New to Ham still scratching my head?

[K7MEM]

I agree entirely KM4GGD, W9BU made a good post. I did pick up a MFJ 259b for a fair price. Can't wait to tune my 4 element 2 meter beam I have constructed. It's is suppose to be direct feed but if I can't tune it 50 ohms by cutting the driven elements then I'll have to study baluns. Then can't wait to make my 5/8 wave collinear 3 element antenna and I read it requires a 4:1 baluns. Also have ordered a 100w do it yourself amp kit for VHF, but all of these are a new thread to post for when I get started .

IMHO, you are doing things backwards. When you are feeding a balanced antenna with unbalanced transmission line, a balun is the first thing you should consider. It shouldn't be an after thought for when nothing else works.

A balanced feed, like your driven element, will tend to have a low impedance. This is mostly due to the proximity of parasitic elements and the boom, if it is metalic. So trimming the driven element or adding a balun will not necessarily bring the feed point to 50 Ohms.

The balun is intended to transform the unbalanced feed to a balanced feed. In many cases it is also used to transform a impedance, like 4:1 or 9:1. But what if your feed point is 25 Ohms and capacitive? A balun won't fix that. You will still have a bad SWR.

I have a three element yagi for 2 meters. The driven element is a split dipole. For matching, it first uses a Hair Pin match (Beta match) This is to cancel out some capacitance and increase the feed impedance to around 200 Ohms. Then it uses a 1/2 wavelength 4:1 coaxial cable balun (RG-58) to bring the impedance back to 50 Ohms. A coaxial cable balun is very simple to construct. It shows a 1.1:1 SWR across the whole 2 meter band and has worked great for about 50 years now.

Martin - K7MEM

 

[KG6ABF]

IMHO, you are doing things backwards. When you are feeding a balanced antenna with unbalanced transmission line, a balun is the first thing you should consider. It shouldn't be an after thought for when nothing else works.

A balanced feed, like your driven element, will tend to have a low impedance. This is mostly due to the proximity of parasitic elements and the boom, if it is metalic. So trimming the driven element or adding a balun will not necessarily bring the feed point to 50 Ohms.

The balun is intended to transform the unbalanced feed to a balanced feed. In many cases it is also used to transform a impedance, like 4:1 or 9:1. But what if your feed point is 25 Ohms and capacitive? A balun won't fix that. You will still have a bad SWR.

I have a three element yagi for 2 meters. The driven element is a split dipole. For matching, it first uses a Hair Pin match (Beta match) This is to cancel out some capacitance and increase the feed impedance to around 200 Ohms. Then it uses a 1/2 wavelength 4:1 coaxial cable balun (RG-58) to bring the impedance back to 50 Ohms. A coaxial cable balun is very simple to construct. It shows a 1.1:1 SWR across the whole 2 meter band and has worked great for about 50 years now.

Martin - K7MEM

Just a quick response, I think you misread his post. He said "direct feed" not balanced connection. Also the feed point of a dipole is 100 Ohms. If you are feeding it with a true 50 Ohm load the mismatch would be 2:1 and usable. It wouldn't be a 1:1 but still usable. Years ago amateurs were less concerned with a minor mismatch but since the proliferation of meters everyone is adamant about the "perfect match" or 1:1 as must have before operation. The benefit of a match closer to 1:1 is more power is radiated out of the antenna, while less reflected power, common mode currents and other issues are mitigated down.

Striving for a 1:1 match is desirable, but if you are able to only get say a match of 1.5:1 or even slightly higher it isn't end of the world, it just means your system needs more development, possibly a BALUN, UNUN or other matching device such as a tuner to help.

BTW if you do use a tuner it simply lets the rig "see" a match more in line with the optimum, it doesn't resolve the mismatch and power isn't really reaching the radiating element as you would allow yourself to believe. For best transfer of power many Amateurs who have operated for a reasonable period of time will often use Balanced line. Balanced line can be 75, 300, 450, 600 ohms or even higher. In reality 450 Ohm ladder line works out to be about 400 ohms. In the 1930,40s, 50s, 60 and into the present day an Ammeter showing the current up both legs of a balanced line is used to see if you are get maximum power to the feed point of say a dipole or other type of wire antenna.

