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Maco Alpha V5/8 Groundplane Question

Lazybones1222

Lazybones1222

W9WDX Amateur Radio Club Member
Apr 6, 2005
948
28
28
Tampa Bay Florida
Hello antenna Elmers. I just assembled on of these Maco Alpha V-5/8 Groundplane and pondered the "tuning ring" design and the more I thought about it the less I understood it.

As most of you know, the feeding coax center conductor goes to that ring, and the ring goes to the radiating part of the antenna AND to the part of the antenna that is mounted to the mast (ground side?).

I don't understand why the "hot" rf feedline goes to both places. Someone please enlighten me.

Thanks,
Lazy
 

Hello Lazy:

The MaCo V5/8 uses what is called a double inductive (I think thats it) matching network to match the 50 Ohms Coax to the ground plane antenna. Yes one inductor is in series to the antenna and the other is in parallell, which goes to ground. It doesn't look right at first, but thats how its supposed to be. Many antennas use this matching system.

The MaCo also has a slight amount of Capacatance from the vertical element being housed into the base assembly which also figures into the matching network.

Jay in the Mojave
 
im002605nf8.jpg
 
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Maco Alpha V5/8 Groundplane

The Maco V5/8 is feed with an LC circut. If you look close you will see that the center of the antenna is encased in a plastic sleeve. The sleeve acts as a insulator between the antenna (RF hot) and the mounting bracket with the radials (RF cold). This forms a capacitor. (C) The feed point it then tapped up from ground to a 50 ohm point on the ring (L). This enables the antenna to have a 50 ohm feed point, good bandwidth and still be DC grounded for lightining protection.

Steve / K6SCA
 
Switchkit - good picture - it is flipped though according to the assembly manual.

Just looking at the assemble antenna it looks like the rf would flow in both directions on the ring and the mounting mast if metal would radiate, and the blue line switchkit put on the picture would go both ways as well. Very interesting.

Anyway, thanks for the replies. Made me think. I know, imagine that. ;=)
 
Lazybones1222 said:
Switchkit - good picture - it is flipped though according to the assembly manual.

Just looking at the assemble antenna it looks like the rf would flow in both directions on the ring and the mounting mast if metal would radiate, and the blue line switchkit put on the picture would go both ways as well. Very interesting. /quote]

It would do just that at DC; however, RF does things a little differently. What might look like a dead short at DC will be 50 ohms, or 50K ohms, at a particular frequency.
Click to expand...
 
they work either way Lazy , some instructions have them one way and others have them another way. They will work evenly either way.....at least they have for me in the past.
 
I have had a time at figuring out these new settings around here :( edit / picture posting ect. ect. , it's just one thing after another. .....Just wanted to say that you were very observant when it came to the ring and wire clip Lazy , Also , it's a shame that there was some very good threads lost in the antenna section on the change over :( some very good ones on the Maco Alpha V-5/8s as well. )))))))))UPDATE(((((((( LAZY ? you can look in the cb antenna section and find the links that seem to be there now , not lost anymore under 5/8 wave . There's some real good stuff there.
 
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This isn't exactly the best way of showing it, but below is the equivalent circuit;

.___center conductor____//////__!__//////__o <--ground
=============================|

The "/////" are coils. The "!" is the feed point and vertical radiator. The "o" is ground, or groundplane. And the shield of the feed line "==" goes to ground/groundplane.

Another aspect of this that it's good to keep in mind is that there is no (+) and (-) sides like a DC circuit. RF is AC, meaning that the (+) and (-) 'sides' swap each cycle. So the vertical radiator is (-) half of each cycle (Hz), and that the radial/groundplane does the radiating instead of the vertical element during half of each cycle/Hz. (@#$% ! This is getting to be even MORE fun, ain't it?)
- 'Doc


[The first part is true. The last paragraph is just to introduce a little more confusion into the whole thing. Still true, just another aspect of how you 'look' at this stuff. (not enough coffee yet)]
 
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be honest with you here Jay , even after they explain the hell out of it and how it works , I still don't completely understand it , other then it just works. :)
 
Hello SK:

I don't know of anyone who can see the energy being radiated from the antennas. So we are forced to measure the antennas values and patterns. And make a decision on many things no body knows. The developement process is full of trail and error.

I am not sure I know how it works either. I have had the dis-pleasure of many times going inside not knowing what the next move is. But if you keep working at anything long enough you will get er figured out, or at least working.

Jay in the Mojave


Switch Kit said:
be honest with you here Jay , even after they explain the hell out of it and how it works , I still don't completely understand it , other then it just works. :)
Click to expand...
 

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