The FCC has revised the power level thresholds to trigger a routine Amateur Radio station RF exposure evaluation, and the changes will be welcome news for most hams. When the FCC first decreed a year ago that ham radio stations would have to comply with RF exposure guidelines, it set a 50-W threshold level. The updated guidelines, announced August 25, increase that threshold level on all HF bands except 10 meters, where it remains at 50 W. The FCC made no changes in the RF exposure limits it announced last year. The new RF safety guidelines are scheduled to become effective January 1, 1998, for Amateur Radio stations.

The FCC went along in part with a request by the ARRL to establish a sliding scale for threshold levels, depending upon frequency. The revised thresholds are 500 W for 160 through 40 meters, 425 W on 30 meters (where the maximum permissible power is 200 W), 225 W on 20 meters, 125 W on 17 meters, 100 W on 15 meters, 75 W on 12 meters and 50 W on 10 meters. The threshold for all VHF bands is 50 W. On UHF, the threshold level is 70 W on 70 cm, 150 W on 33 cm, 200 W on 23 cm, and 250 W on 13 cm and above. Stations operating at or below these respective power levels are categorically excluded from having to perform a routine RF radiation evaluation. However, all stations, regardless of power level, still must comply with the RF exposure limits.

Along with its August 25 Second Memorandum Opinion and Order announcing the changes, the FCC released the ''core'' text of its long-awaited Office of Engineering and Technology (OET) Bulletin 65, Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields. The bulletin contains generic equations that can be used to analyze fields due to almost all antennas, although the FCC warns that ''the resulting estimates for power density may be overly conservative in some cases.'' Hams leery of formulas might opt to wait for the easier-to-use Supplement B to OET Bulletin 65, which will include information designed specifically for evaluating Amateur Radio installations. The supplement promises to detail how hams can determine more simply if their individual stations comply with the new regulations. The FCC says the supplement will contain ''information on projected minimum exclusion distances from typical amateur antenna installations.''

The FCC said it would issue Supplement B ''as soon as a review of the current draft is complete.'' When it's ready, Supplement B will be available to download from the FCC's Web site, http://www.fcc.gov/oet/rfsafety. The FCC directed inquiries as to the availability of the supplement and other RF-related questions to its RF Safety Program, 202-418-2464; e-mail [email protected].

Last year, the FCC established time-averaged maximum permissible exposure (MPE) limits for RF fields in two tiers--for controlled environments (ie, a ham's immediate household, including visitors) and uncontrolled environments (ie, neighbors, the general public). If a routine evaluation of a ham station indicates that human exposure to RF fields could be in excess of the FCC's MPE limits, the licensee must act to correct the problem and ensure compliance. This could include changing operating patterns, relocating antennas, restricting access, changing frequency, output power or emission type or any combination of these and other remedies.

The FCC says that ham radio facilities ''represent a special case for determining exposure, since there are many possible antenna types that could be designed and used for amateur stations.''

The revised regulations categorically exclude most mobile installations, including those in the Amateur Radio Service, from having to comply with the RF-exposure or station evaluation guidelines. Since the FCC issued its guidelines, additional questions on RF safety have been added to the Amateur Radio examination question pool.

As you can imagine, a free service draws a lot of activity. All this activity has made the site increasing slow and un-reliable during peak times, making it difficult. for users to read the site, and making it difficult for me to maintain.

To help with the reliability, I’ve moved SARA’s site to space that is provided to me by my internet service, Road Runner. Road Runner’s servers are maintained by Time Warner Cable, a company with the money and resources to maintain an industrial grade site. Road Runner’s servers also have some special features that have allowed me to add several new features to the site.

Some of the new features that have been added are:

Discussion Forum:
Allows you to post questions, comments, or items for discussion in a bulletin board format. You can also reply to the posts that others have put up. This feature is handy for technical questions, items for sale, etc.

Site Search:
Allows you to search SARA’s site (including newsletter articles) for specific words. This allows you to find past newsletter articles and other pages that refer to the words you are looking for.

Feedback Form:
The feedback page allows people that visit the site to request more information, and offer comments, suggestions, and critizism.

Amateur Radio Web Ring:
SARA is now a member of a "web ring". A web ring is a group of other amateur radio related internet sites that have all joined a common index. You can jump to the sites of other clubs that have internet sites, and learn about what others are doing. There is also a "random" link feature that will pick a ham radio site at random, and take you there. This is nice if you have a little extra time to go exploring. The web ring is a totally free service, that currently has over 300 member sites.

Also, don’t forget that the club roster is available on SARA’s internet site. It is available in a normal web page format, and now can also be downloaded as a text file or a Microsoft Excel spreadsheet.

 What makes up the Microrover Telecommunications System?
The telecommunications system is composed of two UHF radios and two UHF whip antennas. The Microrover radio is located inside the Rover WEB (Warm Electronics Box) where it is protected from the extreme cold of the Martian environment. The radio is connected to the Microrover antenna using a short piece of coaxial cable that passes through the wall of the WEB. The radios that are used in the Microrover telecommunications system were purchased from Motorola's Paging Products Division. Several components that were designed and used in these radios were made by a company named DataRadio. These are off-the-shelf commercial radio modem's (modulator+demodulator) that were modified to meet the communication needs of the Microrover mission. The antennas were designed and built by our Telecom team here at JPL.

