Radio Navigation - ADF & NDB

Summary

Highlights

• ADF and NDB work together to determine aircraft direction relative to the beacon. 📡✈️
• The ADF principle involves measuring voltage changes as it aligns with NDB signals. 🔄📊
• Electromagnetic circuits mimic rotation, helping in accurate bearing depiction. 🔄📍
• Interferences like static and night effects can disrupt ADF/NDB signals. 🌩️📉
• NDBs operate within 190-1750 kHz frequencies, but mostly 250-450 kHz range. 📻
• Despite being foundational, ADF/NDB systems are becoming obsolete. 📜🔄

Key Takeaways

• ADF stands for Automatic Direction-Finding, an onboard aircraft equipment. 🛫
• NDB is a Non-Directional Beacon, a ground-based signal transmitter. 📡
• ADF measures the bearing of an NDB relative to the aircraft's fore-aft axis. 📍
• Electronic circuits simulate rotating loop antennas to determine accurate bearings. 💫
• Factors like static interference and night effects influence ADF and NDB accuracy. 🎯
• NDBs are being replaced by VOR systems due to higher accuracy. 🔄

Overview

Chapters

• 00:00 - 00:30: Introduction to Radio Navigation and ADF/NDB The chapter titled "Introduction to Radio Navigation and ADF/NDB" is part of a series focused on radio navigation techniques. The speaker, identified as "Plains over it," begins with a standard disclaimer about the ownership of images used in the presentation. The chapter covers the concepts of Automatic Direction-Finding (ADF) and Non-Directional Beacon (NDB). ADF is defined as an onboard equipment used in aircraft for navigation, while NDB refers to a ground-based transmitter that generally operates within the low to medium frequency ranges.
• 00:30 - 01:00: Functioning of ADF and NDB The chapter 'Functioning of ADF and NDB' explains how vertically polarized radio signals are transmitted in all directions. It emphasizes the importance of these vertically polarized signals and describes the process where an Automatic Direction Finder (ADF) onboard an aircraft is tuned to the Non-Directional Beacon's (NDB) fixed transmitting frequency. Upon tuning, the aircraft can identify the NDB's callsign and determine the direction of the NDB using instruments like the RBI (Radio Bearing Indicator) or RMI (Radio Magnetic Indicator). However, detailed discussions on RB and RMI are not included in this chapter.
• 01:00 - 02:00: Principle of Operation The principle of operation revolves around measuring the bearing of the Non-Directional Beacon (NDB) relative to the aircraft's fore and aft axis, known as the longitudinal axis. When the loop aerial of the Automatic Direction Finder (ADF) is aligned with the plane of the transmitted radio frequency, a voltage is generated, which plays a crucial role in determining the bearing.
• 02:00 - 03:30: Signal Processing and Polar Diagrams The chapter 'Signal Processing and Polar Diagrams' explains the principles of signal processing, focusing particularly on how voltage changes as a loop is oriented with respect to a wave. It discusses how the voltage drops to zero when the loop is perpendicular to the wave and reverses when the loop continues to rotate, aligning again with the wave. A major focus is on understanding relative bearing by switched cardioid, with illustrations provided to show side and top views of the wave transmission and the associated loop positioning. The chapter aims to explain these concepts clearly, using visuals to depict the orientation of loops within the wave plane to maximize signal processing efficiency.
• 03:30 - 05:30: Types of NDBs and Frequency Range The chapter 'Types of NDBs and Frequency Range' explains the behavior of current in relation to wave direction, highlighting the phenomenon of a 'null' when currents become perpendicular. It describes the loop's rotation leading to the creation of a polar diagram resembling a figure-eight with two nulls. This visualization helps in understanding the interaction between the loop and the wave direction.
• 05:30 - 07:00: Emission Types and BFO Usage The chapter discusses the challenges of determining direction using beacons, which can be inaccurate when using only two nulls for positioning. To resolve this, the introduction of a sense aerial is presented. The sense aerial, also known as a simple dipole aerial, can provide a more accurate direction by utilizing its polar diagram.
• 07:00 - 12:00: Factors Affecting Accuracy and Range The chapter titled 'Factors Affecting Accuracy and Range' explains how polar diagrams are electronically combined to simulate the presence of a real object in the middle of a loop aerial. When relative signal strengths are aggregated, it produces a specific polar pattern visible on the screen. This resultant pattern is known as a cardioid.
• 12:00 - 14:00: Conclusion and Viewer Interaction The chapter titled 'Conclusion and Viewer Interaction' discusses the limitations of using a single null for determining accurate bearings. A single null, by itself, cannot provide an accurate bearing, as it may not meet the required accuracy demands of plus or minus five degrees to a station. To improve accuracy, the chapter explains that the cardioid polar diagram is rotated using a loop aerial. This rotation, which is performed clockwise, results in an increase in signal strength, thereby enhancing the accuracy of the bearings obtained. The discussion highlights the importance of precise adjustments and viewer interaction for achieving desired results in navigational or signal processing applications.

