It used to be a major rite of passage for a hardware hacker to acquire an oscilloscope. Until recently, new instruments were rarely in normal people’s budgets, so you probably made do with a used scope. Now, there are lots of inexpensive options, especially if you include low-end PC scopes and “scope meters.” Digital meters are also now inexpensive (often free at some major stores), along with signal generators, frequency counters, and even logic analyzers.

But there is one piece of test equipment you don’t see as often as you used to and its a shame, because it is a very versatile piece of kit. Admittedly, if you aren’t doing wireless work, it might not be high on your wish list, but if you do anything with RF, it is not only a versatile tool, but a good value, too. What’s it called? That depends. Historically, they went by the name “Grid Dip Oscillator” or GDO. Sometimes you’d hear it called a “Grid Dip Meter” instead. However, modern versions don’t have tubes (and, thus, no grid) so sometimes you hear them now called dip meters or maybe just dippers.

Why Does it Dip?

Regardless of what you call them, the theory of operation is the same and it is pretty simple. The instrument is nothing more than a very broad band oscillator with a way to couple the output to an external circuit. There will also be some way to monitor how much power is being taken out of the oscillator. This is most often done by looking at the peak amplitude of the oscillator.

The reason for the dip has to do with the way inductors and capacitors behave at different frequencies. Just about any circuit or component has three sources of impedance: the resistance, which shouldn’t change based on frequency; the capacitive reactance, which is due to–of course–capacitance; and the inductive reactance from inductive elements. In some cases, you only have a significant amount of one of these. For example, in a carbon resistor, you shouldn’t have very much of either type of reactance. A capacitor should be predominantly capacitive reactance.

Reactance and Impedance

For a given capacitor, the reactance is very high at low frequencies and very low at high frequencies. Inductance is the opposite: low frequencies produce a lower reactance than higher frequencies. It is pretty easy to remember this if you think of a DC current as a zero Hertz wave. An inductor (a coil of wire) will clearly pass DC (low reactance) and a capacitor (two parallel plates) will clearly not pass DC (high reactance).

Even though the total impedance of the circuit depends on these three elements, it isn’t as simple as just adding up the values. That’s because resistance and reactance aren’t the same kind of quantity. If you have a 1V signal going into a 2 ohm load with 3 ohms of reactance, you’d like to know it would behave the same as 1V going into an ordinary resistor. If the resistance and the reactance are in series, the value of that effective resistor is the impededance and it is the vector sum of the resistance and the reactance.

In the example, then, 2²+3²=13. The square root of 13 is just around 3.6, so the magnitude of the impedance is 3.6 ohms. To complicate things further, inductive reactance and capactive reactance tend to cancel each other out. It is customary to treat capacitve reactance as negative, although since we will square it, it really doesn’t matter which one you consider negative to do this particular calculation. For the math inclined, you are really treating the resistance as the real part and the reactance as the imaginary part of a complex number. The conversion to polar form gives the magnitude and the phase angle.

In parallel it is sort of the same thing but the reactances add just like resistors in parallel. Here’s the point though: At some frequency, the inductive reactance and the capacitive reactance equal. In a series circuit, that means the reactance goes to zero and all you have left is the resistance. In a parallel circuit, the zero winds up in the denominator of a fraction, and so the effective reactance is infinite (and, in parallel with a pure resistor, doesn’t change the value of the resistor). Either way, reactance cancels out leaving pure resistance.

Resonance

The point where the reactances cancel each other out is resonance. The dip meter works because at the resonance point, the meter’s oscillator will have the highest load on it (lowest impedance), and thus the voltage will drop (or dip). At any other frequency, some reactance will be left and the total impedence of the circuit under test will be higher than at resonance.

Clearly, the most basic function of the dip meter is to measure the resonant frequency of a circuit. If that were all there was to it, it would be pretty useful. But with just a little extra effort, the dip meter can do so much more.

What Can you Measure?

First, it can also measure other tuned circuits, not just capacitors and inductors made from components. For example, antennas, crystals, and transmission lines can all have a particular resonance points, and the meter can measure them. For a crystal, the frequency is the one the crystal should oscillate at (with a little error based on loading capacitance and other factors). Antennas may be resonant at more than one frequency, not just the one you are interested in, so some judgement is required. Anything that doesn’t have a coil (like an antenna or a crystal) will need a little wire loop to couple energy from the meter to the circuit.

