Marconi's Eznec 5 model of the Big Mack

[Marconi]

I was reading some old post form guys that use to own this antenna, so I decided to try and guess at the dimensions and model it.

Here it is, pretty much like the manufacture predicts for gain over real Earth, and it looks like a real collinear and the gain shows it. <gotproof>

View attachment Big Mack a real collinear..pdf

BTW, I was thinking it had 4 radials so I put 4 radials on it instead of three.

 

[Henry HPSD]

Hello,
a while ago i bought a bigmac brand new in box. With the idea to bring it back in production. " copy" what is good and improve what needed to be done. Bare in mind the antenna was from the 80s.

I did put it up (very very wobbly thing hihi) but havnt been able to put some time in it (yet). But i can provide all the original diameters.

Dont expect too much lol, But Ill see what i can do.

Kind regards H.

 

[bob85]

i would be interested in the measurements henry,
my big-mac worked great but far too bendy in light wind making tx/rx fluctuate like a mobile,

it would be nice to build a heavy duty version
heres another guys model of a 5/8 over 1/4wave, i don't have any info on how the model was done

 

[Marconi]

Hello,
a while ago i bought a bigmac brand new in box. With the idea to bring it back in production. " copy" what is good and improve what needed to be done. Bare in mind the antenna was from the 80s.

I did put it up (very very wobbly thing hihi) but havnt been able to put some time in it (yet). But i can provide all the original diameters.

Dont expect too much lol, But Ill see what i can do.

Kind regards H.

Thank you Henry.

I have two different sets of instructions and I believe both are incomplete. Could you also send me your instruction manual?

I hear stories occasionally talking about this antenna, but mainly only guy's saying they are as rare as hen's teeth, with first one guy saying it worked great, and another guy maybe saying it was a little better than his other antennas. Nobody seems to rank it high on the survivability scale however, and it looks pretty flimsy at what I guess is about 391.5" in length from the radials to the tip, not including the top hat I added to the model I posted.

Today I plan on checking all the wires out for symmetry and segment count, maybe I'll be able to fix the skewed pattern it shows. I don't think there is anything in the design that should cause this asymmetrical skewing. I might also try and fix it with only three 1/4 wave tuning elements, even though working with three 360* degree equal elements can be tedious to get the dimensions right, even if I use the auto feature that makes radials. I figure a little error with these 4 radials is probably where I'll find my skewing problem, but we'll see.

BTW the Average Gain can be made to show less than .20 db, by moving the tap point around on the bottom coil like I suspected, and it changes with every change in the length as one might expect.

Thus far I haven't seen a good SWR match yet, and I'm not sure my idea of making the physcial matching device for this model...ever will show a good match.

Could you get me a close-up snapshot or two of the vital areas and some detail dimensions for the two coils?

There are a couple of dimensions in the sparse paperwork that I've found thus far, so I figure the antenna kit was pretty much plug and play as it came and the dimensions were all basically fixed by their using screws to secure the tubing. I can't make much from an artist rendering however, and I can only guess where the insulators are located and how they look. I also just used the radiator dimensions I had for my Sigma 4, and added the other elements and guessed at their diameters.

If I'm seeing a insulator inside the mounting section of the tubing inside of the bottom coil, do you think that setup is working as a capacitor and is it maybe adjustable a bit for fine tuning? It looks like the top bracket on the bottom coil is all that is securing the whole radiator inside of this insulator, if I'm seeing this all correctly. In other words does it look similar to this idea?



You can email the dimensions at edromans@comcast.net I'll send you the copy of the file if you PM me your email address. I think the address I have for you here is wrong.

Thanks again.

 

[Marconi]

i would be interested in the measurements henry,
my big-mac worked great but far too bendy in light wind making tx/rx fluctuate like a mobile,

it would be nice to build a heavy duty version
heres another guys model of a 5/8 over 1/4wave, i don't have any info on how the model was done

Hey Bob, that pattern looks like it was made over a perfectly conducting ground, and maybe up pretty high. If true, I find little use for models done this way, but it does suggest that the antenna is showing very good potential for gain at a very low angle.

