2 element beam

[blueangel-eric]

I want to make a 2 element beam for use inside my apartment and i have an idea how to make the dipole and the reflector out of copper pipes but i need the spacing info and how good will it really work anyways? this is for 2meters but hopefully work for VHF and UHF for scanning.
edit: i found this http://www.qsl.net/w4sat/tiny2.htm
last few times i looked and found nothing. anybody else have anything?

Eric Burris kc0ldt

 

[jonny290]

0.2 wavelengths should be a good starting point - you can adjust the spacing for best performance.

it should give you a fair amount of directivity and front to back ratio. Half of the appeal of beams is that you can point them directly at something you want to hear; the other half is that you can point them directly away from something you don't want to hear.

 

[blueangel-eric]

0.2 wavelengths should be a good starting point - you can adjust the spacing for best performance.

it should give you a fair amount of directivity and front to back ratio. Half of the appeal of beams is that you can point them directly at something you want to hear; the other half is that you can point them directly away from something you don't want to hear.

how do you know how many inches 0.2 wavelengths is? i forgot. and how do you know if the performance is the best with the spacing? Will the SWR meter work for that part?

Eric Burris

 

[jonny290]

yeah, if you can tune it with an swr meter (make sure to do this legally, ham license etc).

Calculating that is easy - take your wavelength (which is 2 meters, we'll use that for simplicity's sake) * 0.2. This comes out to .4 meters or 15.75 inches. That would be a good start (remember you can make the antenna shorter, not as easy to make it longer).

 

[jonny290]

just for giggles i modeled up a 2 element beam made of 12.0mm diameter copper pipe

driven element - each side is 45cm long for a total of 90cm - this is split in the middle and fed with coax

reflector - spaced 41cm (measured from center to center of element) and is 49cm on each side for a total of 98cm - this is one continuous length of metal

calculated 50ohm swr:

144mhz: 1.27 gain: 9.9dBi F/B: -7.3 dB
145mhz: 1.13 gain: 9.9dBi F/B: -6.9 dB
146mhz: 1.05 gain: 9.8 dBi F/B: -6.5 dB
147mhz: 1.13 gain: 9.7 dBi F/B: -6.1 dB
148mhz: 1.25 gain: 9.7 dBi F/B: -5.8 dB

2:1 SWR bandwidth is approximately from 141 MHz to 155 MHz.

keep your coax connections less than one inch between where you unravel the coax braid to the driven element clamp point, and you may need to hack off a few MM of tubing to compensate for those little stubs. Build it to spec, though, and see how she runs first.

edit: this likely won't tune on 440 or higher but check it out, you might get some decent performance out of it. yagis are narrowband by nature, they won't cover it all

 

[blueangel-eric]

just for giggles i modeled up a 2 element beam made of 12.0mm diameter copper pipe

driven element - each side is 45cm long for a total of 90cm - this is split in the middle and fed with coax

reflector - spaced 41cm (measured from center to center of element) and is 49cm on each side for a total of 98cm - this is one continuous length of metal

calculated 50ohm swr:

144mhz: 1.27 gain: 9.9dBi F/B: -7.3 dB
145mhz: 1.13 gain: 9.9dBi F/B: -6.9 dB
146mhz: 1.05 gain: 9.8 dBi F/B: -6.5 dB
147mhz: 1.13 gain: 9.7 dBi F/B: -6.1 dB
148mhz: 1.25 gain: 9.7 dBi F/B: -5.8 dB

2:1 SWR bandwidth is approximately from 141 MHz to 155 MHz.

keep your coax connections less than one inch between where you unravel the coax braid to the driven element clamp point, and you may need to hack off a few MM of tubing to compensate for those little stubs. Build it to spec, though, and see how she runs first.

edit: this likely won't tune on 440 or higher but check it out, you might get some decent performance out of it. yagis are narrowband by nature, they won't cover it all

How can the gain be smaller in the center of the band instead of bigger?
and do you have the measurements in inches? I'll either be useing 1 inch or 1/2 inch for outside diameter copper tubing/pipe.

