Say you've properly tuned an ADF station in COMP mode so that the BRG needle on your RMI is pointing towards your station. Then you tune the same ADF frequency on your V/UHF radio. Does anything happen to your needle at this point? How about when you transmit on that frequency?

Edit: Meant RMI


1 Answer 1


NDBs in the U.S. transmit between 90 kHz and 535 kHz, and VHF is between 108 and 137 MHz. Of the VHF frequencies, the nav/com is only capable of transmitting between 118 MHz and 137.

So aside from electromagnet interference, no VHF radio should transmit on a frequency that he ADF receives.

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    $\begingroup$ EMI should be pretty limited - even the "dirtiest" radios I can think of (Narco Mk12-D & King KX-155 with gas-discharge displays) shouldn't leak enough RF at the radio to mess with an ADF, and the possibility that a badly-designed (or malfunctioning) VHF radio could be transmitting harmonics in the ADF range is pretty remote. These are also things the avionics shop should be checking as part of the installation. $\endgroup$
    – voretaq7
    Jul 10, 2015 at 2:44
  • $\begingroup$ Just one thing; while the ADF tunes to NDBs in the stated range, an RMI has a second needle to point to a VOR station, and those do operate in tunable VHF frequencies (the signal is often modulated by a voice transmission; the VOR station might do double duty as an airfield's ATIS or AWOS transmitter). This might cause the RMI's VOR needle to deflect if you were to tune COM1/2 to that same frequency and try to transmit on it. But, that would be rather pointless as VOR frequencies are reserved for ground-to-air transmission. $\endgroup$
    – KeithS
    Jul 10, 2015 at 15:28
  • $\begingroup$ That's a really good point. I thought you meant the bearing needle on the ADF. if you have a true RMI that picks up both MF and VHF, then your comment makes perfect sense $\endgroup$
    – rbp
    Jul 10, 2015 at 15:35
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    $\begingroup$ @KeithS Your VHF radio doesn't tune down into the frequencies that VORs transmit on either. Also, the RMI needle that "points to" the VOR station isn't working on ADF principles of determining which direction has the strongest signal, but by displaying the bearing data that the VOR signal is giving you. Voretaq7's answer is correct. $\endgroup$
    – Ralph J
    Jul 10, 2015 at 21:33

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