I'll run my model this way and post it up. It might look similar over a simulation for perfect Earth.

BTW Bob, yesterday I was reading some old threads where you and some others were discussing this old antenna.

 

[bob85]

the way my big-mac acted in wind vs the sigma4 or sigma2 on 68-73ft of mast in a field gave me the impressiion it had a narrow main lobe or deep nulls,
it worked great in low wind, a little better than my stock sigma4 but not if there was any wind, no other antenna i have owned caused the same magnitude of signal fluctuation,

the model came from a ham who built a 5/8 over 1/4 for vhf, i have not found the article since and don't remember if he mentioned how the model was done.

 

[Marconi]

the way my big-mac acted in wind vs the sigma4 or sigma2 on 68-73ft of mast in a field gave me the impression it had a narrow main lobe or deep nulls,
it worked great in low wind, a little better than my stock sigma4 but not if there was any wind, no other antenna i have owned caused the same magnitude of signal fluctuation,

the model came from a ham who built a 5/8 over 1/4 for vhf, i have not found the article since and don't remember if he mentioned how the model was done.

Well Bob, you might be right. The Big Hair 5/8 wave collinear shows a pattern like you describe, a very low primary lobe with a narrow beam width and a deep null starting a degree or two higher in angle. I also don't doubt the lack of stability we find in any of these longer type antennas.

This model has skewing in the pattern and I don't believe it should. So, besides the dimensional errors I made, something is causing the pattern distortion. If Henry gets me the dimensions, then maybe I can fix it.

I thought about asking you, but I figured you were probably 13, when you did your Big Mack, so you probably didn't save the instructions.

View attachment Collinear .625 vertical .pdf

This antenna was just a guess as to dimensions also.

 

[bob85]

heres the only info i have found so far, it would be nice if henry posted whatever info he has.

bigmack pictures by ukmudduck - Photobucket

 

[Marconi]

heres the only info i have found so far, it would be nice if henry posted whatever info he has.

bigmack pictures by ukmudduck - Photobucket

I agree Bob. If Henry sends anything to me via email, I'll post it up.

I think you might have sent the above to me before. I had everything except the picture of the coil. I didn't account for the couple of inches for the tap device at the feed point. More importantly I only see two coils in the image and in the artist rendering, I see three coils, that too makes a big difference. Most folks just don't consider the finer details until they start to model. All those little wire lengths can make a difference.

 

[Marconi]

Bob, here a page shot of my 5/8 wave collinear Big Hair antenna that I had to go up to 144' feet high to get even close to your image. This is also over perfect Earth for which sea water would be the only surface that would come close, and that is not really close. Your model's image is overlaid to the right.

This is as big as the forum will allow me to post without going to a third party site to store the image and then link back, I think. Sorry it is not real clear, but you should be able to get the idea...that this pattern, at 4 wavelengths, is far from realistic for 11 meters.

 

[Marconi]

Bob, here is an image of the coils with notes. Check the dimensions, and see if they might be close to what you can recall?

The software calls for the number of coils in a helix, what would you consider the number of coils to be for each. I think I see 2 on the bottom and 4 coils on the top.

 

[bob85]

it looks like 1.5turns on the bottom coil not including the straight bits to the radiator and 3.5 turns not including the straight bits on the phasing coil,
i can't rely on memory its been too long since i owned one but your guestimate looks reasonable,

we need henry's input for some accurate measurements,

i also think the model i posted was done on vhf where several wavelengths above ground is normal.

 

[Marconi]

Bob are the three 1/4 tuning elements attached to the radiator electrically, or are they floating?

 

[bob85]

electrically connected to the lower 1/4wave at both ends via aluminum hubs

 

[Marconi]

electrically connected to the lower 1/4wave at both ends via aluminum hubs

That is what I thought, but the color made me think they might be plastic like the insulators.

I can't get this thing to act right. I'm back to waiting for Henry again. I can't get my Wolf model to work like a collinear either.