maco v5/8 vs wolf .64

[Marconi]

Well sherlock and Devildog, I read freecell’s reference to Static and it is way too complicated of an issue for me to consider as understood, at least for me.

I suspect in this discussion we were probably just referring to some way to cut down the noise we hear on our radios by using a cap hat and we referred to it generically as static. I have not studied why folks use cap hats on their antennas specifically, but I don't really think it is in order to remove the noise we hear and refer to as static or white noise either. I don’t think cap hats and static dissipation are really related unless it is consequential.

There are some lightning prevention ideas about increasing the size of the tip surface of a thin element that is exposed to conditions high above ground level. Maybe doing this will help discourage an electrical strike by lightning. Maybe this has some relationship to this notion, when we talk here about dissipation. So maybe this is how cap hats, static dissipation, and white noise all got connected as an issue. It is just pretty complicated stuff.

A discussion about why cap hats are used on some antennas, what they do, and why, might be interesting. I’m sure that noise suppression ideas will come up in doing that and I guess it is as valid as other ideas.

Just for example, I can’t understand why the f’glass type antennas always seem to be nosier that metal antennas, cap hats or no. That is not to say that the f’glass sticks are always noisy, because local conditions always rules there. But even when conditions are generally quite, on an Imax for example, I have always noticed that the Imax is still nosier than the metal antennas I have used. In this regard, it has been reported by a professional in the field of radio broadcasting and found at:

http://www.video-observer.com/imax/imax2000.htm

Here it states, that if the GPK is added to the Imax, it will create a null in the radiated field pattern area located at about 50 degrees to the horizon and this null will substantially reduce the man made noise present on a Rx’r connected to this antenna. So I guess this also suggest that man made noises are at 50 degrees to the horizon, but I'm not sure if that is true or not.

How say you?

 

[W5LZ]

Wouldn't it be nice if noise (man made or not) were limited to a particular angle in relation to the horizon? Unfortunately, it isn't.
- 'Doc

 

[freecell]

i have a problem with this article and IMHO it is flawed from the get-go. using the Mantissa bench top calculator the length of a 5/8 wave element cut for 27.000 Mhz. with no capacitive fringing present is 273.4 inches. if anything the overall length (270.5") is on the short side for a 5/8, indicating the cancellation of some amount of inductive reactance still present at the junction of the matching circuit and the feedpoint at resonance. .64 wl operation would not occur at 27 Mhz. until the length approached 280".

in any case the 2000 remains a 5/8 wave antenna as advertised.

 

[Marconi]

Well you know Jack that most of us mortals just go by the math for 5/8's wave antennas being .625. No disrespect intended. We do not look at what is required to bring a radiator to resonance as you suggest. Which is the correct way to look at it, I agree. This is not meant to say there is anything wrong with your idea, it is just not the way most of us CB'ers think about this issue of non resonant length radiators that are a bit longer than .5 wavelength.

The author’s own math, or the lack of it, domes his report to the question pile, as you say "...from the get go."

36' x 12 = 432 x .625 = 270" His claim is that the antenna is 270.5" so that is pretty close to 5/8, strictly using the math. If we use his claim, and use .64 then the antenna should be closer to 276.5" using simple math. No doubt your estimate of the correct length is closer to the truth that this even.

This is why I claim that this business of .625 and .64 is a bit over blown. I would think that the resonant length of any radiator would depend of the feeder and the other factors concerning matching. That is not to say that these longer radiators might not be better in some instances however.

Just my thoughts on the subject.

 

[freecell]

984 / 27 Mhz. = 1 wl. or 36.4444444444444444444444444444444.
the slight amount of error is produced by the 36. the number there should be 36.4444444444444444444444444444444. times 12 =:
437.333333333333333333333333333333. multiplied by .625 =:
273.333333333333333333333333333333.

the formula for a 5/8 wave is: 615 / fmhz. = answer in feet.
22.77' feet or 273.33 inches. Mantissa is good enough for me. i'm not going to quibble over .07 (seven thousandths) of an inch.

i hear what you're saying.

 

[Master Chief]

.....if it is true that gamma's do balance the antenna at the feed point pretty well, then I would pick the gamma for doing the best job, all other things being more or less equal. I know we hear all kinds of stories about TVI and this or that antenna doing better or worse, but can we agree that CMC's are probably the one most common cause of TVI?

What is it about a coil loop that allows it to be more efficient?

Marconi

Gammas do not balance currentsin practice. As a matter of fact, they are known for skewing the signal on an element and not desired by those who want a balanced feed system (T-Match or Beta Match).

