Dipole Balun Question

[Buckmangomer]

I am frustrated. I am new here so I will apologize if this sounds like a rant. But I am trying to do something that should be fairly simple. I wish to construct a general purpose antenna for a shortwave radio. I do not wish to transmit. I just want to receive. When I was a kid (in the 70's) my father had a shortwave radio. We strung a wire up in the attic and I had a blast listening to radio shows from all over the world while I worked on my balsa gliders and rockets. Now I'm middle aged, my daughter is 8 years old, and I want to give her a similar experience.

So when I decided to build a shortwave antenna I went to the library and checked out several books, read several blogs and web references, read piles of magazine articles, watched youtube videos, lurked in message boards, and the only thing I have learned is that no one agrees on even one tiny aspect of antenna design and my reception is still for crap.

So I have come here asking for help. Here are the particulars:

I have an older I-Com R71A receiver that seems to be in good working order. (I can get a 3 or 4 shortwave stations(sometimes) and most local AM band broadcasts.) I have plans to build a larger antenna in the future, but for now I am just trying to get something smaller to work in my attic. (Proof of concept design before convincing my wife that I need to build the 80 foot outdoor monstrosity to come.) Currently I have a dipole antenna in my attic that runs about 12 feet on either side for a total of 24 feet. Both leads fit into a 50 ohm coax cable hanging straight down from the middle. One end of the dipole is soldered to the center wire, and the other end is soldered to the outer sleeve. This has not been done with a nice PL connector (waiting for a few things to arrive from Amazon so I can build something more substantial) but I did use heat shrink to protect my connections and there is no short and continuity tests are okay. From the middle of this dipole 50 feet of indoor 50 ohm coax runs straight down into my basement two stories below and attaches to the receiver with a nice PL connector.

By my rough calculations I should be able to get fair reception for about 20 MHz on up. But do I? Of course not. If I am lucky I can get 2 or 3 stations to barely come in on the low side of the band (about 4 to 7 MHz seems to be the sweet spot) and those are mostly covered in static. Actually, everything is covered in static. Static, static, static.

So...from all my reading I think what I need is a balun to connect the dipole antenna to my coax thereby taking the balanced dipole and turning it into the unbalanced signal that my receiver and coax cable need. So I started researching baluns...sheeeesh...I thought the other parts of the antenna were a hotbed of argument.

So some sources say a balun made of coax cable is just the thing. I have seen several versions of this. Some are just wound around PVC pipe, while some are spliced and connected in various ways. Other smaller types of baluns just use regular wire. Some use two wires, and some three. Some authors advocate spacers in between certain wires. Some are wound around nothing. Some are wound around a ferrite rod. Still others are wound through a doughnut looking thing made of another material. And then there are the ratios. Some are 1:1, while others are 4:1. From all my reading I have failed to learn the difference in ratios. And several sources posit yet another theory that states that baluns are useless when used with coax cable. About half of these articles suggest that I purchase an antenna tuner. I could go on, but I think I'll stop there. Actually there is another thread on this board that covers most of the above and basically just stopped after no one agreed.

So which is it? What is the best way to proceed?

Through all my research I have the following plan. (Please note that my 'plan' is a shot in the dark, but a little more than half the sources I read seem to lean vaguely this way.) I would like to build a 3-wire balun around a ferrite rod. I would like to encase the whole thing in PVC. Believe it or not, the only video I have been able to find on youtube which shows a good illustration of a 3 wire 1:1 balun going from a dipole to coax is in Spanish. The diagram is awesome, but I can't tell how long it should be or how many winds to make. I grew up in Texas, but my Spanish is just not that good.

For the love of God will someone please help me with this? Am I barking up the wrong tree, or am I near the answer?

 

[prcguy]

Adding a balun, of any ratio to the antenna you describe will probably not make any noticeable difference.

Antennas are very complicated and there may be better designs but your poor reception compared to when you were a kid could be from lousy propagation due to the sunspot cycle or a house full of RF noise making devices polluting the RF spectrum that did not exist when you were younger.

Try taking your R71A up the street somewhere away from power lines and buildings, run from the car battery, string a wire up to a tree and see how that works as a baseline test. If your noise floor is much lower and you can hear more stations then your house may be full of noise generating switching power supplies that need to be dealt with.

