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Re: [Discuss-gnuradio] False Packets for benchmark TX/RX

From: Yahya Ezzeldin
Subject: Re: [Discuss-gnuradio] False Packets for benchmark TX/RX
Date: Wed, 5 Dec 2012 09:23:40 +0200

Thank you Tom and Marcus,

I finally managed to make it work with 100% delivery rate using this configuration.

Tx-Amplitude = 0.4
Rate = 1M
Samples per Symbol = 4

Rate =1M
Receiver Gain = 10
Samples per Symbol = 4
I do have some question that  I don't understand :
1) The main issue turned out to be the rate. When I increased the rate from 250k to 0.5M some packets started to pass as true. Increasing it to 1M made most of them be accepted as True (pass the CRC32 check if I understand correctly). What is the explanation for this ?

2) Increasing the samples per symbol further improved the reception, why is that ?

3) The two FFT screenshots at 250k and 1M are as follows. How does the difference between them solve the nonlinearity problem, Tom ?

Inline image 1
                                   Rate = 250k

Inline image 2
                                      Rate = 1M

Best Regards,
Yahya Ezzeldin

On Wed, Dec 5, 2012 at 5:06 AM, Tom Rondeau <address@hidden> wrote:
On Tue, Dec 4, 2012 at 8:51 PM, Marcus D. Leech <address@hidden> wrote:
On 12/04/2012 08:39 PM, Yahya Ezzeldin wrote:
I am using RFX900 (FLEX 900) and the VERT 900 Antennas

Best Regards,
Yahya Ezzeldin

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.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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. 


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