Tracking Generator FAQ

TG3000 and TG6000 Tracking Generators (Replace HP  HP 85640A) FAQ

DS Instruments

May 2014

 

Q. Can I use my TG3000/6000 with any spectrum analyzer?

A. No. The spectrum analyzer used must have a certain signal processing architecture internal to the instrument. Specifically they must be of the swept type, all sweeping done by 1st LO and the SA used must provide access to the first LO . Many HP/Agilent Spectrum Analyzers have this architecture and 1st LO  access.  For a list of currently supported SA’s click here.

Q. What Spectrum analyzers are supported by the TG3000/TG6000 systems?

A. For a current list of supported spectrum analyzers please see  “Supported SA’s for TG3000/6000” under the DOCUMENTS tab of our website.

Q. Which TG should I use, the TG3000 or the TG6000?

A. It depends on the SA being used and if you wish to sweep above 3GHz. Many Agilent/HP analyzers use a multiple band approach to cover their entire specified frequency range. For example the HP8561 SA covers from DC to 2.9GHz in band0 and from 2.9 to 6.5GHz in band1. The TG3000 can cover band0 of the HP8561 but not band1. The TG6000 can cover both band0 and band1 of the HP8561. If you have the HP8560 it only has band0 so the TG3000 covers this instrument while the upper band of TG6000 would be unused in this case.

Q. What is the output level of the TG3000/6000?

A  Typically TG output is 0dBm.

Q. Should I use an attenuator between the TG output and my DUT input?

A. A 3db pad is recommended between the TG3000/TG6000 output and the DUT input. This improves the VSWR of the TG output. For improved match use a 6dB pad. The attenuator pads should be rated to at least 3GHz for the TG3000 and 6GHz for the TG6000.

Q. What settings should I use for my SA when operating with TG3000/TG6000?

A. It is recommended that at least 6dB internal SA attenuation be used to maintain low VSWR at DUT output port. The reference level should be set to approximately 0dBm, RBW 3 to 10KHz, VBW 1KHz, Sweep time to 1/10sec. Note that the SA may report “uncal’d” for this combination of settings, particularly sweep time and RBW settings. Sweep time normally is on AUTO and changes with SPAN and RBW. Changing this to MAN and setting to 1/10 sec may trigger warning. Typically much faster sweep times can be done using a SA with a TG as the signal is always inside the RBW filter. In other words in typical SA operation the RBW filter must have time to settle hence max sweep speed is limited.

Q. Is it possible to correct the flatness of the TG3000/TG6000 using my SA video memory and operations on it?

A. Yes, if your analyzer supports a display line, A and B video memories and video subtraction (most HP/Agilent Instruments have these features). Typically this operation is only needed over large spans as over smaller spans the flatness of the TG3000/6000 is quite good. Connect a THRU type DUT that has a flat response between the TG and the SA. If you are using a matching pad on TG output make sure it’s connected also. With the THRU DUT being swept over the frequency range of interest turn on the DISPLAY line. Adjust display line until its about in the center swept response curve. Now subtract the DISPLAY line from video memory A ( active trace) and store in video memory B. Now subtract video memory B from the active trace, A , and make this result the active trace ( on HP this last part is automatic). Now the swept response should very flat as the variations have been cal’d out. This is a video correction only; if the frequency settings of the host SA are changed the “cal” routine outlined above must be redone.

Q. I have a mixer in my network that converts an RF input to an IF output. Can I use the TG3000/TG6000 to sweep the entire chain all at once so as to see the RF and IF combined response?

A. Typically, yes. As long as the IF frequency is not too high the TG3000/6000 can be reconfigured to include the frequency OFFSET of the DUT IF in the TG output. This will require the internal signal generator (SG) of the TG3000/6000 to be changed to a different frequency, for a single IF type  DUT the internal SG  frequency is OFFSET from its nominal value by the DUT IF amount. The user will have to connect the TG3000/6000 to a PC via USB port and program the internal SG frequency to this new value for this DUT.

Q. If I use the TG3000/TG6000 as a signal generator is there any limitations imposed by the TG function?  Should I terminate the unused TG output?

A. No. The SG portion of the TG3000/TG6000 is independent of the TG specific operations which are done internally to the TG. It is not necessary to terminate the unused TG output when using just the SG function of the TG3000/6000.

Q. Can I set the SG output to a custom frequency using the rear panel rotary switches?

A. Only if you have programed the rotary switch look table using the PC software and USB interface beforehand. There is no way to enter the frequencies except using the PC/USB interface.

Q. I notice that your TG3000/6000 need a 10MHz input, which isn’t available from the 8590A.  Can I use an external 10MHz frequency standard for this input, or does the 10MHz need to be specifically from inside the SA? If so, where in the 8590A can I get the 10MHz for the TG?

A: Using another 10MHz signal for reference is acceptable. The issue that occurs is when the SA is set to use a narrow RBW for processing/sweeping. When using narrow RBW the tolerance for 10MHz error is proportional. Specifically if I use a 1KHz RBW the error on the 10MHz source must be small with respect to the internal 10MHz used by the SA, which in your case would be the 10MHz inside the 8590. When the TG3000/6000 uses the 10MHz from the SA this issue goes away ( mostly,see below for step size limitation) as now the internal SG of the TG3000/6000 is LOCKED to SA reference.   The bottom line is this: If you use a good stable 10MHz, say a double oven type, from anywhere in other equipement you will be able to use the Tg3000/6000 just fine. What you may have to do is use a larger RBW. Typically 10KHz RBW will be okay, 30KHz is even more forgiving of relative error beteween SA 10MHz and your lab supplied 10MHz. What does this mean in terms of performance?   Performance Issue: As RBW decreases, noise floor goes down. When using a TG3000/6000 with 3KHz RBW setting dynamic range is on the order of 80dB ( HP 8566/68). With a 30Khz RBW setting dynamic range will be reduced by 10dB. Some dynamic range can be recovered by reducing attenuation in TG output path and SA attenuation setting, but the bottom line is maximum dynamic range occurs with narrower RBW’s.   What is the narrowest RBW that can be used with TG3000/6000?  You did not ask this but it is related. Even if we lock the TG3000/6000 to SA by using the SA’s 10MHz reference we have a step size limitation. The internal SG of the TG3000/6000 has a step size of approx 1KHz in the 2.2 to 4.4 band. This means use of the 1KHz RBW is iffy. If the errors work out you can be in the center of the 1KHz RBW, if not you are off to the side of the 1KHz RBW and TG output is down a dB or two.

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