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Guest Ron Freimuth

how to calculate the range of an NDB

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I found a table with some antennas and their power is rated in dBW. How can I calculate the range at which I still can pick up the signal with an avarage ADF? Is there some sort of formula?I know the signal will drop distance squared, but I assume that air and lots of other things will be relevant. I also have mast height and frequency if that's necessary.Cheers, Christian

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Christian,The reception range, or service volume, of an NDB will fall in to one of four categories.Compass Locator - 15NMMedium-High - 25NMHigh - 50NMHigh-High - 75NMSee table 1-1-2 from the Aeronautical Information Manual.http://www1.faa.gov/atpubs/AIM/Chap1/aim0101.html#1-1-8Regards,Michael CollierDispatcherSystem Operations ControlAmerica West Airlineshttp://jdtllc.com/images/RCbeta.jpg

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EDITED: I misread the original post. The others answered it pretty well.

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Sorry, your answers don't help at all. I knew those NDB ratings.I'm trying to add AM radio stations to MSFS, so I want to get an approximate range value for those. I know I can't get a good range value, because it depends on lots of things, but there must be some relationship between transmitted energy and range that I could use.I found this which helps me come up with some very rough estimates though:MH - <50 wattsHH - >2000 wattsH - in betweenWould be good to have a formula instead though. I know the the Bendix/King ADF can still receive at a s/n ratio of 6dB (4:1). If I would know how much energy (watts) background noise typically has, then I could calculate an approximate range like this:range[metres] = sqrt( mast energy[watts] / 4 * noise energy[watts] )I know the reality is more complicated since the range is dependent on frequency, antenna shape and height, etc, but would be good to get an approximate.Cheers, Christian

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I know on my instrument cross country from Daytona to Gainsville, we picked up an AM station from Alabama. We were cruising about 7000 feet halfway along our route.

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When trying to figure the range of a Broadcast AM station typically in the frequency range of 550khz to 1600khz, there are so many variables to the problem. For instance you must take into account the power of the station, the type of antenna to get the ERP or effective radiated power, and most importantly the time of day. In the daytime a 50,000 watt clear channel station such as KOMA or KSL or KFI, may be picked up for as far away as 100 to 200 miles, at night these same stations may well be heard in excess of 2,000 miles depending on the conditions in the ionosphere. Smaller stations 10,000 watts and smaller may be pushed to be heard 25 miles away again depending on the ionosphere.Of course broadcassting companys do use some really heavy engineering techniques, (MATH), extemely complicated and EXPENSIVE electronic measuring devices and still usually miss what they were aiming for.I would guess that if you set your AM stations for an average of 250 miles reception it would not be totally unrealistic, I have picked up KOMA in the daytime in Dallas Tx at any altitude. KOMA is in Oklahoma City OK or about 200 miles. It is a 50,000 watt station and plays Oldies :) Or i can pickup WBAP in Fort Worth from Oklahoma City quite often.

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It's great if you can get yourself some elevation while travelling at night. On more than one occassion, I have picked up AM broadcasts from Minneapolis (WCCO), Chicago, Fort-Worth, and Santa Fe while driving along I-80 in Wyoming (which is more or less a plateau at ~6000-7000 MSL).J

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Thanks, that helps a bit. My stations have a range between 2000 and 150,000 watts, so quite a difference. I may just have to come up with some approximate guesses.Cheers, Christian

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In the U.S. AM broadcast stations are limited to 50,000 watts maximum and there are not too many of them. Mexico limits there AM stations to 100,000 watts.

