[amsat-bb] Flex radio for satellites

David dwarnberg at verizon.net
Fri Nov 27 14:09:36 UTC 2015

FYI... FLEX RADIO's OFFICIAL RESPONSE... the 6000 series radio's..


I can also confirm, on my 6500 running SmartSDR 1.5.1 bottom of screen, 3
selections (TNF CWX and FDX)  FDX toggles full duplex on and off..

" We will be introducing Full Duplex operation in v1.5 which is due out in
September.  I'd like to spend a few minutes talking about the specifics.
Full Duplex will allow you to transmit and receive at the same time, but
there are limitations.  The FLEX-6700 has the most capability in this area
and you will be able to transmit on one antenna and receive on up to two
different antennas at the same time.  When you receive while you are
transmitting, there are a number of important considerations to ensure good
operation.  Here are the considerations:

Isolation and overload: If your transmit energy enters the receiver at
sufficient levels with the preamp off (greater than about 5mW in the
FLEX-6300 and greater than about 10mW in the 6500 and 6700) or with the
preamp on (generally subtract the gain of the preamp from the provided
overload point), the radio receiver will overload.  The FLEX-6000 Signature
Series radios have a "soft overload" where they will show signs of an
overload before going into a complete overload some 5-10dB later.  The key
sign of a soft overload are numerous spurs in the panadapter.  There is
40-100dB of isolation inherent in the radio itself.  This will be added to
the isolation between your antennas and the total must be below the radio
overload point.  More details will be provided, but here's a math example:

Transmitter: 100W = +50dBm
Overload on FLEX-6700 = +9dBm
Isolation from ANT1 to RXA: 90dB
Antenna isolation (at your shack): 40dB

+50 - 90 - 40 = -80dBm ... well below the +9dBm limit (89dB margin)

Transmitter: 100W = +50dBm
Overload on FLEX-6300 with 20dB preamp on: +7dBm - 20 = -13dBm
Isolation from ANT1 to ANT2: 40dB
Antenna isolation (at your shack): 30dB

+50 - 30 - 30 = -10dBm ... we are 3dB above the overload with the preamp on 

We'll show you how to run these calculations, but you can see there is a
wide range of possibilities so you will need to do a little math to
determine if everything will work for you.  Bandpass filters may also add
another 30dB or so of isolation of you are transmitting on one band and
receiving on another if your antenna selections are correct.

The radio will also protect itself if you put too much energy in the
receiver port and the radio will disconnect the antenna and alert you.

Receiver must be on different frequency from transmitter: The delay that
occurs during filtering is guaranteed to drive someone mad if the
transmitter and receiver are on the same frequency.  For this reason, we
mute the slice that you are transmitting on so you will not hear your own
signal.  This may seem counter intuitive at first, but it should fit most
use cases.  For example, if you are chasing DX, you can create two slices, a
RX slice on the DX and a TX slice where you will TX up (generally) and when
you transmit, you can still hear the DX frequency.  You will not hear under
your current transmit signal, unless you are in QSK in which case you will
hear in-between your transmissions.

Antennas: In all cases, you will need two antennas for full duplex.  We will
not be transmitting and receiving on the same antenna.

This is an exciting and new capability for all FLEX-6000 radios, but it will
require a little planning and thought to be sure it will work at your
location.  We hope this will bring hours of new operating fun!


9/17/15 There are a few errors in the calculations above and rather than
just change the text, I'll explain the issue and provide the correct
information.  There are really two paths from the transmitter to the
receiver.  The first path goes from the transmitter to the transmit antenna,
to the receive antenna and into the receiver.  The second path goes from the
transmitter directly to the receiver inside the radio.  It is the latter
path that prevents most manufacturers from offering full duplex.

For the scenarios above, you should always look at the isolation in the
radio AND the isolation outside and take the lower of the two.  

Antenna Path:
Transmitter: 100W = +50dBm
Overload on FLEX-6700 = +9dBm
Antenna isolation (at your shack): 40dB
Receiver Preselector Filters: 20dB (assuming different bands)

+50 - 40 - 20 = -10dBm ... this is acceptable 

Internal path:
Transmitter: 100W = +50dBm
Overload on FLEX-6700 = +9dBm
Isolation from ANT1 to RXA: 90dB

+50 - 90 = -40dBm ... this is also acceptable

So in scenario #1, the configuration will work with full-duplex

Antenna Path:
Transmitter: 100W = +50dBm
Overload on FLEX-6300 with 20dB preamp on: +7dBm - 20 = -13dBm
Antenna isolation (at your shack): 30dB
Receiver Preselector Filters: 0dB (not available in FLEX-6300)

+50 - 30 - 0 = +20dBm ... we are 33dB above the overload with the preamp on.
More antenna isolation is needed

Internal path:
Transmitter: 100W = +50dBm
Overload on FLEX-6300 with 20dB preamp on: +7dBm - 20 = -13dBm
Isolation from ANT1 to ANT2: 40dB

+50 - 40 = +10dBm ... we are 23dB above the overload with the preamp on 

In this case, full duplex may not be run.

More details will be made available in a white paper on Full Duplex and
SO2R.  Hopefully I haven't made too many mistakes in the corrected text!

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Richard Lawn
Sent: Thursday, November 26, 2015 8:51 AM
To: Amsat BB
Subject: Re: [amsat-bb] Flex radio for satellites

In answer to your questions, yes the Flex 5000A could be fully equipped with
2 rcvrs and the V/U module, however they discontinued it with the release of
their 6000 series radio. For satellites I've used the FT736f,
Ts2000 and ft847 and none compare to the ease of operation and rx quality of
the Flex5000A, which is why I'm holding on to mine.

But you could do what I'm now doing which is to use another radio capable of
V/U transmission on all modes as your uplink radio and use a 6000 series
radio with inexpensive down converters for rx. I then built a USB relay
controlled box that drives antenna switching relays. I found this to be much
cheaper than the other alternative which is to buy DEMI transverters or
possibly Elecraft. And you also end up with another really useful radio as a
backup for HF and other purposes at less cost than the 2 DEMI transverters.
I've used this arrangement before (minus the automated relay switching ) I
got my tricked out Flex5000. At that time I used the
TS2000 as uplink with a Flex 5000A for downlink wth converters and it worked
great! Stay tuned for exciting articles by Ron Parsons, W5RKN, and Dave
W0DHB in the AMSAT Journal about all this. What I'm doing is a spin off of
their ideas and working with them.

Rick, W2JAZ

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