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#1
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I am looking for recommendations for a dual band antenna that will serve tw
o separate radios. The reason that I want to use a single antenna is that I have a limited number of mounting points for antennas. At present it wil l be hard for SWMBO; as in Rumpole's spouse, She Who Must Be Obeyed; to tol erate the use of both our home's gable ends and the chimney being used to s upport antennas. I am planning to replace my Diamond X-30 with a triband v ertical for Six, Two, and .7 Meters. The chimney will then support a rotor aimed Two and .7 Meter beam. The second gable end will support the Two me ter / Seventy Centimeter dual band vertical that I am asking for help in se lecting. One radio will be a two meter packet node which will be used as a Winlink R adio Message Server. The other radio will be a UHF D-STAR hotspot. I am w illing to pay what is needed to to get the best antenna for this applicatio n but I don't want to waste money ineffectively. So the two meter radio wi ll be in the 144 MHz portion of the band and I don't yet actually know were the D-STAR hotspot will be run. I have a DCI filter and diplexer to keep the two radios from actually knowing of each others existence. Since a hot spot is not supposed to be a terribly wide area installation I would imagin e that I do not want an extremely high gain antenna but I am perfectly open to be reeducated on that. The difficulty is that I would guess that the R adio Message Server / Packet would benefit from as much horizontal gain as can be achieved. I have a home brewed collinear two meter J-Pole that has been a good performer on two meters and presents a low SWR on 440 MHz. I h ave yet to master antenna modeling but I would imagine; given all the warni ngs I have read on line; that it has poor radiation pattern on UHF. Is it likely to be too poor a performer for a hot spot on UHF? I really am asking because I want to know. I am not looking for encouragem ent to do something that will be ineffective. Thank you in advance for any help you may be willing to offer. -- Tom Horne W3TDH |
#2
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On Sat, 14 Mar 2015 10:12:20 EDT, Tom Horne wrote:
I am looking for recommendations for a dual band antenna that will serve tw o separate radios. The reason that I want to use a single antenna is that I have a limited number of mounting points for antennas. Many years ago I had a similar problem on a commercial tower. I was paying for tower space essentially by the antenna. My boss at the time did not want to pay for two antennas. I had to devise a scheme that would share a single mount point. I asked if two coax cables were acceptable, to which he agreed. So, I built a dual 5/8 wave VHF antenna, with one antenna mounted above the mounting arm, and the other mounted below the arm, pointing downward. Getting the isolation right and camouflaging the fact that it was really two antennas, was tricky. I wish I had antenna modeling software, but resorted to optimizing by cut-n-try. Sorry, no NEC antenna models, but I may have some photos buried somewhere. One useful trick was to make the two coax cables the same length. The leakage between antennas was about 1/2 wave apart, resulting in cancellation in the respective receivers. As I vaguely recall, I had about 12-15 dB isolation, which I consider to be quite good for such a derangement. I don't know how dual band will work, but I suspect it will be usable. If you have a line stretcher (or huge collection of barrel connectors), you can test the effects of coax line length differences. Also, be advised that commercial antennas are designed to drain water only in their normal mounting position. After filling the lower antenna with water in a garden hose spray test, I had to drill a hole in the end of the antenna to provide an exit path. Of course, I was generating considerable intermod if both transmitters were on at the same time, but I didn't know much about intermod at the time making it a non-problem. Within a few months, some of my competitors on the same mountain top discovered my trick and cloned it (with varying degrees of success). That worked for a few years, until the tower/building owner figured out what was happening and began to charge by the coax cable. After that, common receive antennas with multicouplers became the cost saving method of choice. Good luck and remember that with antennas, the uglier it looks, the better it works. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#3
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On Sat, 14 Mar 2015 10:12:20 EDT, Tom Horne wrote:
I am looking for recommendations for a dual band antenna that will serve tw o separate radios. The reason that I want to use a single antenna is that I have a limited number of mounting points for antennas. One radio will be a two meter packet node which will be used as a Winlink R adio Message Server. The other radio will be a UHF D-STAR hotspot. I am w At the hospital we use a tri-band (144, 222, 440) Comet vertical antenna fed with a single coax cable, and at the radio end a three-way splitter and a set of Polyphaser bandpass filters for each radio. That is necessary because of the high rf environment. Has worked well for over 10 years. The dual-band (2m/440) equivalents are available off-the-shelf from your favorite ham radio supplier (store or on-line). It sure beats messing around with any of the other schemes reported here. 73 de K2ASP - Phil Kane Member, Washington County, OR Emergency Communications Team for ARES/RACES and HEARTNET Station Co-manager - W7PSV / K7PSV Providence St. Vincent Medical Center Disaster Communication Team |
#4
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On Sunday, March 15, 2015 at 3:59:22 PM UTC-4, Phil Kane wrote:
On Sat, 14 Mar 2015 10:12:20 EDT, Tom Horne wrote: I am looking for recommendations for a dual band antenna that will serve tw o separate radios. The reason that I want to use a single antenna is th at I have a limited number of mounting points for antennas. One radio will be a two meter packet node which will be used as a Winlin k R adio Message Server. The other radio will be a UHF D-STAR hotspot. I a m w At the hospital we use a tri-band (144, 222, 440) Comet vertical antenna fed with a single coax cable, and at the radio end a three-way splitter and a set of Polyphaser bandpass filters for each radio. That is necessary because of the high rf environment. Has worked well for over 10 years. The dual-band (2m/440) equivalents are available off-the-shelf from your favorite ham radio supplier (store or on-line). It sure beats messing around with any of the other schemes reported here. 73 de K2ASP - Phil Kane Member, Washington County, OR Emergency Communications Team for ARES/RACES and HEARTNET Station Co-manager - W7PSV / K7PSV Providence St. Vincent Medical Center Disaster Communication Team Phil How does the use of Polyphaser band pass filters instead of Digital Communi cations Incorporated band pass filters make your situation different from w hat I have been asking about here. What would be a tremendous help is for you to provide the model numbers for the filters you are using there. That would give us a different manufacturer to turn to for band pass filters co upled with the knowledge that the models you are using are already working in a very similar application. The only difference that is obvious to me is that you appear to only need o ne transceiver to be able to operate on each of those bands at one time wer e on two of them I will have a need for two transmitters at the same time. Between the vertical separation of the two multi-band antennas and the two MHz separation of the co band operating frequencies I am hoping to make it work. -- Tom Horne W3TDH |
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