For transmission lines, you can measure by making a small loop to couple the dip meter (the smaller the better). Search for the lowest dip, and that will show the 1/4 wavelength frequency of the transmission line. For example, if the cable is resonant at 7.5 Mhz (40 meter wavelength) then the cable is about 10 meters long. Don’t forget, however, to factor in the transmission line’s velocity factor. That is, a quarter wave transmission line with a velocity factor of 0.66 will be shorter than the theoretical length (it will only be 66% as long, in this case).

Of course, you can use the transmission line relation either way. That is, you can get the resonant frequency to measure the cable, or you can set the frequency and trim the line for a dip. In fact, using what you know to get what you don’t know is generally a good principle with the grid dip meter. Want to measure an unknown capacitor? Resonate it with a known inductor. Or start with a known capacitor and find the value of an unknown coil.

One of the main problems, though, is reading the frequency accurately enough. Some modern meters have digital displays (like the DipIt shown on the right). Most common meters, though, don’t. On the other hand, you can easily couple them to a frequency counter or use a receiver to determine the frequency accurately.

If you don’t mind a little estimation, you can do even more measurements. Coils have a Q (quality factor) that indicate how much resistance they have relative to their reactance. Using a good reference capacitor, form a resonant circuit and dip the meter. Note the frequency. Then tune the dip meter down until you find the frequency where the meter reads about 30% higher than it did at the dip. Now tune the dip meter up, through the dip again, until you find the 30% mark again on the other side. The Q will be roughly equal to the dip frequency divided by the difference between the two 30% frequencies.

It might be obvious, but the dipper can also just be used as a signal source. For example, to repair a radio, you might put the dip meter at a frequency the radio should be able to hear and trace it through the circuit. Many dip meters also have a mode where they will turn off their oscillator and use the coil (and tuning capacitor) along with a diode to act as a wavemeter. The meter, then, shows the strength of RF energy at the tuned frequency. Some meters even have a headphone jack so you can listen to the signal (making it almost a crystal radio).

Finding a Dip Meter

One reason many people don’t have dip meters today is that they aren’t as readily available as they used to be. Heathkit was a very popular provider for dip meters and had several models. Other popular older models (often found on eBay) were Eico, Millen, Boonton, and Measurements Corporation (be careful, though; the ones with tubes are probably not a good deal unless you are a collector). You can find a list with pictures of many GDOs at [n4xy’s] web site (the pictures are a few clicks of the next button away from the main page). To the left is a picture of one of my old Measurements GDOs (and, yes, it does use tubes).

You can still find new dip meters from MFJ (they sell the MFJ-201 shown on the right, and you can also convert some of their antenna analyzers into a serviceable dip meter). There are also plenty of plans on the Internet. If you want a real tube model (not recommended) [w4cwg] has plans. A more modern FET design that has a novel bridge to help make the dip deeper is available from [SM0VPO].

On the other hand, it seems a shame to build a new unit without a digital display. You can add one, of course, or you can go with one that is integrated like the DipIt or the ELM. There are plenty of other project and even kits out there. Look around. The hardest part, usually, is winding the coils, although some will call for variable capacitors that may be hard to match. Really, though, any oscillator that can be made stable will work. In fact, I have two old Heathkit dippers that use a negative resistance tunnel diode as an oscillator (one of them is in the picture to the left).

If you want a video demonstration of using a dip meter, I couldn’t do better than [w2aew] already did, so you can find his video below.

This module is a sensor package for monitoring the electrical activity of the heart. It is the product of an effort to create a Wireless Body Sensor Network node that is dependable while consuming very little electricity, which means a longer battery life. To accomplish this, the microcontroller in charge of the node compresses the data (not usually done with wireless ECG hardware) so that the radio transmissions are as short and infrequent as possible.

[Igor] sent us this tip and had a short question and answer session with one of the developers. It seems they are working with the MSP430 chips right now because of their low power consumption. Unfortunately those chips still draw a high load when transmitting so future revisions will utilize an alternative.

Oh, and why the iPhone? The device that displays the data makes little difference. In this case they’re transmitting via Bluetooth for a real-time display (seen in the video after the break). This could be used for a wide variety of devices, or monitored remotely via the Internet.

Spectrum analyzers are adopted to analyze signal frequency and amplitude in logarithmic scale when the electric signal pass through the system such as real-time spectrum analyzer.

Spectrum analyzers are widely adopted for manufacturing, designing and engaging in the field services and repairs electrical devices and are also used to determine performance, error detection and troubleshooting errors.

