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FLEX-6000 Signature Series - SmartSDR for Windows Software User’s Guide

Page 144

The Spectral Capture Units (SCU) in the FLEX-6000 transceivers contain three primary component

blocks:

• Preselection band filters (except in FLEX-6300)

• A preamplifier / attenuator

• A high-performance analog to digital converter (ADC) also known as a digitizer

Each of these blocks plays a role in receiver performance and must be considered when planning full

duplex operation.

34.4.1 Preselection Band Filter Block

Preselection band filters, when present and active, can reduce out of band signal levels by 20dB or

more. Preselection band filters are enabled by default in the FLEX-6400/M, FLEX-6500 and FLEX-

6700 any time the radio is not in the WIDE mode. An indicator in the upper right corner of the

panadapter will show when the radio is in the WIDE mode and pre-selectors are not enabled. The

FLEX-6300 is always in WIDE mode since it does not have preselection band filters, but this is not

indicated in the panadapter.

For the purposes of calculations, assume a 20dB reduction in out-of-band signals when the

preselection band filters are enabled.

Example 1: FLEX-6500 with two Slice Receivers on 20m in a single panadapter. Both receivers are set

to listen on RXA and transmit on ANT1. The WIDE indicator is not present in the panadapter. In this

case, the pre-selector filter for 20m is enabled, but the receiver and transmitter are on the same

band. The pre-selector will not reduce the transmit signal (it is in-band) and no 20dB reduction in

signal can be used for calculations.

Example 2: FLEX-6500 with two Slice Receivers, one on 20m, one on 40m in two panadapters. Both

Slice Receivers are set to receive on RXA and transmit on ANT1. Because two different bands are

received on the same antenna, WIDE mode is indicated in both panadapters. Preselection band

filters are not used and a 20dB reduction in signal cannot be used for calculations.

Example 3: FLEX-6700 with two Slice Receivers, one listening on 20m and one on 40m in two

panadapters. Slice A is set to receive on RXA and transmit on ANT1. Slice B is set to receive on RXB

and transmit on ANT1. Neither panadapters indicate WIDE. In this case, preselection band filters are

enabled on both bands and a 20dB reduction can be used in calculations.

34.4.2 Preamplifier / Attenuator Block

The preamplifier / attenuator block can raise or reduce signals before they are sampled in the ADC

block. The overload limit of the SCU is reduced by any gain that is added by the preamplifier. For

example, if 10dB of gain is selected using the preamplifier selection under the antenna controls in

the panadapter, this 10dB addition must be factored into the overload calculations. The same holds

for other amplification levels: if +20dB or +30dB are selected, the respective value must be added to

overload calculations. You should only use pre-amplification when necessary and only what is

required to raise the noise level in the receiver by 8-10dB over the noise level when the antenna is

disconnected.

FlexRadio Systems FLEX-6000 Signature Series User Manual

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