Article: 18990 of rec.radio.shortwave Newsgroups: rec.radio.shortwave Path: news.cs.tut.fi!news.funet.fi!news.tele.fi!uunet!wupost!uwm.edu!linac!att!cbnewse!parnass From: parnass@cbnewse.cb.att.com (Bob Parnass, AJ9S) Subject: Re: frequency-sweeping type affects Organization: AT&T Bell Laboratories, Naperville, IL Date: Tue, 16 Mar 1993 14:25:48 GMT Message-ID: <1993Mar16.142548.10712@cbnewse.cb.att.com> Summary: reprint of article on "sweepers" References: <215@g0gku.demon.co.uk> Lines: 88 [Reprinted from the RCMA Journal, June 1989] STRANGE HF SIGNALS MAY BE PROPAGATION SOUNDERS by Bob Parnass Many scanner and shortwave listeners are curious by nature, and want to know the identity of stations they hear. Pirate broadcast stations have a cult following, as do "spy numbers" and military transmissions. But, some signals seem to defy explanation. They are nei- ther voice nor data. What are those clicks, tweets, and bursts one hears on the shortwave bands? Perhaps you stum- bled on signals from over the horizon radar, or even an RF induction heating oven. There is another source of these puzzling signals -- your receiver may have intercepted a sounder system used for propagational studies. A recently released U. S. Navy report gives us a peek at several such radio sweeper systems: HF Maximum Usable Fre- quency (MUF) Model Uncertainty Assessment, Technical report 1184, by T. N. Roy and D. B. Sailors. June 1987. Naval Ocean Systems Center, San Diego, CA. A sounder system consists of a transmitter that emits sig- nals sequentially on several frequencies, and a distant receiver which is programmed to follow the transmitter fre- quency and measure the signal strength at each channel. Navy Tactical Sounder System The Navy has used a system of several shore-based AN/FPT-11 (XN-1) sounder transmitters and shipboard and land based AN/UPR-2 receivers to determine propagation conditions. Known as the Navy Tactical Sounder System (NTSS), the FPT-11 transmits a double, biphase pulse sequence every minute on each of 80 frequencies between 2 and 32 MHz. The 80 fre- quencies are spaced in 100 kHz increments between 2 and 4 MHz, 200 kHz increments between 4 and 8 MHz, 400 kHz incre- ments between 8 and 16 MHz, and 800 kHz increments between 16 and 32 MHz. Both receivers and transmitters are synchronized to WWV so the receivers can follow the transmitter frequency sequence. Granger Model 900 Sounder The Stanford Research Institute has used a different system to study propagation. Their equipment consists of Granger Associates Model 900 sounders, which cover the 4 to 64 MHz range in four bands of 40 linearly spaced channels each. The Granger sounders are high power, and transmit 30 kW peak pulses of 0.1 ms or 1.0 ms. The scan sequence takes 29 seconds to complete, and is repeated every 20 minutes. A search of FCC records shows SRI may also be using linear sweepers. SRI was granted license KA2XNH as an experimental contract station to fulfill U.S. Navy contract N00014-83-C- 0267. This license permits a 50 watt SRI transmitter to sweep the 2-32 MHz band in 1 Hz increments not more than 3 times per hour at a sweep rate of not less than 5 minutes sweep for the entire band. Other Systems Another sounder system consists of a device called a C-3 iosonde, which transmits 0.1 ms pulses and is swept linearly between 2 and 25 MHz. The BR Communications HF Chirpsounder System takes 5 minutes to sweep between 2 and 30 MHz, and the sweep is repeated every 15 minutes. Sights and Sounds It's tough to follow frequency agile signals using only shortwave receiver. Connecting a panoramic display (pana- daptor) makes it easier to identify sounders. One can actu- ally see the sweeper signals moving up the band. -- ============================================================================== Bob Parnass, AJ9S - AT&T Bell Labs - parnass@ihlpm.att.com - (708)979-5414