Measurement of quality of modulation is carried out for smooth transmission of data and it is crucial in both transmission and receiver end.

The important characteristics of spectrum analyzer are signal to noise ratio test and noise figure test which improves overall performance of the system.

With a rising boom in telecommunication industry and increase in wave analysis, spectrum analyzer market has flourished with many new emerging players such as Keysights Technologies and LP Technologies.

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Spectrum Analyzer: Drivers and Challenges

The major driving factor of spectrum analyzer market is increasing demand for wireless technology among users across globe that has led to a significant growth in spectrum analyzer market.

The other key driving factors of spectrum analyzer includes the rising adoption of portable and handheld spectrum analyzers, multitasking feature, bandwidth and frequency advancement.

At present, the high demand of second hand spectrum analyzer is one of the important growth factor of impeding spectrum analyzer market.

The major restraint faced by spectrum analyzer market is due to less availability of low cost spectrum analyzers with maximum features. However, in future the widespread operation of LTE (Long Term Evolution) services is expected to boost the market of spectrum analyzer in positive manner.

Spectrum Analyzer:Key Players

Some of the key players of spectrum analyzer market are:Advantest Corporation, Anritsu Corporation, Avcom, B&K Precision Corporation, Cobham PLC, Fortive Corporation, Giga-Tronics Incorporated, Keysight Technologies, LP Technologies, National Instruments Corporation, Rohde & Schwarz, GmbH & Co., Stanford Research Systems, Teledyne Lecroy and Yokogawa Electric Corporation.

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Spectrum Analyzer:Regional Overview

Presently, North America region is holding the largest market share of spectrum analyzer due to rising adoption of second hand handheld spectrum analyzer. The adoption of portable spectrum analyzer is also impacting the market of spectrum analyzer in a positive manner.

The market of spectrum analyzer is witnessing high growth rate in the European and Asia Pacific regions due to rising boom of telecommunication and wave analysis.

Regional analysis for Spectrum Analyzer, market includes development in the following regions

• North America
• Latin America
  • Argentina
  • Mexico
  • Brazil
  • Rest of Latin America
• Europe
  • U.K.
  • France
  • Germany
  • Poland
  • Russia
• Asia Pacific
  • Australia and New Zealand (A&NZ)
  • China
  • India
  • ASEAN
  • Rest of Asia Pacific
• Japan
• The Middle East and Africa
  • GCC Countries
  • North Africa
  • South Africa
  • Rest of MEA

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The report is a compilation of first-hand information, qualitative and quantitative assessment by industry analysts, inputs from industry experts and industry participants across the value chain.

The report provides in-depth analysis of parent market trends, macro-economic indicators and governing factors along with market attractiveness as per segments.

The report also maps the qualitative impact of various market factors on market segments and geographies.

Spectrum Analyzer: Segmentation

Segmentation on the basis of network technology:

Segmentation on the basis of offering:

• Product (Type, Frequency Range, Form Factor)
• Software (Apps and OS)

Segmentation on the basis of type:

• Swept-Tuned Spectrum Analyzer
• Vector Signal Spectrum Analyzer
• Real-Time Spectrum Analyzer
• Fast Fourier Transform (FFT)
• Parallel Filter Analyzer

Segmentation on the basis of end user:

• IT & Telecommunication
• Medical & Healthcare
• Semiconductors & Electronics
• RF Tuning Method
• Super Heterodyne
• A&D

Segmentation on the basis of form factor:

• Handheld Spectrum Analyzer
• Portable Spectrum Analyzer
• Benchtop Spectrum Analyzer

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Jun 29, 2022 (The Expresswire) -- Global “Combustion Analyzer Market” report cover all crucial aspects of industry like market size, share, growth rate, revenue trends, business developments and new investment opportunities of industry. The Combustion Analyzer market report describes valuable source of insightful data for business strategies, regional and country wise growth segments, industry valuation bases on top key player’s analysis. The report also elaborates historic and future trends, exact developments, manufacturing cost structure, supply and demand analysis with production and consumption scenario. Furthermore, the Combustion Analyzer market report delivers a complete overview of product scope, competitive landscape, CAGR status, developments strategies, PESTLE and SWOT analysis across all regions.

The MarketWatch News Department was not involved in the creation of this content.

