[amsat-bb] Re: Sequencer
Alan P. Biddle
APBIDDLE at UNITED.NET
Mon Mar 12 08:05:19 PST 2007
>From the instructions which come with the units:
Connection of the preamplifier into the system is quite straightforward. The
coaxial cable from the antenna is connected to the
preamplifier input terminal (labelled ANT). Preamplifier output (labelled
XCVR) feeds the coaxial cable that connects to the station
transceiver or amplifier. Control cable used with the MSPXXXVDG should be
shielded. Non-shielded cable acts much like an antenna.
Nearby lightning strikes are capable of inducing sufficient voltage on this
"antenna" to damage the preamplifier. Shielded cable
effectively eliminates this problem. Always mount the MSPXXXVDG with the
connectors facing down to avoid water accumulation
around the connectors.
Wiring of the power connector is illustrated on the schematic diagram. For
rf keyed operation only the VDC and GND connections are
necessary. The preamplifier will sense the presence ofrfand automatically
switch the preamplifier out of circuit. Hard keying of the
preamplifier for transmit/receive changeover can also be accomplished. The C
terrminal of the power connector places the preamplifier
in transmit when grounded. Also, transmit/receive changeover can be
controlled with only the +VDC connection. Apply +12VDC for
receive and remove for transmit. The dropout delay function should be
defeated for hard keying operation.
For hard keying operation transmit/receive relay sequencing is mandatory if
preamplifier failure is to be avoided. A circuit such as the
ARR TRS04VD will provide sequentially keyed outputs that accurately control
the timing of all system transmit/receive changeovers.
Review the TRS04VD instruction sheet for more detailed information.
I OCRed this, so the formatting is not great. My understanding is that
"hard keying" they mean something like QSK where you will beat the relays to
death. Certainly CW, and perhaps SSB. However, there is a "relay delay
dropout capacitor" which as shipped will protect the unit, and of course
preclude QSK. So I suspect the answer to your question is no. In my
satellite operations, I have always been tranmitting on a different band
than receiving, so I just left the pre-amp on the TX side off. No harm if
you forget, of course, unless you do it all the time.
Hope this helps,
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