I have a weird coverage area problem. First the facts- I have a 15 watt transmitter feeding approximately 25' of super premium RG 6, (swept to 300mhz, whatever that means). That feeds a 1/4 ground plane fixed to a 10' mast mounted on the roof above the third floor, so what, about 50 to 60 feet above ground. it is above or equal to everything in the line of sight. I have an unbelievable signal up to 8 miles to the south. I only have an acceptable signal around 2 miles to the north. Further than that it is a fringe signal. I also share a frequency with a 10 watt repeater about 15 miles northeast of my location. There is a four square block park a quarter mile to the north. Since it is winter, the trees are bare. There are no tall buildings until downtown, about 5 miles away.
Question- Could I be getting interference from the park, or possibly some kind of multipath problem from the tall buildings? It is VERY strange that the signal is SO different between north and south. East and west are about the same as south. This wouldn't really be a problem except I have a few businesses that would play the station but can't get a clear signal. I'm testing the signal with the radio in my truck.
Side note-I live on one side of a river, the repeater is on the other side, like I said, about 15 miles northeast. My signal pretty much dies across the river, which I like because it barely interferes with the repeater. The only time our paths cross is at the extreme fringe of our respective coverage area. Fortunately I sound exactly like a regular station, except for call letters or commercials of course, so I'm not that worried about a complaint.
Post by Ozone Express Radio on Dec 28, 2010 18:04:11 GMT -6
I'm not a Field Engineer, but I did stay at a Holiday Inn last night...
Seriously, I had a similar problem using a Comet 5/8 wave and a 25 Watt transmitter. The antenna was mounted at around 30 feet. To my North, South and East I was putting out a strong signal 6-7 miles and up to 9 miles depending on weather and foliage without an issue, but to the West I couldn't get more than maybe 2 miles on a great night. It is hilly in that area, but not so much so that other stations were disappearing.
After trying everything and having my SWR at 1.3:1 running very low loss LMR400, I kinda just figured it was the terrain and left it at that. Later, just for the heck of it, I decided to build a J-pole and did so installing it a couple weeks ago at around 25 feet high. No real difference in the coverage of the North South and East, but I am definitely now penetrating the area to my West at probably a 50% improvement. That is with an SWR that is still a bit higher than I want at 2:1 and running cheap RG58 coax that I found online and had laying around the shop.
I suspect that there isn't a one-size-fits-all when it comes to antennas, and as such, the 5/8 wasn't the best suited for my terrain. Once I get some better coax and dial in my SWR I will report the results.......
Everybody raves about the "J" pole. I'm hesitant for two reasons, at least until I get a good meter. The main reason, though, is that I live in one of those "Historical" areas, and they get Hysterical about anything unusual. So far the excuse that I have a shortwave receiver has worked. Thanks for the input though. Thanks Tink- now I'm going to be paranoid the rest of the day-
Post by Ozone Express Radio on Dec 30, 2010 18:15:03 GMT -6
The nice thing about the j-pole is that it can also be painted. That means that it could be "camoflauged" to match the surrounding architecture to some degree. Mine is just shiny copper right now, and where I am at it really doesn't matter as no one can see it unless they come onto my very secluded property. I'm sure in a few mohs it will lose its shine as the copper gets that patina that weather exposure brings.
Except for my signal strength to the north, I'm VERY satisfied with my coverage range. I was hoping for a couple of square miles. I have MUCH more than that. The only reason I'm looking for the northern exposure is that a good friend owns a thrift store less than a mile away and no matter what we try, he can't get a decent signal. He supports me with posters and helps another DJ put together shows for my station, so it's really frustrating. He is part of a trial community feedback network I'm setting up. Obviously I can't give out my phone number or address, which kind of limits listener response. So I promote "Friends of..." I make the point that we receive no compensation from these businesses, but if anyone wants to comment on the station, make requests, complain, whatever- then stop by and visit these friends. So far I have a guitar store, the thrift store, a high-end antique shop and my mechanic. And no, nothing yet. However, I DO know that I'm gaining listeners. At Radio Shack the other day I mentioned that I'd heard a new all music station and gave the frequency. One of the clerks said he'd heard it. Walking my dog I heard my music coming out of an open window. Stuff like that MAKES my day. So I may have to spring for an outdoor antenna at this shop. I've already given away several dipoles and donated a radio to the guitar store. Ego-thy name is "Private Radio Station"
That's an interesting idea. I'm not sure that a single directional antenna would still give the same coverage in the other directions though. However, one idea would be to mount an additional element on the mast. The main problem would be correctly loading it. I've installed multiple high gain directional TV antennas on a single mast with success, but I'm not enough of an engineer to figure out how to make two broadcast elements equal 50 ohms without any cancellation. Any comments on this idea would be appreciated. Thanks
You can use an additional element on the mast without having to load it. Use it as a "director" element... just like one on a yagi. It's not directly loaded either.
