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Circuit Surgery Regular clinic by Ian Bell Frequency Shifting and Superheterodyne Receivers – Part 2 𝑆𝑆! = 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) Frequency shifting and superheterodyne receivers – Part 2 L ast month, we started looking 𝑠𝑠"# = 𝐴𝐴$ (1 + 𝑘𝑘𝑆𝑆# ) a sinusoidal message of amplitude AM two input frequencies (two sinusoid at superheterodyne radio receivinputs) multipliers output just the sum the modulation depth is: ers, mainly concentrating on the and difference frequencies, whereas with 𝑘𝑘𝐴𝐴# principles of heterodyning (frequency other nonlinear circuits there may also be 𝑚𝑚 = × 100% 𝐴𝐴! shifting) and the mixers that provide many other output frequencies. We often this function. This month, we will only want one of the sum or difference look at the structure and operation of frequencies, so we have to filter the The maximum modulation depth superheterodyne radio receivers in mixer output to remove the unwanted without causing distortion is 100%, 𝑆𝑆# = 𝐴𝐴#that cos(2𝜋𝜋𝑓𝑓 more detail. signals. Multiplier circuits require a beyond we have overmodulation. # 𝑡𝑡) Frequency Shifting and Superheterodyne Receivers – Part 2 Radio transmission systems are relatively large number of transistors Real AM voice/music radio systems Frequency Shifting and Superheterodyne Receivers – Part Frequency Shifting and Superheterodyne Receivers – Part 2 2 fundamentally based on heterodyning. to implement so are more commonly have modulation depths well below this, Superheterodyne Receivers – Part The signal to be transmitted, referred found on Frequency integratedShifting circuitand receivers. maybe to 60% in2sinewave terms, 𝑆𝑆! = 𝐴𝐴30% ! cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) to as the message signal, (for example, The nonlinearity of a single transistor because real signals do 𝑠𝑠"# = 𝐴𝐴$ (1but + 𝑘𝑘𝐴𝐴 cos(2𝜋𝜋𝜋𝜋 𝑡𝑡)) cos(2𝜋𝜋𝜋𝜋 % $ 𝑡𝑡)not have 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓 𝑆𝑆! =𝑆𝑆% 𝐴𝐴 ! !=cos(2𝜋𝜋𝑓𝑓 ! 𝑡𝑡) ! 𝑡𝑡) speech) is upshifted from its original or diode (or tube/valve in the old days) constant amplitude their modulation cos(2𝜋𝜋𝑓𝑓 frequency range (called the baseband) can be used for mixing in circuits with 𝑆𝑆depth expressed in rms (root mean ! = 𝐴𝐴! is ! 𝑡𝑡) to the much higher frequencies a relatively low component count. square) terms, where the typical values 𝑠𝑠"# = 𝐴𝐴$ (1 + 𝑘𝑘𝑆𝑆# ) (radio frequencies – RF) required may the 20% to 40% 𝑠𝑠"# = 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓 + in 𝑘𝑘𝐴𝐴𝑠𝑠% cos(2𝜋𝜋𝜋𝜋 𝑡𝑡) ! 𝑡𝑡)be $𝐴𝐴 # 𝑡𝑡) rms (1 𝑠𝑠range (1 𝐴𝐴 = +$ cos(2𝜋𝜋𝑓𝑓 𝑘𝑘𝑆𝑆+ "# "# = # )𝑘𝑘𝑆𝑆# ) for practical wireless transmission (for example, see$ the International Amplitude modulation = 𝐴𝐴$ (1 + 𝑘𝑘𝑆𝑆# ) of electromagnetic signals. This is Telecommunications Union report Superheterodyne receivers can be used 𝑠𝑠"# achieved by varying (modulating) one or ITU-R BS.2433-0 (10/2018)). with a variety of modulation schemes, 𝑘𝑘𝐴𝐴# more properties of an RF carrier signal but we will just refer to amplitude 𝑚𝑚 = × 100% 𝑘𝑘𝐴𝐴# 𝑘𝑘𝐴𝐴# 𝐴𝐴! × 100% in sympathy with the message signal. modulation (AM) in this article to keep AM signals 𝑚𝑚 =𝑚𝑚 = × 100% 𝐴𝐴message ! 