HAM BIG MAC

[bob85]

somebody on another forum posted some info on the old big mac,
what do you guys think of their claims, can a 5/8 over 1/4wave make the gain figures they claim?,
my bigmac worked fantastic when the wind was low.

 

[Beetle]

"Gain: 7db".

Over what?

 

[bob85]

when they dont say i presume its dbi, dbi seems common among european cb antenna makers,
7db seems high even if they do mean dbi
what do you think beetle is it all smoke and mirrors or could that design have some merit over conventional groudplane antennas.

 

[W5LZ]

bob85,
I think I would take those gain figures with a very large dose of 'salts' (Ex-Lax might be more like it). No idea what the supposed purpose of those 'vertical radials' are. Oh well, wouldn't be the first time I've seen something 'new'/different like this. It would be the first time if it was worth doing, though. Not something I'd spend much money on.
- 'Doc

On second thought. I think it lives up to it's name... especially if compared to a home made hamburger.

 

[Captain Kilowatt]

I find most gain figures are high except in a few cases. By the time you realise what the referance is,add in the "ground gain" and also the BS gain (a lot of that) then it becomes quite feasible that that antenna could have 7 dBbc gain. BTW dBbc=dB over a bent coathanger

 

[KingCobra_CDX882]

Got to be-careful
Most these high gain figures are not worth the paper they are printed on

if memory serves me
5/8 wave antenna is nearly the best
(actually .625 wave is)
anything beyond it presents problems with interacting lobes

 

[Beetle]

Let me see...5 divided by 8 is ... (wait for it!)

...exactly 0.625! So what's the "difference" between a 5/8 wave and a .625 wave??

 

[bob85]

a few inches,
the big mac is not one radiator its a 5/8 over 1/4 colinear so the over .625 rule dont apply here,
5/8 over 1/4 is fairly common in vhf/uhf antennas,

doc the vertical radials are in parallel with the main radiator and connected top and bottom, does it increase intensity from the 1/4wave section as they claim i dont know,
one thing is certain its not just another groundplane cb antenna.

 

[W5LZ]

"the vertical radials are in parallel with the main radiator and connected top and bottom, does it increase intensity from the 1/4wave section as they claim i dont know..."
I don't think that's very realistic at all, not increasing 'intensity'. Increasing the relative diameter of the 1/4 wave element, yes, which would therefore decrease it's relative length for resonance, I can go along with that. Not a huge benefit, but different.
A 5/8 w over a 1/4 w vertical array IS sort of common on VHF/UHF, and does increase the overall effective gain. (The coil being a phasing device, not something to 'load' the antenna.) It's also possible for those 'vertical' radials to be part of the phasing network, never seen it done that way before though, which also doesn't mean much.

Whats different about that ad is how it's written/phrased, not exactly the 'standard' for antenna advertising in the USA. That means you have to sort of 'adjust' your way of thinking/understanding about what it says. THAT can be a very interesting job! I would sort of give it the benefit of the doubt, but maybe not very much. (One 'easy out' is if it were such a 'miracle' of an antenna, why don't you see a bunch of them?)
I don't know anything about this thing, other than I have doubts about their claims. There are 'standards' for reporting gain figures and this ad doesn't exactly follow them (exaggerated or not). That makes me wonder if it's an honest mistake, or just more advertising...
- 'Doc

 

[Marconi]

Bob, physically how does the the SWR adjustment at the base work? Is there an adjustable tap to the coil? Is the black thing inside the bottom coil an insulator that the radiator mounts in?

Where does the 1/4 wave colinear mentioned come into play here? Are the two vertical elements between the coils about a 1/4 wavelength long overall? Or, do the lengths of the coils maybe figure in to increase this length to make up about a 1/4 wavelength?

 

[bob85]

hello marconi,
yes the matching is done with a moving tap on the coil at the base, you can also alter the groundplane length and the top 5/8 section but the 1/4 section is fixed length if i remember correctly,
the setup uses an insulator between the groundplane assembly and the radiator, the first 1/4wave of radiator consists of a central tube and 3 thinner parallel tubes about 1/4wave in physical length maybe slightly shorter than 1/4wave, then theres another insulator with the coil to bring the top 5/8 into phase with the lower 1/4, total length 32feet 6inch.

 

[Mr Clean]

I have heard afew praise this antenna as being the best they ever used. I have never ran or saw one.

 

[formulamojo]

I thought this thread was about a sandwich.

 

[mackmobile43]

I thought this thread was about a sandwich.

Yeah with a little secret sauce

 

[ericcson]

i used to have one in 1988 it cost 110 pounds gosh i was on goverment yts scheme then hehe saved up for weeks i finally got it delivered, i set it up with my pretty 148 gtl dx here the funny bit i was causing bleed over to people in outer manchester 14 miles away lol, gosh then as i was warned yup 65 70 mph winds brought her crashing to the grounds "crys rubs eyes " i miss my big maccy may she rest in peace , ericcson.