AU2018203890B2 - An antenna for receiving broadcast signals - Google Patents

Abstract

An antenna for receiving a UHF signal and a VHF signal, including: a first receiving element for 3 receiving the UHF signal; a second receiving element for receiving the VHF signal; and a multiplexer for frequency-multiplexing the UHF signal and the V HF signal to produce an output signal at an output of the antenna.

Description

AN ANTENNA FOR RECEIVING BROADCAST SIGNALS FIELD OF INVENTION

The present invention relates to an antenna for receiving broadcast signals.

INCORPORATION BY REFERENCE

This patent application is a divisional application from Australian patent application no. 2016202547, filed 21 April 2016, and which claims priority from Australian Provisional Patent Application No. 2011904892, entitled "An AntennaforReceivingBroadcastSignals"filed 23 November 2011, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Information, including video, voice and music, is often broadcast from transmission towers for entertainment, commercial, non-commercial or emergency purposes. To receive such in formation, a receiver or an antenna is used. The received information is then sent to a television, radio, electronic device or computer which will in turn present the information to one or more persons.

To be able to broadcast different information at the same time without interference, different information is transmitted using different frequencies. Television programmes are often broadcast in VHF band 3 and UHF band 4, in either analogue or digital form. Within a band, different programmes occupy different channels. Thus, if one would like to receive or watch a particular program, one would need to use a receiver or an antenna which can effectively receive a signal within a particular frequency channel or frequency band in which the particular program is being broadcast, and use a tuner and a decoder to retrieve the information from the receive signal. If the receiver or the antenna cannot effectively receive that frequency channel or frequency band, the information is distorted, misinterpreted or lost.

To receive information in both VHF and UHF bands, it is common to use two separate UHF and VHF receiver or antennas, both connected to the receiver. A selector may be used so that only one of the antennas is connected to the decoder at one time but usually a diplexer is used so that the output of the UHF antenna and the output ofthe VHF antenna are frequency-multiplexed into a single signal to the decoder.

A combined VHF and UHF antenna (a combination UHF/VHF antenna) is also known. In this case, the combined antenna has elements suitable for receiving VHF signals and also elements for receiving UHF signals. The signals from these elements are fed into a single output, which is connected to a receiver/decoder.

BRIEF SUMMARY OF THE INVENTION ) According to a first aspect of the present invention, there is provided an antenna for receiving a UHF signal and a VHF signal, including: a first receiving element for receiving the UHF signal; a second receiving element for receiving the VHF signal; and a multiplexer for frequency-multiplexing the 5 UHF signal and the VHF signal to produce an output signal at an output of the antenna, wherein the second receiving element includes a VHF dipole array including at least a first VHF pole and a second VHF pole extending from, and perpendicular to, a plane defined by a printed circuit board (PCB) of the multiplexer, wherein an axis of the first pole is offset from an axis of the second pole.

In one form, the multiplexer includes filters provided by PCB tracks.

10 In one form, the antenna of the first aspect further includes a first matching circuit for improving an impedance matching between the first receiving element and a cable connected to the output of the antenna. In one form, the first matching circuit includes a transformer.

In one form, the antenna of the first aspect further includes a second matching circuit for improving an impedance matching between the second receiving element and a cable connected to the output of the 15 multiplexer. In one form, the second matching circuit includes parallel PCB tracks. In one form, the first receiving element includes a dipole. In one form, the dipole includes a first pole and a second pole extending from, and perpendicular to, a plane defined by a PCB board of the multiplexer. In one form, an axis of the first pole is offset from an axis of the second pole. In one form, the first receiving element includes a UHF Yagi array and the second receiving element includes a VHF dipole array, 20 wherein the VHF dipole array provides a reflecting element for the UHF Yagi array. In one form, the second receiving element includes a forward dipole. In one form, the antenna further includes a capacitive element for effectively shorting the forward dipole such that the forward dipole operates as a reflector at UHF frequencies for the first receiving element. In one form, the antenna further includes an active component to amplify the UHF signal and/or the VHF signal.

