RF problems in the shack, ever.
 
RE: RF Problems and the HF Vertical Antenna  
by NI0C on April 25, 2005 Mail this to a friend!
Thanks to Scott, N4ZOU, for bringing up this topic. There are a lot of folk tales and myths out there concerning antennas, feedlines, and baluns. I'll put my money on advice from W8JI, who has put together a world-class station that demonstrates performance!

73,
Chuck NI0C
 
RF Problems and the HF Vertical Antenna  
by K5UJ on April 25, 2005 Mail this to a friend!
<<<4" PVC pipe coupler works well and it's cheap.>>>

This is a small diameter coil form. If you are going to use this you have to take into consideration the bend radius of the coaxial cable you are going to use. It is probably okay for the small diameter coax such as 8X and 58U, particularly with the solid dielectric, but a larger 1/2 inch size feed with a foam dielectric would probably experience center migration on such a tight bend.

I am much more comfortable with larger forms and you get the highest impedence in cases where the diameter of the coil and its length are equal. For small chokes I use plastic paint buckets. For the low bands where I am using 1/2 inch diam. feed I use small plastic garbage cans. You need to get at least 20 to 30 turns on the form.

If you place multiple coax chokes in your feedline you can lengthen it significantly. For a feed such as RG213, you may begin to experience loss due to length on the higher HF bands in particular that you may want to avoid. In most cases you probably only need one at the feedpoint when it is made to have a high Z.

When it comes to verticals it can be useful to take a page from medium wave broadcasters. The typical 90 or ~190 degree insulated broadcast tower site is constructed with 120 radials, usually no. 10 or 8 solid, coaxial feed buried around 5 feet below grade, and a matching network at the feedpoint. For hams, this would all be pretty difficult and expensive to do, but some of the principles are worth following: As many radials as possible to reduce the amount of current return on the external shield of the feed (burying it a few feet below the radial field helps but may not be an option) and a choke (technically an unun in the case of verticals) on the feed at the feedpoint to cut of or isolate the feed from the counterpoise. For hams the matching network is optional depending on the circumstances.

By the way, when it comes to no. of radials, forget all the articles and studies about how x no. of radials gives so many db gain, such and such takeoff angle etc., or for N feet of wire, x radials of y length each is best. Who puts down radials with a preordained total length of wire in mind? What matters is increasing current distribution across the radials; lowering the current in each one, maximizing current return to the feedpoint, and lowering ground resistance relative to feedpoint resistance to get the highest % of power delivered to the feedpoint in the air. this is done by putting down a lot of radials.
 
RE: RF Problems and the HF Vertical Antenna  
by K5UJ on April 25, 2005 Mail this to a friend!
<<<4" PVC pipe coupler works well and it's cheap.>>>

This is a small diameter coil form. If you are going to use this you have to take into consideration the bend radius of the coaxial cable you are going to use. It is probably okay for the small diameter coax such as 8X and 58U, particularly with the solid dielectric, but a larger 1/2 inch size feed with a foam dielectric would probably experience center migration on such a tight bend.

I am much more comfortable with larger forms and you get the highest impedence in cases where the diameter of the coil and its length are equal. For small chokes I use plastic paint buckets. For the low bands where I am using 1/2 inch diam. feed I use small plastic garbage cans. You need to get at least 20 to 30 turns on the form.

If you place multiple coax chokes in your feedline you can lengthen it significantly. For a feed such as RG213, you may begin to experience loss due to length on the higher HF bands in particular that you may want to avoid. In most cases you probably only need one at the feedpoint when it is made to have a high Z.

When it comes to verticals it can be useful to take a page from medium wave broadcasters. The typical 90 or ~190 degree insulated broadcast tower site is constructed with 120 radials, usually no. 10 or 8 solid, coaxial feed buried around 5 feet below grade, and a matching network at the feedpoint. For hams, this would all be pretty difficult and expensive to do, but some of the principles are worth following: As many radials as possible to reduce the amount of current return on the external shield of the feed (burying it a few feet below the radial field helps but may not be an option) and a choke (technically an unun in the case of verticals) on the feed at the feedpoint to cut of or isolate the feed from the counterpoise. For hams the matching network is optional depending on the circumstances.