𝐴𝐴! A radio receiver must then downshift things simple. Before discussing the For a𝑘𝑘𝐴𝐴sinusoidal at frequency # 𝑚𝑚 = × 100% the signal from the RF carrier frequency receiver, it is worth looking at AM fM and 𝐴𝐴!amplitude AM, that is given by: to the original baseband to recover signals, so we know what the receiver 𝑆𝑆# = 𝐴𝐴# cos(2𝜋𝜋𝑓𝑓# 𝑡𝑡) the message, which is referred to as is dealing with. As the name suggests 𝐴𝐴# cos(2𝜋𝜋𝑓𝑓 𝑆𝑆# =𝑆𝑆# 𝐴𝐴#=cos(2𝜋𝜋𝑓𝑓 # 𝑡𝑡) # 𝑡𝑡) demodulation or detection. amplitude modulation involves changing the amplitude of a fixed 𝑆𝑆#The modulated signal, using = 𝐴𝐴resulting # cos(2𝜋𝜋𝑓𝑓# 𝑡𝑡) frequency carrier wave in proportion the equation above, is: Mixer recap 𝑠𝑠"# = 𝐴𝐴$ (1 + 𝑘𝑘𝐴𝐴% cos(2𝜋𝜋𝜋𝜋% 𝑡𝑡)) cos(2𝜋𝜋𝜋𝜋$ 𝑡𝑡) to the message signal. The carrier signal The principle of the superheterodyne 𝑠𝑠"# 𝑡𝑡)) cos(2𝜋𝜋𝜋𝜋 (1𝐴𝐴+$ (1 𝑠𝑠"# = 𝐴𝐴$= 𝑘𝑘𝐴𝐴+%𝑘𝑘𝐴𝐴 cos(2𝜋𝜋𝜋𝜋 cos(2𝜋𝜋𝜋𝜋 % cos(2𝜋𝜋𝜋𝜋 % 𝑡𝑡))% $ 𝑡𝑡) $ 𝑡𝑡) (SC) is a high-frequency receiver is downconversion a fixed Frequency Shiftingtoand Superheterodyne Receivers – Part 2(RF) sinusoid intermediate frequency (IF) before at frequency fC and amplitude A𝑠𝑠C, which "# = 𝐴𝐴$ (1 + 𝑘𝑘𝐴𝐴% cos(2𝜋𝜋𝜋𝜋% 𝑡𝑡)) cos(2𝜋𝜋𝜋𝜋$ 𝑡𝑡) further downcoversion to the baseband. we can write as: Multiplying out: 𝑠𝑠"# = 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) + 𝑘𝑘𝐴𝐴% cos(2𝜋𝜋𝜋𝜋$ 𝑡𝑡) cos(2𝜋𝜋𝑓𝑓# 𝑡𝑡) The intermediate frequency used in 𝑆𝑆! = 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) 𝑠𝑠"# 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓 𝑠𝑠"# = 𝐴𝐴!=cos(2𝜋𝜋𝑓𝑓 𝑘𝑘𝐴𝐴+%𝑘𝑘𝐴𝐴 cos(2𝜋𝜋𝜋𝜋 ! 𝑡𝑡) % cos(2𝜋𝜋𝜋𝜋 $ 𝑡𝑡) cos(2𝜋𝜋𝑓𝑓 ! 𝑡𝑡) + $ 𝑡𝑡) cos(2𝜋𝜋𝑓𝑓 # 𝑡𝑡) # 𝑡𝑡) superheterodyne receivers is at a much higher frequency than audio (hence Note that the 2π factor converts 𝑠𝑠"# = 𝐴𝐴! the cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) + 𝑘𝑘𝐴𝐴% cos(2𝜋𝜋𝜋𝜋$ 𝑡𝑡) cos(2𝜋𝜋𝑓𝑓# 𝑡𝑡) the ‘super’ part of the name). The fact ordinary frequency of the signal (fC) in Frequency Shifting and Superheterodyne Receivers – Part 2 that the IF is a fixed frequency makes hertz angular frequency (w) in The signal is equivalent to the carrier plus 𝑠𝑠"# =to𝐴𝐴an $ (1 + 𝑘𝑘𝑆𝑆# ) the design of a receiver with good radians. The message signal (SM) is at the carrier multiplied by the message. performance much easier than if most Based on this and using a similar approach a lower frequency (for example, audio) 𝑆𝑆! = 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) of the circuitry has to cope with (be and varies the instantaneous amplitude tuneable to) the full range of carrier of the 𝑘𝑘𝐴𝐴 carrier to give the modulated # 𝑚𝑚 = (SAM× frequencies which need to be received. signal ): 100% 𝐴𝐴! Heterodyning is achieved using 𝑠𝑠"# = 𝐴𝐴$ (1 + 𝑘𝑘𝑆𝑆# ) Introduction to LTspice mixers. These are nonlinear circuits that combine signals to produce new Want to learn the basics of LTspice? frequencies (heterodynes) not present In this expression, k is the modulating Ian Bell wrote an excellent series of 𝑆𝑆# = 𝐴𝐴which # cos(2𝜋𝜋𝑓𝑓 Circuit Surgery articles to get you up in the input. We discussed mixers in factor, is #a𝑡𝑡)value greater than 𝑘𝑘𝐴𝐴# and running, see PE October 2018 detail last month. To recap briefly, an zero. of k, together with the 𝑚𝑚 =The value × 100% to January 2019, and July/August ideal mixer multiplies two signals, relative𝐴𝐴!amplitudes of carrier and 2020. All issues are available in but if signals are combined (added) message determine the modulation print and PDF from the PE website: 𝑠𝑠"# = 𝐴𝐴$ (1 + 𝑘𝑘𝐴𝐴(m), % cos(2𝜋𝜋𝜋𝜋 $ 𝑡𝑡) and applied to any nonlinear circuit depth that % is𝑡𝑡)) thecos(2𝜋𝜋𝜋𝜋 amplitude of the https://bit.ly/pe-backissues then heterodyning will occur. With modulation relative to the carrier. For 𝑆𝑆# = 𝐴𝐴# cos(2𝜋𝜋𝑓𝑓# 𝑡𝑡) 48 Practical Electronics | January | 2024 𝑠𝑠"# = 𝐴𝐴! cos(2𝜋𝜋𝑓𝑓! 