If your reception in a deserted area is the same then propagation is not so great on the bands at the time your listening. There could be other factors but you have to know a few things before condemning your antenna or going crazy with baluns or other gizmos that may take a lot of time to install and not give any or much bang for the buck or time.

Otherwise I am a big fan of feeding dipoles with balanced feedline and TV twinlead can make a dipole that works poorly at some frequencies come alive. An 80ft center fed dipole fed with twinlead is plenty big enough for general SW reception.

Some people have good success with end fed wires provided there is a balun or matching transformer at the feedpoint. The PAR series is an example and you can make a similar one with a high ratio balun and some wire.

So run some tests and see what the radio can do at another location and proceed accordingly.
prcguy

 

[WA0CBW]

Listen to prcguy. From your description it sounds like your antenna is fine. As he said there will be little difference with or without a balun when receiving. The recent sunspot eruptions have made the HF bands pretty poor. Hearing static (and not just radio background noise) would indicate external noise sources (motors, computers, wall warts, etc) If you can power the shortwave radio from a battery try shutting off the main electrical breaker. If the static disappears you know something in your home is creating the static. If it doesn't it could be something in the neighborhood (maybe from your neighbors house). There is also the possibility that something is wrong with the radio.

BB

 

[ridgescan]

two points from my humble SWL experience
1-as prcguy and WA0CBW said, for at least the last 4-5 days, there have been solar eruptions that have flattened the bands to nothing but noise. What I personally was getting normally at +30 on my r71a meter, was barely pushing s9 and the normally s5-6 noise floor was at s8. When ma nature decides to flare it up, no antenna is exempt.
2-aside from a few broadcast stations between 21500-22kHz, there just aint a lot above 20 megs.
Try taking that leg of wire coming off the center conductor and increasing its length to at least double, wrapping around the attic perimeter. You need more length.
I live at the top floor in an apt building and before I got a PAR EF antenna I ran a 100' wire with no balun but did have a good ground and I had wonderful reception-the PAR system with its magic matcher only increased that reception a bunch.
Your wife needs to allow the outside wire if your daughter is to ever truly hear the world-the vast majority of english BCs are beaming overseas to overseas targets and an indoor antenna limits what you could potentially receive.

EDIT
try your SWL after 0100utc in these spots
5700-6270kHz
7200-7600kHz
9200-10000kHz

I don't know if you can get this as well in Ky but I get a ton of Asian BC's and Australia/NZealand between
11500-12100kHz
15000-15900kHz in that time

If you have a copper aerator pipe within 8' or so from antenna feedpoint you could tap into for ground, I would ground the coax braid to that and like I said increase the main lead wire.

 

[majoco]

+1 on what Ridge said.

There's nothing above 20MHz (unless the skip starts up) now we're in a high sunspot cycle. I hear round the world late afternoon (0500z) on the 49m band - 5.8 to 6.2MHz on a 66ft wire outside.

 

[Buckmangomer]

Thanks for the replies

So I'm not crazy...that makes me feel better. When I grew up in Texas we lived in a fairly new neighborhood with all lines buried below ground. The house was large and the attic was huge.

My current situation has good points and bad. We live in a very old neighborhood. My house is almost 100 years old and all lines (and I mean EVERYTHING) is above ground. So power, cable and telephone run down both sides of the street and the lines are stretched everywhere. This is bad due to obvious interference. But it is also good because none of my neighbors will spend two seconds looking at an 80 foot dipole strung along my house and out to the detached garage. Don't worry. I plan to run this line on the other side of the house from the power line, perpendicular to it and away from it. But it is there. The lines run absolutely everywhere.

Question: So I should run the outer jacket to ground? A whole series of copper water pipes is available. But then it wouldn't be much of a dipole, would it?

Question 2: When I do run this outside I planned on running the coax from the center of the dipole down towards the ground. There is a metal fence pole that I installed there that goes at least two feet into the ground through my concrete driveway. Should I split the coax to this pole for safety, or is it inadequate? There is a real ground rod for the house about 30 feet away, but I would hate to run coax all the way there when there is a giant metal pole buried in the ground right where I want the coax to enter the wall of my house,

Thanks for the excellent feedback.