By the way, when it comes to no. of radials, forget all the articles and studies about how x no. of radials gives so many db gain, such and such takeoff angle etc., or for N feet of wire, x radials of y length each is best. Who puts down radials with a preordained total length of wire in mind? What matters is increasing current distribution across the radials; lowering the current in each one, maximizing current return to the feedpoint, and lowering ground resistance relative to feedpoint resistance to get the highest % of power delivered to the feedpoint in the air. this is done by putting down a lot of radials.
 
RE: RF Problems and the HF Vertical Antenna  
by KC9AGG on April 25, 2005 Mail this to a friend!
"The problem is if you fix the GAP groundplane the SWR goes up, because the antenna is designed to "match" with a very marginal (poor) ground."
thankyou, that answers my question which i've been pondering for months...my gap vert dipole is 25 feet in the air!!! swr all over the place!! it's a fairly good dx antenna, though...if i were to do it again, i'd build my own...in fact i have for 40 meters---20 feet elevated, 36 radials and more to be added...people are getting away from ground-buried radials....they work better when elevated---see "on4un low band dxing"...as this old man likes to remind himself: " all antennas are dipoles". very good commments all around---i love it when i learn something new.
 
RF Problems and the HF Vertical Antenna  
by WA7NDD on April 25, 2005 Mail this to a friend!
A Radio Works T4 Line Isolator right at the base of the 6BTV will solve any RF problems. The big plus is that it takes the coax out of the picture when tuning up 6BTV. But, if you do not use radials, like Hustlers suggests, and just use a pipe in the ground, the only radial you had was the coax shield which screws up the tuning every time and gives you RF in the shack. Isolate the coax, Isolate the mounting bracket if it is not right at ground level, and use as many radials as you can install. The less you have to lengthen the asjustments on the Hustler verticles, the better the radial system is. If you find your Hustler won't tune it is directly related to the antenna seeing the coax as part of the tuning system, no radials, and the mounting point, either pipe or some othter metal structure has taken the verticle out of the tuning range of its built in adjustments. This problem comes up several times a year using the Hustler, and there is no better antenna out there for the amount of money.
Jim, WA7NDD
 
RE: RF Problems and the HF Vertical Antenna  
by WB2WIK on April 25, 2005 Mail this to a friend!
A choke-type current balun as described can help when installed at the antenna feedpoint, if it has high enough impedance to actually do anything. 4-5 turns on a 4" form on 7 MHz or 3.5 MHz usually won't do anything at all -- not high enough impedance.

But another issue is high RF levels in the shack due to simple proximity, especially with ground-mounted verticals. All the chokes in the world won't help with that.

When scouting a site for the installation of a ground-mounted HF vertical, try to keep it as far away from the shack as possible. Remember one wavelength on 80 meters is 250 feet!

WB2WIK/6
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 25, 2005 Mail this to a friend!
.
-----------------------------------------------------------------------

Three common terms describe reflected waves in transmission systems: voltage standing wave ratio (VSWR), return loss and rho.

Each term expresses the amount of energy reflected and returned from a load or antenna to the source in a transmission system.

Every transmission system has the following three elements:
1. a generator
2. a transmission line (and not necessarily a perfect one).
3. a load (usually an antenna, however punc an open and a short are loads, too).

In the ideal transmission system, all energy emits from the generator and passes unattenuated through the transmission line to be radiated or absorbed by the load.

Actual systems have losses, though. For example, transmission lines may not exhibit their rated impedance; they radiate some of the energy they pass; and their dielectric absorbs some energy.

Loads--especially antennas--may present an incorrect impedance. Often, they are tuned to the wrong frequency.
.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 25, 2005 Mail this to a friend!
I think that I would ask these questions of the author:

If I build a quarter-wavelength Ground Plane antenna for lets say 2 Meters, and I mount it at a good typical height for such an installation, how does this differ from the installation you are speaking of?