I have used many different types of antennas, often I run a Balun or UnUn if needed for that particular antenna. I have used directly fed antennas and magnetically coupled antennas (with either Balanced or unbalanced coax), it depends on what I need for that project, activity or event. I have used commercially built antennas and home-brewed antennas, antennas manufactured by various companies both good and bad. Some worked very well and some were of poor design and of cheap materials. Again even some of the cheapest antennas worked well in some instances and other times weren't worth the cost or the time to even connect up for use.

I have read posts here from people who obviously know and have experience in this area, while some demonstrate less experience and haven't had as long a career as the more knowledgeable amateurs have had. When reading and following advice one must realize that some have provided good advice, have experience and know the subject, while separating it from those who lack experience and don't have the background sufficient to offer it on the subject at hand. Even experienced well meaning Hams get things wrong on occasion, which is why everyone must be aware and investigate fully from several sources before acting on the volunteered information.

I hope this will be taken in the spirit of sharing and continue to keep this thread going in a positive manner, I tried to carefully post my concerns so new and old alike would be able to understand my points.

Thanks and I hope everyone will continue this thread in a calm manner after reading this.

 

[K7MEM]

Just a quick response, I think you misread his post. He said "direct feed" not balanced connection.

No, I think I read and understood it just fine. Maybe he will clarify.

With no other definition of "direct feed", I read it as simply tying the coax directly to the center of a split dipole driven element. While you can certainly do that, it is not a recommended method to use. What is your definition of "direct feed"?

Also the feed point of a dipole is 100 Ohms.

Is that right? Under what conditions would that be? All the antenna books that I've read in the past 50 years have it more in the 70-75 Ohm range, for a 1/2 wavelength dipole 1/2 wavelength above ground. But I guess, what's 25-30 Ohms between friends.

You may want to be a little less condescending.

 

[AK9R]

Folks, let's stay focused on BrettL's questions and on helping him learn about amateur radio.

 

[BrettL]

I have built a direct connect beam from this website Beam Lengths.

Its suppose to be a direct feed 50 ohms at those measurements. Atleast that's what they are advertising. Also I did not use 1/2'' tubing as stated in the specs. I made the beam from an old VHF tv antenna. The old ones with the thin elements that are folded in a circle. They are not solid and very thin. So It may not be 50 ohms.

Only way I will know is to hook up my antenna analyzer. The antenna analyzer will be here sometime this week.

If its really close to 50 Ohms then all I will have to do is trim or adjust the driven elements to get best swr. Does not sound hard to me at all. Now if its way off then I will recheck everything. If still not 50 ohms maybe I could build a balun of some sort to achieve a match.

I'm not sure if its a rule of thumb to achieve a certain impedance first so you can then balance it with a balun?

100Watts on 2m/70cm? Why? What antenna are you going to pump all that power into? Spend your money on a tall pole, a yagi and a rotator. Then you'll only need 25Watts.
The old adage "If you can't hear them, then you can't work them" still holds true on the VHF bands. A good antenna and good elevation is always the best investment.

Why not? If I get a 2 meter transceiver with SSB then I can have lots of DX fun. Also with me living at a high altitude it would be fun trying to get into other repeaters far off. If I can hear them I SHOULD be able to talk to them. Then revert back to my lower wattage for the local repeaters. I live in a "hot spot". !00 watts is nothing. I would never own a antenna that could not hold 100 watts. A cheap remote controlled rotor. Sit back and QSO.

.

 

[KG6ABF]

No, I think I read and understood it just fine. Maybe he

will clarify.

With no other definition of "direct feed", I read it as simply tying the coax

directly to the center of a split dipole driven element. While you can

certainly do that, it is not a recommended method to use. What is your

definition of "direct feed"?



Is that right? Under what conditions would that be? All the antenna books that

I've read in the past 50 years have it more in the 70-75 Ohm range, for a 1/2

wavelength dipole 1/2 wavelength above ground. But I guess, what's 25-30 Ohms

between friends.

You may want to be a little less condescending.

Perhaps I should have gone into greater detail, as in reality height above ground can and does affect the feed point of a 1/2 wave dipole.

Since you asked for a source perhaps this might serve to answer your request:

Palomar Engineers

I am sorry if my writing style caused you to consider it anything but straight ahead factual responses, but if you can let me know what part of my information posted you felt caused you to think of it in some manner other than my intent of simply stating the accurate information please let me know
and we can work it out.