Radio Navigation - ADF & NDB Transcription

• 00:00 - 00:30 alright guys welcome to Plains over it and we are continuing with the radio-navigation series that is being started and the standard disclaimer whatever images are there in this video not owned by me so let's just begin today we're gonna do a DF + nd area stands for automatic direction-finding which is an onboard equipment loaded on the aircraft NDB is a non-directional beacon which is a ground-based transmitter and is generally in the low frequency in the mid medium frequency
• 00:30 - 01:00 bands what it does is transmits vertically polarized radio signals in all directions very important to note vertically polarized radio signals and how does it work is when the ADF that is there onboard is tuned to the ndb's frequency that is being fixed the transmitting frequency the callsign is identified and the direction of the NDB is indicated on the RBI or the RMI that is on the aircraft we shall not be discussing RB n RM I in detail in this
• 01:00 - 01:30 video because it is out of context but that's the instrument that is used to show the bearing of the NDB okay so principle of operation so principle of operation the ADF measures the bearing of the NDB relative to the fore and aft axis of the aircraft that's the longitudinal axis so it measures the bearing relative to that so when the loop aerial is placed in the plane of transmitted radio frequency a voltage will be generated I shall explain this
• 01:30 - 02:00 in the coming few minutes this voltage drops to zero when the loop is perpendicular to the wave and when the loop continues again to rotate it will induce in the opposite sense so bottom line is the principal is relative bearing by switched cardioid I shall explain all of this how it works so this is the wave that is being transmitted this is the side view and this is the plan view from the top so this is your loop as you can see this is your loop here so the loop whenever it is placed in the plane of the wave there's maximum
• 02:00 - 02:30 current when it is in the same direction and the current keeps on reducing as it turns and it becomes zero when it is perpendicular to the wave and creates a null okay so this null again the point is again when the loop is rotated there's another null that gets created because of the other side so this leads to a polar diagram of the loop as something like this a figure of eight with two nulls placed like this
• 02:30 - 03:00 okay now this doesn't give you a good you know position because it's two nulls and the direction of the beacon though can be determined is not pretty accurate it gives an approximate direction now what to solve that so you know problem we introduced something like called something called a sense aerial or it's a simple dipole aerial which has a polar diagram like this okay so the these both
• 03:00 - 03:30 polar diagrams are combined electronically as if the sense a real was in the middle of the loop aerial okay so this relative signal strengths you know get added up like this and this is the polar diagram that you can see on the screen okay that's how it looks like now this polar diagram resulted polar diagram gives a cardioid okay this is what is called a cardioid as as a single
• 03:30 - 04:00 null as you can see here single null and this itself all alone would not be able to provide a accurate bearing now how do you improve the accuracy because if our demands an accuracy of plus or minus five degree to the station okay so what is done is the cardioid polar diagram is rotated loop aerial is rotated clockwise as you can see so this produces an signal increase in signal strength of
• 04:00 - 04:30 the cardioid which gives you a right-hand cardioid as well so this improves the strength of this null and gives you much accurate bearing okay but now what the problem is you cannot have a rotating our aerial loop aerial on the load on the aircraft from the outside so electronic electrical magnetic magnetic circuit is used to make the loop feel as if it's rotating by
• 04:30 - 05:00 switching circuits logic circuits and hence this resultant polar diagram comes into play okay and that's how the bearing is depicted on to the RMI or the RBI frequency types of ndb's frequency is 190 to 175 0 kilohertz but most ndb's will be used between 250 to 450 kilohertz two types of ndb's locator and
• 05:00 - 05:30 enroute locator at low power NDB co-located with the ILS approach to guide the aircraft run to the localizer range is about 10 to 25 miles and route ndb's they have a range of 50 nautical miles or more and oceanic ndb's have range ranges several hundreds of miles that's because of the ocean effect okay the range on the oceans are much greater and they're used for homing holding enroute and airway navigation now important point is ndb's for both the above purposes have become largely obsolete because now it is being
• 05:30 - 06:00 completely replaced by the way was even locator it is barely there on most runways across the world there is no more locator concept at all an end route also has been moved by the viewer because it's much more accurate Doppler you are and the ranges of further high so we are discussing something that is kind of getting moving out of aviation okay now the emission is a two or three letter identifier okay and the emission
• 06:00 - 06:30 code is November 0 November alpha 1 alpha or November 0 November alpha 2 alpha so these are the two types of NDB emissions that are there so the point the problem is this is not easily detectable okay so there's a device that is installed within the equipment in the receiver ADF receiver onboard the aircraft is called a BF o beat frequency oscillator which offsets the received frequency within the receiver to make it detectable and audible now for alpha 1
• 06:30 - 07:00 alpha you require BFO to be on for manual tuning and also fire and if occasionally monitoring alpha 2 alpha you choir before to be on for manual tuning but identification and monitoring it is not required why because the alpha one alpha part is the emission of an interrupted and modulated carrier wave which requires the be a for to be on for identification an aural reception but the alpha to alpha is a mission of an