The LabRoots 4^th Annual Genetics and Genomics free virtual conference was a wonderful event for research scientists, post docs, principal investigators, lab directors and other genetics professionals to learn about exact advances in genetics research. This year's conference highlighted some fabulous presentations from Robert Green, Amalio Telenti, David Bentley, Alexander Wait Zaranek and many more.

Watch this video to learn about some of the featured speakers.

This virtual conference is now On Demand and allows you to participate in a global setting with no travel or cost to you. You can participate in exactly those parts which you are interested in and be back at your desk or bench in an instant. Virtual events remove time and place restrictions and ensure that everyone who wants to participate can do so. This virtual conference also offers increased reach for the global genetics community with a high degree of interaction through live-streaming video and chat sessions.

Genetics plays a crucial role in the constantly growing and challenging fields of diagnosis and treatment of genetic disorders, infectious diseases and acquired diseases. This conference will focus on "Biology to the Clinic", and will highlight the syllabus below.

Innovations in Genomic Tools and Technologies

Genome Editing; Synthetic Biology; Methods and Technologies for Multi-Center Genetics Platforms and Research; and Moving Beyond GWAS with Functional Approaches

-Omics in Health and Disease

Single Cell Genomics; Metabolism, Mitochondria and Microbiomes; and Systems Approach to -Omics

Clinical Utility of the newest Technologies

Radiomics/Radiogenomics; Clinical Quality Variant Annotation and Databasing; Reimbursement Issues in Clinical Molecular Diagnostics; Data Knowledge and Integration to Medicine; and Methods for Network Inference

Genomics in the Clinic

From Tumor Mutation Profile to Clinical Trials; Nucleic Acid Therapeutics; and Precision Medicine (including Noninvasive Pre-Symptomatic Disease Detection; Individualized Vaccines; Genotype-Phenotype Warehousing: Technologies for Large-Scale Analyses; Pediatric Genetics and Genomics; and Liquid Biopsy, Exosomes, Circulating DNA and Tumor Cells)

Genetics and Genomics conference participants benefit from interacting with field experts and networking with colleagues. Attendees can also “walk” through the virtual exhibit hall to learn about the latest in genetics and genomics tools and assays. Join LabRoots in leading progress toward understanding the genetics behind disease and treatment.

Continuing Education
By participating in this virtual event and watching webcast presentations, you can earn Free CEU, CE, and/or CME credits. To earn educational credits, you must view an entire presentation. Following the presentation you must click on the educational credit link provided for that particular speaker and follow the required process. Once you have completed the process, you will receive a certificate for the educational credit. The American Board of Genetic Counseling, certifies genetic counselors and accredits genetic counseling training programs. The National Society of Genetic Counselors (NSGC) is the professional membership association for the genetic counseling profession.

Use #LRgenetics to follow the conversation

Abstract and Introduction

Background: The fraction of exhaled NO (FeNO) is valuable for the follow-up of asthmatic patients. However, its usefulness as a screening tool for asthma is not established.
Methods: We screened a population of 961 university students with a modified European Community Respiratory Health Survey questionnaire that has been previously used for the screening of respiratory symptoms related to asthma. All subjects with a positive answer to at least one question (n = 149) were submitted to FeNO measurement with a portable nitric oxide analyzer. Subsequently, they were submitted to spirometry and evaluated by a physician blinded to FeNO measurements. Seventy students with no respiratory symptoms served as control subjects.
Results: Asthma was diagnosed in 63 subjects, and allergic rhinitis was diagnosed in 57 subjects. Asthmatics presented higher FeNO values than control subjects (median, 20 parts per billion [ppb]; interquartile range, 14 to 31 ppb; vs median, 11 ppb; interquartile range, 7 to 13 ppb, respectively; p > 0.0001), whereas they did not differ from patients with allergic rhinitis (median, 17 ppb; interquartile range, 12 to 23 ppb; p = 0.28). FeNO values < 19 ppb presented 85.2% specificity and 52.4% sensitivity for the diagnosis of asthma (area under the curve [AUC], 0.723). The diagnostic performance of FeNO was better in nonsmokers (AUC, 0.805), yet FeNO values < 25 ppb were characterized by specificity < 90% for the diagnosis of asthma both in smokers and in nonsmokers. However, FeNO was not a good marker for the differentiation between asthma and allergic rhinitis.
Conclusions: FeNO measurement with a portable analyzer is useful for the screening for asthma in young adults. Significant confounding factors are allergic rhinitis and current smoking.