At the bottom of the page (link listed) is a chart covering various antennas and the impedance of them.
A company called INNOV sells a line of direct 50 ohm antennas of which I own an 11 element 2 meter beam.Their website is: Home - InnovAntennas - Manufacturers and Suppliers of Innovative Yagi Antenna Systems - Home of the LFA Yagi

They use a very small single loop air choke or coaxial balun which is simply a small loop in the feed line. Their driven element is a loop laid horizontal to the boom and with careful alignment a close to flat match can be achieved using the method described above.

I also wanted to mention a 1/2 wave loop used in a quad or quagi for instance a 2 meter antenna I recently built for a new ham, I measured the feed point impedance and it was 100 ohms. In addition I want to be clear about the impedance I am writing about being the point where the feed line and the antenna are connected together not the resistance at the end of the feed line that connects to the back of an antenna tuner or rig.

Hopefully this response will demonstrate I meant no offense and as you read more posts from me in the future you will come to understand my writing style is what it is and no offense is intended in my responses or posts.

Thanks

 

[KG6ABF]

BrettL

I have looked at that website as well but decided to buy an INNOV antenna based upon reports from some folks I know. Most of them are way more experienced than I am at VHF and UHF DXing so I opted to follow their advice and I am very happy with this antenna. I also use an M2 19 element UHF beam and that one is another wonderful piece of engineering.

You can't go wrong with either company's products if you should want to have recommendations for a commercially built antenna. Both companies put out a very well made product built with excellent materials.

The INNOV 11 element is by far the quietest antenna I have used and has the best rejection of any 2 meter antenna I have used. I have built many very nice antennas but this one exceeds anything I ever constructed and is well worth the cost.

 

[BrettL]

I did not mean to say adjust the driven elements to get 50 ohms. I meant to say adjust the driven elements to get a good swr. The antenna suppose to be 50 ohms by the website but only analyzer will tell.

So why is a direct feed not a recommended choice? So wich is better direct feed @ 50 ohm or balun of some sort @ 50 ohms?

Oh well Im not going backwards but now Im getting confused .

 

[KG6ABF]

I did not mean to say adjust the driven elements to get 50 ohms. I meant to say adjust the driven elements to get a good swr. The antenna suppose to be 50 ohms by the website but only analyzer will tell.

So why is a direct feed not a recommended choice? So wich is better direct feed @ 50 ohm or balun of some sort @ 50 ohms?

We understood what you meant. there is nothing wrong with the direct feed antenna. If you are happy with the results of the build great, if not experiment like the rest of us. That is part of the fun of this hobby, never stop trying.

Best of luck and keep researching and trying out new things eventually you will find something you like and works until the bug bites again or the itch starts up and you once again get moving onto another project.

 

[majoco]

An antenna at resonance doesn't necessarily present an impedance of 50 ohms to the feedline - you have to make it 50 ohms or whatever by phasing loops, transformers, baluns or whatever. Your VSWR meter can be used to adjust element lengths to produce a low SWR but it won't show if the antenna is resonant. See where I'm coming from?

Old style TV antennas with a loop are usually 300 ohms and 300 ohm ribbon cable was 'invented' to get the signal to the TV. You can make a balun to adapt the 300 ohm loop to 75 ohm cable, or you can make a phasing loop. The antenna is resonant at the design dimensions, you have changed the impedance to match the cable and hopefully the transmitter or receiver.

 

[K7MEM]

Perhaps I should have gone into greater detail, as in reality height above ground can and does affect the feed point of a 1/2 wave dipole.

Since you asked for a source perhaps this might serve to answer your request:

Palomar Engineers

I am sorry if my writing style caused you to consider it anything but straight ahead factual responses, but if you can let me know what part of my information posted you felt caused you to think of it in some manner other than my intent of simply stating the accurate information please let me know and we can work it out.

Well I checked your source and the only place it mentions 100 Ohm feed impedance is when it is talking about a low frequency multi-band antenna, at less then 1/2 wavelength in height. At higher heights, the feed impedance is lower. But I thought we were talking about a mono-band 2 meter antenna. I doubt that anyone would use a 2 meter dipole at those low heights. From that source you should note that, as the the height increases, the height above ground has less and less effect, and settles around 72 Ohms.

But that is with a dipole by itself. The presence of parasitic elements, as in a Yagi, can cause the feed impedance to be much lower than 72 Ohms. About 2 months ago I ran a series of tests with the parasitic element space varying from 0.02 to 0.3 wave length spacing (0.01 wavelength increments). The results show that, if the spacing is too close, the feed impedance can drop to 25 Ohms or less.

