Most of us do not have zero horizon from our home QTH but you can still receive 10 GHz signals by pointing your dish up at a cloud layer.  I suspect that the low level 10 GHz signal we are receiving from low-level to mid-level and the upper tropospheric cirrus clouds would go unnoticed on a typical transverter connected to a commercial radio.  This paper is about how some of us in the Pacific Northwest are doing it over paths up to 240 miles. Weather patterns in other parts of the country may be different compared to ours.

Mike, KD7TS (CN87ui) and W7LHL (CN87ua) are using the W7CQ beacon at CN83jx as a test signal to further investigate the upper tropospheric and the mid_level cloud scattering.  While we were studying the upper troposphere for the article in QEX we didn't pay much attention to the mid-level clouds for scattering because of the minimum dish elevation at our locations and there was no beacon at that time.  Mike can go down to zero degrees, my minimum is 8 to 9 degrees to the south because of a hill, W7SZ (CN85uo) and W7PUA (CN84io) are 4 degrees minimum when pointed north.  W7CQ beacon is near zero degrees.  I received the beacon signal from the upper tropospheric or cloud tops as my common volume is around 23,083 to to 29,373 feet if the beacon is from 0 to 0.5 degree up.  Mike's dish is at 1 degrees and his common volume would be around 14,254 to 17,586 feet.

I use the satellite water vapor imagery to forecast when I may receive a signal from the beacon and Mike uses the radar summary cloud tops to tell when he may receive the beacon signal.  Most of our cloud tops do not go above 20,000 feet here and it is a good way to tell if there might be mid-level clouds.  Also we check Portland, OR weather radar and aviation TAFs for clouds.  There seems to be no single source for cloud information for our investigations.  A good starting point is for both stations to start off with a 1 degree elevation.  Better yet run the height program and the program will tell you where the common volume location is with various elevation angles.  The height program can be downloaded from Mike's Web site and the name of the program is HEIGHT1.ZIP.  Just unzip, type HEIGHT1 and press the Enter key.          

The characteristic of these low level signals are narrow unlike rain scatter signals. When we do have thunderstorm type clouds or rain the signals are much broader and stronger.  The dishes must be pointed straight at each other and being off by two degrees makes a big difference in signal level.  At times the signal level is strong enough to make contact by CW or SSB but most of the time you would have to use a digital mode.  One thing we know about these clouds is that when there are no clouds there is no signal. There must be clouds at the common volume area.  We are still studying this type of condition to see what is the actual mechanism for these low level signals. Bob, W7PUA and Larry, W7SZ are running similar tests.  Mike has many pictures on his Web page.

 I have been asked what type of equipment is required to receive and to make contact using these low level 10 GHz signals. The minimum equipment I recommend is a two foot dish, 10 GHz transverter into a commercial radio and a waterfall program like Spectran.  Better yet the L.O. in the transverter should be phase locked to a GPS setup.  The way I do this is by using a PTS160 Frequency Synthesizer tuned to the crystal oscillator frequency inside the transverter.  I  mounted  an  SMA  connector  on the transverter box near the crystal oscillator.  Inside of the transverter box the connector is terminated to ground by a 51 ohms quarter watt resistor.  A 2 pf silver mica capacitor is connected between the connector and to one side of the crystal.  The signal level required from the PTS160 to lockup the crystal depends on how close you set the crystal frequency.  Anywhere from -30 to 0 DBm.  I have done this to all of my DB6NT, SSB and old Down East microwave transverters.  Phase noise is quite low. There are other methods that we have used to phase lock the crystal L.O. but using a PTS160 is by far the easiest method and the transverter can still be used without the PTS160.  The later Down East tranverters use crystal frequencies around 192 MHz.  The PTS160 goes up to 160 MHz and so you need a higher frequency PTS or use a frequency doubler with a PTS160.  The 10 MHz reference frequency for the PTS160 should be locked to the GPS setup.

Another powerful setup, that does not require much effort, is to use an EZ-Kit Lite DSP as a audio processor connected to the commercial receiver audio output and using the W7PUA DSP10 software.  Now you have almost all features of a DSP-10.  I use the audio processor setup connected to my Kenwood TS790A.  Most commercial receiver audio output is not very flat and a audio equalizer should be used. If you want the best weak signal setup then I recommend a DSP-10 transverter and the reference 10 GHz frequency locked to a GPS setup.

A few words about using digital modes on 10 GHz.  We have tried JT44 and JT65C weak signal modes but they did not fair out very well because of frequency spreading of the 10 Ghz signal.  The two JT modes channel bandwidth and tone separation is 10.7 Hz while the DSP-10 PUA43 mode tone separation is approximately 37.6 Hz when using the 4800 bandwidth.  This is one of the reason why PUA43 mode works so well at 10 GHz.

The W7CQ beacon is running 230 mw to a 1 foot dish, KD7TS is using a 3 foot offset dish with a low noise preamp into SSB transverter and W7LHL is using a 2 foot offset dish with a low noise preamp into a DB6NT transverter.  KD7TS and W7LHL are both using Qualcomm 2556 MHz synthesizer boards for L.O. and DSP-10s.  It does not take high power or big dishes to receive a signal from clouds.  Just need low-level, mid-level or high-level cirrus clouds and with the dishes pointed in the right direction.

Footnotes:

     Microwave Propagation in the Upper Troposphere by Bob Larkin,
     W7PUA, Larry Liljequist, W7SZ and Ernie Manly in QEX, Jul/Aug
     2003.
     http://www2.arrl.org/qex/larkin.pdf
     
     The DSP-10 transceiver project was originally described in a three
     part article by Bob Larkin, W7PUA in QST, Sept, Oct and Nov 1999.
     
     http://www.arrl.org/tis/info/pdf/9909033.pdf
     http://www.arrl.org/tis/info/pdf/9910034.pdf
     http://www.arrl.org/tis/info/pdf/9911042.pdf

     A GPS-Based Frequency Standard by E. B. Shera, W5OJM in QST, July
     1998.
     http://www.rt66.com/~shera/QST_GPS.pdf

     Clouds tops URL
     http://aviationweather.gov/data/iffdp/2080.gif

     TAF URL
     http://www.wrh.noaa.gov/sew/aviation_tafs.php
     Click on TAFs across USA for other locations.

     Satellite URL
     http://www.wrh.noaa.gov/satellite/

     Portland, OR Radar URL
     http://radar.weather.gov/radar_lite.php?product=NCR&rid=RTX&loop=no
     Click on U.S. Views, National for other locations.

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