How To Set Up Antenna On Sharp Tv

The Pocket-size Vertical Loop Antenna for HF Reception

Matt Roberts - matt-at-kk5jy-dot-net

Published: 2022-01-13

Updated: 2022-09-26

My original interest in small receiving loops was focused on two-element arrays of such elements, used to course a phased assortment for improved receive performance on the HF bands. The individual elements of that antenna design were simple wire loops, very small compared to the wavelengths to be received, and not resonated nor tuned for any of the bands where it is used. Such arrays tin compete with enormous Drinkable antennas many times their size. However, even a single wire loop of this type can exist a very effective HF receive antenna for long wavelengths, offering a substantial advantage over many types of transmitting antennas for HF reception. Equally such, information technology deserves some additional discussion of its own.

The lossy, untuned, electrically-pocket-sized antenna, whether a vertical, loop, or horizontal dipole, turns out to be an excellent transducer for HF skywaves. The efficiency of such an antenna is very low, sometimes on the club of dozens of dB below an isotropic antenna. Yet, information technology turns out that the low efficiency actually helps to improve the overall indicate-to-dissonance ratio of received signals. The reasons for this are best discussed in another article, but information technology should suffice to say that HF operators have known nearly the desirable properties of lossy receieve antennas since the primeval days of radio, and the Beverage antenna is but one case of a family unit of antennas that exploit low efficiency to meliorate the SNR of skywave signals.

A small, vertical, untuned (nonresonant at the desired reception frequency) loop antenna is essentially a compact vertically-polarized antenna that is self-independent, and does non require radials or counterpoise. The loop can be placed in relatively close proximity to the ground, although its overall blueprint shape is like to what you might expect from a dipole that is raised to nearly λ/2 to a higher place the ground. The ground dependence of a vertical loop element is very low, with the main effect of the ground being its influence on far-field gain (efficiency). Since we will assume the efficiency of the antenna element to be already low, given its small size with respect to wavelength, this effect on efficiency is not critical to the antenna.

For the purposes of this commodity, I will refer to such an untuned electrically-small loop antenna, used only for receive, every bit a "modest receiving loop," or SRL. There are a number of antenna types that could be considered to exist a small receiving loop, but herein I am referring just to those loops that see the clarification above.

Far-field patterns for the 40m, 80m, and 160m bands for a SRL are shown in Figure ane through Figure 9. The loop being modeled is diamond-shaped, 30in (ii.5ft) per side, and fed at the bottom corner. The loop base of operations is approximately five feet (v') above basis, which places its acme corner at almost eight feet (8') in a higher place ground. An case of such a loop is shown in Figure 10. Click on each figure to overstate.

Figure one: 40m Summit Pattern (Peak Elevation)	Figure 2: 40m Elevation Pattern (-3dB Elevation)	Figure 3: 40m Azimuth Blueprint (-3dB Acme)

Figure 4: 80m Top Blueprint (Meridian Elevation)	Figure 5: 80m Superlative Blueprint (-3dB Elevation)	Figure 6: 80m Azimuth Design (-3dB Elevation)

Effigy seven: 160m Elevation Pattern (Pinnacle Acme)	Figure 8: 160m Elevation Design (-3dB Height)	Effigy ix: 160m Azimuth Pattern (-3dB Tiptop)

Figure 10: Loop Element

Loops are "balanced" antennas, and when fed from coaxial cable, they require conscientious decoupling from the outer usher surface of the feedline. The SRL shown in Effigy ten is directly-driven, using a coaxial feedline choke at the feedpoint to prevent RF pickup from the coax shield. I later replaced the choke with a DC-isolated Drinkable antenna transformer (Figure eleven), similar those used by W8JI for his Potable antennas. This is the same type of transformer I used on the loop-on-basis blueprint, and information technology is the same blueprint used past DXE for their commercial version of W8JI's device. The Potable transformer did a much improve job of preserving the loop's rather sharp nulls—and over a broader range of frequencies—than the asphyxiate. The transformer DC-isolates the antenna element from the feedline, and provides a DC-shorted feedpoint, which is prissy for preventing any static build-up.

