Simultaneous measurements of the frequency and bearing of h.f. radio waves

The presence of travelling ionospheric disturbances (t.i.d.s) at the reflection point of h.f. radio waves, propagated at oblique incidence, has been monitored by means of a Doppler-frequency sounder. The bearing error measured by a direction finder at one end of the oblique path is shown to be correlated with the t.i.d. activity at the path mid-point. The magnitudes of the bearing errors have been calculated from the Doppler observations, and these are shown to be in good agreement with those observed experimentally using the direction finder. The errors caused by the travelling disturbances are an order of magnitude greater than the instrumental accuracy of the direction finder. Correction of these errors is therefore essential before the inherent precision of modern h.f. direction finders can be realised.