𝑡𝑡) + 𝑘𝑘𝐴𝐴% cos(2𝜋𝜋𝜋𝜋$ 𝑡𝑡) cos(2𝜋𝜋𝑓𝑓# 𝑡𝑡) Fig.1. LTspice schematic for behavioural simulation of amplitude modulation. Fig.4. LTspice modulator special function component. is the same as in Fig.3. If there is no DC offset on the AM input the modulator component (configured for AM) will act as a multiplying mixer. Sidebands Fig.2. Waveform results from the circuit in Fig.1 with k = 0.3 (30%). to that used for mixers last month, we can create an LTspice behavioural simulation of amplitude modulation (see Fig.1). Like last month, to make it easier to see both the carrier and message waveforms, we are not using typical radio frequencies for the carrier. In the example the value of the modulation factor (k) is set up as a parameter. Fig.2 shows the results from the simulation in Fig.1 for k = 0.3 (30%). Fig.3 shows the modulated waveform for k = 0.6 (60%). As mentioned last month, when considering the operation of radio systems, we are often more interested in the signal spectra rather than the waveforms in the time domain. Therefore, the simulation is again configured to facilitate viewing of the spectrum with LTspice’s FFT function. In the circuit in Fig.1, we used a behavioural source to implement an AM modulator. An alternative approach is to use the ideal modulator component that is available in LTspice. This can be found in the ‘Special Functions’ folder of the component selector. It provides both amplitude and frequency modulation (AM and FM) functionality. It has two parameters – mark and space – which set the upper and lower FM frequencies. These should be the set to the same value, equal to the carrier frequency, for AM. An example circuit with the modulator component configured for AM is shown in Fig.4. The example uses a 0.6V-amplitude sinewave message signal on a 1.0V DC offset, with a 20kHz carrier signal. This produces AM with 60% modulation depth, so the output Fig.3. Waveform results from the circuit in Fig.1 with k = 0.6 (60%). Practical Electronics | January | 2024 From the discussion on mixers last month, we know that the multiply term in the equation for AM with sinusoids given above will produce an output with two signals at the sum and difference frequencies (f C – f M ) and (f C + f M), the carrier term in the equation means that this frequency (f C ) will also be present in the AM modulator output. This is shown in Fig.5, which is the spectrum (LTspice FFT) for the modulation waveform from the circuit in Fig.1, where the sum (20 + 2 = 22kHz) and difference (20 – 2 = 18kHz) and carrier (20kHz) peaks can be seen. In the context of modulation, sum and difference frequencies are referred to as the upper and lower sidebands respectively. They are single frequencies in this LTspice example, but in general they comprise the full message bandwidth upshifted to ranges above and below the carrier frequency. This is illustrated in Fig.6. The spectrum on the left of Fig.6 is the baseband and comprises a range of relatively low frequencies (from fm,min to fm,max); for example, audio from a few tens of hertz to several kilohertz. Like Fig.4, the frequency axis is linear and includes zero frequency (DC) unlike the logarithmic scales commonly used for plots such as amplifier frequency responses. The right of Fig.6 shows the spectrum of the AM signal produced by using the baseband signal on the left to modulate a carrier of frequency fC. The baseband