Doug Lung /
04.19.2013 10:39 AM
RF Shorts for April 19, 2013
A review of RF-related news during the past week
A $600 spectrum analyzer

It's here! A thumb drive sized spectrum analyzer that plugs into a USB port! The Triarchy TSA5G35 USB spectrum analyzer is one of several spectrum analyzers reviewed by Kenneth Wyatt in EMC troubleshooting roundup: Low-cost spectrum analyzers on TMWorld.com. The TSA5G35 has a frequency range of 1 MHz to 5.35 GHz, resolution bandwidths (RBW) of 50 through 500 kHz (not selectable), frequency spans from 1 MHz to 1 GHz, and an input level range of -110 to +30 dBm (using a supplied 30 dB attenuator for the higher power levels). Typical noise levels range from -80 to -100 dBm depending on the span and RBW. It's available on eBay for $599.

Wyatt covers other spectrum analyzers. The RF Explorer sells for less, while others from Wyatt sell for more than $2,000. For a high performance analyzer, the Signal Hound BB60A looks interesting. Wyatt didn't have a sample for review but for $2,479 the BB60A specifications look interesting: a range of 9 kHz to 6 GHz with a 20 MHz real-time bandwidth. A fast i7 based computer with a USB 3.0 port is required to run the unit. While it can record a 20 MHz slice of RF spectrum I didn't see any way to output the recorded RF to test receivers or for other purposes. If it was able to do that, it would be an amazing bargain! Signal Hound supplies an API so it may be possible for someone to find a way to play back and output a 20 MHz wide swath of RF spectrum.

I'm tempted to add one of these inexpensive analyzers to my travel bag, probably the Triarchy due to its small size and low cost. The Signal Hound BB60A is tempting. However, not only does it cost more but I'd have to upgrade my laptop, increasing the total cost! Signal Hound has a lower cost, lower performance model that will work with USB 2.0. It can be upgraded to a scalar network analyzer using one of their USB tracking generators. A USB-SA44B/USB-TG44A combination would cost $1,518 and cover 1 Hz to 4.4 GHz. Wyatt notes in his article that the maximum span available with the lower cost device is 20 MHz, probably enough for most broadcast transmitter and antenna applications but not enough for other measurements such as wide band field strength measurements and EMC work. The unit is a software defined radio so conceivably with the right software you could use it as a vector signal analyzer to check digital modulation quality!

Active antennas explained

Jeff Shamblin, Chief Scientist at Ethertronics offers a practical overview of active antennas in his article Reality Check: Why active antenna systems are the superior antenna tuning solution.

Shamblin discusses the limitations if antenna tuning alone, writing, “Equally important to understanding the benefits of antenna tuning is a discussion on its limits. An antenna tuning circuit can’t overcome a poorly designed, inefficient, low-performance antenna. Nor can the tuning circuit increase the bandwidth of the antenna itself. For example, antenna tuning doesn’t make an antenna radiate more efficiently, so it can’t compensate for the noticeable performance degradation that comes with an antenna with low efficiency. Nor can it overcome an antenna that’s electrically too small to cover a wide frequency range, as is the case with LTE.”

The solution, Shamblin explains, is to use an active antenna rather just matching the antenna using components located at the antenna feed point. “Unlike passive antennas, an active antenna system automatically adjusts itself to compensate for changes such as frequency and the detuning effects that occur due to the user’s head and hand. As a result, smartphones and tablets that use active antenna systems are better equipped to provide consistently fast uplink and downlink connections, as well as significantly fewer dropped calls.”

Comments and RF related news items are welcome. Email me at dlung@transmitter.com.



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