Hi David,
Thank you for disclosing and sharing the motivation of the current FDM frame
architecture of Dxpedition mode.
Then, the following is my words to the person behind you, not you.
It is obvious that DxPedition mode specification is written for high power
conventional DX peditionists and development schedule is controlled by DXCC
marketers. Therefore, it does not make sense to use the resource of weak-signal
favorites for system design, code development, operation frequency allocation
and field tests.
Regards,
take
de JA5AEA
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10
________________________________
From: Bill Somerville <g4...@classdesign.com>
Sent: Monday, May 14, 2018 4:46:54 PM
To: wsjt-devel@lists.sourceforge.net
Subject: Re: [wsjt-devel] Signal variation during latest test
Hi Take San,
you are quite correct and a different protocol using a higher symbol
rate for the Fox has been considered, this would allow a single constant
envelope signal to be transmitted without any need for power adjustments
to compensate for IMD products. It also has another benefit in that the
Fox callsign need only be encoded once for any transmission period
rather than the current protocol where each individual message slot
needs messages including the the Fox callsign or a hash representing it.
This last encoding gain is indeed attractive along with the constant
envelope attribute but overall under time pressure to get the mode
working, developing a whole new source encoding and protocol for Fox
messages was considered too big a step. For now the Fox messages use
near identical source encoding as other FT8 messages and are sent at the
exact same symbol rate with identical FEC and checksum attributes, the
only difference other than message content is the use of one of the
three spare payload bits added when FT8 was initially developed.
73
Bill
G4WJS.
On 13/05/2018 23:31, Tsutsumi Takehiko wrote:
> Hi Dave,
>
> I do not have any intention to hijack your mail but I hope you allow
> me to state again that we should not concede "signal would drop around
> 12dB when 3 channels were used" as weak signal favorites.
>
> By my simple spread sheet calculation, we can achieve 4-3dB
> degradation range at 5 channels maintaining symbol length longer than
> 64mS, which is sufficient for multi-path interference guard under
> shortwave ionospheric propagation model, with simple single carrier
> TDM frame architecture. Keep in mind that RTTY or PSK31 symbol length
> is around 22mS - 32mS. Thus, I do not see any significant reasons to
> adopt FDM frame architecture.
>
> Regards,
>
> take
>
> de JA5AEA
>
> On 5/13/2018 1:53 AM, David Birnbaum wrote:
>> Hi Joe
>>
>> Bands were not helpful this morning, but I did notice something that
>> might be important.
>>
>> Aside from the QSB there appears to be some variation in your
>> transmitted signal even if only one frequency is being used. I would
>> see K1JT call CQ and then the response with a RR73; K2xxx -yy <K1JT>
>> response would be down about 3 dB. I did see that the signal would
>> drop around 12 dB when 3 channels were being used by the Fox which is
>> expected but I did not expect to see a response with a single channel
>> being down relative to a CQ.
>>
>> dave
>> k2lyv
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