Will a gamma help eliminate CMCs? I don't know. I do know they are prone to problems due to moisture and at higher voltages will break down.

I didn't take the time to dig out the reference, but the gamma does not make a physical connection to the antenna. It is rather a capacitive matching system.....much like the thru-glass antennas.....and we all know how well those work compared to a normal antenna. I'll take the matching network on the Maco over a gamma anyday! I've always felt that the Sigmas IV would be better if they didn't use a gamma match on it!

 

[Master Chief]

i have a problem with this article and IMHO it is flawed from the get-go. using the Mantissa bench top calculator the length of a 5/8 wave element cut for 27.000 Mhz. with no capacitive fringing present is 273.4 inches. if anything the overall length (270.5") is on the short side for a 5/8, indicating the cancellation of some amount of inductive reactance still present at the junction of the matching circuit and the feedpoint at resonance. .64 wl operation would not occur at 27 Mhz. until the length approached 280".

Are you taking into account the diameter of the wire when you come up with this length vs wavelength? A 5/8 length of wire will be longer than a 5/8 element made up of stepped elements of a larger diameter.

 

[Master Chief]

This is why I claim that this business of .625 and .64 is a bit over blown. I would think that the resonant length of any radiator would depend of the feeder and the other factors concerning matching. That is not to say that these longer radiators might not be better in some instances however.

My opinion is that .64 may be the absolute longest element and calling it a 5/8 was just easier. In other words, its more about the name than the actual length.

(other thoughts)
Capacity hats are used to load elements. These will make an antenna electrically longer while still being physically short(er). They will move the currents up the element and there is something to say about Wolf's use of coils. It would be interesting to study that antenna is depth.

You CAN add a capacity hat to a Maco and it will make it perform better (but by how much is the question). You will need to shorten the actual length of the main element. Some experimentation is in order.

 

[freecell]

"Are you taking into account the diameter of the wire when you come up with this length vs wavelength? A 5/8 length of wire will be longer than a 5/8 element made up of stepped elements of a larger diameter."

the author didn't calculate the length, he simply reported it. if the formula was customized for anything except an almost infinite length to diameter ratio (in comparison to tubing) then my number would have been the smaller of the two. that wasn't the case here. it makes far more sense to consider the fact that the element might have been shortened somewhat to create a small amount of capacitive reactance to offset or compensate for some remaining amount of net inductive reactance still present at the feedpoint for the target frequency. i've already demonstrated that regardless of whether wire or tubing was used, it would require at least another 7 - 10 inches of length to move from .625 - .64 wl in either case, or you could simply change the operating frequency.

if you wanted .64 wl operation with the antenna as is then all that is required is to move the operating frequency to 28 Mhz. it remains a 5/8 wl at 27 Mhz.

the only thing that surprises me is that the advertising department didn't capitalize on this. given the operating range of the antenna usually they would think nothing of claiming .64 wl operation if only to add to the hype and the bottom line.

 

[W5LZ]

It still amazes me that anyone would really care if the thing is a 5/8 wave (0.625) or a 0.64 wave (16/25) length. There just isn't much practical difference between them. Nice selling point though...
- 'Doc

 

[Marconi]

Well 'Doc, you just missed the important part in the article, that's all. Here it is, just for you; "The .64 wave is one of the best kept secrets in CB and 10 meter antennas." Now doesn't that make this information more practical?

 

[W5LZ]

Marconi,
You're right, I missed it. I'm still missing it. From the practical point of view, what possible difference does it make? (Key word here is 'practical'.)
- 'Doc

 

[Marconi]

Well 'Doc, I guess that is why they kept it secret until this report disclosed this startling new information.

 

[bob85]

i make it a .64 or close to that using the basic maths from arrl,
1/2 wave in free air = 492/frequency in mhz
taking vf of wire into account 1/2wave = 468/frequency
1 wavelength of wire @27mhz = 936/27 = 34.66666667 feet
34.66666667 feet x .64 = 22.19 feet or 266.24", i also get a 5/8 of wire to be 260"
this is what has been taught to thousands of hams the world over, why do our numbers differ????, what are you taking into account that i am not?. :shock:

 

[Highlander_821]

I think what 'doc is saying is that, for the person sitting beside the radio and listening to and transmitting signals with it, the difference between having a 5/8 wave antenna or a .64 wavelength antenna, all other factors being nominal, would be negligable. While the theory and math involved in the discussion may be interesting to many, the "end-of-the-day" difference between the two in terms of who you'll be able to hear and talk to on your radio will not be noticeable.