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RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2
From: |
Ian Holland |
Subject: |
RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2 |
Date: |
Thu, 4 Feb 2010 18:13:16 +1030 |
Hi Matt
Apologies is you got a similar reply about 10 minutes ago, but the webmail logged me out whilst I was trying to send it and it didn't appear in my sent items when I logged back in.
>You should know that we only spec the boards from 2.4 to 2.5 GHz and 4.9
>to 5.9 GHz. When we test XCVRs before shipping, we make sure that they
>will lock from 2.35 to 2.55 and 4.85 to 5.95 so that there is 50 MHz of
>margin in case of variation due to temperature or other factors. But
>there is no reason to think that they would lock all the way to the
>edges of the ranges you list since those are well outside of what we
>(and the chip manufacturer) specify.
Thanks. I had thought the low and high limits in the source code were the spec'd ones. Based on your above comment, combinations A, C, and D would seem to be within spec, though I didn't try all the stepped frequencies for case C or D, but just a few (e.g. 2.4G, 2.462G, 5G).
> Combination ID | USRP2 Serial | XCVR2450 Serial | Working
> A | 933 | 990 | YES
> B | 933 | 988 | NO
> C | 1159 | 990 | YES
> D | 1159 | 988 | YES
>
> In my testing today, an additional problem was also noticed, as below.
>To simplify testing, you only need to run either RX or TX since they
>both share the same synthesizer on the XCVR2450.
Thanks. I will do this in future.
>Normally I would tell you to send the parts back for me to check them,
>but since you are in AU, it would be expensive and take a long time.
>Instead, we may be able to debug this if you have an oscilloscope. If
>so, can you look at the signal on R45 and R56 on the XCVR? Note the
>frequency, and high and low voltages for each of the 4 combinations you
>mention above. They should look like a square wave in all cases.
We have a borrowed oscilloscope spec'd to 1.5 GHz with no probe. I will try to borrow or buy a suitable probe. Can you confirm R45 and R56 are just digital logic signals, as would seem to be the case from what you state above?
>Assuming the signal you were transmitting was a sine wave with a
>baseband frequency of 0, then what you are seeing here is completely
>expected and normal. When the clocks are not locked to the same
>reference, there is some frequency error, and the signal received is at
>some frequency other than exactly on the LO of the receiver, and it will
>get through just fine. However, when the 2 clocks are locked to the
>same reference, the transmitted tone will be received exactly on the LO
>frequency of the receiver. When this is downconverted to baseband, it
>will appear at DC, and it will be nulled out by the DC offset
>correction, which occurs in both the analog and digital domains. You
>can turn off the digital one, but not the analog one on the XCVR.
>To demonstrate this, you can run the following commands:
>- To show a good tone being received:
> usrp_siggen.py -f 5.65G -A 0.1 -x 100k --sine
> usrp2_fft.py -f 5.65G
>- To show the tone being nulled out:
> usrp_siggen.py -f 5.65G -A 0.1 -x 0 --sine
> usrp2_fft.py -f 5.65G
Whoops. Didn't think about the DC offset correction. It was a sine wave at the carrier frequency that I tried. I will hence try your suggestion tomorrow, as it is evening here and I am at home without access to the radios.
Thanks
Ian.
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, (continued)
- Re: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Matt Ettus, 2010/02/04
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/04
- Re: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Manav Seth, 2010/02/04
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/03
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/03
- Re: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Matt Ettus, 2010/02/04
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/04
- Re: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Matt Ettus, 2010/02/04
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2,
Ian Holland <=
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/04
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/05
- RE: [Discuss-gnuradio] Unable to tune Tx or Rx with XCVR2450 on USRP2, Ian Holland, 2010/02/05