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M104C converted to 10

airplane1

airplane1

W9WDX Amateur Radio Club Member
Apr 15, 2005
1,051
32
58
Lebanon county PA
I have a M104C 4 ele. beam I want to run on 10 meter. I was looking for an online calculator to figure spacing and boom length and all but I only seem to find 3 ele. calculators. I thought about just building it as per instructions and shortening the elements a little and keeping the boom at 26ft and using the original gamma match which I am sure would be close enough to work on 10 meter.

Any one have a calculator site I can access on the web to do this or any ideas? Here is the manual to pull up and see how Maco has the elements spaced but it is not equal like I thought they should be so I guess they do this because it is for 11 meter.

http://www.macoantennas.net/assembly/support2/Assembly_M104C.pdf

AP
 

You could do it the way you say and just tune it with a swr meter/antenna analyser.

Or if you really wanted to be technical about it you could find the scale factor,and adjust all the dimensions by it,which would work for converting any antenna from a known centre frequency to a new centre frequency.

ie,say you had an antenna centred on 27.185 mhz and you wanted to scale it for 28.500 mhz,you would divide 27.185 by 28.500 = .953 or .95 when rounded down,now you multiply all known measurements for 27.185 by .95 and that should put you right in the ballpark for your new centre frequency,

as the antenna materials velocity factor was already figured out during the original tuning for 27.185 you don't need to worry about it for the new frequency.

hope that helps.
 
26 feet of boom, thought it was 16 feet boom?

The manual you linked states 16 feet.


shorten each element by 4 inches on each side, right side of boom left side of boom. total of overall 8 inches shorter in length.

This should center you up on 28,4mhz, you can leave the spacing the same and still be in the ball park.

Antenna handbook is a great thing to have, all the formulas you need are in it.
 
airplane1 said:
Thanks, And I am sorry, I meant 16ft boom. I must have hit an 2 instead of one lol.

AP
Click to expand...

No worries I do it all the time when I do not wear my glasses and try to use the keyboard by memory.

Good luck tuning that yagi and you may have to play with the gamma to get it correct.
 
I am going to get an antenna book to help me figure things out. I got the maco free for taking it down and thought it a great idea to use it on 10 with an A99 or Imax 2000 above it.

AP
 
Price was right, can not beat free.

antenna handbooks are good resource, google is even better as you can ge many different point of views in a google search.

Put the maco horizontal and mount the IMAX 2000 above it, should work out great.
 
I have it started but got involved in other projects, I am putting a 20ft tower up and installing a tv antenna to get over the air brodcasts.

I am tired of dish, direct tv and cable. According to TV Fool I will get like 15-20 channels and alot of them in HD for free.

Then I will start to get my 4 ele finished.

AP
 
Well I got myTV antenna up and running and it is great. Lot more channels than I thought. More than enough for the amount of TV we watch.

Anyway, I started mounting my elements on 16ft boom per the spacing on the maco 104 manual but when I was looikng on the internet I seen a manual for the Cushcraft 10-4CD Skywalker. The spacing is different than the Maco 104 so I am not sure what I want to do.

Here is the spacing for the Maco.

from reflector to driven is 63 3/8in then to first director it is 45in and then 86in to last director.

Here is the spacing for the Cushcraft.

from reflector to driven is 52in then to first director is 52in and then 83 1/2 to last director.

they are both 16ft booms and now I dont know which to do, I am trying to figure how to work a free program I found on the net to model these but just can not figure it out.

I might just build it the Cushcraft spacing as it is designed for 10 meter.
 
for 10 meter

you will want to use the 10 meter spacing, this will optimize it for that bandwidth.
 
airplane1, check out the Maco instructions for their M103c at: http://www.macoantennas.net/assembly/support2/Assembly_M103C.pdf.

The 105C also has instructions for 10 meters.

These instructions have measurements up to 29 mhz. Use the frequency you wish for your 10 meter operations and occupy your M104c boom with the M103 measurements given. Then install the last director at the end of the boom. The element lengths are probably the more critical measurements for you to get close to at this point, so try D2 length @ 5% shorter than Dr, or 1/2 again as short as D1 is shorter than Dr.

