Mike, et al,
What I am asking for is a change in the software - Writelog in
particular - so that Writelog first asserts the PTT line and tells the
transmitter to turn on. This will, as you say, generate a continuous
carrier (Mark signal). Then, after a specified time interval of xx
milliseconds, Writelog would then start sending the characters and the
frequency shift keying would then begin.
The idea is to allow time for the transceiver and/or amplifier, to be
fully stable BEFORE starting the character sequence. The point is to
ensure that the receiving station is able to synchronize from the very
first START bit.
Joe,
As for the MicroHam USB II interface, we were using this interface at
PJ2N in the RTTY RU when this synchronization issue surfaced. We were
keying a Ten Tec Titan II amp at about 600 watts when we started
receiving reports that the first few characters of every message were
garbled. We tried the Writelog CW Delay parameter, but it had no
discernible effect - we still received reports of garble on the first
few characters. But I am unaware of how the MicroHam keys the amp
independently from the transceiver. How would I do this?
After a fair amount of experimenting, I have come to the conclusion that
the front end garble is a synchronization issue. But I now see that
there are two ends to the issue:
--- on the transmit end, it is essential that the text (i.e. the
character bit patterns) not be sent to the transceiver until the
transceiver and amp, if used, is fully transitioned and sending stable
RF. MMTTY does have a command which can be inserted into a Macro
message which can "Send a Mark Signal". This can effectively add the
necessary delay and my experiments show that it does the trick. But
there is no similar way to insert such a command in a Writelog message
(that I am aware of). Also on the transmit side, it is possible to
improve synchronization by adding diddles - but in a contest exchange,
the first character of the message is sent immediately and no diddle
(LTRS usually) characters precede the message. So the diddles only help
(I think) if there is an idle period (no text in the buffer).
---on the receive end, the signal has to be clear enough for the
decoding algorithm to be able to sense the START bit correctly. Things
that can mess this up are weak signal, QRN, QRM, mis-tuning, and too
high of a squelch setting (to name a few). BTW, I found the SQL setting
as well as the sound card input level to be fairly critical. It took a
bit of experimenting with these two controls until I was able to
eliminate the vast majority of front end synching problems and tail end
random characters appearing on the screen.
What exactly was going on with our PJ2N RTTY signal before the contest
started is still a bit of a mystery, but adding two spaces, a CR/LF, and
another space before the exchange text seemed to solve the
synchronization problem and cleared up the garble. But it also slowed
us down and should have been unnecessary. I'd like to see a way to
reduce the likelihood of synchronization problems by adding a RTTY DELAY
parameter to Writelog, MMTTY, N1MM, and any other RTTY program, so that
those who feel they would like it could use it. The delay period
doesn't have to be long and the continuous Mark signal would help ensure
synching up with the first character START bit.
73,
Ron N6EE
On 1/21/2012 2:25 PM, Mike McCarthy, W1NR wrote:
> The delay would have to be in the rig. When my Icom ProIII and similar
> rigs are in FSK mode, as soon as PTT is applied, the carrier comes on
> soon after. Unlike CW, which is on/off keying, the only keying that gets
> done is the "shift" for the mark/space elements. There is no way to
> apply external delay as the carrier is on all the time.
>
> On 01/20/2012 10:51 PM, Don Hill AA5AU wrote:
>> I'm wonder if the PTT to CW delay also applies to FSK? Does anyone know
>> this? It would seem that it would since perhaps both may
>> be keyed from a serial port when using PC generates. Seems like it's the
>> same thing only one uses DTR (CW) and the other TxD (FSK).
>>
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