Asthma is a common chronic inflammatory airway disorder that is underdiagnosed and undertreated.^[1] The diagnosis of asthma is based on clinical history and presentation, combined with evidence of reversibility after inhaled bronchodilators or a trial of corticosteroids. The presentation is not always straightforward, and clinicians may need to confirm the diagnosis with objective measurements that present several limitations. Spirometry results are often normal in asymptomatic asthmatics, and bronchodilator reversibility testing may not constantly be evident, presenting low sensitivity and specificity,^[2] whereas the recording of peak expiratory flow variability requires patient compliance.^[3] Bronchial challenge tests present higher sensitivity and specificity^[2] but require a dedicated laboratory and experienced technicians and are usually offered in tertiary centers.^[4]

Biomarkers in exhaled air have been used for the assessment of airway inflammation.^[5] The fraction of exhaled nitric oxide (FeNO) is the most extensively studied biomarker and is increased in steroid-naive patients with asthma.^[6] FeNO is related with airway hyperresponsiveness, sputum and blood eosinophilia, and total IgE in patients with asthma.^[7,8,9] FeNO is reduced after treatment with inhaled corticosteroids^[10] and has been used as a guide to determine appropriate asthma treatment.^[11] Moreover, FeNO is elevated in patients with allergic rhinitis.^[12] FeNO has been studied as a screening tool for asthma^[13,14] and as a predictor of exercise-induced bronchoconstriction in children.^[15] However, FeNO has not been evaluated as a screening tool for asthma in an adult population.

The aim of the present study was to evaluate the performance of FeNO measured with a portable nitric oxide analyzer as a screening tool for asthma in a population of young adults, including smokers, during pollen season. Possible confounding factors and the repeatability of FeNO measurements were additionally evaluated.

09 August 2022

USCG faces logistical and operational challenges in Alaska for Island-class patrol forces


 To maintain its Island-class boats and continue patrolling the treacherous Alaskan coast, the US Coa...

The 5th Annual Genetics and Genomics virtual conference is now On-Demand! This event covers the most exact and exciting advances in genetics research. LabRoots invites research scientists, post docs, principal investigators, lab directors and other genetics professionals to learn about new discoveries and discuss their own findings with like-minded colleagues and experts in the field.

As the foundation of life, Genetics provides a base for other sciences to grow from. As we learn more about genetics and genomics applications, further knowledge can be integrated into diagnosis and treatment of disease and learning more about the complexities of human biology.

The syllabus discussed in this years Genetics and Genomics event includeed:

• Gene Therapy
• Gene Modifiers and Disease Progression
• Single Cell Genomics
• Liquid Biopsies and Exosome
• Precision Medicine

Our virtual conference allows you to participate in a global setting with no travel or cost to you. You can participate in exactly those parts which you are interested in and be back at your desk or bench in an instant. Virtual events remove time and place restrictions and ensure that everyone who wants to participate can do so.

Genetics and Genomics conference participants benefit from interacting with field experts and networking with colleagues. Attendees can also “walk” through the virtual exhibit hall to learn about the latest in genetics and genomics tools and assays. Join LabRoots in leading progress toward understanding the genetics behind disease and treatment.

Continuing Education:
By participating in this virtual event and watching webcast presentations, you can earn Free CEU, PACE, and/or CME credits. To earn educational credits, you must view an entire presentation. Following the presentation you must click on the educational credit link provided for that particular speaker and follow the required process. Once you have completed the process, you will receive a certificate for the educational credit. The American Board of Genetic Counseling, certifies genetic counselors and accredits genetic counseling training programs. The National Society of Genetic Counselors (NSGC) is the professional membership association for the genetic counseling profession.

Use #LRgenetics to follow the conversation

Methods and Materials

A screening questionnaire based on the European Community Respiratory Health Survey II short screening questionnaire^[16] was distributed to 1,053 students of the University of Thessally and the Technological Education Institute of Larissa in the spring of 2006. This questionnaire has been previously used for the screening of respiratory symptoms related to asthma^[17,18] and is provided in the online depository. All students with at least one positive answer were considered eligible for the study. Subjects were excluded if they had any of the following: (1) previous diagnosis of asthma or rhinitis treated with antiinflammatory medication (inhaled or nasal corticosteroids, long-acting β₂-agonists, leukotriene modifiers, antihistamines, or methylxanthines), (2) history of respiratory tract infection within the past 6 weeks, and (3) exact smoking cessation (< 2 months prior to the study). We excluded exact quitters on the basis that FeNO levels return to normal levels 4 to 8 weeks after smoking cessation,^[19] in order to stratify our subjects as either current smokers or nonsmokers. Seventy healthy subjects with no respiratory symptoms were randomly selected as control subjects. Study participants were initially submitted to FeNO measurement and were subsequently submitted to spirometry and evaluated by a respiratory physician who was blinded to FeNO measurements. The study protocol was approved by the local ethics committee, and participants provided informed consent.

