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Date: Sat, 14 Nov 2015 15:08:18 +0000
Message-ID: <CAA8k23SKh84+0XXJfHxOVHWV7FgP+=oZXcuT79ye1Te24yqhdA@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org, rsgb_lf_group@yahoogroups.co.uk
Subject: LF: Ramped BPSK
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The recent resurgence of interest in BPSK on the LF bands reawakened my
unease at using this hard switched mode with high power transmitters.

I recall ages ago using Coherent (10 B/s BPSK)  and hearing audible clicks
coming from my PA and / or antenna loading coil.  It all survived, but
feels iffy.
And as for the keyclicks that must have been spreading a long way either
side of the carrier !

So, I've been looking at using a DDS to generate a Gaussian ramped phase
shift, where the phase glides from 0 to 180 or back following a curve.

I've implemented an approximation to the ideal curve by including a 32 step
phase ramp, using a Gaussian curve lookup table, into an AD9852  DDS
frequency source.   A lonk on the PIC allows hard swited PSK to be selected
to allow quick comparisons, or for when sharp edges really are needed, or
for faster response

The spectra of both types can be found here
http://www.g4jnt.com/RampedBPSK.pdf

At the moment PIC code exists for driving the high resolution AD9852 DDS
with its 48 bit frequency setting and 14 bit phase register (although I
only use 8 bits of phase from the lookup table).
The same PIC code could be modified for the simpler to drive AD9850 DDS
beloved by many, although the phase register in that device only has 32
values (5 bits), meaning the ideal curve will be further degraded

Andy  G4JNT

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<div dir=3D"ltr"><div>The recent resurgence of interest in BPSK on the LF b=
ands reawakened my unease at using this hard switched mode with high power =
transmitters.</div><div><br></div><div>I recall ages ago using Coherent (10=
 B/s BPSK)=C2=A0 and hearing audible clicks coming from my PA and / or ante=
nna loading coil.=C2=A0 It all survived, but feels iffy.</div><div>And as f=
or the keyclicks that must have been spreading a long way either side of th=
e carrier !</div><div><br></div><div>So, I&#39;ve been looking at using a D=
DS to generate a Gaussian ramped phase shift, where the phase glides from 0=
 to 180 or back following a curve.</div><div><br></div><div>I&#39;ve implem=
ented an approximation to the ideal curve by including a 32 step phase ramp=
, using a Gaussian curve lookup table, into an AD9852 =C2=A0DDS frequency s=
ource.=C2=A0=C2=A0 A lonk on the PIC allows hard swited PSK to be selected =
to allow quick comparisons, or for when sharp edges really are needed, or f=
or faster response</div><div><br></div><div>The spectra of both types can b=
e found here <a href=3D"http://www.g4jnt.com/RampedBPSK.pdf">http://www.g4j=
nt.com/RampedBPSK.pdf</a></div><div><br></div><div>At the moment PIC code e=
xists for driving=C2=A0the high resolution AD9852 DDS with its 48 bit frequ=
ency setting and 14 bit phase register (although I only use 8 bits of phase=
 from the lookup table).=C2=A0=C2=A0 </div><div>The same PIC code could be =
modified for the simpler to drive AD9850 DDS beloved by many, although the =
phase register in that device only has 32 values (5 bits), meaning the idea=
l curve will be further degraded</div><div><br></div><div>Andy=C2=A0 G4JNT<=
/div><div><br></div></div>

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