 

[jonny290]

go 1/2" for the pipe, 1" is too expensive and too heavy for the antenna. also your lengths and spacings will have changed - that's why I modeled it up with 1/2" copper pipe, most common for this stuff.

the gain of this particular yagi goes down as the frequency goes up because I used the spacing of the elements to give an impedance match, using gain and front to back ratio as secondary factors, rather than trying to peak the gain and then fix the SWR. There's not that much tweaking you can do to a 2 element, really - driven length, reflector length, and spacing. for all intents and purposes this antenna has very flat response and will likely compare favorably with a 5/8 wave vertical mounted at the same height, but with directionality.

you're just not going to get much gain and f/b out of 2 elements, it's too unfocused. so there's no reason to go for another half dB of gain at the expense of a bad SWR.

divide all centimeter measurements by 2.54 to get inches

 

[blueangel-eric]

go 1/2" for the pipe, 1" is too expensive and too heavy for the antenna. also your lengths and spacings will have changed - that's why I modeled it up with 1/2" copper pipe, most common for this stuff.

the gain of this particular yagi goes down as the frequency goes up because I used the spacing of the elements to give an impedance match, using gain and front to back ratio as secondary factors, rather than trying to peak the gain and then fix the SWR. There's not that much tweaking you can do to a 2 element, really - driven length, reflector length, and spacing. for all intents and purposes this antenna has very flat response and will likely compare favorably with a 5/8 wave vertical mounted at the same height, but with directionality.

you're just not going to get much gain and f/b out of 2 elements, it's too unfocused. so there's no reason to go for another half dB of gain at the expense of a bad SWR.

divide all centimeter measurements by 2.54 to get inches

thanks i'll get to it whenever I can. I like the portable telescopic 2 element beam antenna at Universal Radio from Diamond that is adjustable for VHF-HI or UHF but it's like $100!!! i don't think diamond will sell very many of those.

 

[k9rzz]

In my opinion, 2 elements isn't going to do much for you. If you're gonna make the effort to build 2, you may as well go 3 or 4.

4 el:

Unless we're talking 40, 80, or 160 meters of course!

That's just my .02 cents.

 

[blueangel-eric]

In my opinion, 2 elements isn't going to do much for you. If you're gonna make the effort to build 2, you may as well go 3 or 4.

4 el:

Unless we're talking 40, 80, or 160 meters of course!

That's just my .02 cents.

I'm talking about a small antenna for inside my apartment. i have a 3 element for the RR and a 5 element for 2meters but I don't think i want them sticking out over my bed. My antennas are in the bedroom as to keep away from the computer noise.

 

[blueangel-eric]

go 1/2" for the pipe, 1" is too expensive and too heavy for the antenna. also your lengths and spacings will have changed - that's why I modeled it up with 1/2" copper pipe, most common for this stuff.

the gain of this particular yagi goes down as the frequency goes up because I used the spacing of the elements to give an impedance match, using gain and front to back ratio as secondary factors, rather than trying to peak the gain and then fix the SWR. There's not that much tweaking you can do to a 2 element, really - driven length, reflector length, and spacing. for all intents and purposes this antenna has very flat response and will likely compare favorably with a 5/8 wave vertical mounted at the same height, but with directionality.

you're just not going to get much gain and f/b out of 2 elements, it's too unfocused. so there's no reason to go for another half dB of gain at the expense of a bad SWR.

divide all centimeter measurements by 2.54 to get inches

Well i gathered some old and some new copper tubing 1/2 inch and built the antenna it works real good on receive but the SWR's are high. i took the reflector off and the SWR's still was high. so i cut the dipole down to 17 inches on each end, measuring from the outside of the boom to the ends, and got a good SWR across the ham band and no further up like your model projected. so i then had to cut the reflector down to reflect the changes but no good. what now, change the spacing? I don't know what else to do. or why the model predicted so good and i can't seem to built it right. that' s why i personally don't use software for antennas. the only thing i can built right, is a groundplane and a dipole. I thought 2 element beams are susposed to be easy. HELP?