FeNO was measured using a portable nitric oxide analyzer (NIOX MINO Airway Inflammation Monitor; Aerocrine; Solna, Sweden) that provides FeNO measurements at 50 mL/s exhalation flow rate, expressed in parts per billion (ppb).^[20] Measurements with this device are in clinically acceptable agreement to measurements provided by a stationary analyzer (NIOX; Aerocrine) according to American Thoracic Society guidelines.^[21,22,23] The accuracy range of the NIOX MINO device is ± 5 ppb for measured values of > 50 ppb and ± 10% for values 50 ppb. All FeNO measurements were performed in the morning (between 10:00 and 12:00 AM) and subjects had not consumed food or beverages and had not smoked 2 h before, under supervision of one investigator. A single NIOX MINO analyzer was used throughout the study. Details on FeNO measurements with this analyzer have been provided in the online Supplement.

Diagnosis of asthma and allergic rhinitis was established after FeNO measurements, based on evaluation by a respiratory physician blinded to FeNO measurements (K.K.) under prespecified criteria.^[1,24] Asthma was defined based on a history of relevant lower respiratory tract symptoms, along with one of the following: significant bronchodilator reversibility, positive methacholine bronchial challenge test, or clinical and spirometric response to a 4-week trial of inhaled corticosteroids, prescribed after FeNO measurements. Allergic rhinitis was defined based on compatible symptoms (nasal obstruction, rhinorrhea, sneezing, itching of the nose and/or postnasal drainage, with or without ocular symptoms) in patients with atopy. In patients without previously confirmed atopy, positive skin-prick test results to 10 common aeroallergens (dermatophagoides mix, birch, parietaria, cypress, sycamore, olive, alternaria, cladosporium, cat epithelium, dog epithelium) confirmed the diagnosis. Patients with concomitant asthma and allergic rhinitis were considered asthmatics. Subjects with positive answers to the questionnaire not fulfilling criteria for diagnosis of asthma or rhinitis were classified in the “nonspecific” respiratory symptoms group.

Spirometry was performed with a dry spirometer (KoKo Legend; Ferraris; Hertford, UK).^[25] Bronchodilator reversibility was evaluated after inhalation of 400 μg of salbutamol; an increase in FEV₁ > 12% and > 200 mL from baseline was considered significant.^[1] Methacholine challenge testing was performed in a subgroup of patients with diagnostic uncertainty (n = 47) in order to confirm the diagnosis of asthma in this subgroup using a commercially available system (APS; Viasys; Hoechberg, Germany) according to American Thoracic Society guidelines.^[4]

Repeatability of FeNO measurements was evaluated on 2 consecutive days in 30 study participants (10 patients with asthma, 10 patients with allergic rhinitis, and 10 control subjects) in the morning (between 10:00 and 12:00 AM), following the same protocol. Subjects for repeatability testing were selected randomly based on their availability for a second evaluation on the following morning, until the predefined number of 30 was reached. Repeatability on 2 consecutive days was chosen to evaluate short-term within-subject variability of FeNO measurements.

Demographic data are presented as mean ± SD; FeNO data were skewed and are presented as median and interquartile range. Comparisons of FeNO values were performed with Mann-Whitney U tests (between two groups) or with Kruskall-Wallis tests (among three or more groups). Repeatability of FeNO measurements in stable subjects on 2 consecutive days was evaluated with the Bland and Altman method.^[26] A multiple linear regression model was created to define independent predictors of FeNO, using FeNO as dependent variable, and age, sex, height, FEV₁, FEV₁/FVC, current smoking, diagnosis of asthma, and diagnosis of rhinitis as independent variables. Diagnostic performance of FeNO was evaluated with receiver operating characteristic (ROC) curves created by plotting sensitivity against 1 - specificity, and the area under the curve (AUC) with 95% confidence intervals (CIs) was calculated. Additionally, sensitivities and specificities with 95% CIs were calculated for specific FeNO cut-off points.