• 07:00 - 07:30 amplitude model modulated signal so this is unmodulated carrier wave we dropped it and modulated carrier wave which cannot be heard but alpha to alpha is emission of an amplitude modulated signal which can be heard on a normal receiver so hence identification monitoring bf4 should be is not required it's off okay factors affecting accuracy okay that's important for us to know so designated operational coverage is called as d OC so the UC of ndb's is during the date of
• 07:30 - 08:00 day time protection ratio which is signal-to-noise ratio and you know what happens is what you want signals you want and what are unwanted so that improves your accuracy so according to the ndb's performance it is good to use it in daytime nighttime it's not good static interference is pretty simple that is precipitation thunderstorms or any electrical activity that is there in the atmosphere will disturb the
• 08:00 - 08:30 frequencies you know because it collides with the water droplets or static electricity discharge which affect the LF & MF frequency okay so that will make the needle move rapidly and will absolutely not give you any bearing at all night effect night effect is something to do with what we discussed in the earlier video at night what happens is the D region that is there disappears so this allows the skywave
• 08:30 - 09:00 contamination to take place so skywave contamination happens and the surface waves gets contaminated because of the sky wave so this will reduce your you know the rain accuracy of these bearing and it becomes very significant from 7,200 nautical miles from the NDB where you are actually the needle will just try to hunt further in deeply so to avoid all of this you should avoid to avoid the you know night
• 09:00 - 09:30 effect fly in the day is simple and avoid using ADF within one hour of sunrise and sunset and you know you can always cross-check with other nav aids or any other charts station interferences near the antenna that is the NDB you have any metallic installations or any other disturbances that cause the frequency to be you know troubled interfere with mountain effect mountain effect is something to do with reflections and refractions due to
• 09:30 - 10:00 terrain so this is very common the valleys if you're flying low and of course can be avoided if you fly high up above the mountainous area so basically in the valley or ADF accuracies degraded largely coastal refraction now radio waves what happens is this speed up over water due to you know reduction in absorption of energy by water you know the terrain absorbs more water absorbs less so there's more attenuation
• 10:00 - 10:30 on the land so what happens is this speeding up of wave causes a diffraction turn of the radio wave refraction and diffraction so this pulls it towards the coast and gives it wrong bearing but this can be avoided by using the nd bees which are closer to the coast which because that will not give any reflection chance because you right at the coast NDB or you can now fly higher
• 10:30 - 11:00 because that will minimize and use signals that cross the coast at or near 90 degrees because ninety degrees you will have no refraction it will go straight through quote because there's no bending of the radio waves basically quadrantal error is because of the bearings basically so on relative bearings of zero four five one three five two two five and three one five there's a airframe quadrantal error okay
• 11:00 - 11:30 so the polar diagram gets affected because of the strong electrical field that is aligned with the foreign aft so whenever you are in this relative bearing of 45 degrees 135 to 25 and three one five in each quadrant there is maximum okay so the only way is the manufacturer has to you know test this and loaded in the equipment to remove this error angle of bank is pretty simple since the if you remember what I told you was the NDB
• 11:30 - 12:00 transmits in vertically polarized waves so the moment you bank the vertical polarized wave hit at a different angle to the loop causing it to give reduce the accuracy and ADF for NDB has a lack of failure warning system so the accuracy you do not know at all what's the heck if the instrument has failed or you know what is it showing so that is one factor that affects accuracy and bottom line is the accuracy which is
• 12:00 - 12:30 required by cow the minimum is plus or minus five degrees within the designated operation coverage which is during day only all right factors affecting range of ADF NDB transmission power which the range is directly proportional to the square root of the power so if you have to you know double the NDB range you have to quadruple the power of the power output of the transmitter the in Jobo water is greater this is how it gets
• 12:30 - 13:00 affected so three times this is over water two times the wool and because of the attenuation capacity of the land is more then lower frequency because ADF uses lower frequency greater surface wave lower attenuation okay so this is what affects the range so if slower frequency later surface wave and lower iteration it travels faster father the recitation reduces range of course as we discussed
• 13:00 - 13:30 it decreases accuracy also and it also reduces the range alpha one alpha ndb's have greater range and receivers quality of also affects the range all right now alpha one alpha and DBS have a greater range because of the fact that they are unmodulated carrier wave you know so that is why the ranges better so then again you need a B effort to keep it on for both even manual tuning and also for identification and monitoring and the receiver qualities of
• 13:30 - 14:00 course would depends from company to company what quality it is so I hope you guys understood the basics of the NDB and AD if you guys have any doubts please drop a comment below I will surely get back to your doubts and thank you for watching guys subscribe to the YouTube channel if you like this video give it a thumbs up and like the Facebook page for also regular updates and share it with your friends too I'm available on the links shown on the screen I'll be attaching a quiz on this video
• 14:00 - 14:30 in the description find the link below cheers and happy landings guys have a great day