is upshifted to the sum and difference frequencies and so appears both above and below the carrier frequency as the upper and lower sidebands. Note the ‘reversal’ of the lower sideband – the highest baseband frequency is shifted to the lowest frequency in the lower sideband. The gap between the carrier and sidebands on both sides is equal to the lowest baseband frequency. The plots in Fig.5 are not to scale – the 49 Fig.5. Spectrum of the modulated waveform of the circuit in Fig.1 with k = 0.6 (60%). break in the AM plot axis indicates that a typical carrier frequency is much further along the axis (relative to the size of the sidebands) than where it is located in the drawing. The full AM signal takes more bandwidth and power to transmit than is strictly necessary. For normal AM the sidebands are symmetric (see Fig.6), so only one needs to be transmitted, halving the bandwidth – this is called Single Sideband (SSB). The carrier contains no message information, so can be reduced in amplitude or removed (referred to as suppressed carrier), which can be applied to both single and double sidebands (SSB-SC and DSBSC). Not transmitting a sideband and/or the carrier reduces power requirements or increases coverage with the same power. Receiving SSB and suppressed carrier signals is more complex and requires higher receiver performance Intermediate frequency As previously explained, a key feature of the superheterodyne receiver is the downshifting of the received signal to a fixed intermediate frequency. The idea of what is required is illustrated in Fig.7. There is a range of possible received signals, that is different carrier signals and their associated sidebands from the various stations or channels that can be received. One of these is selected (by tuning to that station or selecting that channel) and it is downshifted to the fixed IF. The downshifting does not change the shape of the spectrum of the AM signal – it just shifts it to a new centre frequency (fIF instead of fC). The AM signal Magnitude Magnitude Message (baseband) than full AM, so is generally avoided for commercial AM stations, but is used in other contexts. For simplicity, we will assume full AM signals when discussing receivers here. Carrier Lower sideband fm,min Message bandwidth f fm,max fm,min fc – fm,max Upper sideband fc f AM bandwidth fc + fm,max Fig.6. Signal spectra for AM. Magnitude Wide range of possible received AM signals Magnitude 0 0 fc,min f Selected AM signal shifted to fixed IF fIF Fig.7. Shifting a received AM signal to IF. 50 fc,max IF AM signal can then be demodulated to recover the message signal. As we know from the detailed discussion of mixing last month, shifting to IF can be achieved by mixing (ideally multiplying) the received signal by a sinusoidal signal at an appropriate frequency. In a receiver, this signal is generated by a local oscillator (LO). The mixer produces sum and difference frequencies, which means that either the sum or difference frequency of the received carrier with respect to the LO frequency must match the required intermediate frequency. Using a local oscillator frequency below the carrier frequency is called ‘low-side injection’; if the local oscillator frequency is above the carrier frequency it is ‘high-side injection’. Both can be used, but for basic AM high-side injection is more common. The multiple frequencies produced by nonlinear mixers are more likely to produce disruptive signals