Neil Radio 8z
Delighted to hear about the good result of the 2-antenna project. Perhaps many FM-casters can benefit from knowing that it works.
Do you suppose that it resembles the practice of large FM stations having several "bays" to magnify the effective radiated output of their transmitters?
If so, I think it is different in one sense, because rather than increasing the signal from a single point, it appears to create two separated points of radiation, kind of like having 2-transmitters.
Why not set this up with a "leaky" coax, or use one of those adjustable TV antenna amplifiers and in-line attenuators to match up the signal emissions at both antenna points.
I laugh at some of the comments about losses and so forth with Y and T. True it happens, but honestly we are not talking about splitting 5 watts of power and overly concerned with return losses and VSWR. Considering the flea power on a Part 15 FM transmitter....your lucky to even get enough signal through that video cable at all much less CATV coax.
I would use RG58. Much more flexible, and its at the proper impedance of 50 ohms. Your use of 75 ohm coax alone is absorbing that tiny signal already.
Use in-line attenuators to maintain the infamous 200 feet emission limit if your going to use sticks at the ends of those coax runs after the splitter. Put the adjustable amplifier before the splitter.
If you want to go the "leaky" coax way...use the same RG58 coax and cut slits into it near the end of the coax run, and terminate with a 50 ohm 1/4 watt resistor. Make the slit cut about 1/4 wavelength and ground shield intact. Only cut the ground shield of the coax just enough to create a "slot" so that the center conductor can emit the signal through the slot....and face the slot in the direction of where you need the signal to go.
If your going to go the multi-antenna method...there are proper ways to do this so that you phase these antenna bays correctly. It will require a phasing harness which can be made with coax and T fittings. But by the time that flea signal reaches the phase harness and T fittings, especially if it is some distance from the TX...you will end up with the same results as if using a single short whip connected directly to the TX.
I believe the leaky coax method will give you far better results and easier to maintain the 200 foot and 250 microvolt per meter limit.
RFB
because, as I posted earlier, the coax was already installed from my basement to the second floor and it had been abandoned from cable feed use years ago.
It is RG6 but so what? The loss compared to RG58 is negligible since with a perfect 50 ohm antenna the SWR is only 1.5:1. My antenna is purposefully short (about 8 inches) to create a severe mismatch with the coax as a means of limiting the range. It doesn't make sense to me to optimize the system and then pad it to restrict range when what I did accomplished the same end very simply.
This was one of those "try it and see if it works" projects and it worked.
Neil
This was one of those "try it and see if it works" projects and it worked.
Excellent. Glad that worked out. I was suggesting the leaky coax method to prevent any issues with excessive range produced by the dual antenna setup, but I also mentioned about using in-line attenuators with the dual antenna setup to help keep that range within the limitations of the 250 microvolt/meter rule.
In any case...thats fantastic that the problem got solved! 🙂
RFB
RFB, OK, I thought you misunderstood what I was doing. Your suggestions are a guide to optimizing performance and add to the body of knowledge.
Neil