This month I want to report an unusual DTV reception problem that I newly experienced. I did not create this up until I learned from an additional retired Tektronix engineer the he could not receive one of our local DTV signals with a rooftop antenna. The asked me about probable causes and I told the of my experience. That reported that by replacing his balun he currently receives all neighborhood stations. With a score of 2 out the two, possibly others may have actually this problem, too, and also have not even suspected the cause. Whoever thinks around baluns?
All rooftop antennas to be designed because that 300-ohm pair lead. As everyone now uses 75 ohm coaxial cable for their downlead, many outdoor antennas come v a balun, which has actually an intake impedance of 300 ohms (matching the output impedance the the rooftop antenna). The balun transforms from 300 ohms to 75 ohms by method of a balanced-to-unbalanced transformer. The is dubbed a “balun to unbalanced” device.
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This matches the 75 ohm impedance of RG 59 and RG6-U coax cables. The insertion ns of this baluns in less than 1 dB, but mine measured over 7 dB. The was complete of water! I suggested that probably the engineer’s problem might be a “water-logged” balun.
He has actually just notified me that his balun was certainly defective and, upon replacing it, he currently receives all our local stations. He sent the defective unit to me and I discovered an open winding, which I suspect was due to corrosion, again because of rain water.
When friend examine one of these baluns it appears to be water-tight, however with exposure to both rain and sun end time, water may gain inside and also ruin it.
I suspect water-logged baluns will be just as lossy at high VHF frequencies as we have uncovered them to be because that UHF channels. I additionally expect the there are countless old baluns out there that need to be replaced.
As displayed in Fig. 1, when I changed my wet balun, I installed the new one in a PVC pipe. The 1-1/4-inch PVC pipe has actually a PVC pipe cap cemented in place and also the balun is currently out of the weather and out of the sun, too.
My girlfriend did the same thing, so neither of us will ever have to perform it again.
F-CONNECTOR PROBLEMSWhile on this topic of boosting DTV reception, a colleague and also I have uncovered that in the day-to-day checking of ours RF test bed, which feeds DTV signal to 26 DTV converter boxes, one or an ext of lock exhibits abnormally short sensitivity.
Fig. 1: Rain-proof enclosure that PVC pipe for the new balun mounted on the antenna mast. The white cable is RG6-U to the receiver. The dark flat ribbon is the 300-ohm twin lead from the antenna to the balun within the brand-new enclosure.
The difficulty is fixed either by tightening the F-connector or by loosening the Fconnector, rotating the coax cable ago and forth a few times and then re-tightening the F-connector. Just finger chop is no satisfactory, we’ve found. We use a tiny wrench.
I would like to hear from my readers around their very own experiences v F-connectors and also baluns. Numerous folks out there have actually a marginal signal ~ above one or more channels. We’ve checked out a change in sensitivity of approximately 3 dB when we attack the F-connectors as outlined above.
In our experimentation regimen, we begin with the desired signal below threshold and also increment the D strength in little steps to uncover the threshold strength of every unit every time we run experiments. That is just how we detect this F-connector problems.
I suspect plenty of of your viewers room experiencing intermittent agree due one of two people to wet baluns or negative connections between the coax and the receiver, or both. I’d prefer to pass her experiences along to various other readers.
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Charles Rhodes is a consultant in the field of tv broadcast technologies and planning. He deserve to be got to via email atcwr