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On 04/12/12 07:47 PM, Yahya E. wrote:
Inline image 2
ok = False pktno = 230 n_rcvd = 6 n_right = 0
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The usual reason for this is frequency-offset between RX and TX. In the
‘real world’ this is a constant problem,
which is why complete, market-ready, radio-based digital comms systems
have a frequency locking mechanism
in the receiver.
Try offseting the RX frequency in small amounts in either direction, and
see if you can get good packets.
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On Tue, Dec 4, 2012 at 8:51 PM, Marcus D. Leech [email protected]
wrote:
baseband magnitude exclusively to control RF output gain.
Actually, the signal in the screen shot looks pretty ugly. I’d recommend
reducing the amount of power at the receiver. GMSK is tolerant of
nonlinearities, but there is a limit.
Tom
On 12/04/2012 08:39 PM, Yahya E. wrote:
I am using RFX900 (FLEX 900) and the VERT 900 Antennas
Best Regards,
Yahya E.
The RFX900 doesn’t have analog TX gain setting – you have to use the
baseband magnitude exclusively to control RF output gain.
Try dropping the amplitude to 0.4, and also adjust RX gain and RX
center frequency.
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On Wed, Dec 5, 2012 at 2:23 AM, Yahya E.
[email protected]wrote:
made most of them be accepted as True (pass the CRC32 check if I understand
correctly). What is the explanation for this ?
Often, the reason higher rates work better is that the relative
frequency
offset is lower. You said that you couldn’t find a frequency offset that
helped with your 250 kbps signal, so I’m not sure if this is really the
right answer for you. But that’s generally the case.
- Increasing the samples per symbol further improved the reception, why
is that ?
Off the top of my head here… GMSK actually introduces ISI, but how
that
happens is based on the shaping filter used, which we determine by the
number of sps. Increasing this is probably making a better shaped
signal.
- The two FFT screenshots at 250k and 1M are as follows. How does the
difference between them solve the nonlinearity problem, Tom ?
Both of these looked good. I’m not sure it was really nonlinearities,
that
was just a guess. The original signal you showed us had a strange bulge
in
left half of the signal. These signals here look symmetric and properly
shaped.
Tom
Thank you Tom,
I have been experimenting with the working setting that I have now.
Why do other modulations like bpsk, qpsk fail while gmsk works perfectly
?
Best Regards,
Yahya E.
On Thu, Dec 6, 2012 at 10:44 AM, Yahya E.
[email protected]wrote:
Thank you Tom,
I have been experimenting with the working setting that I have now.
Why do other modulations like bpsk, qpsk fail while gmsk works perfectly ?
That’s a very open-ended question and can’t be answered. There are so
many
physical realities to getting signals to work, so it’s likely not just
one
thing (and certainly won’t be as easy as it sounds when you read a
textbook
on the difference in BER performance of modulation schemes).
One thing to keep in mind, though, is that you don’t want to use BPSK or
QPSK. Use DBPSK and DQPSK instead. There is no mechanism for resolving
the
phase ambiguity at the receivers. So when running these signals, make
sure
that they are differentially encoded (use the -v option to get a verbose
output of the parameters).
Tom