25 According to a second aspect of the present invention, there is provided a multiplexer for frequency multiplexing a UHF signal and a VHF signal having a printed circuit board (PCB), the multiplexer including: a first input for receiving the UHF signal from a first receiving element; a second input for receiving the VHF signal from a second receiving element; filters for frequency-multiplexing the UHF signal and the VHF signal to produce a multiplexed signal; an output for providing the multiplexed 30 signal; wherein the second receiving element includes a VHF dipole array including at least a first VHF pole and a second VHF pole extending from, and perpendicular to, a plane defined by the PCB of the multiplexer, wherein an axis of the first pole is offset from an axis of the second pole.

In one form, the filters are provided by PCB tracks. In one form, the second matching circuit includes parallel PCB tracks. In one form, the multiplexer further includes a capacitive element for effectively shorting an element of the second source at UHF frequencies.

According to one embodiment of the present invention, there is provided an antenna for mounting onto a PCB board, including a first pole and a second pole extending from, and perpendicular to, a plane defined by the PCB board, wherein an axis of the first pole is offset from an axis of the second pole.

BRIEF DESCRIPTION OF THE FIGURES Figure I depicts a UHF VHF antenna with an internal diplexer according to the present invention; Figures 2A and 2B depict functional block diagrams of a diplexer; Figure 3 depicts one embodiment of a circuit layout of the diplexer; Figure 4 depicts a UHF dipole mounted on the diplexer; Figure 5 depicts UHF characteristics of the diplexer of Figure 3 as measured; Figure 6 depicts VHF characteristics of the diplexer of Figure 3 as measured; Figure 7 depicts another antenna suitable for receiving a UHF signal and a VHF signal; Figure 8 depicts yet another antenna suitable for receiving a UHF signal and a VHF signal; Figures 9(A) to (C) depict different views of a diplexer with parts of the UH-F and VHF antennas disconnected; Figure 10 depicts an example PCB of an active diplexer; and Figure 11 depicts UHF and VHF characteristics ofthe diplexer as shown in Figure 10.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Figure I depicts an antenna 101 suitable for receiving a UHF signal and a VHF signal. The antenna includes a portion which is designed to receive a UHF signal, and another portion which is designed to receive a VHF signal. The portion designed to receive a UHF signal is shown as a UHF Yagi antenna 103. The portion designed to receive a VHF signal is shown as a VHF dipole array 105. While the VHF dipole array 105 coupled with a UHF Yagi antenna 103 is a particularly useful combination for the invention because their conventional feed points are adjacent, any one of the portions can be of any other antenna type deemed appropriate by a person skilled in the art. For example, the portions can be a simple dipole, folded dipole, V-shaped dipole, dipoles arranged in various forms (Yagi, simple array, stacked, log-periodic array), a reflector/dish antenna etc.

The UHF signal and the VHF signal need to be sent to a decoder so that the information carried by or contained within the UHF signal and the VHF signal (such as information modulating the carriers of the UHF signal and the VHF signal) can be recovered and presented in a meaningful way to a person interested or intended to receive thatinformation.

It is possible to simply combine the UHF signal and the VHF signal so that only one physical medium (i.e. cable, wire etc.) is required to send the signals from the antenna to the decoder. However, the quality of the combined signals may be degraded due to noise and distortion introduced during the combination of the signals, and thus affecting the decoding process and the presentation ofthe information.

A technique is to frequency-multiplex the UHF signal and the VHF signal prior to sending the signals through a physical medium. A device for frequency-multiplexing two signals different frequency bands is known as a multiplexer. If there are only two input signals to be multiplexed, the device is also known as a diplexer.

A diplexer serves to defeat the signals from each portion of the antenna that are within the intended operating band of the other portion of the antenna. in other words, noise contributed by unwanted in band reflected signals that are gathered from off-boresight directions due to an uncontrolled out-of band radiation pattern is suppressed.

A system with a UHF antenna and a VHF antenna connected to a standalone diplexer with the output of the diplexer connected to a decoder exists. The present invention differs from known antennas or antenna systems in that a diplexer 107 is incorporated into a UHF and VHF antenna 101 so that there D is only one output 109 from the antenna. The present invention is not a mere combination of a UHF antenna, a VHF antenna and a diplexer, and does not require external cables (for example a coaxial cable) to connect the diplexer to the VHF and UHF antenna terminals. A person skilled in the at would understand that performance ofan antenna may be greatly affected if a conductive object is present at a close proximity to theantenna. Thus, incorporation of a UHF antenna, a VHFantenna and a diplexer as a single antenna item requires careful simulation, design, and testing.

