Signal Hound USB-TG124A, Руководство пользователя

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Theory of Operation |
Measuring Return Loss
5
3.2.1 Adjusting an Antenna
To adjust an antenna for a certain frequency, it is often sufficient to simply maximize return loss at that
frequency. This may be done in a swept or CW tracking generator mode. Mount your antenna and
ground as you normally would, then connect to the "IN" port as above. Lengthen, shorten, and tweak
impedance matching elements until the desired return loss is achieved. Be aware that you will be
radiating some RF during this process. It is your responsibility to understand and obey laws regarding
transmitting on those frequencies.
4 Theory of Operation
Learn about the internal blocks that make up the Signal Hound Tracking Generator
The Signal Hound Tracking Generator is built around a 32-bit programmable modulus DDS. This allows
the firmware to set precise 10 Hz steps. The DDS generates frequencies from 10 Hz to 28 MHz directly.
To produce higher frequencies, the DDS output frequency is multiplied by an integer from 5 to 500.
Below 28 MHz, the output has low harmonic content. However, above 28 MHz, harmonics are
generated and not filtered. From 4 GHz to 7.2 GHz, an Fout / 2 subharmonic will also be present, and
above 7.2 GHz there will be Fout/3 and 2*Fout/3 subharmonics. Harmonics and / or subharmonics,
sometimes as high as -10 dBc, will be observed. For use as a tracking generator, the presence of
harmonics has very little impact on the measurement, since the harmonics will generally be well outside
the spectrum analyzer's input bandwidth.
However, when verifying the output power level with an RF power meter, the harmonic content can add
typically up to 0.7 dB to the measured output.
Please note that the phase noise of the USB-TG124A is higher than the USB-SA124A. However, this will
have minimal impact on readings as out-of-band energy is rejected by the spectrum analyzer.
5 Troubleshooting
5.1.1 General Troubleshooting Procedure
1. Before troubleshooting the TG124A, make sure your USB-SA124B is working properly.
2. The most common cause of the TG124A not working is a missing or damaged BNC cable
between the TG sync and the SA sync.
If the LED on the TG124A is red during scalar network
analyzer sweeps, this is likely the problem.
3. Unplug the USB cable from your Tracking Generator, count to 10, and plug it back in. If the LED
is green, proceed. Otherwise, try a different USB port or cable.