Posted: 3/9/2010 4:21:44 AM EDT
Ok, I have a Diamond X50 and an Arrow yagi. Both are for 2 meter. I want to mount them on the same pole. This is them mounted on a test pole at 12 ft.
A closer view: 
The mast are fiberglass. Before I move this up to 35 ft I wanted to see if there was any reason this will not work. |
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Ok, I have a Diamond X50 and an Arrow yagi. Both are for 2 meter. I want to mount them on the same pole. This is them mounted on a test pole at 12 ft. A closer view: The mast are fiberglass. Before I move this up to 35 ft I wanted to see if there was any reason this will not work. Question - do you intend to use both at the same time? |
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Ok, I have a Diamond X50 and an Arrow yagi. Both are for 2 meter. I want to mount them on the same pole. This is them mounted on a test pole at 12 ft. A closer view: The mast are fiberglass. Before I move this up to 35 ft I wanted to see if there was any reason this will not work. Question - do you intend to use both at the same time? No, just one at a time. The X50 will be for 90% of the work. The yagi when I need to reach out futher, |
I have a small discone antenna mounted underneath my X50A on the same mast in the attic. Prior to making the discone mount permanent I did extensive testing to make sure the discone wasn't adversely impacting the X50A's effective range. Since my antenna farm is hidden in the attic I'm wary of attenuating my signal any more than I have to. Long story short, I don't think the X50A even "saw" the discone-there was absolutely no difference whatsoever in effective range or signal quality 
Good luck with your project! Also, what did you use to paint your fiberglass mast black? I'd like to mount two of my antennas outside eventually, but I would like to paint them black for obfuscation purposes. Thanks in advance for your insight. |
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Good luck with your project! Also, what did you use to paint your fiberglass mast black? I'd like to mount two of my antennas outside eventually, but I would like to paint them black for obfuscation purposes. Thanks in advance for your insight. Thanks, I hope to have this up to 35-40 ft in a week or 2. I got the diamond x50 used and it was already painted flat black. The mast I paint with flat black spray primmer. My subdivision does not have any restriction so I don't have a problem with that. |
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Never using them at the same time can let you position them closer.
Here are a couple references on spacing of antennas - though I didn't spot a discussion on exact what you want to do: http://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm http://forums.qrz.com/showthread.php?t=162627 http://forums.qrz.com/showthread.php?t=166190 In a similar style of stacking Gary K9AY has written This one should be modeled, as both polarizations need to be accounted for, and the other antennas are beginning to "look" like large surfaces.
A good starting point is 1/2 wavelength (3-1/2 feet) between the ends of the vertical elements and other antennas. Charts seem to start with .05 lamba (1/2 wavelength) spacing and run to 3.0 lamba. For similar antennas appropriately phased the charts suggest around 2 wavelengths spacing is optimal. |
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Mounting the yagi like that, you'll get pattern distortion from the coax. Doesn't matter that the mast is non conductive if you run a conductor down the side of it.
I'd recommend mounting the yagi completely clear of the mast and routing all coax behind the reflector element. The will add more twisting force from windloads. A steel mast would be a lot stronger. |
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I'd rotate the yagi 90 degrees sise to side so you get horizontal polarization of your signal. Yes after reading the links that K9ZW posted It looks like that is what I will need to do. Are you using it for 2m SSB? CW/SSB is traditionally done with horizontal polarization and FM traditionally uses vertical. You just need to match whatever the station at the other end of your QSO is using. |
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I'd rotate the yagi 90 degrees sise to side so you get horizontal polarization of your signal. Yes after reading the links that K9ZW posted It looks like that is what I will need to do. Your polarization of the Yagi would depend on what you want to do. Most FM 2m are likely to be Vertically Polarized. Most SSB 2m would focus on Horizontal Polarization. Cross Polarization attenuates your signal, basically negating much of your Yagi Gain. There is a nice mini-project about this in the ARRL EC-009 Course Material: Construction Project (Optional)
If you undertake the construction project, report to your mentor: a. What construction problems did you have? Did you improvise with other construction methods or materials? b. Were you able to observe the predicted effects from aiming the antenna in different directions? c. How might you mount this antenna permanently? 1. Construct the 2-meter quarter-wave ground-plane antenna as described in the reference text and connect the coaxial cable to the SO-239. 2. Hold the molding or dowel against the cable with one end against the flange of the SO-239. Use the electrical tape to attach the dowel to the cable as shown in the following figure. The dowel will be used as a handle for the assembled antenna. 