In one embodiment, the UHF portion (which is a UHF Yagi 103 in this embodiment) andthe VHF portion (which is a VHF dipole array 105 in this embodiment) of the antenna are arranged with one or more capacitors coupling the transmission line of the VHF dipole array 105 (see Figure 2B where, at least capacitor 271 is coupling the transmission line). This allows an electrical short of part of the VHF dipole array 105 over the UHF operating band, thus allowing it to serve as a reflector element for the UHF Yagi 103. This eliminates the need for a separate reflector element and its potentially negative effect on the performance of the VHF dipole array 105.

Figure 2A depicts a functional block diagram of a diplexer 200. The diplexer includes a first input port 201 fbr connection with a first antenna, and a second input port 203 for connection witha second antenna, and an output port 205 for connection with a decoder. The input/output ports 201, 203, 205 can take many forms, but more commonly, take the form ofcoaxial male/female connector. The first input port 201 connects the first antenna to a first matching circuit 207, and the second input port 203 connects the second antenna to a second matching circuit 209. The output 211 of the firstmatching circuit 207 is connected to a first filtering circuit 213, and the output 215 of the second matching circuit 209 is connected to a second filtering circuit 217. The first filtering circuit 213 and the second filtering circuit 217 have different transfer functions,such that a selected band of frequency components of a signal from the first antenna and a selected band of frequency components from the second antenna (with both selected bands not overlapping) can co-exist without interfering each other in an output signal at the output port 205 of the diplexer.

Figure 2B depicts one embodiment of a diplexer 200, with reference to the functional block diagram of Figure 2A, suitable to be incorporated into a UHF VHF antenna. In particular, the first input port 201 is for connection with a UHF antenna 251; the second input port 203 is for connection with a VHF antenna 253; the first matching circuit 207 is a transformer 255 for matching the UHF antenna 251 to a cable or wire to be connected at the output port (typically 75C, or 50a of impedance); the second matching circuit 209 is a balun matching circuit 257 for matching the VHF antenna 253 to a cable or wire to be connected at the output port 259(typically 750, or 500 of impedance); the first filtering circuit is a high pass Filter 263, and thesecond filtering circuit 217 is a low pass filter 267, allowing the UHF band of interest, and the VHF band of interest to be multiplexed.

!0 Figure 3 illustrates one embodiment of a circuit layout of the diplexer. in this embodiment, the matching circuits and the filtering circuits are effected by printed circuit board (PCB) tracks 301. However, it is also possible to introduce discrete components, such as inductors and/or capacitor(s) 303, to provide part or all of the required inductance and/or capacitance. By implementing matching circuits and filtering circuits using PCB tracks predominantly, it is possible to improve the manufacturing process efficiency and reduce manufacturing costs.

As shown as one embodiment, the VHF matching circuit, a balun, is realised by means of parallel PCB tracks 311, which simulate the function of a bifilar winding The capacitive coupling within the winding has been achieved with surface mount devices (for example capacitor 303 which may range from I pF to 22pF in this embodiment), which provide more reliable characteristics than can be achieved in large-scale production than with twisted wires.

Figure 3 also depicts a set of values of the discre components with reference to the following Table 1.

Table 1: Values of discrete components in Figure 3 according to one embodiment of the present invention Label Value A Not connected B 4.7pF C 6.SpF D 1l5pF E 22pF F 3.3pF G IpF Z A short

By incorporating a balun between the coaxial cable and the transmission line of the antenna, it is possible to improve the matching ofthe impedance of the coaxial cable and the impedance of the transmission line of the antenna over the operating frequency.

In this case, the matching circuits aim to improve the impedance matching of the UHF antenna and VHF antenna to the transmission line linking the antennas and the decoder/receiver. A good match can reduce signal reflection and thus improve the strength of the signal. However, in practice, aperfect matching is not required, for example, the balun does not need to transform the impedance of the transmission line of the antenna to a true 751 over the operating frequency. This allows greater freedom to configure the antenna for optimum gain and pattern shape.

