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Ft to suit reception of long wave signals at any distance. It was recognised that effect of adjacent land masses on transmitter sites and also that of atmospheric conditions at Sun rise and sunset had to be considered.

Direction Finding Systems

In early trials, some warships these large aerials were at lower level and fitted between the funnels or in one funnelled ships between the funnel and bridge structure. The beam loop was suspended from the triatic stay and connected to stump masts or booms.

This arrangement presented difficulties in the physical handling of the portable lengths of wire which had to be kept rigid using bottle screws 2. Operational efficiency was affected by the effects of radiation from the main transmitting aerial and bearing errors were also caused by proximity to fixed structures as well as the movement of boats or gun mountings.

Different sizes at varying heights in and on both masts may have been used in some ships for conduct of trials 3. The main advantage of fixed rigid loops was to avoid the problems of rotating such a large assembly. It also would suit reception of signals transmitted from positions over a long distance. Although the aerial circuit could be tuned this would require adjustment for each received signal and introduce large errors since the exact size of each loop would not be identical. Use of tuned aerial circuits was not continued. T his had to established by turning the ships through a full circle which was inevitably a long process and could involve several time-consuming operations involving significant man-power.

It follows that by use of two loops there are two positions in which maximum and minimum signals from the bearing of the transmitter site are received. In order to overcome this ambiguity the two loops are connected to a Sensefinder 1. Accuracy of the determination of the actual bearing of the received signal depends on there being no mutual coupling between the loops and that the received aerial current fed from the loops produces a uniform magnetic field 1.

A goniometer comprises two fixed Field Coils, connected to the two loop aerials and a separate rotating Search Coil fed from a separate Sense aerial.


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As result of this, the combined signal sent to the main receiving circuits is modified by movement of the rotating component. There are two positions when the received signal is at maximum during one complete rotation. When turned clockwise the true bearing as indicated on the Bearing Indicator Dial is being received.

However due to the combination of the Sense aerial input with that from the two loops, the reciprocal bearing is identified when the signal strength increases See Figure 21 in Reference 1. Transmissions on frequencies about KHz were a more complex matter because of the effect due to movement of layers in the ionosphere.

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Contribution of the polarization diversity in H.F. direction finding systems

Use of a super-heterodyne receiver was more efficient at higher frequencies. Shore trials at a special establishment exclusively for aerial design were carried out first. During trials at sea using one of the loop aerials to instead of a separate Sense Aerial proved unsatisfactory compared with results obtained when a completely separate wire aerial was used.

Amongst the factors considered during these early trials was the effect of coincident wireless transmissions on trials ships when direction finding was being carried out and these were forbidden. In addition it was discovered that the physical length of the ship also had an influence on the accuracy of bearing errors on frequencies whose wavelength was related to the received signals. It was therefore evident that improvement had to be made to the aerial design in order to reduce bearing errors although this could not be eliminated on some frequencies 2. Clearly they would also be much more suitable for fitting on smaller vessel, especially destroyers.

Finding Books in the H F Library

This proved to be most significant step and the fixed Frame coil design used had two rotatable smaller loops and became a standard fit in TRIBAL Class destroyers on build before September 3. The final design used one of two different designs of aerial units, identified as Frame Coils S16 and S The size of aerial used depended on the structure of structure of particular ships mast.

HF Direction Finding Antenna SDA-30

The aerial unit was mounted on a pole mast fitted at the top of foremast of the ship. Both Frame Coil and Pole-mast could be struck using a separate beam to lower or raise the complete assembly when necessary to allow passage under a bridge or for replacement. In addition, efficient earth connections had to be used for the aerial cabling. You have only 2 significant digits in your pKa and only 1 in your value for C.

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