3. Connect the cable to your radio and tune in an active repeater or have a friend transmit on low power from several hundred feet away while holding his antenna vertical. Hold the antenna above your head, oriented vertically. Note the received signal strength. If the signal strength is at the maximum displayed level, either find a weaker repeater signal or have your friend reduce power so that the indicator shows about 80 –– 90% of maximum signal strength. 4. While the repeater or your friend is transmitting, watch the indicator while you slowly lower the antenna directly towards the transmitted signal source. By carefully pointing the antenna directly at the source, you should be able to see a "dip" or "null" close to directly off the end of the antenna. 5. As the repeater or friend continues to transmit, slowly pivot, swinging the antenna in an arc until it is perpendicular to the direction to the transmitter. Note the signal strength as you swing the antenna. It should increase again, but will probably not reach the same strength as in step 3 because your antenna is now horizontally-polarized while the transmitted signal is polarized vertically. The two antennas are "cross-polarized" and the difference in signals is called "polarization loss". 6. Continue to pivot until your antenna is pointed directly away from the transmitted signal source. In this direction, the received signal will be even weaker than in step 4 due to the shielding effect of the antenna's ground-plane and your body. 7. Continue to pivot while watching the received signal strength until you are again pointing directly at the signal source. Return the antenna to point directly overhead. This exercise should allow you to visualize the antenna's radiation pattern described earlier in this lesson. Selecting your polarization based on your expected needs, not to gain clearance. |
| So I came home today, flipped the yagi to a Horizontal Polarization and put my missing element back in. I tested it and was able to hit a reperter that before I could not. I guess the repeter is a Vertical Polarization being as I am using fm. If I move it back to vertical, I will have to deal with the coax of both antennas acting as an element, correct? |
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If I were you I'd measure the spacing on the elements on that yagi. If the two are the same, I'd switch the director and reflector around, so as to have a "tail" of boom length to use for mounting. Coax from the yagi needs to be routed down the boom, behind the reflector then down the mast. Coax from the vertical should stay behind the reflector.
Horizontal polarization getting you into a repeater you hadn't been able to access before makes me think you probably have some kind of obstructed path and you're getting some kind of reflection or multipath... or even knife-edge diffraction over a ridge or something. Very few FM repeaters use circular polarization, although there are a few... I've never known of an FM repeater that used horizontal. |
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If I were you I'd measure the spacing on the elements on that yagi. If the two are the same, I'd switch the director and reflector around, so as to have a "tail" of boom length to use for mounting. Coax from the yagi needs to be routed down the boom, behind the reflector then down the mast. Coax from the vertical should stay behind the reflector. How about adding a "tail" to the boom and leave all the element in place. The tube is a normal square tube, If I add a foot to the end, and keep the coax on the boom till it gets past the last element, the go down the mast- right? |
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If I were you I'd measure the spacing on the elements on that yagi. If the two are the same, I'd switch the director and reflector around, so as to have a "tail" of boom length to use for mounting. Coax from the yagi needs to be routed down the boom, behind the reflector then down the mast. Coax from the vertical should stay behind the reflector. How about adding a "tail" to the boom and leave all the element in place. The tube is a normal square tube, If I add a foot to the end, and keep the coax on the boom till it gets past the last element, the go down the mast- right? Yep, I like that sort of idea. Why not remove the rear reflector and use the mast for a reflector instead. You'd have to beef up the square tube boom attachment to the mast with some braces/gussets but they should not affect the radiation pattern or VSWR if kept well less than a 1/4 wavelength. Then you can run the coax from the vertical right down the mast w/ no hassle. The element you remove to make space for the new "mast reflector" could be used to replace the missing director after you cut it to the correct length. [note that the reflector length if longer than a wavelength probably isn't important -as a reflector only] ETA, maybe some 3/16" aluminum sheet stock cut to roughly 2 triangles 15" in length and 8 inches or so vertical to sandwich and attach the antenna boom to the mast. Hope this makes sense... |
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So I went to the source about this, Sent an email to Arrow Antennas with a link to this this thread. Got a quick reply.
Hello, Mickey This is WRONG on many counts. The Arrow II Antennas are made for portable use ONLY. The connector is not weather proof, the elements will come loose in the wind. The antenna is mounted upside down. The coax is not routed properly. (coax will act as a metal mast) What you need is the 146-4S made to me mounted outside, comes with a Mounting Bracket that will allow it to be end mounted. (Must me end mounted if not at the top of a mast) 73 Allen Lowe NØIMW So, either I buy a diffrent antenna, or roll my own... looks like I need to make a metal order. |