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Hello,
I’ve did some simple tests with TG44 (without spectrum analyzer, TG is controlled with TGStandalone) and my oscilloscope (Rigol MSO2302A).
1. I see, that it uses 2 different generators, first for low frequencies (<28MHz), which generates sine signal, and second gen for high frequencies (>28MHz), which generates rectangular signal. Low frequencies have a 10Hz step, so I can set 10Hz, 20Hz … Any frequency lower than 10 Hz turns off generator, so it can be very simple to add turn on\off switch to software.
2. I’ve noticed some negative DC offset on low frequencies, see pictures. I know there are some devices which require zero DC offset on input, and this can be a potential problem for somebody.
3. I’ve connected TG44 and my function generator (Rigol DG4162, which allows me to set amplitude in dBm from +10 to -50), set both generators to 1MHz and compared output amplitude. I see, that TG44 power -10dBm, -20dbm, -30dBm look correct (+-1dbc error), -40 is -38dBm (a bit higher, but still ok) but 0dBm outputs only -7dBm. On picture yellow line is TG44 output (Vrms =100mV, ~-7dBm), blue line is DG4162 output (Vrms =232mV, close to 0dBm). On -20dB picture both show almost identical Vrms ~22mV. Is it a hardware issue?
4. I see that TG44 generates 10MHz output reference, but it can’t use external (OCXO or GPSDO) reference. It’s looks strange to use external reference in analyzer and not being able to use the same reference in generator.
Ivan,
The TG44A produces 10 Hz to 4.4 GHz, -30 dBm to -10 dBm. This is why 0 dBm and -40 dBm do not read accurately–they are beyond the amplitude range of the device.The TG44A, as a tracking generator (not a signal generator), has a very simple job: generate a signal that tracks the SA44B’s input frequency, at a specific frequency and a repeatable amplitude. Since the SA44B can filter out harmonics, we do not filter them on the TG44A. This reduces cost, size, weight, and power, without really affecting performance as a tracking generator.
Below 28 MHz, the frequency is generated with a DDS, thus the sinusoidal output. Above 28 MHz, it is produced by a clock or divided LO, and will be closer to square than sinusoid. A external low pass filter can easily remove harmonics to produce a sinusoid if needed.
Also, below 28 MHz, the output is DC coupled (as it goes down to 10 Hz). This small DC offset has a 50 ohm impedance, so it adds a little to total envelope power, but will not damage the SA44B input.
Thank you for the answers.
I see in specs, that TG44 can output power from -10dBm to -30dBm, and it does so (and even a bit more), there’s no issues here. But software sometimes makes me puzzled, it shows me that TG44 is capable to output 0..-40dBm power and 0..13GHz frequency. I think it’s good to reflect in the software realistic abilities of the connected generator.
I was expecting to see rectangular output of the tracking generator (as it do some other analyzers), and sine output on low range was a little bonus to me.
Regards, Ivan
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