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Wire_saber
Junior Member
Username: Wire_saber
Post Number: 20
Registered: 4-2015
| | Posted on Monday, September 14, 2015 - 9:49 pm: | 
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My son’s Magnum CB-4 was damaged by tropical storm Ericka. Wire elements were tangled with branches from a tree that knocked the antenna down across the road. The emergency response crew that was rushed to clear roadways was kind enough to spare the boom and spreaders, but they cut off all the tangled wire elements to free the Magnum. I’m relieved that the ‘skeleton’ of the Quad survived, as testimony to its quality-built. Now we must reconstruct. I’m trying to purchase the 4 elements through Cubex/ Tennadyne. However, if unable to obtain, I will need info about the exact length of each element and wire gauge. Since the wires were pre-cut, and worked so well right after initial installation, I wish not to change specifications.
I do not want to rely on calculators available on the web because most do not consider wire gauge as a variable. I’m asking for a Tech's assistance or someone who may have a manual for the Cubex Magnum CB-4 (or the information that may be useful to rebuild the wire elements). The quietness and F/B rejection of this antenna is, by far, the absolute best I've found in any commercial 4-element directional antenna (nothing compares). The CB-4 is less than 3 years old. My son is not ready to settle for lesser-quality QSO’s. |
Tech833
Moderator
Username: Tech833
Post Number: 2333
Registered: 8-2002
| | Posted on Friday, October 16, 2015 - 1:40 am: |
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A true quad does have excellent front to back ratio, and is extremely quiet. That is just the nature of quads.
The driven element wire will be 1/4 wave on each leg, regardless of wire diameter. All the wire diameter will affect is the element Q. True, if you go to a real huge diameter, like 4/0, then you will have to shorten the elements'length by an amount equalling the diameter of the wire x 3.14.
Directors should be 5-10% shorter than the driven element. Reflectors 5-10% longer than driven element.
Rest assured, the dimensions are not very critical for a quad. If you get within 5% either way on your driven element, it will have no affect.
Your radio 'Mythbuster' since 1998
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Wire_saber
Junior Member
Username: Wire_saber
Post Number: 25
Registered: 4-2015
| | Posted on Friday, October 16, 2015 - 11:32 pm: |
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Hello Tech 833: Thanks for the formula. Bught 14 AWG stranded copper wire, and found a good samaritan whom is willing to assist my son with the project to rebuild. However, this friend insists that I must also buy a 1:1 current balun to connect the coax to the driven element of the Quad. There was no balun when I purchased the antenna. He says that a balun is the best way to avoid 'lobesidedness' of the radiated signal and insure proper directionality. Will you please provide some feedback on this issue? Does a current balun improves or helps in keeping the path of the signal from deviation? |
Tech833
Moderator
Username: Tech833
Post Number: 2336
Registered: 8-2002
| | Posted on Thursday, October 22, 2015 - 12:34 pm: |
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Well, your friend is a little bit right, but not quite for the right reasons.
If the quad is oriented with the elements in the diamond shape (the prettiest looking, in my humble opinion), then the coax cable can cause some pattern distortion. However, let me be very clear about this- It has very little effect on the pattern, assuming the driven element is tuned. If the driven element is not tuned, and let's say you use an antenna tuner to make the radio happy, the antenna will still work, but the coax cable being in the field and not at exact phase zero can have some effect, increasing by the amount out of tune of the driven element.
If you let the coax just hang off the element instead of dressing it nicely back to the boom and then down the mast, then the coax will effect the pattern also. I see a lot of hams that do this- It is like a public declaration that they just don't know what they are doing. Good for a laugh every time.
A 'current balun' is a fancy way of saying ferrite or coil choke that keeps current from flowing back down the outer shield of the coax cable. You could purchase some #43 material snap-on chokes from Farinon or somewhere similar and snap those over the coax near the feedpoint and maybe every 7 feet or so along the cable near the feedpoint to completely uncouple the cable from the high-Q loop elements. You don't need to purchase an expensive or bulky current choke from some ham supplier. You also don't want the bulk way up there on your antenna and raising the wind resistance, which reduces storm survivability.
Your radio 'Mythbuster' since 1998
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Wire_saber
Junior Member
Username: Wire_saber
Post Number: 31
Registered: 4-2015
| | Posted on Monday, November 09, 2015 - 10:18 pm: |
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Thank you Tech 833. Just received the 4 wire elements from Tennadyne, for a nominal fee. The value of the pre-cut & pre-marked wires far exceed the minimal fee. In addition to an unsurpassed quality antenna (Magnum CB-4), I'm pleased to report there is an outstanding customer service. According to Roger, installing the elements by the pre-marked wire folds, eliminates any need for a balun. I trust that is what Tech 833 refers to as tuned elements. Other than for this Cubex antenna, my son's station is identical to mine. Having operated his station during a few casual visits, I've experienced the superior quietness of the quad, as compared to my 4-element yagi. After DX QSOs with him for years, USA to overseas, I can attest that quads are the elite/ Alpha dogs of antenna performance. |
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