in the received signal range if low-side injection is used. Mixing the received carrier at fC with a high-side local oscillator at fLO produces signals at (fLO – fC) and (fLO + fC), with their sidebands. Assuming we want an IF which is lower than the carrier frequency (it does not have to be) we need fIF = fLO – fC. This means we need to tune the local oscillator to fLO = fC + fIF. We need the local oscillator to be able to tune to fC + fIF throughout the range of frequencies we want to receive. In addition to the required IF signal at f LO – f C the mixer will also produces a higher frequency signal at fLO + f C. This needs to be removed by filtering. As a round-number example, for a carrier range of 1.0MHz to 1.5MHz and an IF of 400kHz (0.4MHz) the local oscillator needs to tune from 1.4MHz (1.0 + 0.4 = 1.4) to 1.9MHz (1.5 + 0.4 = 1.9). The mixer will also produce signals in the range 2.4MHz (1.0 + 1.4 = 2.4) to 3.4MHz (1.5 + 1.9 = 3.4), which need to be filtered out. This example is similar to traditional broadcast AM receivers where an IF of 455kHz was commonly used (from the early days of widespread superhet use). An advantage of high-side injection is that a smaller LO tuning range (ratio of highest to lowest LO frequency) is required than for low-side injection, which makes things easier if the tuning is implemented with a variable capacitor. IF mixer simulation fc f We can simulate the IF mixing in LTspice by adding a LO signal and behavioural multiplying mixer to the circuit in Fig.1. This is shown in Fig.8 – the carrier (from source V1) is at a higher frequency (80kHz) than in the circuit Practical Electronics | January | 2024 Fig.8. LTspice schematic for behavioural simulation of shifting an AM signal to an intermediate frequency (IF). in Fig.1, but the modulated signal generation is essentially the same. The modulated signal (signal modulated from source B 1 ) is multiplied by a 110kHz sinewave from the local oscillator (LO signal from source V3) using behavioural source B 2 . This produces the intermediate frequency Fig.9. Waveform results from the circuit in Fig.8. output (signal IF) at 30kHz (fIF = fLO – fC = 110kHz – 80kHz = 30kHz). The schematic includes a filter which we will discuss later. The results of simulating the circuit in Fig.8 up to the IF mixer output are shown in Fig.9. The top three traces (carrier (80kHz), message (2kHz) and AM modulated signal) are similar to Fig.2, but the carrier frequency is higher, and the waveforms are zoomed in more. The fourth trace is the local oscillator (LO) at 110kHz. The bottom trace is the IF signal from the mixer. This has a complex-looking waveform, which is difficult to interpret from its shape. It is more useful to look at the spectra. Fig.10 shows the spectra of the modulated and IF waveforms from Fig.8. It can be seen that the AM waveform comprises the carrier (80kHz) and the two sidebands (at 78kHz and 82kHz), corresponding with Fig.5 and Fig.6, as discussed earlier. The IF spectrum shows the presence of two ‘AM’ signals of equal amplitudes, one centred on 30kHz and the other on 190kHz. This is the required IF signal centred on 30kHz and the additional signal from the mixer centred on fLO + fC = 110kHz + 80kHz = 190kHz. Unlike the waveform, the spectrum clearly shows that the IF signal is behaving as expected from mixing (ideal multiplying) the local oscillator and AM signal. Looking at the lower trace in Fig.10 we see that to obtain the