The M103 instructions may also have some tips on setting the gamma what might help get you close to a start point for your fine tuning. If at this point in the tuning process you find the resonance is close and the match is not bad, then try tweaking the gamma in very small steps, like 1/8" inch or less, to improve the bandwidth. You might be surprised to find how easy it is to skip right past a good tune point when making changes of 1/4" to 1/2" inch at a time. It is a lot of work and keep a good record of your tuning steps can prove to be important when you get to chasing your tail---so-to-speak.

IMO it is important to watch your BW and resonance as you fine tune a multi-element beam and not just watch the SWR. The tuning range has a lot of good SWR points where the antenna may not work so well.

Good luck and be careful,
 
Last edited:
Looking at the formula 1005/freq in mhz gives wave length
1005/28.4 is 35.38 feet multiply the .38 to get inches since it is decimal by 1.2 so roughly 35feet 4 1/2 inch or 424 1/2 inches.

element spacing.

Reflector to driven is .15wl,, driven to first director is .125 wl, first director to second director is .15wl

This is the basic beam configuration, there are many and various different configurations of how to design a yagi, for me this formula was the all around best for gain vs rejection as any yagi is a compromise on the element spacing
(moonraker four dimensions on wave length spacing)

reflector to driven is 63.75"
driven to first director is 53"
first director to second director is 63.75"

I rounded off for simplicity sake but that only gives you 15 foot and you do have 16 foot of boom, so if you want to move the reflector back 6 inches to make it 69.75 " from the director and move the second director 6" more to 69.75" this will increase the bandwidth by moving the reflector back from the director and by moving the front director further away it should make your front lobe a little tighter.

some yagi programs have all elements spaced .25wl apart, that will work, but not optimal.

The fun thing about yagi's is experimenting to see which works best for your QTH, the basics are always the same.

As far as element lengths? your driven will be same as a dipole, velocity factor is given consideration.

468/28.4 = 16.47 so round it off to 16'6" divide by two so each element will be 8' 3" from center of boom. This may be a fraction of an inch to long but you are in the ball park for 28.4mhz.

the reflector is 5% larger than the driven.
the first director is 5% smaller than the driven. the second director is 5% smaller than the first director.

In a nutshell that is yagi design by formula use. Now some one can transpose all that information into an antenna modeling program and tell you how it is going to work from their pc monitor screen, I prefer to build it and try it in the real world, on the air.

those dimensions and spacing will get you in the ball park, the rest is for you to have fun with and try different things.

Good luck and hopefully the band will open up and you can try some contacts.



Here is the spacing for the Maco.

from reflector to driven is 63 3/8in then to first director it is 45in and then 86in to last director.

Here is the spacing for the Cushcraft.

from reflector to driven is 52in then to first director is 52in and then 83 1/2 to last director.

they are both 16ft booms and now I dont know which to do, I am trying to figure how to work a free program I found on the net to model these but just can not figure it out.

I might just build it the Cushcraft spacing as it is designed for 10 meter.[/QUOTE]
 
Good point waverider. I don't know what dimensions that airplane1 will end up with, but the best spacing I ever got with my old Wilson 4 element yagi was using a Moonraker4 boom and everything else from the Wilson. Therefore my spacing was limited to using the two smaller tube ends of the boom. It turned out almost as you describe, my boom was 16'6" and the distribution was about 70" - 55" - 70". This spacing and a good tune produced the strongest responding 4 element I've ever had and it was only 27' high. I tried several optimized settings for this 4 element, but they never worked out, so I stuck with a more balanced distribution.

Maybe I just never got the right combination, but I didn't have to guess when using the above combination and the results were obvious and effective. I thought about it a lot, and I soon figured out that maybe the 16' boom just wasn't long enough to really take advantage of optimizing with 4 elements. Maybe when we get a boom with 22' and 5 elements we can start seeing some real affects with optimizing the spacing.
 
airplane1, I have a three element 10 meter Cushcraft. I can't find my manual at the moment, but I recall it never worked good for me. It was very lightweight and maybe used 5/8" - 1/2" tubing vs 3/4" - 5/8" - 1/2" like the Maco. This CC beam also mounts on top of the boom, but it is much smaller than the Maco throughout I think. If this is correct, it will make a difference that you will have to tune for using you Maco kit and the CC dimensions.
 

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