If I build this Ground Plane antenna with 4 radials for the counterpoise, that are about 5% longer than a quarter wavelength, should I also install a ‘choke balun’?
 
RE: RF Problems and the HF Vertical Antenna  
by W4DL on April 25, 2005 Mail this to a friend!
Unless you have a large piece of property, put that vertical in the air with a minimum of 5 radials cut to resonance for each band. Place 8 to 10 ferrite beads over the cable at the feedpoint for choking purposes. Make sure the angle of the radials is near 45 degress to the mast. Tune the vertical and radials for each band and enjoy the low angle DX unattainable with dipoles mounted at reasonable heights.

Good DX!

Mike W4DL
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 25, 2005 Mail this to a friend!
.
John, WA6BFH,

I will answer that for you after you get the answer from the author. No I'll do it now.

One thing I must bring out is a fact that with four radials on any ground plane, there, that is the ground. The earth has little to do with the ground plane with the exception there will be some reflected power gain from the radials if a one tenth to a quarter wave above ground. A 2 meter ground plane up full wave, 20 or 30 feet above ground doesn't see too much of a wave return.

With any and all antenas, there should be no rf on the outer connector and therefore no balun should ever be needed. With a swr ("a swr meter" not a "vswr measurement") does not necessarily mean that the antenna is at resonance. Especailly with traps and base loaded gimmicks.

For example: Let us take a coil and capacitor that are resonant at we will say 14 Mhz and connected to a coaxial cable. We measure the swr and reads 1:1, wowie, that looks good, not really as this will radiate the full power right off of the coaxial line. It is a reactive load and not a pure resistive load. This will happen to a vertical of matching networks.

Of course if you mount your vertical between two mobile homes, yes, you may have a problem.

The only reason that I would raise my vertical up 20 ro 30 feet is for two reasons: To get it above adjacent buildings and the second to get it up above the television antennas.

.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 25, 2005 Mail this to a friend!
Gee, thanks Vito!
 
RF Problems and the HF Vertical Antenna  
by KL7HF on April 25, 2005 Mail this to a friend!
A word of caution with the coaxial choke if
you're running high power. With a multiband vertical
such as the 40/10 meter models available, there is
a real good chance of having resonance at one or
more frequencies causing some real high voltages
between windings. The result is arcing between the
windings, destroyine the coil and possibly doing
some damage to the amplifier.

I prefer making current baluns using ferrite sleeves.
Several have documented losses of the various types
of baluns and checking those results might also be
smart before taking any approach.
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 25, 2005 Mail this to a friend!
.
You are welcome John, anytime.
.:

So many practical people and no theory, have you noticed?

.:Cut and try takes too much time, theory cuts time by 4 times.

.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 26, 2005 Mail this to a friend!
Hmmmmmm, Inverse Square Law?
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 26, 2005 Mail this to a friend!
.
I have 2 baluns, home made with the T200-2 core. I run tests on them and compare to many other devices. They have a purpose in life and a use, but not for eliminating something that is caused by a human error and the human error can be corrected.

I see where the new antenna couplers called the Balanced Balanced tuners are using a 1:1 balun on the input and using two inductors for balancing the open wire lines. I will make comments on this so called tuner when someone puts a post on it. Keep your eye on it and notice the prices. Egads, you need to be working for congress to afford this hobby.

By the way, I forgot to mention that a ground plane antenna is not 50 Zohm. Also, just another variation of a dipole.

A "J" pole antenna is an end fed Zepp. Oh so much to learn from the past to the present.

,:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 26, 2005 Mail this to a friend!
When my dipoles are 72 Ohms, my Ground Plane's will probably be 36 Ohms!

It would be nice some time to try some experiments with typical 10 through 20 Meter Trap Mono-poles on a 211 foot tower. I would say 10 through 40 Meter but, then I would need a 422 foot tower!