desired signal, that is the AM signal centred at the IF frequency of 30kHz on its own, we need to filter the IF mixer output to remove the component of the waveform centred at 190kHz. In this simplified example there are no other signals present in the spectrum, but in general the IF mixer output spectrum will contain many other significant peaks. These will include the result of mixing signals from adjacent radio stations/channels with the local oscillator, and additional spectral components resulting from non-ideal mixer behaviour (see last month’s discussion). Thus, a bandpass filter is required to remove all the unwanted parts of the IF spectrum before the IF signal can be demodulated to recover the message. Tuning Fig.10. Spectra of ‘received’ AM and IF waveforms from Fig.9. Practical Electronics | January | 2024 It is not the whole story, as we will see shortly, but the tuning of a superheterodyne receiver to the desired station/channel is fundamentally achieved by a combination of the local oscillator frequency, which selects which received frequency is shifted to the IF, and the bandpass filter after the IF mixer which removes everything apart from the wanted signal. This 51 requires a filter with a sharp cutoff outside the bandwidth of the received signal; however, because the IF is at fixed frequency a fixed filter can be used, which is relatively easy to achieve. The IF filter was implemented using LC circuits in the earliest superheterodyne radios, but later replaced by ceramic filter components which provide better accuracy at low cost. As mentioned above, 455kHz is the traditional IF frequency for broadcast AM receivers and many ceramic filters for this (and other related) IF frequencies were manufactured. However, some of these specific components may be harder to source now as technology has moved on. (eBay may be your best bet, as is scavenging old radio equipment.) These days, filtering (and other processing) of IF signals can often be achieved using DSP (digital signal processing). A bandpass filter is implemented in the circuit in Fig.8 using two LTspice second-order behavioural bandpass filters (U1 and U2). These are configured as a fourth-order bandpass filter, centred on the IF frequency of 30kHz, with a bandwidth which means that message signal (sidebands) will not be significantly attenuated. This filter is for illustration using these example waveforms and chosen for convenience of quick set-up in LTspice. It is not necessarily similar to the requirements for real radio signals because the IF, LO and carrier frequencies in the example are very low for purposes of displaying the waveforms, and there are no unwanted signals very close to the IF frequency in the example. The waveform of the filtered IF mixer output (signal filtered) for the circuit in Fig.8 is shown in Fig.11 with the original message signal for comparison. We can see that it looks like an AM signal modulated with the 2kHz sinewave message. The spectrum of the filtered IF mixer output is shown in Fig.12 and the frequency response of the filter is shown in Fig.13 over the same range as the spectrum. The frequency response was obtained using the circuit in Fig.14. Comparison of the filtered mixer output spectrum with the unfiltered spectrum in Fig.10 shows that the signal centred at 190kHz has been significantly attenuated. Fig.11. Waveform of filtered IF mixer output from the circuit in Fig.9. Fig.12. Spectra of filtered