Without a balun coupling, the centre conductor and outer shield conductor of a coaxial cable connecting the antenna to a decoder/receiver(also known as a downlead cable) is attached directly to the ends of the transmission lines connecting the elements of the antenna. This means that the outer shield conductor of the coaxial cable may carry stray currents at the operating frequency of the antenna that will affect the performance of the antenna. In order words, the matching circuit also functions to convert the balanced output of the antennas to unbalanced signals to be sent through an unbalanced transmission line (such as a coaxial cable),

Figure 4 depicts a mounting of a UHF dipole onto the diplexer. The two poles 401, 403 of the UHF dipole are extending from, and perpendicular to, the PCB board 405 of the diplexer. The axes of the two poles 401, 403 are offset 407 from each other, in contrast with a conventional dipole configuration where the two poles are co-axial. The conventional co-axial poles are also often placed parallel to the plane of the PCB board, thus allowing a simple way ofsecuring the poles to the circuit board. However, such a conventional way generally requires several components such as saddles, washers, etc. to be stacked with the fastener, which makes the connection between the poles and the tracks on the PCB board more susceptible to failure vialoosening of the screw fixing or corrosion ofone or more of the required components in the current path.

This aspect of the invention may improve the manufacturing process in securing the poles to the PCB board without affecting much of the performance of the dipole. For example, the two poles as shown are secured by fasteners (fastener 409 with another fastener hidden by PCB board 405 and pole 403). While fasteners are shown in this example, the offset poles can be secured through riveting, soldering, bending, or any other means deemed appropriate by a person skilled in the art. The fset distance is approximately 16mm in the embodiment shown with reference to Figure 4. However, the offset distance may be varied with a minimum offset distance depends on, for example, the size of the poles, the size of the fasteners used etc. The maximum offset distance on the other hand depends on the required gain for an acceptable performance of the poles, as the gain of the poles has been shown to decline as the offset distance increases.

Figure 5 depicts UHF characteristics of the diplexer as shown in Figure 3 as measured by a network analyser. Trace 501 shows the return loss (Sl 1) of the UHF Balun, which shows how close the UHF antenna is matched to the coaxial cable; the lower the return loss the better the matching. In this case, it can be seen that the return loss is low 503 in the UHF range, thus the matching is good there. Trace '0 505 shows the transmission coefficient (S21) of the UHF filer, a higher transmission coefficient indicates minimal loss while a lower transmission coefficient indicates a higher loss. The y-axis 507 of the graph is in logarithmic scale, and thus a lower point of trace 505 indicates a smaller/lower number. In this case, it shows that VHF frequency components experience massive losses 509, and thus are effectively isolated, while the UHF frequency components experience minimal losses 511, and thus are effectively transmitted.

Figure 6 depicts VHF characteristics of the diplexer as shown in Figure 3 as measured by a network analyser. Trace 601 shows the return loss (SI 1) of the VHF Balun, which shows how close the V HF antenna is matched to the coaxial cable; the lower the return loss the better the matching. In this case, it can be seen that the return loss is low 603 in the VHF range, thus the matching is good there. Trace 605 shows the transmission coefficient (S21) of the VHF filter, a higher transmission coefficient

indicates minimal loss while ala wer transmission coefficient indicates a higher loss. The y-axis 607 of the graph is in logarithmic scale, and thus a lower point of trace 605 indicates a maller/lowr number. In this case, it shows that UHF frequency components experience massive losses 609, and thus are effectively isolated, while the VHF frequency components experience minimal losses 611, and thus arc effectively transmitted.

Figure 7 depicts another antenna 701 suitable for receiving a UHF signal and a VHF signal. The antenna includes a portion which is designed to receive a UHF signal, and another portion which is designed to receive a VHF signal. The portIon designed to receive a UHF signal is shown as a UHF Yagi antenna 703. The portion designed to receive a VHF signal is shown as a VHF dipole array 705. A diplexer 707 is incorporated with the UHF and VHF antennas, 703 and 707, such that diplexer 707, the UHF and VHF antenna 703 and 707 are compacted as antenna 701 with only one output 709 from the antenna 701.