 

[mmckenna]

There are a few things I didn't see mentioned above:

What is your roof made out of? Is it wood shingles? Composite? Metal?
What about the attic space, is it wood studs? Metal studs? Lots of metal pipes, wiring, conduit, ductwork?

Try tuning to the following frequencies:
2.5MHz, 5MHz, 10MHz, 15MHz. Let us know if you can pick up WWV or WWVH on these frequencies. These are signals from the atomic clock in Colorado/Hawaii. Using those as a reference can tell you a lot since they are always running on those frequencies.

What type of coax is running down to the radio? Shouldn't matter too much unless you are really running something small.

 

[ridgescan]

So I'm not crazy...that makes me feel better. When I grew up in Texas we lived in a fairly new neighborhood with all lines buried below ground. The house was large and the attic was huge.

My current situation has good points and bad. We live in a very old neighborhood. My house is almost 100 years old and all lines (and I mean EVERYTHING) is above ground. So power, cable and telephone run down both sides of the street and the lines are stretched everywhere. This is bad due to obvious interference. But it is also good because none of my neighbors will spend two seconds looking at an 80 foot dipole strung along my house and out to the detached garage. Don't worry. I plan to run this line on the other side of the house from the power line, perpendicular to it and away from it. But it is there. The lines run absolutely everywhere.

Question: So I should run the outer jacket to ground? A whole series of copper water pipes is available. But then it wouldn't be much of a dipole, would it?

Question 2: When I do run this outside I planned on running the coax from the center of the dipole down towards the ground. There is a metal fence pole that I installed there that goes at least two feet into the ground through my concrete driveway. Should I split the coax to this pole for safety, or is it inadequate? There is a real ground rod for the house about 30 feet away, but I would hate to run coax all the way there when there is a giant metal pole buried in the ground right where I want the coax to enter the wall of my house,

Thanks for the excellent feedback.

For question 1 ya you will be running an endfed instead but that dipole you have is too short for wideband HF anyway plus it being possibly hindered inside the attic. You can spread your wings outside and run a bigger dipole out there but IMO a dipole aint the only SWL antenna. Like I said I ran a 100' endfed without a balun and it rocked. To me, it's all about getting up enough wire and having a good RF ground. That ground makes all the difference.
Question 2- that driveway pole isn't deep enough into the dirt to make ground. You need to be at least 8' down. Again, how about a cold water pipe at the house near the feedpoint entry? BTW if you ground to plumbing do not ever use hot water pipes. Only cold water or as in my case, I discovered that the aerator pipe at the roof that I have my antenna tripod anchored to, is solid copper so I grounded to it and it kills noise exactly the same as the cold water pipe ground I had going here inside the shack to my toilet supply.
Also, how about a groundpoint used by the cable tv guys at the house that is closeby to the feedpoint?
How about driving your own ground rod where you want? Time for good old experimentation

 

[W2NJS]

One of the biggest obstacles to "quiet" and normal HF reception is the large number of interference-generating devices found everywhere today. First of all, if you're trying to listen, first shut off your computer completely; it's a source of many low-level RF signals, none of which you want or need. Another source of hash is the light dimmer you may have in your dining room for instance; turn it off completely. Then look around for other electronic devices that may be running and eventually you'll find the noise level on the Icom is lower. Your local power company is also a source of problems due to possible leakage from their system. Best way to find the hash is to walk around with a cheap transistor radio tuned to the AM broadcast band, tuning back and forth, including a walk outside your house to hunt for power line problems which, if they exist, the power company has to fix.

 

[kb2vxa]

Using a balun to decouple the antenna from the coax should mitigate your static problem, presently circulating currents in the shield are making it part of the antenna system. A 1:1 ham balun commonly available will serve the purpose quite well, you don't need a high power one just for receiving so no reason to pull your hair out making one when they're cheap enough.

A "tuner" which really doesn't tune the antenna but rather matches impedance is an asset for several technical reasons we don't need to go into here. For general coverage SWLing avoid those with switchable tapped inductors, they only cover ham bands. One with a rotary inductor will serve you well on SW bands as they're continuously adjustable from 3-30MHz, one for 1800KHz-54MHz is a little pricey.
MFJ Enterprises Inc.
Now if that's too hard to swallow they can be bypassed with their internal antenna switches for out of range reception, you don't have to break the bank.

