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tuning dipole question

9

9Lives

Active Member
Oct 3, 2012
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Hi everyone. I'm working on setting up my base. Magnum 257hp 50ft of bury flex going into the attic with a falcon dipole in inverted v config. I've got the power supply, bird, and scope all setup and is looking good.

I've even got a arm boom stand and behringer condenser mic.

My question is about the antenna. I'm having trouble separating myth and fact. From the radio I have a 3 ft jumper into the bird and then the 50ft run goes up. I folded the leads back 6 in and swr is reading pretty good on cb band.

What I'm wondering is, the swr is high as hell on high, lowest bands. I know it's a broad freq stretch but is there any way I can get them lowered? I've read about baluns. Can I use the excess coax to make one? Got PLENTY left over. Also its bleeding into my tv something fierce. Please no snake oil. Only real life applications. Thanks in advance

Ps I chose inverted v bc it appears best compromise for mostly dx, omni directional, a lil local. I have plenty of room there it's just kind of hard to get up there.
 

I can't tell you much theory, cause I know little electronics. Enough to keep my fingers out of light sockets and that's it.

But I do have a 27 meter dipole. I bought mine from Dr. Dipole, and had him build it with a Balun in it. He sells the dipole for $20 on E-bay and added another $25 to build it with a Balun. The legs are solid copper wire, looks like 12Ga. Very stiff. Everything about this dipole is built like a tank. I do believe it will take years of weather and elements outside and still be going strong. From the second I unrolled the legs and attached the coax, it got 1.00 SWR.

First, I wanted stealthy, so my plan was to use it inside my room here. The room is about 13'x13' more or less and 7.5' ceiling. Didn't work. I heard a few distant stations. I tried every possible configuration.

Next, it went outside, I put one end up at a corner eve, ran the other along the wall, North to South. It was about 10 feet off the ground, but right against the outside of the house, plastic siding. Nothing. I was getting discouraged.

I live in a trailer park, no antennas. I was worried about Colonel Klink seeing it. There is an old dead telephone pole at the corner of the trailer, North end. About 18' high, nothing on it but one guy wire. I said to hell with Kilink, got on the roof, found there was a hole drilled through the top of the pole and fed some clear weed eater line through that and down to the ground on both sides.

Attached one end of the dipole to the clear line and pulled it to the top and tied it off. Went to the other end, tied on some line and ran that to the corner of the porch, which is 12' out at a right angle from the side of the house. I put a screw in hook on the eve, ran the line over it and pulled it up. Now, one end is about 4 feet above the end corner of the trailer, the other is at least 14 feet up and sloped to the South. The length to the corner of the porch is much more though and I filled that in with the clear line.

Bingo. I have talked to Jamaica, Florida, Bahamas, Texas, New Mexico, Arizona, Cabo San Lucas and most of California with my barefoot Uniden 980ssb.

Even worse, I am in a geographical hole. In a narrow Canyon, up stream is 800 feet elevation bluffs, down stream is open to the Mississippi River. Power lines directly over head, and I mean directly, with a transformer and streetlight on a pole, right over the corner of the porch. 300 yards to the West are a 4 wire run of high tension lines. None of that seems to matter to the dipole. It shoots right through it all, up to the D-layer and then bouncing out to the world. I heard Australia the other day.

In summary, it had to be away from roof and wall and outside. Maybe in a tall attic, might work, but you never know what them shingles are made of. They might block the RF, you can't ever tell. But outside, mine works in the rain and thunder, sunshine or clouds.
 
By the way, No bleed over, none whatever. We got speakers all over the house, old clock radios, nothing at all.

Also, I can "aim" the antenna in a shotgun fashion, but it works. I slope the low end down more to get tip of the Baja or into Mexico. I pull that end up to get Southern California and up to Frisco. I can swing the low end around to aim more East or West. As a Sloper, it works both as a horizontal and a vertical. I can talk to both.
 
