Just got the go ahead from the boss. It will be mounted at 36'. Now just have to figure out where to buy one. And, do you's think 50' of mini8 coax will be o.k or should I get 213. I had 64' of mini8 on the ground plane, and switched it out for 213. The only difference I saw was in my pocketbook
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sirio sd-27 mounted flat
- Thread starter canoe
- Start date
Thanks Homer, for confirming my recollections on this issue to Canoe about the issues with an offset mounted center fed dipole mounted on his tower.
I repeat what I have claimed before, experts in field/lab testing have told us that such an install will results in some effects on the dipole.
Like I often contend, such effects are almost non-existent for the simple type of operations we do in the CB band...just working our radios. We do not have to have a perfect setup, in all respects, in order to work our radios. IMO this is just like the motto in my signature is suggesting.
BTW Homer, did you possibly have your dipole setup isolated at the antenna or the mast connection to the standoff extension?
Canoe, would you be interested in seeing some modeling information that might help you see what my Eznec model suggest could happen if you mount your SD-27 horizontally, a short distance out, 3' feet from your tower, at about 36' high?
I have a model of a center fed dipole 36' feet high and it is on top of a 35.5' foot mast so it is isolated. It has a very good match as a result of isolating the mast, so I can use it to make another to compare to your idea using an offset of 3' feet similar to what Homer did.
It does not have a feed line, but if I do this for you as a series of models, I could easily add a feed line as a separate model and we could see how that effects things too. That would be more revealing and maybe suggest to us if you need a choke.
I think I might expect that Homer probably used both isolation and a choke on the setup he tell you about above.
If you think this will help you consider your options...I think I can do this and maybe I'll learn something in the boot, OK?
I have a model of a center fed dipole 36' feet high and it is on top of a 35.5' foot mast so it is isolated. It has a very good match as a result of isolating the mast, so I can use it to make another to compare to your idea using an offset of 3' feet similar to what Homer did.
It does not have a feed line, but if I do this for you as a series of models, I could easily add a feed line as a separate model and we could see how that effects things too. That would be more revealing and maybe suggest to us if you need a choke.
I think I might expect that Homer probably used both isolation and a choke on the setup he tell you about above.
If you think this will help you consider your options...I think I can do this and maybe I'll learn something in the boot, OK?
Canoe, I will add this feed line idea to my project for your SD-17 idea when I add the coax, and we'll both see what Eznec and my applications of the feed line feature will show us.
I'll start today, and maybe I'll be able to get to all this before you decide on your purchase. This Eznec project will only be informational, so don't take it as a recommendation...because I can't guarantee my modeling is good enough for all that.
Feel free. I love to gain all the knowledge about things I'm interested in. I appreciate your effort and like you said. We can all learn from this. And, like your signature says that goodness for Mothernature. But, I still want things to work at there best.
Like I say. The best is the least we can do, and the least we can do is try
Like I say. The best is the least we can do, and the least we can do is try
Well at this point my original model of the 1/2 wave center fed dipole at 36' feet, shows this antenna needs to be isolated. I would bet that is what Homer did too, and maybe he even used a choke.
So, you may be able to get the best from this setup based on the ideas we may find thru considering what these models might show and what Homer found out.
So, you may be able to get the best from this setup based on the ideas we may find thru considering what these models might show and what Homer found out.
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Canoe, here is what my ideas in Eznec shows if you offset your SD-27 to your tower at 36'. Personally I think it will work best at 42' feet.
I included all the information in the pdf file and it is a little overkill possibly. I would check out the Antenna View, the far-field gain and angle, and the Source Data (feed point data and feed point SWR), and the SWR report of course.
I recapped the four models data so it is easier to view results.
Notice that the last two ISO (isolated) models show similar results. The offset model lacks the significant interference factor that was reported earlier as being significantly bad, typical CB talk. These two model show the same for gain and angle, and their matching is also very similar. I didn't know that before I did these models, but that is what I reported to Homer some time back too.
The offset isolated models use a conductive mast and offset extension. A non-conductive bracket (not shown a 3" space instead) isolates these two elements where the mast and the antenna extension connect.
The high gain noted is due to the horizontal ground reflection effects that antenna and modeling guru's talk about, like W8JI and Cebik perhaps.
I forgot to do an azimuth view of these antenna in free space, but I'll do that next...before I try adding the feed lines to see what that does. The azimuth view will show us much better how the pattern is skewed by the mast, a view looking down from above the antenna. If it is skewed much at all, then I'll be a bit surprised. Seems I recall doing that for Homer and the skewing by the mast to the offset antenna was smaller that CB reports would suggest also.
I just hope that part of this Eznec project works out and shows us something rather than just words. Even if not, then maybe somebody will volunteer give me some better understanding for how this Transmission Line feature should work.
