Skyworks FM Tuners Evaluated

[WHJ]

On Nov 20 Les Rayburn asked about people’s experience with the Skyworks Si4706 FM tuner IC. That IC along with a few other Skyworks IC’s have High Performance RDS capability. According to their specification sheets, the Skyworks tuners have 9 dB greater RDS sensitivity than the TEF6686.

That reminded me of seeing information on their Evaluation Boards in the past. I decided to purchase two of those: Si4743-C-EVB and Si4735-D60-EVB. The 4743 has High Performance RDS and covers FM & AM broadcast plus shortwave, longwave and the weather frequencies. The 4735 is “available with High Performance RDS” and covers FM & AM broadcast plus shortwave & longwave frequencies. I am looking into what “available with” means.

I have done my first tests with the Si4743. The FM tuner and RDS displays are shown below:

A spectrum analyzer type display shows the stations being received:

It also has a band scan feature which provides a spreadsheet file of the received RBDS information:

Since there generally wasn’t much information in the Clock Time column, I corrected the call sign errors there caused by incorrect RBDS’s being sent and weak signals. My corrections are shown in parenthesis. That was just done from my memory, so still more corrections are most likely needed. When two stations are shown on one frequency, that was due to my combining scans from multiple antenna headings. More involved antenna changes would add more stations.

There are not as many unique features for receiving the weather frequencies. Here is a quick look at some of those displays:


It's nice to know the measurement time down to the millisecond. I manually added the above call signs. I previously serviced those three weather transmitters.
More detailed measurements will be coming.

[N1LF]

I spoke to Sjef, PE5PVB who is responsible for authoring most of the firmware that has transformed the TEF6686 into a DX machine. He reports that he tested with both the Si4743-C-EVB and Si4735-D60-EVB but found them to be poorer for FM performance than the TEF6686. The 6686 has many more available bandwidth options, making it better suited for FM DXing.

I'd love to compare them head-to-head however. The chips for both are very inexpensive. I'm also interested in the NOAA Weather Radio performance. Never understood why cars in the U.S. weren't mandated to include NWS.

[WHJ]

The TEF6686 and the long-discontinued Sony HD tuner and receiver are probably better for FM DXing due to their better adjacent channel rejection than the Si4743. The 4743's greater specked RDS sensitivity might make it better for certain situations. And the software with the EVB's appears to be useful. I'd rate the TEF6686's auto-bandwidth to be a mixed bag. It's often useful but it can create switching noise during weak signal reception. I have not had that problem with the Sony's.

The Skyworks Log Raw RDS Data command might be useful for meteor scatter DXing. It checks for a RDS on the received frequency every half-second. That is the default timing which can be changed. I tried to provide an example of that occurring last night. I put the receiver on a relatively quiet frequency and activated the RDS Data Logging. In the morning, I found the log blank other than the log headings. None of my receivers had any MS receptions then.

The Log Channel Info command and others might have other uses. The IC can have its programming changed fairly easily via the EVB software's Register Map:


See the Si47xx Programming Guide for details: AN332: Si47xx Programming Guide

I am completing the Si4743-C-EVB's enclosure now and will beginning my evaluations soon.