Begger’s can't be choosers! 73! de John
PS
If I had such a tower, I'm betting that I could EFFICIENTLY get that Ground Plane to match 50 Ohms!
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 26, 2005 Mail this to a friend!
.
If I had such a tower, I'm betting that I could EFFICIENTLY get that Ground Plane to match 50 Ohms!
==================================================

The only way would be to run it vertically or lower the plane about 45 degrees and approach the dipole configuration and it will be close enough that will be at 1.5:1. You could also make a 6 turn coil, 1 inch in dia., and put a small cap across the coil or in series called a linear match.

There are many ways to skin a cat without the use of baluns or beads.

.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 26, 2005 Mail this to a friend!
Yea coils, right!

Vito, I think in terms of VHF. Coils are lossy!

COILS BAD! BAD COILS!!!!!

..............................................

That was kinda my point in the question I had asked of the author.

How does his 'choke necessitating antenna' differ from a simple resonant Quarter-wave Ground Plane?

Answer: it has all these flipping reactive circuits associated with it to HOPEFULLY get the thing to look like a decent impedance match, without throwing away too much signal!

Also of course, the flipping thing is probably sitting on the ground, either between those two trailers you were talking about, or right next to a stucco wall, with a bunch of chicken wire beneath that stucco!
 
RF Problems and the HF Vertical Antenna  
by KG4UIJ on April 27, 2005 Mail this to a friend!
i have a good rf ground- copper strap, 50 plus ground rods etc- so i used 1 in. braid wound around the 213 feed for about 6 feet at the base of my beloved titan and attached to the ground. works great. bill
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 27, 2005 Mail this to a friend!
.
Actually John, when it comes to 10 meters and above, I see no reason for being a ham radio operator to bother with a ground plane antenna when the antenna can be a horizontal or a vertical antenna a half wavelength at resonance for a given frequency.

For 10 meters a half wave 16.7 foot antenna is not very long. Also less material, less cost to build. No traps or coils are needed for matching the impedance, etc.

A "true" ground plane antenna impedance is around 35 ohms, now what do you propose to match this impedance to a 50 ohm coax? I will tell you a simple system with no coils and such and no loss exceeding 1/10 dB.

.:
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 27, 2005 Mail this to a friend!
.
Check this out John, no baluns, no coils bad or good and just common theory. To match a ground plane or many other antennas for a given band of frequencies.
------ -------- -------- ---------- ----

The line length being an odd multiple of one-quarter wavelength = Zs.

Impedance of the load (pure resistance) = Zr.

Characteristics impedance of line. = Zo.

Zo = square root of the Zs times Zr.

Therefore; 50 times 35 = 1750, square root of 1750 = 41.83.

41.83 divided by 35 = 1.195:1 SWR.

This will prove that a quarter length of coax will act as a transformer. Losses are usually present, but very small.

.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 27, 2005 Mail this to a friend!
Yes, I have done things like that before Vito!

At my place in Mira Loma I had a set of four J’s (J-poles) for 6 and 2 Meters, as well as 135 and 70 centimeters built atop a 33 foot length of 3 inch diameter aluminum tubing. Actually the J’s were not so much atop that tube; they were merely Q-lines at appropriate mounting heights on the side of that tube. I later added a 10 Meter Q-line about 24 feet below the tip.

The mast was insulated above my roof by a white PVC insulator (and had three 35 foot counterpoise radials). I would load the whole thing as a quarter-wave radiator for 40 Meters. Sometimes I would use an ‘Impedance Inverter’ quarter-wave coaxial Q-line to flip the impedance, and load it as a half-wave on 20 Meters.
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 27, 2005 Mail this to a friend!
.
Good work John and can see you do not make use of baluns..Very informative information.

I have used the baluns with my CF Zepp and with a 112 foot flat top and 42 feet of ladder line, the 4:1 balun did work very well and covered all bands from 160 through 10 including the warc bands with a low swr using my MFJ 961, better than 1.5:1. However with my old 1935 balanced line coupler, I find no need for the balun, but do recommend it to those that have the MFJ "tuners" and no other way to correctly tune the Zepp antennas.