Your information on the other antennas is fine, but all it does is obscure the original intent. Your loop element measured as it should. The Quagi design goes back a long time. You could have also used a folded dipole feed. That could have raised the feed impedance even more than 100 Ohms. The very end of your linked source provides some advantages of the folded dipole.

I never thought that BrettL had a problem. He seemed to be working along just fine. I merely suggested that, he not look at Baluns as an after thought. Study them, and consider using them, up front.

Martin - K7MEM
Martin E. Meserve - K7MEM

 

[K7MEM]

I have built a direct connect beam from this website Beam Lengths.

Its suppose to be a direct feed 50 ohms at those measurements. At least that's what they are advertising. Also I did not use 1/2'' tubing as stated in the specs. I made the beam from an old VHF tv antenna. The old ones with the thin elements that are folded in a circle. They are not solid and very thin. So It may not be 50 ohms.

Those measurements, specified on the web site, look good. They say "direct feed", and what they are describing is a 1/2 wavelength dipole (balanced) fed directly with coax (unbalanced). While you can certainly built and use it that way, I still recommend a balun. The length of the dipole, and the spacing of the elements, appear to have been adjusted to account for the presence of parasitic elements.

There is a Dimensional Tolerance associated with a yagi. For a 2 Meter beam the Dimensional tolerance is 1/4". What that means is that, as long as you measure and cut withing 1/4" of the dimensions specified, the antenna should work as advertised.

The TV antenna elements should work fine. Solid elements might be sturdier, but it wouldn't effect the antenna performance. The only thing that might change is the SWR bandwidth. Up to a point, fatter elements increase the bandwidth. A little loss in bandwidth is not usually a big concern.

You can modify anything you want to, but when you deviation from the original, it can cause changes in the specified Gain and F/B Radio. But, if the deviation is small, you probably won't notice the difference.

I would run sim using the dimensions specified but I won't have time till later tonight or tomorrow. I have six horses to feed, water, and clean up after. Plus I have to slip in a trip to town.

Only way I will know is to hook up my antenna analyzer. The antenna analyzer will be here sometime this week.

If its really close to 50 Ohms then all I will have to do is trim or adjust the driven elements to get best swr. Does not sound hard to me at all. Now if its way off then I will recheck everything. If still not 50 ohms maybe I could build a balun of some sort to achieve a match.

I'm not sure if its a rule of thumb to achieve a certain impedance first so you can then balance it with a balun?

A antenna analyzer is a great thing to have. I have one myself and found it very effective. But over time I have started going back to my SWR bridge and Noise Bridge. I guess old habits don't die easily. I still get the same information, but it might take a little longer.

If you build it as close as possible to the specified dimensions, it should work fine.

 

[BrettL]

I do plan getting a high gain antenna soon. Long boom length and a lot of elements. I stumbled across this old vhf antenna one afternoon and said to myself that I could use it for my radio antenna and play around with thAt until I actually purchased a good one. So I asked the people before they scrapped it if I could have it. They said yes.

One thing is for certain, when I build a stick antenna I want a high dB gain omni something like a collinear 3 element made of copper tubing. I have been reading some interesting things about them. I'm not going to jump right into antennas because my real passion is understanding radios and what goes on inside of them. I will try to stay focused on that. All I like is one piece of test equipment or so to begin my journey.

Time for me to go to sleep. I got to get some rest before this baby is born. I'm at the labor and delivery center and she is dilated to 8 cm. Won't be long. Wish us luck, 73's.
KM4IXU

 

[K5MPH]

I think you are talking to some very opinionated people. Not that having strong opinions is bad, but anyone with strong opinions should be able to back them up with sound reasoning for their opinions. You will find that some amateur radio operators are very brand-specific. They've had good experience with one brand and stick to that brand to the exclusion of all others. I like to spread it around--I own radios from all four major Japanese manufacturers (including Alinco).

As for Icom, specifically, I've owned several Icom radios, both for the VHF/UHF bands and for the HF bands. Some of them have been good, some of them have been not so good. My experience, though, with their HF radios has been very good.