Before we purchased a large number of Motorola RNet 9600 radio modems, we did a study to see if it was better to 'make' the radios or to 'buy' them ourselves. The main factors under consideration in the 'make' or 'buy' trade-off study are, in order of priority: funding level (we knew how much money we could spend), schedule of hardware delivery (we knew when we had to deliver the radios) and environmental specifications (we knew the operating environment of space and the Martian surface). It was known based upon a Mars Lander-Rover radio link analysis performed in 1989 that a Radio Frequency (RF) range of 100 to 450 MHz (1Mega Hertz = 1 million cycles per second) should be used for surface-to-surface communications. Consequently an industry search was made for sources of wireless radio modems and antennas in this frequency range.

The journey from commercial-grade radio modems to space-flight ready hardware....
As you'll recall, for this Microrover mission we decided to buy "off-the-shelf" commercial radio modems, then modify them to be space-flight ready. Our concerns were both electrical and mechanical.

Electrically, we could only test these radios to make sure they will work at the low temperatures that are required. On Mars, their real operating temperatures are expected to be -30�C to +40�C. Preliminary tests show that these radios will operate at the low temperatures, with some performance degradation. So we proceeded to address the mechanical issues.

Mechanically, we had to make these radios more rugged, to survive the shock and vibration associated with launch and the harsh landing onto the Martian surface. Further, we had to replace parts that are not suitable for space/vacuum operations. Our philosophy was to modify as little as necessary. With a team of packaging experts, we considered carefully the risks and benefits of these modifications.

 The Environmental Tests (Thermal, Shock & Vibration): Procedures and Results....
As we were deciding what sort of modifications we needed to make on the radio modems, to make them space-flight ready, we worked in parallel on the environmental test procedures.

We understood the expected temperature environment, the shock and vibration environment in which these radio modems will have to survive and operate. For temperature, the radios have to survive -55�C to +60�C, while they will have to operate from -30C to +40C. As for shock and vibration, the radio modems have to survive the launch vibrations and the shock of landing on the Martian surface equivalent to an impact at 40 mph; they are not required to operate during launch and landing.

Once these radios were modified to be space-flight ready, we put them through a series of environmental tests. We first put them through shock and vibration tests, by mounting the radio modems on a 'shaker table' which shook them at the necessary vibration levels. Then we placed the radios inside thermal chambers, which cooled and heated them. By first shaking the radios, and then thermal cycling them, we more closely emulated the sequence of events they will see during the mission - launch, landing and then Martian surface operations. We expected these radios to pass the environmental tests and they did.

What about the outer space radiation environment?
Certain flight components are susceptible to the damaging effects of radiation. There are different types of radiation, some more harmful than others. Spacecrafts need to function in the presence of ultraviolet radiation. This is the type of radiation which we on Earth are protected from by the ozone layer. The ozone layer is about 30 Km above earth's surface and protects us from the damaging effects of ultraviolet radiation by absorbing solar wavelengths between 2,000 and 3,000 Angstroms (1 Angstrom = 10-8centimeters). The entire Mars Pathfinder spacecraft in the cruise and landed configurations was tested in a 25' space simulator where it was subjected to high intensity light twice as bright as the sun. The Martian atmosphere is very thin which does not protect the planets surface from ultraviolet radiation, but the Mars Pathfinder and Microrover hardware have been designed, built and tested to survive this radiation for an extended time period.

The sun gives off other types of radiation which is potentially damaging to spacecraft. Solar flares and prominences erupting from the suns surface eject a stream of high energy ionizing radiation and sub-atomic particles into space. In addition, cosmic rays originating outside the solar system add ultra-high energy ionizing radiation to the mix. These ions can strike certain electronic circuitry on the spacecraft and cause any number of Single Event Phenomena (SEP) to occur. These range from soft errors, hard errors, latchup, burnout and transients. Fortunately, the probability of such particles affecting the rover telecommunications hardware is small because the sun is expected to be at a solar minimum during the mission. But, nevertheless, the experimental radios used during screening were taken through extensive radiation testing at Brookhaven National Laboratories on Long Island using their Van De Graaff accelerator. We learned from these tests what can happen to the radios if highly energetic ions hit them. It did not permanently damage them, but caused a condition called 'Single Event Latchup' or just 'latchup' to occur. Latchup is a condition in which certain transistor junctions in VLSI (Very Large Scale Integrated) and ASIC (Application Specific Integrated Circuits) chips short to ground, thereby drawing very high current (specifically, an abnormal low impedance, high current state induced in a parasitic P-N-P-N structure of a bulk CMOS IC). The latchup current in the radios was high, but limited by the presence of an on-board voltage regulator. It was found that the radio modems can recover from this latchup condition, with no damage, by simply turning them off and then on again (this is known as power-cycling). There are software algorithms in the rover and hardware timing circuitry in the lander which detect this condition and automatically power cycle the radio to provide this protection and restore it to a normal working condition.

What about Electrical Interference from the Lander and its Telecom System?
The telecommunications system on the Lander uses X-band microwave uplink and downlink signals. These microwave signals occupy two narrow bands that are about 15.5 times higher in frequency than the UHF band used by the rover. There is no way that the lander signals can be received by the rover and vice-versa. But to confirm this we had to run a series of EMC (ElectroMagnetic Compatibility) tests. These tests were performed at three different locations:

• At the JPL EMC laboratory with the lander RFS (Radio Frequency Subsystem) and a set of non-flight radio modems,
• At the Mesa antenna range with the Lander High Gain Antenna (HGA), 12 Watt microwave transmitter and a set of radio modems,
• At the SAEF-2 facility at KSC using the fully functional Lander and Rover Telecom systems,

These tests confirmed that the effects of interference by the lander and rover telecommunications hardware on each other were within acceptable limits and not a problem at all!

In following issues of the Salami Merchant, we will examine more details about the Mars Rover communications systems.