 

[k9rzz]

I assume this is a split dipole rather than a gamma feed? Is the SWR better on one end of the band than the other? That would give you some clues as to whether it's too short or too long. You can always solder a few inches of wire on each end of the driven element to see if a longer length will improve the SWR. Trim the wires until you get good results, then either leave 'em or make a new element.

Hope that helps.

 

[blueangel-eric]

I assume this is a split dipole rather than a gamma feed? Is the SWR better on one end of the band than the other? That would give you some clues as to whether it's too short or too long. You can always solder a few inches of wire on each end of the driven element to see if a longer length will improve the SWR. Trim the wires until you get good results, then either leave 'em or make a new element.

Hope that helps.

the swr is 2:1 all the way around with the reflector added on. Oh and the dipole is a beta match or what some websites call a direct connect

eric

 

[blueangel-eric]

i never got any more help on this. what gives? will a beta match/ direct connect even work?
I can't get worthy SWR.

 

[kc0ztz]

2 Element Suggestion (Late)

I want to make a 2 element beam for use inside my apartment and i have an idea how to make the dipole and the reflector out of copper pipes but i need the spacing info and how good will it really work anyways? this is for 2meters but hopefully work for VHF and UHF for scanning.
edit: i found this http://www.qsl.net/w4sat/tiny2.htm
last few times i looked and found nothing. anybody else have anything?

Eric Burris kc0ldt

Pardon my ignorance here, and I'm about 2 weeks late with this, but I built a three element Yagi (40" Reflector, 35" Director, and offset + / - 20" drivers on a 40" boom with an air choke), and then plugged my materials into the below site. It kicked out a model that pretty much mached what I had (except for my hairbrained idea for two drivers being offset by 0.25"). So, you might check it out, and see what it turns out.

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=11183

What I used, and you're going to reach a concensus here that I'm nuts, is 1/8 inch stainless steel whip (old CB antenna I came into) for the reflector and director, and I used brass welding rod for the drivers (easier to solder). It's my first attempt at anything home built as far as antennas go (everyone's gotta start somewhere, guys), and I'm generally pleased. It's 40" long, and 40 inches wide, and hangs nicely close to the ceiling from monofilament (although I've relocated it to the attic). In case you're interested, it's 16" from the reflector to the rear (-) driver, and then 21.25" from the (+) driver to the director. It's pretty crude by the standards of some of you veterans, I'm sure, but for a newbie, I was pleased to hit a tower 35 miles away on 5 watts from kitchen with lots of electronics running in that room and the living room, through which the beam had to pass to trek towards the tower. The calculated gain is only about 3.9 dB, but my SWR checked at 1.2:1. It screams "rookie," but it works.

Anyone wanting to hoot, hollar, laugh, or otherwise point out rookie mistakes (of which I am sure there are plenty), please contact me via email directly.

That's just my two cents.

73's,

Brad Parker
HA - KCØZTZ
ZA - WPVL916

 

[ermin]

I made a 3 element 2m beam out of old tv antenna elements. Just converted meters to inches and did the .2 or whatever it was spacing. Just mounted the 2 pieces of driven element as close as I could and fed it with 59 ohm coax. It worked good enough for a 1 watt HT to hit a repeater 23 miles away with a clear signal. It was just in the atic so it probibly would of done better outside.Never had anything to measure the swr. Just try with what you have.

Good luck and 73 from Ed KE4BMR

 

[kc0ztz]

Just try with what you have.

Good luck and 73 from Ed KE4BMR

EXCELLENT ADVICE that I'm just learning. Tinker and experiment. It seemed to work for Edison...

~parker

 

[ermin]

2 El Beam

EXCELLENT ADVICE that I'm just learning. Tinker and experiment. It seemed to work for Edison...

~parker

That's exactly it. You would not believe some of the stuff I've made that worked. That beam should not have worked. The match must of been very high with 2 aluminum tubes screwed to a piece of wood with the ends almost touching and 2 wood screws holding the coax wires to the ends of the tubing. But it made the difference from not even hearing the repeater to a full quieting signal. I made a 1/4 wave 2m ground plane out of suspended ceiling hanger wire, mounted it in the atic and during a band opening talked on a repeater over 200 miles away with just 3 watts FM.

Ed