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FLEX-3000 Transceiver
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Initial Setup and Configuration
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How to use the FLEX-3000 RF Preamp & Attenuator
How to use the FLEX-3000 RF Preamp & Attenuator
How to use the FLEX-3000 RF Preamp & Attenuator
How to use the FLEX-3000
RF
Preamp & Attenuator
System Dependencies
Minimum
PowerSDR
Version:
1.18.3
Applicable Hardware:
FLEX-3000
Content provided by:
FlexRadio Systems Engineering
Background
(Content used from a National Contest Journal (Nov/Dec 2000) article by Gary Breed (K9AY))
A
receiver
's
dynamic range
is an important fundamental performance parameter. The FLEX-3000's
dynamic range
(
IMD
DR3) includes signal levels ranging from the noise floor of its own circuitry to the highest received signal level that causes audible intermodulation distortion (
IMD
or
intermod
). The narrow spaced (2
KHz
)
dynamic range
with the preamp off for the FLEX-3000 is somewhere in the mid 90
dB
range where the noise floor is ~ -135
dB
. This means that the maximum signal strength would be ~ -40
dB
that equates to a approximately S9+35.
The key to optimal reception is to maintain the received signals within the "
IMD
"free" range of your receivers
dynamic range
. You achieve keeping the input signal strength within this range by controlling the incoming signal levels with gain or attenuation.
So when do you need to use the preamp and when do you need to use the attenuator?
On 15 to 6 meters, the background noise level can very near the bottom of the FLEX-3000's
dynamic range
. At these frequencies, the addition of signal pre-amplification may be necessary to increase received signals that are above the noise level, but below the threshold of the FLEX-3000
sensitivity
.
However, when the higher frequency bands are wide open, signal levels can be
very
strong!
If
we still have a lot of preamplifier gain turned on when those big signals are present, we will
exceed the upper limit of our desired
dynamic range
and generate signal-covering intermodulation
. The challenge is to be aware of the overall range of the received signals.
You want to turn *on* the preamp when we need to hear weak signals, but turn it off (or even use some attenuation) to avoid intermodulation products from strong signals
. The use of a preamp on these bands is not a "set it and forget it" type of setting.
The low frequency bands (160-40m) require special attention to
not
using pre-amplification and possibly need to use attenuation in the presence of strong signals and band noise. The 40-meter band is a unique case, since it can be either quiet or noisy. The band has the added factor of megawatt international broadcast stations.
Like the other low bands, you will never need a preamp on 40m unless you are using an inefficient receiving antenna
. On all the low bands, the question is, "How much attenuation do I need and how do I implement it?"
The easiest way to add attenuation with the FLEX-3000 is to
reduce
the
AGC
Threshold gain (
AGC
-T) on the
PowerSDR
console. When the incoming signals are very strong, you should use the -9
dB
attenuator available in the
RX
Gain drop down control on
PowerSDR
console.
Configuration and Settings for the FLEX-3000
The FLEX-3000 has three (3) states for amplifying or attenuating the input
RF
gain. These setting are selectable from the
PowerSDR
console. They are:
ATTN
- This setting inserts a -9
dB
attenuator into the
RX
signal path
OFF
- This setting provide neither pre-amplification or attenuation in the
RX
signal path
PRE1
- This setting inserts +5
dB
@ 20m and +11
dB
@6m of pre-amplification into the
RX
signal path.
PRE2
- This setting inserts +14
dB
@ 20m and +20
dB
@6m of pre-amplification into the
RX
signal path.
Below are some guidelines for setting the preamp and
AGC
-T settings for various bands.
Band (meters)
Preamp1
Preamp2
Attenuator
Off
AGC
-T Range
160-60
N/A
N/A
On or Off
On or Off
60-80
40-30
Usually Off
N/A
On or Off
On or Off
65-85
20-17
On or Off
Usually Off
On or Off
On or Off
75-90
15-12m
On or Off
On or Off
Usually Off
On or Off
75-95
10m
Usually Not Used
Usually On
Usually Off
On or Off
90-100
6m
Usually Not Used
Usually On
Usually Off
On or Off
100-120
This KB article may reference additional files that are available on the FlexRadio Systems web site Downloads page. Please use the URL(s) below to download the referenced materials.
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KB Source Document(s):
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Details
Last Modified:
Sunday, April 4, 2010
Last Modified By:
Administrator
Type:
HOWTO
Rated 4 stars based on 3 votes.
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