There's nothing wrong with VHF/UHF if that's what interests you. Most public service type of amateur radio operating is done on the VHF/UHF bands. Same for severe weather spotting. Satellite work is pretty much exclusively VHF/UHF. And there are folks who have thousands of hours invested in building their VHF/UHF contest stations. I have found, though, that as I've gotten more interested in HF operating, I spend much less time on VHF/UHF. The nice thing about getting involved in the local VHF/UHF repeater scene is that it's a!
introduces you to the hams in your area. That can be an asset for a new ham.

It's funny we have an local ham here where I live that thinks that vhf/uhf are for loosers in the ham world ,what a bad seed for the ham world............

 

[KG6ABF]

I do plan getting a high gain antenna soon. Long boom length and a lot of elements. I stumbled across this old vhf antenna one afternoon and said to myself that I could use it for my radio antenna and play around with thAt until I actually purchased a good one. So I asked the people before they scrapped it if I could have it. They said yes.

One thing is for certain, when I build a stick antenna I want a high dB gain omni something like a collinear 3 element made of copper tubing. I have been reading some interesting things about them. I'm not going to jump right into antennas because my real passion is understanding radios and what goes on inside of them. I will try to stay focused on that. All I like is one piece of test equipment or so to begin my journey.

Time for me to go to sleep. I got to get some rest before this baby is born. I'm at the labor and delivery center and she is dilated to 8 cm. Won't be long. Wish us luck, 73's.
KM4IXU

First off Congrats Dad!!!

Check out the Verticals from Diamond and Comet. They both provide excellent products and their customer service after the sale is first rate.

Another company makes a copy of the Diamond/Comet verticals and their name is Tram-Browning basically their products sell for about 1/2 the retail price of Diamond and Comet. I use several Comets and also have Diamond antennas on my mobiles.

I have used the Tram-Browning antennas and they work well, although structurally they aren't built as solidly as the other brands. I have some friends who love them and they fit into budgets a little easier.

My Comet GP 9 has what many call ridiculous ratings and the TB brand claims similar specs as well. I share net operator duties in a twice weekly multi state VHF SSB net along with some other ops and they also run the higher gain verticals. Some run M2 beams, others use Cubic Quads, I use INNOV and M2 while others use home brew antennas.Cushcraft, Hygain, ELk, Arrow and others all find use in this net.

I love building antennas, especially if a new licensed Amateur locally can benefit from sharing the building experience and then use the antenna. All in all I build more HF antennas than VHF/UHF about 2:1 on average. You are lucky to have several knowledgeable hams on this forum like K7MEM, W9BU ( a lot of experience in repeaters and VHF/UHF from his QRZ page), KB5ZCS just to list a few who have commented. Keep experimenting, check out as many shacks as you can keep your eyes and ears open, you will quickly learn a lot and especially application of theory not just theory alone.

With VHF and UHF SSB it is both similar and at the same time more challenging than SSB on HF. Sometimes the band is so quiet you wonder if anyone is ever on and other times it opens, some Tropo happens and you are in a QSO running 10 watts and some op in Hawaii is on the other end. Don't forget or stay off of 6 Meters as it can be the same way suddenly open for serious DX and other times if repeaters weren't there you find yourself asking does anyone EVER use this band??

Check out MOXON antennas, very easy to build, lightweight, fantastic rejection but leaves a bit to be desired in forward gain compared to some other designs. There are always trade offs and sometimes the little less gain along with the rejection works out better than a lot of gain and less rejection. I've built Moxons to cover 20meters through UHF frequencies. A roll of copper tubing ( like you use to connect a Fridge ice/water hook up) some PVC and an SO-239 connector is almost all you need to construct one. I have even used some old furring strips, wire a couple of pieces of plastic and feed it directly to the driven element. They don't weigh much and you can make them cheap enough to have several in fixed positions if you like and have the room. One fellow Ham and I made enough to cover several fixed positions for 40,20,17 and 6 meters. He has a lot of acreage so he can have an antenna farm. IF you want to rotate them they are usually very light weight (depending on materials used) to be turned by hand or using a light to medium duty rotator.

As for verticals you can get the parts for a very nice fiberglass one 31 feet or use military masting and go longer. very simple to make, add a good balun and tuner for the bands it needs a bit of help on and you have a great vertical for 80-6 meters and you can even take it backpacking if you use the collapsing pole type. Think of Jack-Kite poles for example of one source. The military masting can be carried but is more bulky and heavier to handle.

Hope that adds to your ideas list.