Most emails I obtain from readers relate to over-the-air TV reception in a technique or one other—viewers and broadcasters alike wish to know the best way to maximize reception. This month I’ll have a look at how protection (and reception means) is calculated and a few methods to maximise reception. When the FCC outlined the protection for DTV stations, they relied on the planning components really helpful by the ATSC and the previous ATTC (Advanced Television Test Center). The planning components are the premise for a hyperlink funds for over-the-air reception, taking a look at positive factors, losses and thermal noise. Table 3 (Fig. 1) from the FCC’s Office of Engineering and Technology Bulletin 69 reveals the weather used for figuring out reception. These planning components resulted within the FCC setting a required area power of 28 dBµV/m for low VHF (Channels 2–6) and 36 dBµV/m for excessive VHF (7–13). Fig. 1: Table 3 from the FCC’s Office of Engineering and Technology Bulletin 69 (Image credit score: Doug Lung)At UHF, the sector power in dBµV/m is decided by the components: 41–20 log[615/(channel mid-frequency in MHz)] The planning components don’t embody an antenna top, however FCC guidelines specify that 9.1 meters (30 ft) be used when calculating protection.New Sources of NoiseThe parameters within the planning components could have matched client TV antenna setups 30 years in the past, however they don’t match what viewers count on to have the ability to use to obtain over-the-air TV at present. For VHF channels, the contribution of domestically generated electrical noise from LED lamps, motors and switching energy provides isn’t included. Compare the show on a spectrum analyzer with and with out the antenna related and you will notice the impression of native noise sources. In my expertise this noise can fully wipe out VHF TV reception on indoor antennas except the sign stage from the transmitter may be very excessive. The antenna acquire numbers clearly seek advice from outside antennas—indoor antennas usually have little or no acquire, if any. On the plus facet, with indoor antennas there may be little downlead line loss. Finally, the planning components don’t bear in mind the loss from a discount in top or the loss getting right into a constructing. The late Charlie Rhodes offered a superb description of those losses in his 2009 TV Tech column “Obstacles to DTV Reception.” The sign distinction between a rooftop antenna and one within the household room was 31 dB at UHF. Removing the ten dB antenna acquire and including again within the 4 dB for line loss leads to a sign requirement that’s 37 dB stronger than that calculated with the planning components and FCC antenna top. If we use 41 dBµV/m because the FCC required area power, including within the further losses means a area power of at the very least 78 dBµV/m will probably be required for indoor reception. This is in step with the “simple indoor” area power of 80 dBµV/m used on the rabbitears.information web site and the 75.5 dBµV/m requirement Meintel, Sgrignoli & Wallace decided primarily based on some restricted early indoor measurements of DTV alerts. I exploit 88 dBµV/m as a reference stage for simple indoor reception to permit for non-optimum antenna placement. For particulars on the calculation of constructing losses, Google ITU-P2040-2, which was up to date in October 2021. Note the variations in loss with completely different polarization—the graphs clearly present the benefit of elliptical or round polarization. Location, Location, LocationWhat could be accomplished to maximise reception? Antenna location might be probably the most important factor, putting it in a location as free as attainable of obstacles. This means avoiding bushes (notably pine bushes) outdoors and minimizing the variety of partitions the sign should cross by with an indoor antenna. Higher isn’t at all times higher. Ground reflections or reflections from buildings can arrive on the antenna out of section and cancel out a part of the TV band. Lowering the antenna will remedy this downside. Ron Shinno, the engineer who maintains the translators for PBS Hawaii on the island of Hawaii, instructed me a couple of case the place a viewer had an antenna excessive within the air, but it surely was aimed proper at a tree, blocking the sign. Lowering the antenna beneath the extent of the leaves on the tree introduced the sign again. I’ve seen circumstances the place reflections from a rooftop or steel construction canceled out a band of frequencies. When I visited with engineers at KXAS-TV in Dallas, they instructed me about one viewer who had issue receiving their OTA sign and a fast examine with a spectrum analyzer confirmed a deep null on KXAS-TV’s channel and adjoining stations. The viewer wasn’t within the adjoining channels so noticed this as a station downside, which he solved by reducing his antenna to a foot or two above the roof line. Raising it greater would possible have labored as nicely however wasn’t an choice. Use a Spectrum AnalyzerUnfortunately, it’s virtually inconceivable to optimize indoor antenna location utilizing a TV set alone, particularly if there isn’t line of sight to the transmitter website. A area power meter will help however received’t present multipath—a spectrum analyzer is required. With the tinySA spectrum analyzer (www.tinysa.org/wiki) accessible for solely $60 from R&L Electronics, there is no such thing as a excuse for not having one. While the planning components use a noise threshold of 15 dB for reception, any multipath will cut back this considerably as a result of the adaptive equalizer within the receiver has so as to add acquire (and noise) to fill within the nulls created by the multipath. Fig. 2 reveals the plot of a well-located Winegard Freevision FV30-BB antenna. If the antenna was choosing up multipath, the spectrum would have had ripples in it, with the spacing of the ripple depending on the gap of the reflection and the amplitude on the power of the reflection. Fig. 2 reveals the plot of a well-located Winegard Freevision FV30-BB antenna (Image credit score: Doug Lung)When orienting an antenna with a spectrum analyzer, look for the flattest response on the specified channel and throughout the TV band (the lean on the higher finish of the channel is because of an LTE filter). The antenna referenced in Fig. 2 has a Winegard LNA-200 LNA on the antenna. Winegard claims a noise determine of 1 dB for this LNA, which reduces the system noise to lower than the 7 dB specified within the planning components. I exploit the spectrum analyzer to search out the perfect spot and orientation for my indoor antenna in a resort room when touring. Where attainable I attempt to get a room dealing with the transmitter website, which makes issues simple, however in some circumstances that’s not attainable. In one resort room in Albuquerque, N.M., I discovered I needed to have the antenna in three completely different locations within the room to get completely different channels, all transmitting from the Sandia Crest Tower Farm. Without the spectrum analyzer, I wouldn’t have been capable of finding a location with sufficient sign from a few of the stations for the tuner to lock onto. My present selection for a journey antenna is the Walmart onn. Indoor High-Quality Clear HDTV Antenna accessible in most shops for lower than $20. Walmart onn indoor high-quality clear HDTV antenna (Image credit score: Walmart)The planning components listed below are for ATSC 1.0. If you’re questioning about ATSC 3.0, most ATSC 3.0 stations are working with parameters that require a noise threshold much like that for ATSC 1.0, so these examples and required area strengths would apply to ATSC 3.0 as nicely. However, in ATSC 3.0, stations can change modulation and coding parameters to work at a a lot decrease noise threshold, increasing protection. This is particularlybeneficial for LPTV and Class A TV stations which might be restricted to a most efficient radiated energy of 15 kW. I confirmed an instance of how to do that on the NTA convention in Salt Lake City in May 2021. Look for particulars in a future column. As at all times, I welcome feedback and questions. Email me at [email protected]. I attempt to reply all emails promptly, but when I’m busy and the e-mail will get buried, I would miss it. If you don’t get a response inside per week or so, e-mail me once more.
https://www.tvtechnology.com/opinion/maximizing-reception-for-over-the-air-tv
