BladeRF, its XB-200 transverter and HF TRX

Discussions related to schematic capture, PCB layout, signal integrity, and RF development
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drew23
Posts: 7
Joined: Fri Nov 08, 2013 8:48 pm

BladeRF, its XB-200 transverter and HF TRX

Post by drew23 »

The BladeRF, its XB-200 transverter and HF TRX; it's been there all the time!

I thought I would start a new topic rather than continue the question regarding BladeRF's HF coverage as HF is treated very differently to the higher frequencies; 30 - 3000 MHz.

I have just made a post to my blog that discusses it in more detail than is possible here. http://vk4zxi.blogspot.com.au/

HF TRX is achieved by bypassing the most of the LMS6002D circuits and going straight to the ADC or DAC via pins RXOUTI/Q and TXINI/Q. As such the RX samples directly via the ADC at for HF. These pins are accessible on the BladeRF. The transverter just adds a balun and connector, shown on the last page of the transverter schematics and not mentioned in the block diagram.

There is nothing wrong with this approach as many SDRs are based on inputs/outputs directly to ADC/DACs. However it does have consequences for BladeRF's use as a HF TRX in terms of different software, extra circuitry and possible limits of its coverage of HF, given a sampling rate of 40 Msps which seems to limit it to 20 MHz.

This is not intended to be a criticism of the BladeRF and its transverter; I look forward to receiving my transverter and am already impressed with BladeRF's capabilities.

Regards Drew VK4ZXI
cmh716
Posts: 15
Joined: Fri Jul 26, 2013 3:16 am

Re: BladeRF, its XB-200 transverter and HF TRX

Post by cmh716 »

Leif used J61 to receive HF. Check this out
http://www.sm5bsz.com/linuxdsp/hware/bl ... direct.htm
r0wla
Posts: 1
Joined: Thu May 15, 2014 11:35 pm

Re: BladeRF, its XB-200 transverter and HF TRX

Post by r0wla »

does anyone understand what the BladeRF expects to receive on its direct sampling pins?

a balun is used, but is this to avoid separate the antenna from the board via transformer e.g. get rid of common mode noise or something, or is it to transform the impedance? what impedance does the BladeRF want on its direct sampling pins, 50? not 50?
bpadalino
Posts: 303
Joined: Mon Mar 04, 2013 4:53 pm

Re: BladeRF, its XB-200 transverter and HF TRX

Post by bpadalino »

The transformer was used to just get the differential signal. 50 ohms should be fine. The common mode voltage can come directly from the LMS6002D itself which is why we decided not to put one on the transformer. I believe, for the RX side, 770mV is the desired common mode. I'd have to double check the datasheet and FAQ for the LMS6002D part.

Brian
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