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>I'm trying to add AM radio stations to MSFS, so I want to >get an approximate range value for those. I know I can't get >a good range value, because it depends on lots of things, >but there must be some relationship between transmitted >energy and range that I could use. Medium Frequency range is tricky, it depends on whether ground or sky wave propagation is involved. During the day, the sky wave, bounced off the ionsphere doesn't exist. Near the ground, the 'ground guided wave' strength depends on the number of wavelenghs from the transmitter. Lower frequency waves suffer less attenuation per mile. The wavelength is 1000 meters (1 km) at 300 kHz, Terman gives a formula for ground wave strength: E = A * Eo/d. From a graph: at 100 wavelenghts (100 km, ~62 sm) A is 0.004. Attenuation is proportinal to d/wavelength. He states "Thus, with a 50 kw broadcast transmitter employing an antenna with vertical directivity that increases the field strength along the horizon by a factor of 1.41 times the field strength obtained from the assumed cosine law, one has Eo = 1.86 * 1.41 SQRT(50) = 1860 mV per m at one mile. So, at 100 km, E = 0.004 * 1.86/100 = 75 micro Volts/m. Now if frequency is doubled to 600 kHz (low BC band), d/lambda doubles and A drops from 0.004 to 0.0025. So signal strenght would drop to 75 * 2.5/4.0 = 47-micro V/m. Voltage varies with SQRT(Power), so a 5 kW station would produce 47/3.16 = 15-micro V/m. That field strenght value is converted by the receiving antenna to a signal voltage which is applied to the receiver. However, I don't know off hand how strong it would sound on a radio. I think 75 micro-V/m would give a 'good' signal if static isn't high. Which one gets from summer thunderstorms. AM stations prefer the low end of the BC band, since ground wave signal attenuation is lower than for higher frequencies. That 50 kW signal would be good at 62 sm but a station at 1600 kHz would probably be too weak. With an external antenna, one can typically recieve BC stations up to 100 sm during the day on the ground. I'm not sure that elevation helps much here. One is further from the ground guided wave, but also from some static sources. Assuming you don't have ignition nose from the AC engine. At night things are completly different. The ground guide wave is about the same, but signals are reflected from the ionsphere. Many stations interfere and small AM stations either go off the air or have to reduce power. "Clear Channel" stations have protected frequencies and one can easily receive them at 1000 sm or more. Near the transmitter, the sky wave and ground wave tend to cancel, and severe fading is possible. >I know the reality is more complicated since the range is >dependent on frequency, antenna shape and height, etc, but >would be good to get an approximate. >Cheers, Christian There are quite a few books on antennas and radio wave propagation, including some by the ARRL. However, one might as well use real experience to set an appropriate range for radio stations in the BC band. For VHF VOR's, etc. it is easier to make these calculations. ---- Now there are some FS Token variables that give current VOR and NDB signal strenghts. I noted that the VHF VOR strenght appeared to vary realistically. It would be over 10,000 near a VOR, but drop as one flew further away, and also if he reduced altitude. When the signal dropped to about '255' the VOR died. It would be better if the noise slowly increased, as it does in a real AC. There is also an NDB signal strenght token. I'm not sure it varied appropriately, it should not change the same was as the VOR strength. I think the NDB also died when this token variable dropped to about '255'. "Recorder.dll" can log any token variable, further one can get the current value by selecting the appropirate token on the Recorder menu. Be neat if AM stations that actually broadcast music, etc. could be added to FS BGL files. Or, otherwise made available. If an internet connection were availabe one could receive real time web broadcasts from many real stations around the world, though hardly every AM station one can receive on an AC ADF receiver. I think it would be possible to simulate short wave radios in FS, but one would have to provide the other end of the SW channel to have anyone to talk to. That could be implemented over TCPIP for transoceanic SW links that were used some decades ago. LORAN is another possibility.Ron W5VOI

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I love where flight simulator is goingthis is way more concern than any of my real world pilots have to anything... I am very impressedif we all listened to the beatles, and really kicked mr. gates in the bum to get things going on something that could promote the real industry, we could really start to have a lot of fun...be well, y'all, I'm off to iceland tomorrowmy question is how much difference line of sight makes with AM, I thought that made little difference versus FM, and it was more daytime versus night time, and errors like shoreling effect and dawn/dusk effect for the errors in AM/NDB freqs....this is a great thread for fs and real life:)

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Hi Ron,thanks for your long post. I couldn't follow it 100%, since I didn't see where some of the values were coming from (eg conversion watts to V/m). Using your input I came up with a very simplyfied formula:coverage = 1E8 * sqrt(E) / freqprobably not very good, but a rough approximation (for your 50kW station I get a coverage of 75 km, should be 50 km really, since the Bendix/King needs 150 microV/m to read an NDB signal, but its close enough if we consider that we have neglected quite a few factors in the first place).However, this isn't consistent with the NDB rating values. With 2kW I should get a coverage of about 75nm! I've read a bit more on ground waves today and your calculation seem reasonably ok, so I don't know how to fix this really.Getting AM broadcast would be great but I don't know how many (and if any at all) AM stations actually broadcast into the net. At this stage, I just wanted to add those stations so there is a bit more 'action' when you tune your ADF.Cheers, Christian

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>Hi Ron, >>thanks for your long post. I couldn't follow it 100%, since >I didn't see where some of the values were coming from (eg >conversion watts to V/m). Using your input I came up with a >very simplyfied formula: I just quoted Terman's 'Electronic and Radio Engineering' to get the Field Strenght for a reference distance from a 50 kW BC transmitter. Only the end number was important here.>coverage = 1E8 * sqrt(E) / freq Yes, for 'ground wave' propagation, range varies with 1/freq.>probably not very good, but a rough approximation (for your >50kW station I get a coverage of 75 km, should be 50 km >really, since the Bendix/King needs 150 microV/m to read an >NDB signal, but its close enough if we consider that we have >neglected quite a few factors in the first place). Ah, so 150 micro-V/m is a low limit of field strength. My 47 and 75 micro-V/m were pretty weak. Hmm, I wonder if the FS Token 'ADF Strength' is in micro-V/m. Since the ADF died around '255'. >However, this isn't consistent with the NDB rating values. >With 2kW I should get a coverage of about 75nm! I've read a >bit more on ground waves today and your calculation seem >reasonably ok, so I don't know how to fix this really. The NDB/ADF receiver may have a narrower BW than a BC radio. Half the BW would cut the noise by 3dB. But, that doesn't make any more difference than doubling the transmitted power (which is not much).>Getting AM broadcast would be great but I don't know how >many (and if any at all) AM stations actually broadcast into >the net. Hundreds! At least a couple of years ago. The Real Audio app can get one to URL's with many live BC's from all over the world. There were at least a dozen in Brazil. And, one can add favorate stations to a listing. I'd think the MS Media Player could be set to compatable BC URL's. In fact, I'd expect some related DLL without the Player window would handle this if interfaced properly. > At this stage, I just wanted to add those stations >so there is a bit more 'action' when you tune your ADF. >Cheers, Christian Yes, It would be nice to be able to pick up even just a few BC stations on the ADF. Or, even mpeg music files. Ron

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