Now if these things don't improve your signal to noise ratio significantly all I can tell you is attack the source(s) so you may have to do without a computer, router, switch, some fluorescent lights, dimmers, fish tank heaters and whatever while you're tuning the SW bands... oh well.

"Your local power company is also a source of problems due to possible leakage from their system."

Uh oh, if that's the case I hope your power company is cooperative like one I encountered a few years ago. They sent out an engineering truck with more radio gear than an FBI van and located not only defective company hardware but several touch control lamps in the neighborhood. All's well that ends well with Atlantic Electric but not Public Service Electric and Gas (a thorn in my side for years) among others I've heard of. They ignored all complaints including flickering lights and even the FCC (yes, they have jurisdiction) until arcing wires, fires and destroyed equipment forced repairs.

What's the point of having a radio if all you hear is static? Good luck guy, I wish you well.

 

[Buckmangomer]

Thanks for the help

I have been reading replies here and doing a bit of research. One of the problems is that I have interference everywhere. I mean...its bad. This radio is in my 'man cave' and there is at least one computer fired up, usually two. I already do podcasting and various other audio things. My receiver is actually hooked up with several other things through a sound board so that I can hear all of it through headphones at once. I currently record through Audacity. The recording is in stereo so that the SW goes through the left channel and an open mic goes to the right. If I hear something I want to note I speak the frequency and time into the mic as an audio note. (Old podcasting trick.) I can hear other things in the man cave through the sound board but they are not recorded. Since this radio is an 'addition' to an already crowded situation I will have to experiment with placement of equipment and the interference each thing causes.

I plan to keep my inside antenna in the attic for use during bad weather and such. I have free reign to play up there so I will experiment. The shingles are composite. The studs are wood. But the attic is semi-finished (previous owners used it as a bedroom but I wouldn't use it for anything but a snuff flick...) and has various florescent lights, a drop down ceiling held up by those little metal rails, water pipes and so on. I have tried to keep the wires as far away from anything else as possible, but the layout is poor. The coax I am using is cheap indoor stuff from radio shack. Nothing special. The outer jacket was kind of sad. Not a mesh like good coax. I was able to gather the strands and twist it to solder to the other side of my dipole fairly easily though.

The outside antenna is the big project for the coming week. It will be 80 feet long. The info I get about baluns is absolutely contradictory. So...I will try it without first and if all else fails I will attempt to build a 1:1 and see if it clears things up. The center of this dipole will be mounted on the side of the house about 20 feet up. A good outdoor coax will drop straight down from this to the entry point into the man cave/basement. There is will split to a spark gap that feeds a bare ground wire along the concrete slab to the official cable company ground rod that is mounted further down in my driveway. The feed will go into my basement and to my radio. A monster knife switch will be used to disconnect when not in use or I may just unplug the cable and set it in a glass jar. Not sure about that part yet.

One I get things up and running I will report results. Thanks for all the help.

 

[zz0468]

The best SWL antennas I've ever had were dipoles fed with open wire ladder line. As prcguy said, TV twinlead would be good, too. What I've done is bring the open wire line to the shack, to a ferrite balun and a SHORT piece of coax to the receiver.

As to static and noise, an indoor antenna will pick up noise from every electronic device in your house. You'll find lots of noise sources outside as well. I've lived in locations where the noise floor is a constant 40db over S9 from 100 khz to 40 MHz, and learned to live with it.

The secret for me was shielded loop antennas, and open wire dipoles coupled with an active noise canceller like the JPS ANC-4.

 

[prcguy]

If you need to transition to coax a choke balun is a good idea. You can use a commercially made 1:1 or even a 4:1 coax to wire balun or just wrap about 10 turns of small coax around a large #43 mix toroid core.
prcguy

The best SWL antennas I've ever had were dipoles fed with open wire ladder line. As prcguy said, TV twinlead would be good, too. What I've done is bring the open wire line to the shack, to a ferrite balun and a SHORT piece of coax to the receiver.