Figure 11: Hand-fabricated
Isolation Transformer

At start glance, the elevation patterns appear unremarkable; in fact, they are somewhat like to the "cloud warmer" pattern of a low dipole antenna. The azimuth plot also seems to back up that assessment. However, if you look closely at the shape and supporting data on each plot, you volition encounter that these are not typical NVIS patterns. In fact, the -3dB elevation angles for the 40m, 80m, and 160m bands are x.3°, 7.8°, and 5.viii°, respectively. These are not NVIS angles -- these are DX angles.

What does that hateful in real life? It means that the SRL is able to receive skywave signals with consistent gain at almost all inflow angles. Its low-angle response is better than most vertical monopole antennas, making it a very capable DX antenna. However, because the high-bending design is also intact, the antenna can also hear NVIS signals with very similar gain figures. This makes the antenna an all-purpose device for reception. Most antennas are either practiced at loftier- or low-bending reception, only non both. Those that can hear low-bending skywaves have enormous gain differences between the low angles and the higher angles above them. This ways that DX signals appear at the receiver with far less free energy than the higher-angle domestic signals, making it sometimes difficult to "dig out" the DX signals from the much stronger domestic stations surrounding them. The more even gain distribution of the SRL tends to equalize the SNR of received signals, to present them at the receiver at a more consistent strength.

Simply that's not all. The azimuth design of the SRL has two nulls in information technology, much like a dipole antenna. And like a dipole antenna, these nulls emit from the "sides" of the antenna. However, a dipole with this low-level pattern would have to be very high, between λ and λ/two to a higher place the ground. That places the center axis of the dipole'due south nulls also very high in the air. In contrast, the SRL's null axis is close to the ground level, where it can exercise the near skilful rejecting local QRM. The high dipole will exist quite "good" at hearing QRM at negative angles off its ends, such equally from a neighboring house, while the SRL has a ameliorate gamble of nulling out such signals.

Where the small receive loop really shines is in Due south/N optimization for skywave signals. Even in an interference-free environment (if such a place exists), the high-loss nature of the untuned small receiving loop allows information technology to hear autocorrelated signals better than it hears the random dissonance around those signals. Users of short untuned vertical antennas accept reported similar furnishings when they deliberately load their vertical antennas with resistive loss. The result is that listening to signals on a small-scale vertical loop tin yield a better indicate-to-dissonance ratio for the signals nosotros care virtually (CW, SSB, RTTY, PSK, etc.).

Effigy 12: Panadapter on 40m CW

Panadapter 40m FT8
Figure xiii: Panadapter on 40m FT8

40m DX Map
Figure xiv: 40m Coverage (12 Hours)

Figure 12 shows a sample of the functioning of the SRL while used on the 40m CW ring during a particularly decorated evening. The antenna was indoors, close to numerous electronic devices, and still provided an fantabulous SNR and low racket floor. Compared to the other antennas I had bachelor at the fourth dimension for 40m, the SRL's SNR performance was by far the best. While there is zilch "magical" about this antenna, the SNR comeback lone tends to cause signals to naturally lift out of the noise.

In late 2022, I did some all-encompassing experiments with FT8 and this antenna. I moved the antenna into an open surface area of my yard, and turned it to null out some interference from what I suspect is a noisy light anchor in a neighbour's house. Using a 33' vertical antenna for transmitting, and the SRL for receiving, I was able to make effectually 4,000 contacts in just over a month'south time, across the 15m, 17m, 20m, 30m, 40m, 80m, and 160m bands. The antenna produced excellent point levels using just the 10dB preamplifier congenital into my TS-590SG. I had intended to add a mast-mounted preamplifier, but I however haven't gotten around to it, because information technology hasn't yet been needed. Effigy xiii shows a sample of WSJT-X running FT8 on 40m with the SRL fastened. Effigy 14 shows a typical coverage map using the SRL over approximately twelve hours.

Using a single loop element has definite advantages over a ii-element array. First, it allows simultaneous reception from opposing azimuth angles. Here in the central US, most amateur signals tend to arrive from the east and from the west. A single SRL chemical element will hear both NVIS and DX signals from both the east and west simultanously. This provides wide geographic coverage from a single antenna, while simultaneously improving Due south/N ratio and providing 2 about horizontal nulls that tin be rotated to remove a specific interference source that might exist closeby.

