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Stacking Winegard HD-6065P antennas
"Jeff Liebermann" wrote in message ... On Sat, 4 Jan 2014 21:23:14 -0500, "Ralph Mowery" wrote: What I am having trouble with is the 'perfect' combiner. I feel your pain. Many years ago, I made a similar mistake on the NEC antenna modeling mailing list. I then processed to make a total fool of myself and had to be corrected by the experts. Even so, I still didn't believe it so I built a Wilkinson combiner and bench tested it for loss. I still have the combiner somewhere as a reminder of my mistake. Incidentally, a Wilkinson combiner might be a tolerable solution for combining two FM antenna. The loss is much less than a bifilar wound toroid. I'm not sure if it will work over the entire FM band. I can grind the numbers if anyone is interested. My problem is where are you going to find a combiner for a broad frequency that does not have any large (say over 1 db ) of loss ? Are the ones for the TV frequencies built differant ? There's only so much you can do with passive only designs. The next step up is an active combiner: http://www.rldrake.com/product-ac1686.php 0-3dB gain per port. 54 to 860 MHz. Has anyone actually put one on accurate test equipment to see about the loss like I have been trying to do ? Yep. I have. There's very little loss between the combiner input ports and the "sum" port. However, in the other direction, there's a bit over 3dB loss due to the power splitting. See the specs on the MCL splitter/combiner that you have and try it with a service monitor or generator. Since it works down to 10 MHz, you might be able to do the test with a function generator, a few dummy loads, some T connectors, and an oscilloscope. I understand phasing harnesses for antennas. They are almost loseless. Only a few feet of coax worth. I have used them on antennas before. They are not usually very broad banded unless the antennas are broad banded and made so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8 dipole arays for VHF/UHF. Lots of 'tricks' used to do that. It's low, but the phasing harness loss for stacked vertical dipoles is not zero. I've never calculated or measured it, but this might help: http://www.kg4jjh.com/pdf/2-Meter%20Vertical%20Dipole%20Array.pdf "The phasing harness loss at 150 MHz is calculated to be 0.67 dB." Scaled for 100 Mhz, I would guess about 0.5 dB. Might as well use a combiner/splitter. -- I understand the idea of using 'perfect' items in electronics, then going for more exect calculations if needed. As most electronic items are often a 5 to 10 percent variation anyway. Often you get a close calculation and build it and trim for the desired results. I did take 2 year course in electronics engineering about 40 years ago for an associates degree, so know about perfect vers real components. The Wilkinson combiner is possiable for relative narrow frequencies. Not sure if building one out of descrete components or full size transmission lines would be broad enough for the whole FM band either. Wild guess it would be about the same if just two pieces of transmission line of the correct impedance and length were used. Isn't the Wilkinson combiner just two pieces of transmission line (or simulated with components) with a resistor across two of the ports to absorbe the diffeance if the loads/sources are not ballanced ? I know what they are and have seen equipment with them in it,but never did much of a study on it. As the subject is combining, I have not looked into the losses of splitting, but it would be 6 db for the simple resistor designs not counting the minor losses. That would be 3 db for the ports and 3 db lost in the resistors. To combind signals you would get the loss of the resistors of 3 db and a fraction of other loss. I am using a HP 8924C for a test set. It has just about everything you can think of for a service monitor. Calibrated from 30 to 1000 MHz but usuable uncalibrated to about a half of a mhz. http://www.amtronix.com/hp8924c60.htm As mentioned the only combiner I have is a MiniCircuits and they spec it at 3 db plus small losses depending on the frequency. That is what I am measuring. The diplexer/combiner will have very low loss. I have checked out 2 of them in the past just to see and the losses were about half a db or so. However that is for frequencies seperated by a very large percentage. Usually one port is a low pass and the other is a high pass filter. Not suited for signals on the same frequency as the origional poster wanted to do. Yes, phasing harnesses on antennas are not totally loseless, but will be mainly whatever the loss of the coax is between the elements. If were the origional poster and there were not too many transmitters near me, I would try a good preamp first. Mast mounted if possiable as it is for receive only. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
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