30,72 clock


#1

Hello,

I have two Myriad- RF1 with deo nano FPGA.

I want to know if the 30.72 clock must be supplied from the same generator for Transmitter and receiver ? when I send to my transmitter board a 30,72 clock from another generator than my recievre board, the transmision is not OK, the siganl that i sent is super noisy.
it is very mysterious, I can not understand !

Thank you

Amina


#2

Hello Amina,

Do you mean clock generated to PLLCLK or TXCLK/RXCLK pins?

Rich


#3

Hello Rich,

I mean the clock generated to PLLCLK

Amina


#4

It can be the same, just make sure it is 30.72 MHz and level is high enough 3.3Vpp.

Rich


#5

Hello Rich,

Thank you for your answer, but let me explain you my situation:

I have 2 myriad RF 1 - and DEO nano and a digital interface board

In the interface board I have a TXCO who generate me 38,88 MHz, I know its not 30,72 but in the SPI software all my registers are passing and I put on the reference clock 38,88 MHz.

in one board I program the transmitter, i apply in analog input a 1MHz CW, in the other board I program the receiver, but the transmission is not OK at the reception my signal is super noisy

In addition, when I generate the same clock PLLCLK at 30,72 from an external generator for my transmitter and my receiver board, this transmission is good, but if I take 2 external generator, one on 30,72 to my transmitter board and the other also at 30,72 to my receiver board, the transmission is again not good, and super noisy

I can not understand, in my application the PLLCLK must not be the same for my 2 board,

I don’t understand another thing, when I want to make the LMS6002D Calibration I don’t have the same result

Amina


#6

amina,

it is not clear how/where do you connect the clocks. Do you have 1 DE0 Nano board + MyriadRF board and Zipper (or your custom build) + Myriad RF board? Can you give more details where and what are you connecting?

Do you have a spectrum analyser to check whether Tx output is noisy? When it is noisy is it still on your wanted frequency or it is quite off your wanted?

Rich


#7

I have (1 DE0 Nano board + MyriadRF + DE0 interface board (that I have made)) * 2, that means one development kit for transmission and the other for reception, I have also 2 antennas

<img src="/uploads/default/original/3/6/36b97e0925b0cbe47caa01f6a98e932a36917d03.PNG" width=“344” height=“264”

In the DE0 interface board I can’t not found the TCXO quartz in 30,72 MHz, so I solder a cable in place of quartz TCXO, I connect this cable to an external generator who generate me 30,72 (I test all my registers are passing)

In one development kit board I apply 1MHz sinus signal to the myriad analog input, I put an antenna to TX output and and I programme TX frequency at 2,14 Ghz, in the other developement kit board i programe RX frequency at 2,14 also I connecte an osciloscope in the I or Q sin wave output and i observe the same sinus signal that I send, ( now all is good. and my transmition is OK) in this situation I have one external generator at 30,72 MHz for the two board transmitter and the receivre.

My problem is if I take two external generator at 30,72 MHz one for the transmitter board and one for the receivere board, and I do the exatly same thing than befor, I can’t observe the sinus signal that I send, the signal that i have is super noisy

I have also the same probleme if put a TXCO quartz at 38,88 to the de0 board

Thank you for your help

Amina


#8

Hello,

only a general remark/info:
If you use a IQ modulator with a reference clock and a PLL to generate a TX signal and a second reference clock on RX side you can introduce systematic frequency and timing errors. This means that a slight frequency shift on TX side or RX side results in a different RX spectrum if the RX side does not fit perfectly to the TX carrier frequency.
Additionally, transmission via antenna and air has influences on the spectrum as well (e.g. by multipath propagation).
Additionally, the RX does not sample the signal at he same time as TX does if both systems are not synchronized and anyway the channel (air) introduces some delay.
Maybe that’s one reason for your noise. Did you try some data-aided estimators for frequency correction or some carrier detection method?