Ramsey Electronics QRP-80 Manual de instrucciones descargar pdf (Pagina 20)

HR-80• 20

BANDSPREAD AND TUNING RANGE:

The easiest way to enjoy finer tuning , if you plan to use your

receiver only for checking your favorite segment of the band, is to

adjust the oscillator coil so that your desired segment falls within the

second half of the rotation range of the tuning control. The first half of

the rotation range covers about 70% of the actual tuning in KHz,

while the other 30% is spread over the other half of the rotation

range. If your interest is in monitoring SSB, the normal alignment will

work fine. For optimum CW only listening, set the lower band edge

with the tuning control in the 12:00 position of its range.

In planning any ‘bandspread’ improvement, it is useful to understand

exactly how varactor tuning works. The control level varies the

amount of DC voltage applied to the diode. The highest produces the

lowest capacitance, while the lowest voltage yields the highest

capacitance. The spread is typically about 30 to 40pF. from minimum

to maximum.The goal in achieving bandspread or ‘fine - tuning’ is to

achieve a smaller variation in capacitance with the comfortable

tuning of a knob.

Any resistor in a range from 500 ohms to 3000 ohms, connected in

series with the ground lead of R2, will set a limiting effect on varactor

capacitance range and therefore create a “bandspread “ effect. The

higher the resistance value, the shorter the available tuning range.

If you wish to reduce the tuning range of R2 down to 40 or 30KHz or

even less for a favorite band segment or calling frequency, reducing

the value of C4 will decrease the capacitance effect of the varactor

diode, D1. Values from 2 to 5pF may give you exactly the tuning

range you are looking for.

If you are using your own enclosure and have room for a separate

fine tuning control, one useful choice is a 250 ohm speaker

attenuation rheostat (Radio Shack model no. 271-265) wired in

series with either outside ‘leg’ of the main tuning control. Such a

control can make fine adjustments to a CW signal so the tone is

pleasant and smooth sounding.

If you want the opposite of bandspread (that is as MUCH frequency

range as possible over full rotation of the tuning knob ) increase the

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Ramsey Electronics QRP-80 Manual de instrucciones Pagina 20