IF waveform from the circuit in Fig.9. Fig.13. Frequency response of the filter (U1 and U2) in Fig.9. Fig.14. LTspice circuit to obtain the frequency response in Fig.13. Mixer Image filter RF amp IF filter IF amp Simulation files Fig.15. Superheterodyne receiver structure. Most, but not every month, LTSpice is used to support descriptions and analysis in Circuit Surgery. The examples and files are available for download from the PE website: https://bit.ly/pe-downloads 52 Practical Electronics | January | 2024 Tuning Local oscillator Image frequency Previously, we discussed using a local oscillator at frequency fLO = fC + fIF to tune to our required carrier frequency (fC) and shift the signal to the IF (fIF = fLO – fC). However, the mixer, with the local oscillator at fLO as one of its inputs, will also shift a different frequency to f IF , specifically fIF = fIm – fLO, where fIm is known as the image frequency. We have fIm = fC + fLO. For example, using the same round numbers as above, for fC = 1.0MHz and an IF of 400kHz (0.4MHz) the local oscillator needs to be at 1.4MHz and therefore the image frequency is at 1.8MHz (1.4 + 0.4 = 1.8MHz). In this example, if the receiver picks up a signal at 1.8MHz it will be shifted to the IF along with the wanted signal. Because it is then at the same frequency, the image cannot be separated from the wanted signal by filtering after the mixer. In general, we have to assume that received signals will be present at the image frequency, so they must be removed before the mixer. This requires a filter before the mixer, called the image filter or preselection filter, which may be tuneable to track with the local oscillator. However, the requirements for this filter are a lot less severe than if we tried to filter the required station/channel directly from the RF signal received from the antenna. In a superhet the more demanding filtering is done by the fixed frequency IF filter, as described earlier. The preceding discussion leads to the structure of a superheterodyne receiver as shown in Fig.15. There are of course variations on this theme – for example, there may be another filter before the image filter to remove all signals outside the band the receiver is designed to work with. The next stage after the IF amplifier is detection or demodulation of the IF signal, which we will look at next month. ESR Electronic Components Ltd All of our stock is RoHS compliant and CE approved. Visit our well stocked shop for all of your requirements or order on-line. We can help and advise with your enquiry, from design to construction. 3D Printing • Cable • CCTV • Connectors • Components • Enclosures • Fans • Fuses • Hardware • Lamps • LED’s • Leads • Loudspeakers • Panel Meters • PCB Production • Power Supplies • Relays • Resistors • Semiconductors • Soldering Irons • Switches • Test Equipment • Transformers and so much more… Monday to Friday 08:30 - 17.00, Saturday 08:30 - 15:30 Station Road Cullercoats North Shields Tyne & Wear NE30 4PQ Tel: 0191 2514363 sales<at>esr.co.uk www.esr.co.uk STEWART OF READING 17A King Street, Mortimer, near Reading, RG7 3RS Telephone: 0118 933 1111 Fax: 0118 933 2375 USED ELECTRONIC TEST EQUIPMENT Check website www.stewart-of-reading.co.uk Fluke/Philips PM3092 Oscilloscope 2+2 Channel 200MHz Delay TB, Autoset etc – £250 LAMBDA GENESYS LAMBDA GENESYS IFR 2025 IFR 2948B IFR 6843 R&S APN62 Agilent 8712ET HP8903A/B HP8757D HP3325A HP3561A HP6032A HP6622A