The performance of a single SRL approximates an unterminated Potable antenna many times its size, while providing the extra advantage of being rotatable. In dissimilarity, the two-element array approximates the performance of a terminated Beverage antenna, which is largely unidirectional.

There are uses for both the a single-element SRL and the two-element phased array version. While the ii-element array provides the extra directivity that many people seek from a receive antenna, the single-element loop still has plenty of advantage over nearly transmit antenna types, such as a full-sized vertical. My ain location is virtually unusable on 160m when using a vertical antenna for both transmit and receive. Yet, when using defended receive antennas, 160m comes alive with signals during major operating events. The usefulness of elementary receive antennas such every bit this should not be underestimated.

In that location is aught special well-nigh the 30" foursquare that I used for my prototypes. I chose a size that was electrically small for the wavelengths where I wanted to operate, and also a size that was easy to measure out, construct, and behave. A smaller SRL volition generate lower bespeak levels, but it will provide deeper nulls to the sides. A larger SRL volition generate more signal, but take less attenuation in the nulls. The size can thus be chosen to balance the needed signal level with the directivity desired. I prefer to have enough betoken to "set up the dissonance" in my receiver when I connect the antenna. If one prefers an antenna that has very deep nulls, and is willing to add together a preamplifier, a much smaller loop tin can be designed that will provide similar signal levels at the receiver. If a preamplifier is used, a model with the everyman practical noise figure should be selected.

Combination devices, consisting of an SRL and a broadband, mast-mounted preamplifier are readily avaiable from a number of manufacturers. Unfortunately, most such devices are quite expensive, and every bit a result, the SRL design doesn't receive the attention information technology deserves. I found that by properly sizing the loop element, and using quality depression-loss coaxial cable, I could forego the preamplifier, or use the preamplifier built into the radio, thus eliminating the bulk of the price of a quality commercial SRL. This makes the loop much less expensive to construct, and information technology as well removes a mutual point of failure, since a mast-mounted preamplifier is decumbent to failure due to static, nearby lightning strikes, temperature extremes, and other such environmental abuse.

If materials are advisedly selected and assembled, a single-element quality SRL can be built for only a few dollars, including the isolation transformer, and have performance every bit equally expert as its $500 commercial brethren. Past using quality coaxial cable, such as flooded F6 cable TV coax, losses can be kept very minimal, eliminating the demand for a preamplifier. Such cablevision is widely available, and very cheap, considering the cable and satellite manufacture uses tons of the stuff for customer installations, so information technology is widely mass-produced. Retrieve, if the receiver racket level goes up when attaching any receive antenna, the antenna system as a whole is generating more than plenty signal to drive the receiver, and a preamplifier is non needed anywhere in the signal path. Constructing a loop that tin generate sufficient signal levels, and and then combining that with low-loss cable to preserve that bespeak all the manner to the receiver, will provide superior performance to any antenna with a mast-mounted preamplifier, because the preamplifier itself will raise the noise floor, canceling some of the SNR improvement that the antenna is supposed to provide.

When I started tinkering with this antenna, I had but nearly given upwardly on HF radio, because of the abiding fight with RFI and the uneven racket floor that I would ofttimes see due to all of the electronics and ability lines that surround me. I don't have room for Beverage antennas, and even a shortened Drink would accept to extend near up to the walls of the neighbors' houses. I built the offset small vertical loop on a whim, simply to see what it might be able to hear, and was shocked to discover that information technology was not only not deaf, but it could hear improve than my total-sized antennas. The signal levels are lower, but the SNR is much better. Since that time, I take spent almost of my ham radio fourth dimension experimenting with non-Beverage receive antennas. This projection led me to experiment with another very effective receive antenna pattern, the loop-on-ground antenna, which I have used successfully on bands from 160m to 20m. The experimentation continues, but I am finding that everything I thought I knew near antennas goes out the window when trying to receive HF skywaves, particularly on the longer wavelengths. The ability of a minor slice of wire, when properly sited and synthetic, to ameliorate the reception of HF skywaves continues to amaze me. Needless to say that I would non still be on HF without such antennas.