As a result, narrrowband IF filters allow the signal analyzer to use higher IF gain without introducing the potential for clipping at the ADC. So when using a narrow IF filter, the signal analyzer is capable of better ACPR measurements with the tradeoff of longer measurement times. In many modern RF signal analyzers, IF filter bandwidth is simply an advanced setting that one can choose to adjust.
A basic understanding of the architecture of the modern RF signal analyzer empowers you to optimize its settings for a given measurement. For more detailed on measurement best practices using RF signal analyzers, visit www.
Hall is a senior product marketing manager at National Instruments, where he is responsible for RF and wireless test hardware and software products. His job functions include educating customers on RF test techniques, product management, and developing product demos. His areas of expertise include instrumentation architecture, digital signal processing, and test techniques for cellular and wireless connectivity devices.
Electronic Design brought to you by. More information about text formats. Text format Comments Plain text. Web page addresses and e-mail addresses turn into links automatically. Lines and paragraphs break automatically. Leave this field blank. Instead, the tuner is wideband and then beat heterodyned to a single intermediate frequency and sent to a very optimized demodulation circuit.
Early radios used Tune RF stages to amplify weak radio signals to the point an AM "detector" could convert them back to audio. These TRF radios would have anywhere from one stage to as many as 12 stages. The more stages, the better the reception for weak signals and the better the image rejection rejection of nearby frequencies. This worked well when there were only a few radio stations but did not work well when more stations started crowding the airwaves.
A TRF radio uses a tuned circuit whose Q for each stage is set to allow all of the frequencies for the audio bandwidth being used to pass through and a little amplification to boost the signal to usable levels. This had a few drawbacks as others have pointed out and a few they missed.
If the stages were too high in gain they might start oscillating and the radio stops working. Even with ganged variable capacitors, getting all the stages to stay on frequency was hard so provisions were made at some stages or all stages for "trimming" the signal.
This is why pictures you see of early radio sets had so many knobs. Quite a few were for the "trimmer" variable capacitors and others were tube bias adjustments to set the gain to prevent feedback. This, as you can imagine, would make tuning in a radio station quite a production and when the "old man of the house" was going to listen to the radio it was a big event.
It was known before the turn of the 19th century that if two oscillators were near each other that they would "beat" against each other and produce a new signal as in the case of two flutes tuned to the same pitch.
This was exploited in several interesting ways at the beginning of the 20th century. The first use was in a baseband CW detector that converted a radio signal to audible sound much more cleanly than the barrater and other convoluted detector devices. The Theremin uses heterodyning of two oscillators where one has it's tuning capacitance supplied by a small plate or wire and the users hand. Major Armstrong in the US and a few others in Europe realized during WWI that this could be exploited to make a receiver that had only a few very high gain stages and much simpler tuning filters.
The mixer stage would take the incoming RF, heterodyne it against the local oscillator and due to the nonlinear behavior of the mixer stage produce both a sum and a difference frequency. Usually it was the difference frequency that was lower than the RF or oscillator that was used.
At 1MHz, the LO is set for 1. Instead of many tuned stages whose gain was tailored to prevent oscillation as their input and output frequencies was all the same, one or two higher gain stages for the RF could be followed by one or more carefully designed stages all operating at a different fixed frequency that did not need to be adjusted.
Questions Tags Users Badges Unanswered. Why the conversion to Intermediate Frequency? Dharmaputhiran 2 6 It isn't an answer, but do note that some receivers use multiple IF stages at different frequencies.
Modern satellite television receivers use several intermediate frequencies. The downlink signal is received by a satellite dish. One of the two blocks is selected by a control signal from the set top box inside, which switches on one of the local oscillators. This IF is carried into the building to the television receiver on a coaxial cable.
Further processing selects the channel desired, demodulates it and sends the signal to the television. An intermediate frequency was first used in the superheterodyne radio receiver, invented by American scientist Major Edwin Armstrong in , during World War I. Armstrong's solution was to set up an oscillator tube that would create a frequency near the incoming signal, and mix it with the incoming signal in a 'mixer' tube, creating a 'heterodyne' or signal at the lower difference frequency, where it could be amplified easily.
After the war, in , Armstrong sold the patent for the superheterodyne to Westinghouse , who subsequently sold it to RCA. The increased complexity of the superheterodyne circuit compared to earlier regenerative or tuned radio frequency receiver designs slowed its use, but the advantages of the intermediate frequency for selectivity and static rejection eventually won out; by , most radios sold were 'superhets'.
During the development of radar in World War II , the superheterodyne principle was essential for downconversion of the very high radar frequencies to intermediate frequencies. Since then, the superheterodyne circuit, with its intermediate frequency, has been used in virtually all radio receivers. From Wikipedia, the free encyclopedia. Problems, Methods and Equipment.
Springer Science and Business Media. John Redford's personal website. Archived from the original on Retrieved from " https: Radio electronics Broadcast engineering.
In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception.
If the demodulation circuit had to be wideband (say, able to work for any frequency from MHz for FM), keeping a flat response across the entire frequency range would be difficult. Instead, the tuner is wideband and then beat (heterodyned) to a single intermediate frequency and sent to a very optimized demodulation circuit.
One extremely important yet not widely known characteristic of today’s high-performance RF signal analyzers is their use of a range of intermediate frequency (IF) filter bandwidth settings. IF bandwidth is a key factor in the selectivity of the instrument. The most commonly used intermediate frequencies are 10–70 MHz in the satellite and radar world. However, the intermediate frequency can range from 10– MHz. Intermediate frequency (IF) are generated by mixing the RF and LO frequency together to create a lower frequency called IF.5/5(1).
Dec 03, · In the digital communication class I took, people talk about how to do detection and processing at the baseband. But from what I read, it seems that many systems do the signal processing at some intermediate frequency without mixing it all the way back to baseband. May 02, · As the name implies, an intermediate frequency is somewhere between the baseband frequency and the carrier frequency. IF circuitry can be incorporated into both transmitters and receivers, though the benefits of IF techniques are more relevant to receivers.