Thanks Andy!
Sanity check now complete. I did as you described before I asked
the general question and strange things happened...
I'm going to need to double check what I was doing to ensure I
didn't succumb to the late at night syndrome. As the basic premise
you and other share made complete sense to me until I tried it and
it didn't seem to work...
Will report when I get some results...
On another note, I was able to detect the 8.970KHz test carrier from
my Earth conduction tests at the 9km mark yesterday. Interestingly
there seemed to be QSB on the signal at that range. More testing
today.
Caps on order for the 'Air loop'.
73 Scott
VE7TIL
On 4/21/2011 10:22 AM, Andy Talbot wrote:
I was half asleep last night when I first replied - hence the
confusion over upconversion. As you're on 9kHz, converting
doesn't apply and the PC generates direct Tx drive. The
quadrature bit is not needed for direct output, so you only use
one audio channel.
As mentioned by several writers now, you need to double the
frequency first to pass into your divide by 2, or bypass that
and drive the transmitter directly - after making sure the
waveform is very close to a 50% duty cycle square wave. The
drive will almost certainly have to be push-pull, so you'll need
to make a squarer / comparator and generate Q/Q-bar drive
signals
Andy (doesn't do late-at-night :-) G4JNT
On 21 April 2011 01:28, Scott Tilley <[email protected]>
wrote:
Hi Andy
Holy mind bogglingness batman...
Here's the parameters to make this real simple:
- I want to generate a MSK signal out of the transmitter at
8970Hz.
- I'm using Spectrum Lab, which allows me to create a MSK
drive and at a baud rate I want at any frequency my sound
card can generate.
- SL allows me to output quadrature outputs.
So, If I understand correctly pump said FET driver with the
quadrature outputs from the sound card audio (squaring up
the sine waves of course) and it should work?
Thanks,
Scott
On 4/20/2011 2:09 PM, Andy Talbot wrote:
Bin too quick to type..
NOt thinking straight...
You need to the upconvert either the resulting
doubled audio tone by twice the RF carrier, or
upconvert first and double the final RF. Same ideas
for frequency doubling can be used.
Must fully check before hitting SEND !
Andy
G4JNT
On 20 April 2011 21:50, Andy
Talbot <[email protected]>
wrote:
I assume you are genrating the MSK from
soundcard output, in which case two options come
to mind:
1) Double the frequency. Full wave rectify
the audio sinusoid, pass the AC part of the
result into a comparator and into the divider.
Alternatively, as the signal bandwidth is
probably quite low, square up the audio to start
with, feed into one inpiut of an XOR gate.
Delay the waveform by 90 deg and feed this into
the othe side of the XOR. Output of XOR to
divider as before
2) Remove the divide by two, and replace
with an inverter / buffer pair to generate the
out of phase drive signals. The input now
needs to be close to a 1:1 squarwave at output
frequency. Pass the soundcard audio into a
comparator and make sure it gives a 50% duty
cycles.
Andy
ps.
or 3) Convince the software author the
S/W needs modifying to give a 2.F output
On 20 April 2011
21:32, Scott Tilley <[email protected]>
wrote:
Hi All
I wonder if someone can explain to me how
to feed an MSK signal into a typical Class
D transmitter?
I mean by typical that the TX has a 4013
type /2 system feeding two FET drivers to
drive FETs in a push-pull configuration.
If I understand correctly due to the fact
MSK does not have amplitude component to
its signal that a non-linear transmitter
can be used.
So, how do you do this with a Class-D TX
as often used in LF/VLF?
Thanks,
Scott
VE7TIL
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