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3.5 VHF FREQUENCIES and CHANNEL SPACING
The bandwidth allocated to VHF frequencies was, for the most part, 25 KHz. That is

the spacing between one channel and another.

In many busy types of airspace, designated by the authorities, the spacing between
channels has been reduced to 8.33 KHz thus creating many more channels.

Channels which are spaced by 25 KHz required 5 digits, not more than 2 digits

after the decimal point, whereas channels spaced by 8.33 KHz require 6 digits, 3
digits after the decimal point.

ICAO standard requires all 6 digits of communications frequencies be passed in
RTF instructions. This means that VHF channels will include 6 digits irrespective of

whether the channel is 25 KHz or 8.33 KHz spaced. The only exception to this is

where the final two digits are both zero, in which case only the first four digits
need to be transmitted.

When using a 5 digit radio, (25 KHz spacing), only the first 5 digits of the given

frequency need be set on the radio.

3.6 DIRECTION FINDING (DF)
Q Codes were used extensively when much of the communication work

(especially HF-long range) was done in morse code. QNH was quicker to “key in”

than A.L.T.I.M.E.T.E.R. S.E.T.T.I.N.G. S.E.A. L.E.V.E.L. P.R.E.S.S.U.R.E.!
Today some Q-codes are still widely used because they are useful abbreviations.

They are spoken in plain English not phonetically.

Commonly used Q codes are listed below.
Q CODE MEANING

QFE Atmospheric pressure at aerodrome elevation

QNH Altimeter sub-scale setting to obtain altitude above mean sea level
QDM Magnetic direction towards facility

QDR Magnetic bearing (radial) from a facility

QTE True bearing from a facility

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