The usable frequency range of a dipole, or any antenna, isn't going to be very wide without some means of adjusting the length of the antenna. There's no 'secret' to that, it's just common physics. How you determine that usable frequency range can make a huge difference. If it's only by using an SWR meter then that usable range can -seem- to get pretty big, but the efficiency of the antenna starts going down too, which is not so good. From what you've posted your set up sounds about normal.
The interference you are having sounds like it's a matter of over-load, the things being interfered with are just too close to the antenna. It isn't just the feed line radiating that does that interfering, the majority of the RF is coming from the antenna it's self.
One way of reducing possible interference like that is by using a 'choke' in the feed line as close to the feed point of the antenna as possible. That choke is a coil of feed line which 'strips' any CMC or RF on the -out side- of the coax. That's not a 'sure-cure' but it can help at times. That coil of feed line, a choke, isn't a balun in any sense of the word. (It's commonly called an 'ugly-baun', but that's just a name.) If you've got some excess feed line it isn't going to hurt anything to wrap it into a coil and see if it helps. The 'size' of that coil determines how effective it can be. For 11 meters, something like 4 or 5 coils should do it, maybe.
- 'Doc
 
Thanks for the replies. I've got the v shape at a perfect right angle. Just in the shape of an up side down v.. now.. conditions in my mobile have been HORRIBLE here all week so I'm not freaking out, but I'm not getting ANY signals at all. A couple very very faint.. seems odd an antenna that high should get something?? One thing I didn't know to do its suspend the antenna. Mines kind of resting on a stud. I think I'm just going to forget about all the directional/radiation patterns and just go with a strait up, horizontal dipole. With bslun. And get it working. Going to attempt to point it west bc all skip on mobile comes from San Diego/ mojave area and England. I'm going to try and suspend it in the angles of the trust and see if it works. Sound solid?
 
Isn't that last "coil" actually the last couple feet of the "working" coax, or is just a dead piece wound on a form and soldered together. It seems I have read articals that lead me to believe it's both ways, so I can't be sure which one is right.

I was also told by the guy that made the Baliun that it makes both legs radiators. Checking it all with an ohm meter, it shows a dead electrical short every where you try it. Electrical short, but not a RF short, and that's the secret.
 
9Lives said:
Thanks for the replies. I've got the v shape at a perfect right angle. Just in the shape of an up side down v.. now.. conditions in my mobile have been HORRIBLE here all week so I'm not freaking out, but I'm not getting ANY signals at all. A couple very very faint.. seems odd an antenna that high should get something?? One thing I didn't know to do its suspend the antenna. Mines kind of resting on a stud. I think I'm just going to forget about all the directional/radiation patterns and just go with a strait up, horizontal dipole. With bslun. And get it working. Going to attempt to point it west bc all skip on mobile comes from San Diego/ mojave area and England. I'm going to try and suspend it in the angles of the trust and see if it works. Sound solid?
Click to expand...

First off, I would take it down, take it outside and set it up and test it there. You just have to know it works in a good environment first. If it does, then bring it back in if you must, and at least you know your not beatin a dead horse. I say this, cause I do not trust your shingles on the roof to be totally clear to RF. Reflecting that RF back to itself would certainly explain the high SWR. And it may not be the shingles, but the membrane under it or even the glue in the plywood roof.
 
I think you would see some improvement if you widened the angle between the two legs of that antenna. Having them that close together isn't doing anything useful.
Making both legs of that dipole radiate? They do anyway, it certainly doesn't take a balun to make that happen (think you were fed a 'line').
A choke can be wound with no 'joints' or soldering, just wind the feed line into a coil. It can be done by making that choke a separate 'device' and putting it in-line but there's no particular reason for that if you've got the 'extra' feed line to start with. The diameter of those coil turns isn't definite by any means. They should be large enough so that bending the coax doesn't deform it, but that's about it. Some people use a 2 liter bottle as a coil form, just a convenient shape/size thingy to wind it on.
The polarity of a dipole depends entirely on how the thing is hung. If it's hung horizontally then it's horizontally polarized. If it's hung by one end then it's vertically polarized. Just because it's an inverted 'V' doesn't contribute to making it vertically polarized to any significant extent, it's still a horizontally polarized antenna. It's not 'black or white', there's some 'grey' in there, but for all significant purposes it's usually a 'one or the other' kind'a deal.
No matter what kind of antenna you are talking about, an 'indoor' antenna will always be at a disadvantage compared to the same antenna mounted 'out side'. How much of a disadvantage depends on how much 'stuff' is between it and the signal being received, and that depends on what that 'stuff' is made of. If you've got the option, put the thing outside. If not, then get used to the performance it provides 'inside'.
Have fun.
- 'Doc
 
A coil of coax is (or can be) a choke, but it's not a Balun. A balun is a transformer that becomes the antenna's feedpoint impedance and transforms it to something the transmitter can use, OR it transforms a system from BALanced to UNbalanced ... which is why they're called BALUNs.

