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.
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