HP6624A HP6632B HP6644A HP6654A HP8341A HP83630A HP83624A HP8484A HP8560E HP8563A HP8566B HP8662A Marconi 2022E Marconi 2024 Marconi 2030 Marconi 2023A PSU GEN100-15 100V 15A Boxed As New £400 PSU GEN50-30 50V 30A £400 Signal Generator 9kHz – 2.51GHz Opt 04/11 £900 Communication Service Monitor Opts 03/25 Avionics POA Microwave Systems Analyser 10MHz – 20GHz POA Syn Function Generator 1Hz – 260kHz £295 RF Network Analyser 300kHz – 1300MHz POA Audio Analyser £750 – £950 Scaler Network Analyser POA Synthesised Function Generator £195 Dynamic Signal Analyser £650 PSU 0-60V 0-50A 1000W £750 PSU 0-20V 4A Twice or 0-50V 2A Twice £350 PSU 4 Outputs £400 PSU 0-20V 0-5A £195 PSU 0-60V 3.5A £400 PSU 0-60V 0-9A £500 Synthesised Sweep Generator 10MHz – 20GHz £2,000 Synthesised Sweeper 10MHz – 26.5 GHz POA Synthesised Sweeper 2 – 20GHz POA Power Sensor 0.01-18GHz 3nW-10µW £75 Spectrum Analyser Synthesised 30Hz – 2.9GHz £1,750 Spectrum Analyser Synthesised 9kHz – 22GHz £2,250 Spectrum Analsyer 100Hz – 22GHz £1,200 RF Generator 10kHz – 1280MHz £750 Synthesised AM/FM Signal Generator 10kHz – 1.01GHz £325 Synthesised Signal Generator 9kHz – 2.4GHz £800 Synthesised Signal Generator 10kHz – 1.35GHz £750 Signal Generator 9kHz – 1.2GHz £700 HP/Agilent HP 34401A Digital Multimeter 6½ Digit £325 – £375 HP 54600B Oscilloscope Analogue/Digital Dual Trace 100MHz Only £75, with accessories £125 (ALL PRICES PLUS CARRIAGE & VAT) Please check availability before ordering or calling in HP33120A HP53131A HP53131A Audio Precision Datron 4708 Druck DPI 515 Datron 1081 ENI 325LA Keithley 228 Time 9818 Practical Electronics | January | 2024 Marconi 2305 Marconi 2440 Marconi 2945/A/B Marconi 2955 Marconi 2955A Marconi 2955B Marconi 6200 Marconi 6200A Marconi 6200B Marconi 6960B Tektronix TDS3052B Tektronix TDS3032 Tektronix TDS3012 Tektronix 2430A Tektronix 2465B Farnell AP60/50 Farnell XA35/2T Farnell AP100-90 Farnell LF1 Racal 1991 Racal 2101 Racal 9300 Racal 9300B Solartron 7150/PLUS Solatron 1253 Solartron SI 1255 Tasakago TM035-2 Thurlby PL320QMD Thurlby TG210 Modulation Meter £250 Counter 20GHz £295 Communications Test Set Various Options POA Radio Communications Test Set £595 Radio Communications Test Set £725 Radio Communications Test Set £800 Microwave Test Set £1,500 Microwave Test Set 10MHz – 20GHz £1,950 Microwave Test Set £2,300 Power Meter with 6910 sensor £295 Oscilloscope 500MHz 2.5GS/s £1,250 Oscilloscope 300MHz 2.5GS/s £995 Oscilloscope 2 Channel 100MHz 1.25GS/s £450 Oscilloscope Dual Trace 150MHz 100MS/s £350 Oscilloscope 4 Channel 400MHz £600 PSU 0-60V 0-50A 1kW Switch Mode £300 PSU 0-35V 0-2A Twice Digital £75 Power Supply 100V 90A £900 Sine/Sq Oscillator 10Hz – 1MHz £45 Counter/Timer 160MHz 9 Digit £150 Counter 20GHz LED £295 True RMS Millivoltmeter 5Hz – 20MHz etc £45 As 9300 £75 6½ Digit DMM True RMS IEEE £65/£75 Gain Phase Analyser 1mHz – 20kHz £600 HF Frequency Response Analyser POA PSU 0-35V 0-2A 2 Meters £30 PSU 0-30V 0-2A Twice £160 – £200 Function Generator 0.002-2MHz TTL etc Kenwood Badged £65 Function Generator 100 microHz – 15MHz Universal Counter 3GHz Boxed unused Universal Counter 225MHz SYS2712 Audio Analyser – in original box Autocal Multifunction Standard Pressure Calibrator/Controller Autocal Standards Multimeter RF Power Amplifier 250kHz – 150MHz 25W 50dB Voltage/Current Source DC Current & Voltage Calibrator £350 £600 £350 POA POA £400 POA POA POA POA Marconi 2955B Radio Communications Test Set – £800 53