I gave up when the bands changed from 5 to 6 meters and our 2 1/2 meter bands to 2 meters. That took the fun out of my UHF.

As far as having RF problems with verticals, never had any and just followed good engineering practices. You hear a lot of how many radials to use and what else to do, but never doped the problem with gimmicks to cover up my problems that were basically my mistakes.

73 Vito W6th
.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 27, 2005 Mail this to a friend!
I read Jerry Sevick's study where he progressively added radials to a quarter-wave tall tower on the roof of a building. He measured radiation resistance each time he doubled the number of radials. I seem to recall that he quit at 64 radials, and estimated that the resistance curve and improvement became asymptotic at about 120 radials!
 
RE: RF Problems and the HF Vertical Antenna  
by W6TH on April 27, 2005 Mail this to a friend!
.
I have a 16.7 foot vertical for 20 meters and using a good field strength meter and others, the max amount of radials came to 12.

"And others" I meant by a similiar vertical 264 feet away with a bolometer as a detector. My property here is with no buildings and no neighbors, perfect flat land for miles in any direction, perfect for a antenna sight testing range.

On 80 meters with a Hustler, "5BTV" vertical mounted 14 feet above earth and Just 2 radials (65 feet long), I could work the world. My elevation is 3475 above sea level. I think this may be more important than the radials.
.:
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 27, 2005 Mail this to a friend!
Cool!

I would love to meet you and visit before you are off to the blue coast.

Say the word, and I will fire up the BFH'mobile for a weekend trip! Send me an e-mail to my direct address!

73! de John
 
RF Problems and the HF Vertical Antenna  
by WA2JJH on April 28, 2005 Mail this to a friend!
a $500 VERTICAL with those problems. Geesh! You saved me some money!
 
RE: RF Problems and the HF Vertical Antenna  
by WA6BFH on April 28, 2005 Mail this to a friend!
Remember the old adage, "you could load up the bed springs!"
 
RE: RF Problems and the HF Vertical Antenna  
by VE7ALQ on April 28, 2005 Mail this to a friend!
Yeah, you can get a 1:1 VSWR into my dry dummy load too.
 
RF Problems and the HF Vertical Antenna  
by AF0H on April 29, 2005 Mail this to a friend!
The solution is simple...
Hang the vertical upside-down with the shack and coax above it. That way the RF runs down the coax into the antenna. Gravity prevents RF from coming back up the coax.

If that isn't practical in your installation, then a step-aside transformer would work for you instead.

As far as SWR, coat the antenna with Possum Grease, that way those little SWR's can't stand up on it.

 
RE: RF Problems and the HF Vertical Antenna  
by VE7ALQ on June 7, 2005 Mail this to a friend!
Hi! I am using a Bencher/Butternut HF6V 23 foot vertical antenna with the optional 160 meter resonator attached. My shack is 125 feet away from the antenna on the roof, and the feedline is Belden 213. I use this Vertical on all bands between 10 meters and 160 meters inclusive. I rely on my Icom AT-180 Antenna Tuner to bring the VSWR down to 1:1, even with bands the HF6V was not designed to work on(!) I have some RF-in-the-Shack on 15 meters, dunno why. Other bands, except 160 meters are clear of RFI problems. I have bought the Stub Tuned Radial STR-II kit from Bencher/ButterNut so as to provide four radials on 40, 20, 15, 10 active at once, as well as enough stranded #14 B&S guage insulated wire for four 23 foot radials for 30 meters (Currently I have no 30 meter radials) and left over is enough for a 67 foot 80 meter radial (just one!) I am also installing an "UnUn" or "Unbalanced to Unbalanced" line isolator, to be installed at the base of the vertical.

Hopefully this should help cure my RFI problem; if not, should I explore the MFJ 931 synthetic ground?
 
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