BTW, take special note of the red curved lines in the models...those represent the currents (in amps) where and how they flow. The farther away they are from the radiating element the more the current is. The currents on the mast are of concern to me only due to common mode currents (CMC). Maybe such heavy currents on the mast tells me that there is possible trouble.
Good luck,
If you have questions please ask.
View attachment Canoes SD-27 project on the side of his tower..pdf
I included all the information in the pdf file and it is a little overkill possibly. I would check out the Antenna View, the far-field gain and angle, and the Source Data (feed point data and feed point SWR), and the SWR report of course.
I recapped the four models data so it is easier to view results.
Notice that the last two ISO (isolated) models show similar results. The offset model lacks the significant interference factor that was reported earlier as being significantly bad, typical CB talk. These two model show the same for gain and angle, and their matching is also very similar. I didn't know that before I did these models, but that is what I reported to Homer some time back too.
The offset isolated models use a conductive mast and offset extension. A non-conductive bracket (not shown a 3" space instead) isolates these two elements where the mast and the antenna extension connect.
The high gain noted is due to the horizontal ground reflection effects that antenna and modeling guru's talk about, like W8JI and Cebik perhaps.
I forgot to do an azimuth view of these antenna in free space, but I'll do that next...before I try adding the feed lines to see what that does. The azimuth view will show us much better how the pattern is skewed by the mast, a view looking down from above the antenna. If it is skewed much at all, then I'll be a bit surprised. Seems I recall doing that for Homer and the skewing by the mast to the offset antenna was smaller that CB reports would suggest also.
I just hope that part of this Eznec project works out and shows us something rather than just words. Even if not, then maybe somebody will volunteer give me some better understanding for how this Transmission Line feature should work.
BTW, take special note of the red curved lines in the models...those represent the currents (in amps) where and how they flow. The farther away they are from the radiating element the more the current is. The currents on the mast are of concern to me only due to common mode currents (CMC). Maybe such heavy currents on the mast tells me that there is possible trouble.
Good luck,
If you have questions please ask.
View attachment Canoes SD-27 project on the side of his tower..pdf
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Here is the last two models from the post above where I just added feed lines set to actual length necessary with VF @ .66%.
View attachment Canoe's SD-27 with feed lines added..pdf
Canoe, there is a little skewing due to the close presence of the mast in this pattern, but again it is very small. Personally I think the polarity difference between the elements is why we see so little effects. If the dipole was vertical, then we might see a notable difference in the Azimuth View. I think Homer was right on the money, but I'm not sure if he noticed a difference in the possible effects when he switched or not.
Whata' you think?
View attachment Canoe's SD-27 with feed lines added..pdf
Canoe, there is a little skewing due to the close presence of the mast in this pattern, but again it is very small. Personally I think the polarity difference between the elements is why we see so little effects. If the dipole was vertical, then we might see a notable difference in the Azimuth View. I think Homer was right on the money, but I'm not sure if he noticed a difference in the possible effects when he switched or not.
Whata' you think?
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Wow, Marconi thanks. Its a little much for me understand, but I truly appreciate it. I ordered the antenna, and when it arrives I'll mount it on a 20' push up poll to set swr's. Then I'll mount it as high as I can. I think I can get it around 43'. That's the height of my tower, and I have 7' of pipe up to the Imax. From the looks of the antenna it has to be mounted on the extension pipe. And, the extension pipe to the mast. I'll have to see when it arrives. I'm actually excited to try it out.
I was thinking on mounting it directly to the pipe a few feet under the Imax, but I'll have to wait and see. Maybe I can fabricate something
I was thinking on mounting it directly to the pipe a few feet under the Imax, but I'll have to wait and see. Maybe I can fabricate something
Marconi, you are correct. I used a non-conductive extension to offset the dipole from the mast, and I used a coax choke at the feed point.
If I recall, it was when we went through the Merlin testing that you built diverse models for me, one of which was a dipole mounted off the side of a mast. There was some skewing that showed up in that model.
As for noticing a difference between the vertical and the horizontal dipoles at the same feed point height, I do not recall the mast as being significant.
If I recall, it was when we went through the Merlin testing that you built diverse models for me, one of which was a dipole mounted off the side of a mast. There was some skewing that showed up in that model.
As for noticing a difference between the vertical and the horizontal dipoles at the same feed point height, I do not recall the mast as being significant.
So I received the antenna, put it together and mounted it at 27' on the flat. Dx has been quiet lately but did make a couple of contacts. Facing southwest I talked to a station in Maryland and one in the Bahamas. Both stations said the dipole was clearer and stronger than the ground plane, as I switched back and forth. Both antennas have the same on rx. Excited to see the outcome when I get the dipole up another 10'. The Imax is at 48 to 50' and hopefully to get the sd-27 dipole up to around 38-40'
interesting..that both have the same rx. but im not surprised it outdid the imax at all
now just imagine if the dipole was mounted directly below the imax be even better