Important Considerations; Lcd Resolution; Significance Of Receive Step Size - AOR SDU5500 Manual

Section 3-3, 3-3-1, 3-3-2

3-3 Important considerations

3-3-1 LCD resolution

The LCD provides high resolution of 304 horizontal dots from the left to right edges of screen.
As a result, there are about 30 steps per graticule division with ten divisions making up the total width.
The relationship between frequency and LCD-step is determined by the programmed SPAN width.
Span is set up in menu 4 while in SPECTRUM DISPLAY mode "OP.MODE : SPECT". The minimum
displayed bandwidth is 1 kHz (+/- 500Hz) and the maximum displayed width is 10000 kHz (10 MHz)
representing ± 5 MHz. Numeric entry is in kHz format from 1 to 10000 inclusive.
To calculate the LCD-step, divide the SPAN bandwidth in kHz by 304. Examples are as follows:
10000 kHz (10 MHz) =
5000 kHz (5 MHz) =
2000 kHz (2 MHz) =
1000 kHz (1 MHz) =
500 kHz =
100 kHz =
It is possible to force the LCD-step to equal the receive tuning step using a similar process. Multiply
the receive tuning step size in kHz by 304 (dots) to obtain the required total span width in kHz.
For example, for a 5 kHz tuning and LCD step, 5 x 304 = 1520 kHz span
The following table presents commonly used step sizes:
1 kHz
5 kHz
6.25 kHz
9 kHz
10 kHz
12.5 kHz
20 kHz
25 kHz
32.89 kHz

3-3-2 Significance of receive STEP size

Due to the necessary calculation of total span width divided by LCD-step resolution of 304 dots, the
marker frequency will usually display an 'approximate' frequency only... especially as the total span
width is increased above 1 MHz or so.
However, if an appropriate step size has been set, the SDU5500 / companion radio will automatically
calculate the 'likely' exact frequency when the MK-CF (marker to centre frequency) key is pressed.
For example: If the centre frequency is set to 125 MHz, the span set to 10000 kHz and step size to 25
kHz, the marker position of a strong airband transmission may appear at 126.15131 MHz, clearly not the
'exact' wanted frequency. However by pressing the MK-CF key of menu 5 will change the centre &
marker frequency to exactly 126.15000 MHz, this is clearly the correct frequency being the closest 25
kHz multiple to 126.15131 MHz.
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32.894736 which is truncated to 32.89 kHz
16.44 kHz
6.57 kHz
3.28 kHz
1.64 kHz
0.32 kHz (320 Hz)
304 kHz (0.340 MHz)
1520 kHz (1.520 MHz)
1900 kHz (1.900 MHz)
2736 kHz (2.736 MHz)
3040 kHz (3.040 MHz)
3800 kHz (3.800 MHz)
6080 kHz (6.080 MHz)
7600 kHz (7.600 MHz)
represents maximum span of 10000 kHz (10 MHz)