How much metallic stuff is in the attic? There might be vent ducting, piping, electrical wiring, foil-faced insulation...as well as the roofing nails and possibly the shingles themselves. House exterior? Please tell us it's not stucco.

And as others have said, you're overloading the TV and other appliances with RF as a direct result of the closeness of the antenna, even assuming your feedline is perfectly intact and the connectors are made properly. No choke or balun is going to change that. I shouldn't have to add that your radio is part of the problem since its output is somewhat greater than 4 watts AM/12 watts SSB.
 
Thanks for all the advice. I probably will end up putting it outside. I raised the end s and trimmed them back a little bit. The swr is 1:1.5. Weird thing is. On the "a band" it's doing 80 watts ssb and on "e band" it's doing like 60. Which is what it's suppose to do. Is this a watt meter trick? With impedance and all that blah blah.
 
Btw, it's a brick house. Roof it's just board & shingle. I made a few contact this weekend with poor conditions. The only thing that concerns me is a old exhaust fan... but the swr is low so... is it ok? I'm experiencing a few lost watts on the upper 5 but I can try and trim it back a lil.
 
That "impedance and all that blah blah" is important, it's what SWR is a measure of, and deals with the 'transfer' of power from one place to another.
A transmitter is optimized to produce it's max power in the center of one 'range' of frequencies. The further the transmitter is from that optimal frequency range the lower it's output power will be. That's absolutely normal. The same thing holds true for an antenna. It's optimized for one 'range' of frequencies and the further you get from that optimal range the less efficient it will be, the less it will radiate. That deals with that nasty impedance thingy again, or at least a 'part' of it called reactance. Reactance doesn't 'radiate' or help to radiate anything in an antenna.
I think your best bet would be to tune/adjust/optimize your antenna for the most used range of frequencies (band) you are interested in, then just put up with less power on other bands. That's what's most commonly done. An antenna doesn't 'do' 'magic', and 'magic' is what you'd have to have to make an antenna work well over a large range of frequencies/bands. You can -make- an antenna that covers a very large range of frequencies but there's a 'cost' to it. Part of that 'cost' is money, the other parts include convenience and complexity.
- 'Doc
 
Brick buildings (most of the ones I've had RF experience with) tend to absorb RF like a sponge. It has to do, I think, with the composition of the specific bricks. You should do much better with the antenna outside, up high, and away from the structure.

I say this a lot: Low SWR is not necessarily an indication that an antenna is working well. A 50-ohm dummy load has a low SWR over a really wide spectrum, but it's really a poor choice for an antenna.
 
Yea.. I'm afraid y'all are right. I'm not getting out. I want to so bad. With the horizontal antenna I'm picking up sine beautiful am on channel 11-15,17 and all sorts of things I never hear in the mobile. I'm not getting out at all.. if I drill a hole big enough through the roof for the coax, how high should I start, when on top of the roof? If I use pvc as a form to keep the dipole strait will this work? Since swr is ok now will it be effected once out in the open?
Is the magnum 257hp enough by it self to skip on am or should I go ahead and build an amp for it? Thanks for the help guys. I really want to get this am going.
 
Even if you do get it outside the roof, just on the shingles probably will not work. I got mine outside and put it first right against the side of the house siding, and got nothing. It didn't start working till at least 4 feet out.

And rather than drill through the roof itself, do you have one of those 2 or 2 1/2 inch vent pipes going through? At the roof point, they have nothing but air in them. Drill a hole through that pipe big enough to feed the coax, right up close to the roof itself, stick the coax through and feed it out the top. Pull out enough for the run, then seal it good with silicone. One of those vent pipes or even a piece of bathroom vent duct work. There is nothing but air inside them.

I have also heard of guys sticking a vertical antenna base inside one from the outside and using that to mount the antenna from. Just don't go drilling holes in your house. LOL
 

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