Figure 1: A weather fax received with the RX320D by Ten Tec. Click to enlarge.
Posted 11/01/2016:
So, I’d been trying to obtain weather faxes, of the type transmitted by the shortwave weather transmitters run by the US Coast Guard, and do that by using the little Soft66 Lite SDR board. I’d added a preamp to that line-up in order to improve results, yet it seemed that improvement was needed still. So …
I purchased a Ten Tec RX320D, to see if I could improve the odds that on any given day I could retrieve very high quality weather faxes via shortwave. The first tests of the setup yielded promising results.
Figure 2: RX320D, by Ten Tec, with “homemade” serial gender changer. Click to enlarge
The power supply that came in the package for the RX320 was stamped “15 VDC.” Before I applied any power to the 320, I checked the supply, and found it was supplying 20 VDC instead of 15 VDC. So, I took one of the little DC-DC converters I’d recently purchased from a seller in Las Vegas, and dialed the supply down to exactly 15 VDC.
I installed the Linux software for the RX320D, using the instructions found on longwire.com, plugged the serial cable into the PC and also into the RX320D, connected an audio cable from the RX320D (line input) to the line-input connector of the PC, and threw the power switch to the “on” position. I expected static, but heard nothing. It turns out that I’d forgotten to install a “gender changer” dongle in the serial line. It should be noted that the serial connection must be made before the RX320D will work at all. NO sound (not even static) will be heard from the device before the serial connection is made. So, I home-brewed a dongle (laughing is expected here) – and again threw the switch on the RX320D to the “on” position. I dialed a WX-FAX frequency into the application GUI interface, and started retrieving faxes from the 8.504 MHz transmitter in New Orleans, LA:
Figure 3: The RX320 software, FLDigi software shown working together. Click to enlarge
The RX320 Linux software, in combination with the FLDigi program, can be seen in Figure three, downloading a weather facsimile from a Coast Guard station in New Orleans:
Figure 4: Weather Fax. Click to enlarge.
My homebrew gender changer uses the usual three wire configuration. Note that the three wire configuration works with the RX320D I’m using, but that may not be the case with all versions of the firmware. Below, I show a (yes kinda crude) drawing of the electrical connections:
Figure 5: Homebrew gender changer wiring diagram
Of course, I intend to put a better setup together for the gender changer, and probably will utilize (yet another) of the aluminum Hammond boxes to hold the crossover wiring as well as the DC-DC converter that I found necessary due to (maybe aging?) of the original wall wart that came with the receiver.
Figure 6: Weather Fax. Click to enlarge.
Wave period is shown on another weather fax received with the RX320D when it was tuned into the Coast Guard station in New Orleans on 8.502 MHz (the advertised frequency is 8.504 MHz, but one must tune about 1.9 KHz lower). Wave period is important! Higher numbers much better, so long as they don’t come with very large wave heights 🙂
Figure 7: Weather Fax. Click to enlarge.
OK, so the Ten Tec RX320D is 1999 electronics. It hasn’t been made in quite a while, so must be procured on the used market. They fetch a premium, relative to what they were originally sold for, because few other devices on the current new market can do what they do, cheaply.
Tuning around with the RX320D, I found that many of the weather fax transmitter signals were NOT coming into the little receiver’s front-end very strongly, and in many instances the resulting faxes were no different than what I had received on the Soft66 Lite SDR. So, what may really be happening, is that due to the RX320D having easy frequency manipulation capability, it is a simple matter for it to look at a lot more frequencies, and thus find one that is very strong. The Soft66 Lite SDR, as versatile as it is, does not have the frequency agility of the RX320D, because the former is rock bound.
In general, my Ten Tec Omni receives signals better than the RX320, but then again it’s a much more complicated radio.
The RX320 can present a “spectral display” up to 1.5 MHz wide, so to discover signals. This is akin to what the SDR can do with its 192 KHz sample-rate audio setup, but it’s done on the RX320D by scanning the frequency range from bottom to top, in narrow increments, rather than having it “all at once”. To be truthful, the scanning approach is just as good for me. The scan method makes me wait a few more seconds for each update, but otherwise is just as good. I wonder why there are not more of these devices available for sale, with a decade or so of advanced design improvements? Oh well.
Figure 8: Use of USB/Serial cable made things simple. Click to enlarge.
I substituted a Trendnet TU-S9 USB/Serial cable for the standard serial port and “homemade” gender changer combination. No gender changer is necessary when using the USB/Serial cable. This makes for a much cleaner arrangement. In figure 8 can be seen a weather fax being retrieved from the Boston Coast Guard station operating at 9.110 MHz. I’ve found that frequency to be good in the late afternoon (this one was around 5:00 P.M.) for the Boston to North Carolina circuit.
The USB/Serial cable that I substituted, works fine with the driver baked into the Rasbian Pi2 image, and I set it up with stty:
- stty -F /dev/ttyUSB0 -crtscts -clocal ispeed 1200 ospeed 1200
The -crtscts option turns off hardware handshakes along with the -clocal option, which disables carrier detection (CD). In other words, it turns the connection into a simple three wire connection (like I used with the “real” serial cable wiring between the radio and the Linux PC). The USB/Serial cable was necessary on the Pi2 powered “homemade” tablet, because the serial port was already being used for GPS on that box. Note that subsequent use of any communications program may (or may not) change the port settings, and I’m not sure what the RX320 software does in this regard (I could check that I suppose).
Figure 3 contains a screenshot that contains an image of a program that has been released under a free software license (FLDigi, located at http://www.w1hkj.com and the license at https://www.w1hkj.com/FldigiHelp-3.21/html/license_page.html). The license is GNU GPL v2. As a derivative work of that program, the part of the screenshot that contains it falls under the same license (GPL2).
Figure 3 also contains elements of a desktop system and associated programs that have been released under a free software license (Copyright: LXDE team: http://lxde.org). As a derivative work of that program, the respective part of the screenshot in Figure 2 falls under that same license. The full text of the licences (GPL 2.0+ and LGPL 2.1+) may be found at http://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html and http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html.
Note: the soft66 hardware is a product that is sold on a Japanese website (http://zao.jp/radio) – and is not affiliated with this site or author in any way. Ten Tec is a subsidiary of Dishtronix, Inc, and trademarked is held by them. They are not affiliated with this site or author in any way. RaspberryPi is a trademark of the Raspberry Pi foundation, and this author and site has no affiliation with them.
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