Compared with the antenna 101 of Figure 1, antenna 701 is a compact version of antenna 101, and is suitable as a mobile antenna, for example, an antenna used in a caravan.

Figure 8 depicts another antenna 801 suitable for receiving a UHF signal and a VHF signal. The antenna includes a portion which is designed to receive a UHF signal, and another portion which is designed to receive a V HF signal. The portion designed to receive a UHF signal is shown as a UHF Yagi antenna 803. The portion designed to receive a VHF signal is shown as a VHF dipole array 805. A diplexer 807 is incorporated with the UHF and VHF antennas, 803 and 807, such that diplexer 807, the UHF and VHF antenna 803 and 807 are compacted as antenna 801 with only one output 809 from the antenna 801.

!0 Figures 9(A) to (C) are different views of diplexer 807 with parts of the UHF and VHF antenna, 803 and 807, disconnected. It can be seen that there is a small visual indication 811 near the output 809. The small visual indication 811 can be one or more LEDs. This small visual indication 811 is to indicate that the antenna 801 (of Figure 8) is working properly. It becomes beneficial when the diplexer 807 is an active diplexer, as the small visual indication 811 can indicate that the active components within the active diplexer are working as intended. A n example PCB of an active diplexer is shown in Figure 10. The part numbers/values of the components (active and passive) are also shown in Figure 10. Most of these part numbers/values representing resisters and capacitors are readily understood by a person skilled in the art. Those relatively uncommon part numbers/values include ODOR representing a short; NC representing no component; BLM471 representing surface mount ferrite beads; BFP620 representing transistor; 78L05 representing voltage regulator; and TCI-1-13M 75+ representing RF transformer.

Figures 9(A)to (C) also provide different views of the UHF dipoles 813 and 814 mounted onto the diplexer. Similar to Figure 4, the two dipoles 813 and 814 dipole are extending from and perpendicular to, the PCB board of the diplexer (hidden by the casing of the diplexer). The axes of the two poles 813, 814 are offset from each other with benefits explained with reference to Figure 4.

Referring back to the active diplexer with an example of its PCB shown in Figure 10, the active diplexer includes an amplifier for each of the UHF antenna and the VHF antenna. The amplifiers can take the form of an arrangement of one or more transistors (in this example, the amplifiers are push pull amplifiers, housed within the balun housing of the diplexer). It Is also possible for the amplilers to take the form of off-the-shelf operational amplifiers,

Each of the amplifiers is used to amplify low signals at the antenna terminals to a level whereby the receiver can detect and decode the signals. The amplifier can also function to filter out of band noise and interference as much as possible in order to provide a high carrier to noise ratio for the receiver.

The input of each of the amplifiers connects via a simple matching circuit directly to an antenna terminal (either of the UHF or VHF antennas). This arrangement provides a number of advantages: 1. Minimal losses before the active gain stage (the amplifier) because ofthe direct connection to the antenna terminals. This translates to superior system noise performance (lower system noise temperature compared to an antenna connected via a cable to a masthead amplifier); 2, Single stage push-pull amplification provides much lower risk of digital television (DTV) signal overload, compared to dual stage masthead amplifiers; and 3. Active gain stage provides extremely good common mode rejection, meaning that the balun can be very effective. !0 Figure I 1 depicts UHF and VHF characteristics of the diplexer as shown in Figure 10 as measured by a network analyser via a factory testjig. Traces shown in Figure 10 is different from those of Figures 5 and 6, in that Figure I 1 shows the characteristics of the diplexer, which includes the UHF and the VHF baluns; while Figure 5 and 6 show the characteristics of the UHF and VHF baluns respectively.

Trace 901 shows the output return loss (S22) of the diplexer, which shows how close the UHF and VHF antennas are matched to the coaxial cable; the lower the return loss the better the matching. In this case, it can be seen that the return loss is low 903 in the VHF range and low 905 in the UHF range, thus the matching is good in both VHF and UHF range. Trace 907 shows the transmission coefficient (S21) of the diplexer, a higher transmission coefficient indicates minimal loss while a lower transmission coefficient indicates a higher loss. The y-axis 913 of the graph is in logarithmic scale. It shows that both the VHF components 909 and UHF frequency components 911 experience gain (any value of more than 1 indicates a gain) due to the active components, and thus are effectively transmitted to the receiver.