Remember, a director element is shorter by a certain amount from the dimensions of the driven element. Point that element away from the mast in the direction that you want the most signal. Be advised that adding another element will change the feedpoint impedance from what you presently have. You will have to correct for that by adjusting your driven element tuning system.
This will make a simple two element beam sending a bit more signal in the desired direction without penalyzing the other directions too much.
Remember, nothing says you have to have a perfectly symmetrical circular pattern anyway. The pattern should be what you want it to be.
The director would be a vertical rod at the end of a short boom placed in the direction (as seen from the view of your GP antenna) of where you wanted max signal.
Two-element Yagi
A two-element Yagi can be formed by adding either a director or reflector alongside the driven element. The optimum spacing for a driven-element/director Yagi is about 0.1 to 0.2 wavelength, with the director tuned to a frequency 5 to 10 percent higher than the resonant frequency of the driven element. The optimum spacing for a driven-element/reflector Yagi is about 0.15 to 0.2 wavelength, with the reflector tuned to a frequency 5 to 10 percent lower than the resonant frequency of the driven element.
(The driven element would be your GP)
A director is always shorter, a reflector is always longer. Either can be used, but I'd go with a director.
Do a search on yagi antennas and you'll find plenty of examples.
I have a local RF go-to guy. He modifies CB's, builds transmitters, antennas, etc. I've copied and sent the information from your comments and I'm waiting to see what he can do. He tuned and mounted the ground plane. My landlord won't allow me on the roof. Too old and fat I guess :-0 I'll keep ya posted.
IMHO, a small two element yagi pointed toward your troubled area would work well for you. I'd take the GP down and substitute it with this.
The little beam wouldn't be expensive at all to build. I'd be interested for you to post the comments from the rf guy you mention to see what he thinks of the idea for your situation.
Except for my signal strength to the north, I'm VERY satisfied with my coverage range. I was hoping for a couple of square miles. I have MUCH more than that. The only reason I'm looking for the northern exposure is that a good friend owns a thrift store less than a mile away and no matter what we try, he can't get a decent signal. He supports me with posters and helps another DJ put together shows for my station, so it's really frustrating. He is part of a trial community feedback network I'm setting up. Obviously I can't give out my phone number or address, which kind of limits listener response. So I promote "Friends of..." I make the point that we receive no compensation from these businesses, but if anyone wants to comment on the station, make requests, complain, whatever- then stop by and visit these friends. So far I have a guitar store, the thrift store, a high-end antique shop and my mechanic. And no, nothing yet. However, I DO know that I'm gaining listeners. At Radio Shack the other day I mentioned that I'd heard a new all music station and gave the frequency. One of the clerks said he'd heard it. Walking my dog I heard my music coming out of an open window. Stuff like that MAKES my day. So I may have to spring for an outdoor antenna at this shop. I've already given away several dipoles and donated a radio to the guitar store.
"Knowledge Is Always Made More Valuable By Sharing It With Others !" Always Remember To Be Kind ! True Greatness Often Has Very Humble Beginnings ! Help A Kid Out Today ! *** High Mountain Radio *** "Broadcasting From Somewhere High In The Remote Appalachian Mountains"
Post by HighMountainRadio on Dec 15, 2017 15:37:00 GMT -6
I, too, love that you heard your station eminating from an open windows as you walked by ! Ultra cool !
"Knowledge Is Always Made More Valuable By Sharing It With Others !" Always Remember To Be Kind ! True Greatness Often Has Very Humble Beginnings ! Help A Kid Out Today ! *** High Mountain Radio *** "Broadcasting From Somewhere High In The Remote Appalachian Mountains"