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<p>Talbot Andrew wrote:
<blockquote TYPE=CITE> <span class=010145508-13122000><font face="Arial"><font size=-1>Thanks
to the recent RadCom article, the first batch of DDS boards has now sold
out and a second set have been ordered from the PCB manufacturers.
We bought the entire stock of AD9850 chips from one UK supplier (13) and
these are being mounted on the PCBs at this moment.</font></font></span><span
class=010145508-13122000></span><span class=010145508-13122000><font face="Arial"><font size=-1>We
hope to produce a version of this frequency source using the AD9851 chip
soon. Although deliveries of this chip are slow, they should arrive
by March 2001. The AD9851 differs from the AD9850 chip by operating
at a higher clock frequency, up to 180MHZ, BUT has an internal x6 multiplier
allowing it to be driven with a 20MHz clock signal. This removes
one problem users have found, that of trying to find packaged oscillators
in the 100MHz region. One of these boards as the source would
solve the 100Hz step problem on the "New PC based 1750 Meter Transmitter"
mentioned in earlier EMails. Complete kits and made up boards
can now be supplied on request. </span><span
class=010145508-13122000>Contact
HF-INST.CO.UK tel (0)1420 590000</font></font></span><span
class=010145508-13122000></span><span class=010145508-13122000><font face="Arial"><font size=-1>I
have been considering the key click problem when using BPSK with switching
transmitters. Traditionally, amplitude shaping is used to limit the
transmitted bandwidth of PSK signals, but this is not a valid solution
for class E Txs . Dave's idea of going part way there by ramping the PSU
to the driver chips to generate Pulse Width Mod being only a temporary
solution. PWM of the drive waveform does not linearly control the
amplitude of the RF component which varies with pulse width in a SIN(X)
/ X manner.</font></font></span><span
class=010145508-13122000></span><span class=010145508-13122000><font face="Arial"><font size=-1>Has
anyone any experience of systems that ramp the phase slowly in lieu of
the amplitude ? My feeling is that this will give a similar
result to amplitude shaping, but the text books don't cover PSK bandwidth
control using a constant amplitude waveform. </font></font></span><span
class=010145508-13122000></span><span class=010145508-13122000><font face="Arial"><font size=-1>Andy
G4JNT</font></font></span>
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