John,
I think you will find , olivia runs more than one tone at any one time and
produces a 'two tone test' envelope , simple check, view the sound card o/p
on a scope ? I had a conversation with Simon (dm780) at the hf convention
last year, you can use none linear, but at the expense of s/n ratio and
side band splatter .. the ultra low conduction angle D and E set-ups can
be observed to generate 'gray noise' close in when handling pseudo linear
transmissions , I assume as they loose 'phase linearity' due to the abrupt
change of sate ? the systems look to be defined in terms of 'stats' ie
side band / noise levels as maximum predicted levels, which presumably are
deemed acceptable when pulse shaping data streams ... may not be ideal for
close in analogue work ?
There is defiantly a play off between data transmissions generated by
conventional analogue mixing / amplification and digital systems in
terms of close in noise, but as to the effect on the readability / decode of
the signal, ive not had the chance to compare , though interestingly, the
JT65 test on 500 , showed the K1JT software to give a constant +3 dB
improvement in the reported s/n over multipsk (at the time) , I was
sending the two systems on alternate time slots, via the same soundcard
through the same transmitter path , AWE64 isa sound card ,Racal MA1723
exciter and 20 Watt Class A solid state Racal 24v drive amplifier, ALC was
'on'
As to the reason, I can only assume there was/is some compromise in the
generation code ?
G ..
--------------------------------------------------
From: "John Andrews" <[email protected]>
Sent: Tuesday, August 19, 2008 8:03 PM
To: <[email protected]>
Subject: Re: LF: Keyboard Modes for 600 Meters
Dear ++ (Graham), <g>
I think that Olivia uses sequential FSK, not simultaneous tones. I don't
believe that Jay and I evaluated any simultaneous systems. We did use
linear PA's during the tests, but that was more for convenience in
switching back and forth between PSK and FSK systems. The claim is
generally made that the various FSK modes do not require amplitude
linearity. It would make an interesting experiment to compare bandwidths
and perhaps audible keying artifacts between linear and switching amps
while driving the fairly high Q antennas we use at LF and MF. I'm always
amazed at how click-free the hard-keyed CW signals are down here.
John A.
Graham wrote:
Interesting list of modes and tests ,
No virus found in this incoming message.
Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database:
270.6.5/1620 - Release Date: 8/19/2008 06:04
|
