Western727 From United States of America, joined Jan 2007, 643 posts, RR: 4 Reply 1, posted (12 years 1 month 6 days 8 hours ago) and read 1519 times:
NDBs, or non-directional beacons, are low and medium frequency aids, which operate on a band between 190 and 535 Khz. They are just like AM radio... In fact, some NDBs double as AM radio stations, and you can turn up the volume on an NDB and listen to the the radio in flight. I wouldn't reccomend this, because you might miss some important flight communication, and it's AM, so their isn't usually anything good on anyway.
So, an ADF (Automatic Direction Finder) Is the instrument that is used to navigate from NDBs. It consists of simply an arrow pointer inside a compass rose. The arrow simply points to the station. That's it. ADFs usually have non-slaved compass cards (the card is the compase rose) however, meaning that there is no connection between it and the compass or directional gyro) So you'd have to adjust that to your actual heading, and then when you make a heading change to get the actual magnetic bearing to the station.
ADFs are subject to a few errors. They are vulnerable to precipitation, lightning, static, etc., and at night they are subject to the same interference from distant stations that normal Am radio is. It's interesting: When lightning strikes, the ADF needle will momentarily point to where the strike occured. ADFs have no flag to warn of unreliable navigation information like VORs do. In this case, the AIM reccomends turning up the volume and continuously monitoring the NDBs identification, because almost all errors also affect the identification signal.
I hope this helps. Let me know if you need any clarification.
Airplay From , joined Dec 1969, posts, RR: Reply 3, posted (12 years 1 month 5 days 18 hours ago) and read 1469 times:
Typical ADFs will receive between 200 KHz and 1700KHz. The "radio stations" you hear on the ADF are broadcasting on the commercial AM band.
Some NDB stations (which are restricted to the 200 KHz to 500 KHz) sometimes transmit transcribed weather but I've never heard of them broadcasting commercial AM. NDBs however are just Omnidirectional AM broadcast stations. The power is usually much lower than commercial broadcast stations.
ADFs monitor 2 aspects of the signal. A directional loop antenna comprising 2 coils 90 degrees from each other, provide the ADF with the direction of the station. Unfortunately there is not enough information in this signal to determine if the station is straight ahead or directly behind you. A second antenna called a sense antenna provides the "tie breaker". By comparing the two the ADF determines which direction is right and drives the ADF indicator pointer to display the relative bearing to the station. (It's a little more complicated than that, but I'm avoiding confusion)
Modern ADF antennas combine the sense and loop antennas in a single unit. Older systems have a separate long wire sense antenna along with the loop.
Small aircraft display ADF bearing on a dedicated ADF indicator which may have a fixed bearing card or a movable heading card or a compass card which repeats magnetic heading.
Airliners typically display ADF bearing on an RMI (Radio Magentic Indicator) which also displays magnetic heading on a moving compass card.
Airliners with EFIS displays will display ADF bearing on the ND if selected.
Western727 From United States of America, joined Jan 2007, 643 posts, RR: 4 Reply 4, posted (12 years 1 month 5 days 8 hours ago) and read 1456 times:
I've never heard of them broadcasting commercial AM.
Here at KPVU (Provo, UT) we have an NDB that is for VFR use only. It's called KOVO, and the frequency is 960. It's also an AM radio station. It's not an IFR NDB, but it's on the SLC Terminal Area Chart and Sectional.
XFSUgimpLB41X From United States of America, joined Aug 2000, 4103 posts, RR: 38 Reply 6, posted (12 years 1 month 4 days 23 hours ago) and read 1440 times:
Just like your VOR and communications frequencies are just above the usual FM radio frequencies, the NDB frequencies are just below the usual AM radio frequencies.
All that an NDB does is broadcast out a non directional signal, and your indicator points to it relative to your airplane. You can also change the setting to point at AM radio stations, and by turning up the volume and flipping the ADF switch to speaker or phone on your communcations selector panel, you can listen to it too..basically by doing the same thing you do to indentify the NDB station.