Synthesizable Frequencies for WBX?

Hello G.s,

I am experiencing some problems in transmitting/receiving at frequencies
around 900MHz for WBX board. While, I am able to do so cleanly at
900MHz, other center frequencies are not.

The signal bandwidth : 50 KHz
The sampling frequency: 200 KHz

I have tried 901MHz , 900.1MHz, 910MHz and many others but the received
signal appears to be wider than it should be. The signal level is higher
than -40dbm over the total 200 KHz range when these frequencies are
used.

The only frequencies I was able to use with no problems are 900MHz, 1.8
GHz , 890MHz, 880MHz.

What could be the problem? I have tried to use “tune_request_t” in the
target frequency paramter but it gave similar bad results . Any
pointers?

Kind regards,
Yahia Tachwali

On Fri, Apr 8, 2011 at 10:22 AM, Tachwali, Yahia [email protected]
wrote:

Hello G.s,

I am experiencing some problems in transmitting/receiving at frequencies
around 900MHz for WBX board. While, I am able to do so cleanly at
900MHz, other center frequencies are not.

The signal bandwidth : 50 KHz
The sampling frequency: 200 KHz

What signal amplitude?
What gain setting?
Which antenna port?

I have tried 901MHz , 900.1MHz, 910MHz and many others but the received
signal appears to be wider than it should be. The signal level is higher than
-40dbm over the total 200 KHz range when these frequencies are used.

This usually indicates a sample rate mismatch in your flowgraph, if
you post an example to replicate your problem, it will be easier to
help you.

The only frequencies I was able to use with no problems are 900MHz,
1.8 GHz , 890MHz, 880MHz.

What could be the problem? I have tried to use “tune_request_t” in the target
frequency paramter but it gave similar bad results . Any pointers?

What parameters did you give to the tune_request_t?

Have you looked at the tune_result_t returned by set_center_freq?

Jason

Hello Jason,

Thank you for the instant reply. Here are the responses to your
question:

The transceiver set-up is really basic:

TX

Random src --> DQPSK MOD --> Pulse Shape --> UHD SINK

RX

UHD SOURCE --> FFT block

so,

Signal amplitude? 1
Gain setting? 0dB at TX and RX sides
Antenna port? TX: TX/RX RX: RX2

I believe it is a mis-sampling mismatch. I am using 4 samples per
symbol. I should add that this problem appears to be ONLY at the TX
side. I am able to see a clean signal when the TX is at 900MHz and RX is
900.050MHz. But not the other way around.

Also, as far as the parameters go: if I want to access 900.05MHz I pass
to tune_request_t :
target frequency = 900M
LO freq = 50K

However, the result is: bad signal (i can see the peak at the center
frequency expected (900.05MHz) but the bandwidth is wide in the same
manner as if I set the center frequency manually at 900.05 rather than
using tune_request_t.

I am pretty sure that the upsampling in FPGA is messed up or the
upconversion setting in the transmitter has to be done in different way.
Any advice please?

Kind regards,
Yahia Tachwali


From: Jason A. [[email protected]]
Sent: Friday, April 08, 2011 12:45 PM
To: Tachwali, Yahia
Cc: [email protected]
Subject: Re: [Discuss-gnuradio] Synthesizable Frequencies for WBX?

On Fri, Apr 8, 2011 at 10:22 AM, Tachwali, Yahia [email protected]
wrote:

Hello G.s,

I am experiencing some problems in transmitting/receiving at frequencies
around 900MHz for WBX board. While, I am able to do so cleanly at
900MHz, other center frequencies are not.

The signal bandwidth : 50 KHz
The sampling frequency: 200 KHz

What signal amplitude?
What gain setting?
Which antenna port?

I have tried 901MHz , 900.1MHz, 910MHz and many others but the received
signal appears to be wider than it should be. The signal level is higher than
-40dbm over the total 200 KHz range when these frequencies are used.

This usually indicates a sample rate mismatch in your flowgraph, if
you post an example to replicate your problem, it will be easier to
help you.

The only frequencies I was able to use with no problems are 900MHz,
1.8 GHz , 890MHz, 880MHz.

What could be the problem? I have tried to use “tune_request_t” in the target
frequency paramter but it gave similar bad results . Any pointers?

What parameters did you give to the tune_request_t?

Have you looked at the tune_result_t returned by set_center_freq?

Jason

Yahia Tachwali,

If you send me your actual .grc or .py file, it will be easier to help
you, because I think you may have different sample rates set on
different blocks.

Also, are you cabling TX directly into RX?

Do you have any screen shots of the good and bad scenarios?

Jason

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