As to static and noise, an indoor antenna will pick up noise from every electronic device in your house. You'll find lots of noise sources outside as well. I've lived in locations where the noise floor is a constant 40db over S9 from 100 khz to 40 MHz, and learned to live with it.

The secret for me was shielded loop antennas, and open wire dipoles coupled with an active noise canceller like the JPS ANC-4.

 

[K5MPH]

Put it outside

Put your antenna out side and make it at least 50 to 100 feet long and yes the noise is very bad these days not like it was in the 70's or 90's hf and shortwave is not like it use to be ,i have a (Drake SW8) and also have noise problems to, but i put an antenna out side and it changed it a lot,also ground the antenna very good i found that this will take some noise away to, and ground the radio it self never forget about grounding.

 

[ridgescan]

The best SWL antennas I've ever had were dipoles fed with open wire ladder line. As prcguy said, TV twinlead would be good, too. What I've done is bring the open wire line to the shack, to a ferrite balun and a SHORT piece of coax to the receiver.

As to static and noise, an indoor antenna will pick up noise from every electronic device in your house. You'll find lots of noise sources outside as well. I've lived in locations where the noise floor is a constant 40db over S9 from 100 khz to 40 MHz, and learned to live with it.

The secret for me was shielded loop antennas, and open wire dipoles coupled with an active noise canceller like the JPS ANC-4.

with a noise level like that did you even copy anything? That was about how it is in my listening environment here but the worst mine was was +10 over. Until I grounded the antenna which brought it to a tolerable average s6 on HF and full quieting in MW/LW..

 

[vagrant]

- A road map of stations available when you listen might help. Short-Wave Frequency Schedule (Do not expect to hear all of the stations listed at a particular time.)

- As a general rule of thumb, tune below 10 MHz at night and above that during the day. By day I mean you can actually see the Sun, as I can still pull in DX stations (other countries) early in the morning while I enjoy some coffee.

- As posted earlier, seeing if you can tune in to 2.5MHz, 5MHz, 10MHz, 15MHz 20MHz to hear the tone should give you an idea if you can hear at all. I can always hear 10MHz. The frequencies above and below that depend on the time of day. (See rule of thumb)

- Another station I can almost always hear is on 11780. It's a station down in Argentina and typically booms in here to California. (I think it's in Argentina. Anyways it's somewhere in South America)

 

[hfflunki]

Wirelessly posted (Mozilla/5.0 (Linux; U; Android 2.3.3; en-us; MID7022 Build/GRI40) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1)

Just take a solid copper wire run it from one endof you attic to the other and
Buy a rf systems mlb llongwire baluan then when you ger it connect
it to the wire then figure out where u want your radio fhen measure length
Of wire you need and order wire the best time for intntl shows is night
most broadcasts are from 7pm-2am est you may want to print out a sceaduale from www.primetimeshortwave.com and get the stuff at universal
radio www.rffun.com
good luck

 

[hfflunki]

Wirelessly posted (Mozilla/5.0 (Linux; U; Android 2.3.3; en-us; MID7022 Build/GRI40) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1)

Just take a solid copper wire run it from one endof you attic to the other and
Buy a rf systems mlb llongwire baluan then when you ger it connect
it to the wire then figure out where u want your radio fhen measure length
Of wire you need and order wire the best time for intntl shows is night
most broadcasts are from 7pm-2am est you may want to print out a sceaduale from www.primetimeshortwave.com and get the stuff at universal
radio www.rffun.com
good luck

 

[hfflunki]

Wirelessly posted (Mozilla/5.0 (Linux; U; Android 2.3.3; en-us; MID7022 Build/GRI40) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1)

I forgrot onething get a ground strap and connect it to your cold watter pipe system and conect a copper wire to radios ground from the ground strap
73

 

[zz0468]

with a noise level like that did you even copy anything?

Yes, I had some very effective countermeasures. ANC-4 noise cancelers that had an effective noise antenna, and a receiving loop antenna that was used for frequencies below 10 MHz. That, coupled with a radio with a good noise blanker and DSP noise reduction, on most frequencies I could reduce the noise level to the point that it was barely perceptible.

Even the loop passed through the ANC-4 to remove excess noise.