A detailed description of one or more preferred embodiments of the invention is provided above along with accompanying figures that illustrate by way of example theprinciples ofthe invention. while the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications, and equivalents. For the purpose of example, numerous specific details are set forth in the description above in order to provide a thorough understanding ofthe present invention. The present invention may be practised according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

Throughout this specification and the claims that follow unless the context requires otherwise, the words 'comprise' and 'include' and variations such as 'compris ing' and 'including' will be understood to imply the inclusion ofa stated integer or group of integers but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge of the technical field.

Claims (15)

The claims defining the invention are as follows:

1. An antenna for receiving a UHF signal and a VHF signal, including: a first receiving element for receiving the UHF signal; a second receiving element for receiving the VHF signal; and a multiplexer comprising a printed circuit on a board for frequency-multiplexing the UHF signal and the VHF signal to produce an output signal at a signal output of the antenna, wherein the second receiving element includes a VHF dipole array including at least a first VHF pole and a second VHF pole extending from, and perpendicular to, a plane defined by the printed circuit board (PCB) of the multiplexer, wherein an axis of the first pole is offset from an axis of the second pole.

2. An antenna of claim 1, wherein the second receiving element is a VHF log periodic dipole array with VHF poles extending from, and perpendicular to, two parallel booms.

3. An antenna of claim 2, wherein the PCB is mounted between the two parallel booms.

4. An antenna of any one of claims 1 to 3, wherein the first receiving element includes a UHF dipole array and the UHF dipole array includes a first UHF pole and a second UHF pole extending from, and perpendicular to, a plane defined by the PCB board of the multiplexer and an axis of the first UHF pole is offset from an axis of the second UHF pole.

5. An antenna of claim 4, wherein the UHF dipole array is a UHF Yagi array and the VHF dipole array is a VHF log-periodic dipole array.

6. An antenna of any one of claims 1 to 5, wherein the VHF dipole array provides a reflecting element for the first receiving element.

7. An antenna of claim 6, wherein the first VHF pole and the second VHF pole form a forward dipole, and the antenna further includes a capacitive element for effectively shorting the forward dipole such that the forward dipole operates as the reflecting element at UHF frequencies for the first receiving element.

8. A multiplexer for frequency-multiplexing a UHF signal and a VHF signal having a printed circuit board (PCB), the multiplexer including: a first input for receiving the UHF signal from a first receiving element; a second input for receiving the VHF signal from a second receiving element; filters for frequency-multiplexing the UHF signal and the VHF signal to produce a multiplexed signal; an output for providing the multiplexed signal; wherein the second receiving element includes a VHF dipole array including at least a first VHF pole and a second VHF pole extending from, and perpendicular to, a plane defined by the PCB of the multiplexer, wherein an axis of the first pole is offset from an axis of the second pole.

9. A multiplexer of claim 8, wherein the second receiving element is a VHF log periodic dipole array with VHF poles extending from, and perpendicular to, two parallel booms, and the PCB is mounted between the two parallel booms.

10. A multiplexer of claim 8 or 9, wherein the first receiving element includes a UHF dipole array and the UHF dipole array includes a first UHF pole and a second UHF pole extending from, and perpendicular to, a plane defined by the PCB board of the multiplexer and an axis of the first UHF pole is offset from an axis of the second UHF pole.

11. A multiplexer of any one of claims 8 to 10, wherein the multiplexer further includes a first matching circuit for improving an impedance matching between the first receiving element and a cable connected to the output, and a second matching circuit for improving an impedance matching between the second receiving element and a cable connected to the output.

12. A multiplexer of claim 11, wherein the first and second matching circuit are implemented using PCB tracks.

13. A multiplexer of claim 12, wherein the filters are provided by PCB tracks.

14. A multiplexer of any one of claims 8 to 13, further including a capacitive element for effectively shorting an element of the second receiving element at UHF frequencies.

15. A multiplexor of claim 14, wherein the first VHF pole and the second VHF pole form a forward dipole and the capacitive element effectively shorts the forward dipole such that the forward dipole operates as the reflecting element at UHF frequencies for the first receiving element.