First thing... this ain't the place for this type of antenna question... there are yahoo groups specifically for this type of discussion. Begging the listowner's pardon... I will address the question at hand...
I guess the first to ask is what exactly are you trying to accomplish? You haven't provided enough information to even begin formulating an accurate answer to the question. Taken literally at face value... yes, you can build a splitting/phasing harness quite easily. For those in the know... Please pardon the enormous bandwidth... ;-) Just delete this message now and move on.... I first considered responding that you should get an 11m radio to go along with the 11m idea. But that is rude, and un-called for... so I have just sat idly by to see how far this would go. It looks as though it isn't going to die a quiet graceful death, so here goes... Phased Directional Antennas 101 Your question... > Someone has told me their is a co-phasing harness > available for two meters has anyone heard of this. to > unite two antennas. In the same way truckers do on > CB's > Thanks > You can create a 50ohm "match to split" by using RG-59 is 75ohm (and is lossy as hell at 2m, but for the sake of argument please bear with me.) cable cut to an odd multiple of a 1/4 wave length combined with a T-connector. Feed the T with standard 50ohm line. Assuming a purely resistive load, the two lines in paralell will present a resistance of approx 37.5 ohms. This is close enough. And I am NOT going to get into complex impedances here. The first thing you need is manufacturers data for velocity of propagation for the line you intend to use... an electrical wavelength is not the same as a physical wavelength.. It will be physically shorter than just calculating a wavelength mathematically. Reason being that no cable is 100% effecient. This is where the velocity factor comes in. A better quality RG-59 will have a velocity factor of something near 82% (0.82). To get to where you need to be.. divide 300 by the desired frequency in mHz.. The result is one physical wavelength. (please pardon the round-off error) 300/freq in mHz= 1 wavelength physical length in meters - ie; 300 / 146.52 = 2.047m multiply this number by 0.25 for the 1/4 wave length we spoke of earlier... 2.047 * 0.25 = 0.512m This is where velocity of propagation comes in to the equation... you now multiply the 1/4 wave physical length by be velocity factor of the specific cable you plan to use... we spec'd RG-59... so the velocity factor is approximately 82% 0.512m * .82 = 0.42m - this is the electrical 1/4 wavelength @ 146.52 mHz using RG-59. Using odd multiples of this number will keep you on a current node, but only at 146.52 mHz... if you change freq by very much, the whole thing falls apart. Staying on the current node is important... you will just have to trust me here. As I am not going to delve into the reason's why. Figure out how much distance you need to cover between the 2 antennas... how far from the split to the connector at the bottom of the antenna. For this discussion, we will use 5 meters (physical) for each half of the phasing harness.... to get to the antenna from the T. We will call this the "cable run" distance. Next divide the cable run by the 1/4 wave electrical length. 5 / 0.42=11.9 quarter waves.... we need to stay on the current node by arriving at an odd multiple, so we must add another 1/4 wave electrical... So each cable run will be 13 electrical quarter waves.... (odd number to stay on the current node) 13 * 0.42 = 5.46m or 17.91 feet. Cut your 2 cables to exactly this length, connector tip to connector tip. Attach one end to your antenna, and the other to the T connector, then use 50 ohm line from your radio to the T connector. This arrangement (method) is only good for the specified frequency used in your calculations. If you change frequency very far.. the match will not be good, and that will "piss your radio off" ... so to speak. Bad match = power "fold-back" or even worse smoked finals. Now you have a phasing harness with 0� phase shift that will present a workable load at 146.52 mHz.... Placement of the antennas presents a whole new world of problems. Assuming you place them exactly 1 wavelength apart (rough guess for mounting on each mirror of a vehicle), fed in phase & unity current, the resulting pattern will resemble a squashed four-leaf clover, with most of the signal being radiated to the sides.... (I tried at first to send this with a EZ-NEC plot of the pattern, but yahoo threw-up. If it is desired, contact me directly.. And I can supply bothe the file and the plot) So I guess my question now is WHY? Is this a "coolness" thing? You will most likely acheive around 2.7 to maybe 2.8 dB of gain.. and a horrible pattern... Why not be cool by being "smart" and buy a higher gain omni antenna? You will be more effecient, avoid all the headaches, and the pattern and match won't go bonkers when you change frequency.... Enough said.... Sorry for the rant guys... but it was a good exercise in practical application of theory. Mike ----- Original Message ----- From: "Warren Beaul�" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Thursday, April 28, 2005 2:10 PM Subject: [Repeater-Builder] antenna's > Someone has told me their is a co-phasing harness > available for two meters has anyone heard of this. to > unite two antennas. In the same way truckers do on > CB's > Thanks > 73 Mike K5JMP www.k5jmp.us Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
