[amsat-bb] Re: Sequencer
kl7uw at acsalaska.net
Mon Mar 12 18:20:54 PST 2007
At 08:05 AM 3/12/2007, Alan P. Biddle wrote:
> >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,
Hard keying is NOT QSK like. It is like PTT: You key your radio for
transmit and it stays in Tx until you un key. Using the C terminal
allows a sequencer to switch the unit into Tx-mode without the unit
needing to sense RF on the coax line. This is much preferred. RF
sensing T/R is more like QSK that you mention (especially when using
CW/SSB). The relays in the ARR preamp will chatter back-n-forth with
each RF peak. There is a RC time constant to smooth this our
somewhat, but they cannot hold the relay too long or it will not
switch fast enough from receive using RF sensing (I've probably
confused a few of you by now). The ARR switching preamp apparently
works just like many brick transmitting amps: you can use auto RF
sensing or hard keying to control T/R.
Short answer: best method is using hard keying of the C-terminal
which is controlled by a sequencer.
The bigger question is how you key the sequencer? You can run the
PTT line from your microphone to the sequencer. Then the sequencer
will have a keying line to your radio's PTT circuit. For CW it is
probably easiest to have manual switch T/R controlling the
sequencer. If you are running digital you can run a line from the
computer (usually the software provides this on a RTS line at the
serial port) to control the sequencer. I do all three on my station.
Ed - KL7UW
BP40IQ 50-MHz - 10-GHz www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
DUBUS Magazine USA Rep dubususa at hotmail.com
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