This month I want to report an unexplained DTV reception difficulty that I newly experienced. I did not compose this up until I learned from an additional retired Tektronix engineer that he can not receive one of our local DTV signals v a rooftop antenna. That asked me around probable causes and also I told that of my experience. That reported the by instead of his balun he currently receives all local stations. With a score of 2 out that two, perhaps others may have actually this problem, too, and have not even suspected the cause. Anyone thinks around baluns?
All rooftop antennas were designed because that 300-ohm pair lead. Together everyone currently uses 75 ohm coaxial cable for their downlead, most outdoor antennas come through a balun, which has actually an intake impedance that 300 ohms (matching the calculation impedance the the rooftop antenna). The balun transforms from 300 ohms to 75 ohms by means of a balanced-to-unbalanced transformer. It is called a “balun to unbalanced” device.
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This matches the 75 ohm impedance of RG 59 and also RG6-U coax cables. The insertion lose of these baluns in much less than 1 dB, but mine measured end 7 dB. The was full of water! I argued that maybe the engineer’s problem can be a “water-logged” balun.
He has actually just informed me the his balun was without doubt defective and, upon instead of it, he now receives all our neighborhood stations. He sent the defective unit come me and also I found an open winding, i m sorry I doubt was because of corrosion, again because of rain water.
When you examine among these baluns it appears to it is in water-tight, however with exposure come both rain and sun over time, water may gain inside and also ruin it.
I suspect water-logged baluns will certainly be simply as lossy at high VHF frequencies as we have found them come be for UHF channels. I also expect that there are countless old baluns the end there that should be replaced.
As displayed in Fig. 1, as soon as I replaced my wet balun, I set up the brand-new one in a PVC pipe. The 1-1/4-inch PVC pipe has actually a PVC pipe cap cemented in place and the balun is now out the the weather and also out that the sun, too.
My girlfriend did the same thing, so no of us will ever before have to carry out it again.
F-CONNECTOR PROBLEMSWhile ~ above this topic of enhancing DTV reception, a colleague and I have discovered that in the day-to-day checking of our RF check bed, i beg your pardon feeds DTV signal to 26 DTV converter boxes, one or much more of castle exhibits abnormally low sensitivity.
Fig. 1: Rain-proof enclosure of PVC pipe for the brand-new balun an installed on the antenna mast. The white cable is RG6-U come the receiver. The dark flat ribbon is the 300-ohm pair lead from the antenna come the balun within the brand-new enclosure.
The problem is solved either by tightening the F-connector or by loosening the Fconnector, rotating the coax cable ago and soon a couple of times and also then re-tightening the F-connector. Just finger tight is not satisfactory, we’ve found. We use a little wrench.
I would favor to hear from mine readers about their very own experiences with F-connectors and also baluns. Numerous folks out there have a marginal signal on one or more channels. We’ve seen a readjust in sensitivity of up to 3 dB when we assault the F-connectors as outlined above.
In our experimentation regimen, we begin with the wanted signal listed below threshold and increment the D power in little steps to find the threshold power of each unit every time we operation experiments. That is how we detect this F-connector problems.
I suspect countless of her viewers space experiencing intermittent reception due one of two people to wet baluns or poor connections in between the coax and also the receiver, or both. I’d prefer to pass your experiences along to various other readers.
Charles Rhodes is a consultant in the field of television broadcast technologies and also planning. He deserve to be got to via email atcwr