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Arpine_Soghoyan
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Re: RF Record and Playback Reference Application

hi Gerardo,

You are right. I can use the toolkit and actually my processing works fine with offline mode using simulator gps generated signal.

But let's imagine a real situation of having a transmitter and a receiver. The processing that I need to do needs to be done on the receiver side. So if we talk in temrs of VSG and VSA. Is it correct to do my processing on VSA side ?In that case what can be the solution ?

 

Thanks,

 

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Yardov
Posts: 331
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Re: RF Record and Playback Reference Application

Hi Arpi,

 

Yes, it is correct in doing it on the VSA side. However, in the real case scenario, the GPS signal is generated by the GPS satellites and you will need the GPS antenna and the amplifier to record your signal.

 

Regards,

Gerardo O.
RF Systems Engineering
National Instruments
Member
Arpine_Soghoyan
Posts: 30
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Re: RF Record and Playback Reference Application

Hi Gerardo,

 

But I don't have amplifier i only got gps antennas. How should i proceed in that case ? 

 

thanks,

Arpi

 

 

Active Participant
Yardov
Posts: 331
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Re: RF Record and Playback Reference Application

Hi Arpi,

 

I'm going to quote what the app note said since is exactly the same:

 

The trickiest aspect of recording GPS signals is selecting and configuring the appropriate antenna and low-noise amplifier (LNA). Observe that with a typical passive patch antenna, the typical peak power in the L1 GPS band ranges from -120 to -110 dBm (the tests showed power at -116 dBm). Because the power level of GPS signals is so small, significant amplification is required to ensure that the vector signal analyzer can capture the full dynamic range of the satellite signals. While there are several ways to apply the appropriate level of gain to the signal, you can achieve the best results when using an active GPS antenna with the NI PXI-5690 preamplifier. With two cascaded LNAs, each providing 30 dB of gain, the total gain applied is 60 dB (30 + 30). Thus, the resulting peak power observed by the vector signal analyzer is increased from -116 to -56 dBm. An example system using this configuration is shown in Figure 4.

 

This means you will have to evaluate if the GPS antenna has enough gain for your custom algorithm signal to noise requirements.

 

Regards,

Gerardo O.
RF Systems Engineering
National Instruments
Member
Arpine_Soghoyan
Posts: 30
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Re: RF Record and Playback Reference Application

Thanks Gerardo,

 

Currently I don't have 5690 pre-amp so in that case I would like just to use VSG as a transmitter and VSA as a receiver could you please advice me what antena should i use for transmission ? for my understanding the transmitting and receiveing antennas need to be symmetrical so as described in gps receiver testing paper my receive antenna should be

gain : 30db

dc bias voltage ~ 2.5-5V

noise figure < 2dB

what about the transmit antenna ?

 

thanks

Member
XiaohuiWang
Posts: 137
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回复: RF Record and Playback Reference Application

Hi all,

I'm sorry to trouble you, but we have met a problem with the "RF Record and Playback Kit", the situation is that:

- my hardwares are PXI-5661, PXIe-5673

- first, I connected a 50 Ohms terminal to RF input of PXI-5661, and recorded the RF IQ signals to disk:

S1.png S2.PNG

- when analyzing the data, it looked fine:

S3.PNG

- but when I connected PXI-5661 to PXIe-5673, and playbacked the RF signal through 5673, there will be a peak at the center frequency of 5661:

S4.PNG

(the reference level is -30 dBm)

- If I set the reference level of RFSA to higher level during the record procedure, the peak at playbacked signal is higher:

S5.PNG

(the reference level is 10 dBm ) 

 

- Second, during the record procedure, I connected RFSG to RFSA, and generated different RF levels (with same frequency 1 GHz) using Test Panel in MAX. The system worked fine unless the RF signal level is smaller than the "inherent" peak level.

 

- In the VIs, there is a parameter "Instrument Peak Power", what's the meaning of that?

 

I know that these VIs are tested under PXI-5661 and PXIe-5672, is PXIe-5673 not compatible to these VIs?

 

BTW, I used the kit from the community:https://decibel.ni.com/content/docs/DOC-4307

Thanks in advance~

 

Best wishes,

Xiaohui Wang

Member
XiaohuiWang
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回复: RF Record and Playback Reference Application

the screenshots are in the attachment:

Member
TimS.
Posts: 141
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回复: RF Record and Playback Reference Application

Hi Xiaohui,

 

The VI's you are using should work with the 5673 so that's not the issue. However, there is a newer version of the R&P kit at http://zone.ni.com/devzone/cda/epd/p/id/5894 (the v02.zip file). All the new version did was remove some property nodes and items that weren't compatible with the newer hardware.

 

I believe that what you are seeing is LO leakage of the 5673. You are seeing ~65 dBc spur from the Peak Output Power setting in both situations (14.64 dBm and -39.30 dBm). The peak power is simply the output power level of the signal that you would see when the file data is equal to +/- 1 (or in the case of I16 data equal to -32768 or +32767). If you look at the specifications for the 5673 (http://www.ni.com/pdf/manuals/374959d.pdf), under the Carrier Suppression section, the measured carrier suppression at 1 GHz is around 63 dBc. Meaning, when your peak output power is at X dBm the RF Carrier will be roughly (X - 63) dBm. This may or may not be an issue depending on your application. What is your application BTW?

 

Regards,

 

Tim



Tim Sileo
RF Field Account Specialist
National Instruments



You don’t stop running because you get old. You get old because you stop running. -Jack Kirk, From "Born to Run" by Christopher McDougall.
Member
XiaohuiWang
Posts: 137
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回复: RF Record and Playback Reference Application

Hi Tim,

Thanks for your reply.

We just want to have a try of this kit~

Since I am not in office at present, one of my colleagues continues with this issue, some more details are here:

http://forums.ni.com/t5/NI-Applications-Engineers/Spurs-on-Carrier-when-using-RF-Record-and-playback...

BTW, I ever tried the newer version you mentioned, but the issue still exists.

Thanks a lot~

Xiaohui Wang

AE in Shanghai

 

 

Member
rtcote
Posts: 3
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Re: RF Record and Playback Reference Application

Hello,

 

I tried getting the VI to capture at 50MS/s per Second but the digitizer is overwriting samples in its memory.  What needs to be changed in the VI so that I can capture a signal at 50 or 100MS/s?

 

Thank you,

Russell