The starting point for an active iDirect connection is the RX indicator, which must be green, and you must have an RX SNR greater than 6.

Troubleshooting a poor RX connection when the DataStorm controller (positioner) indicates that pointing has completed, but you still don’t have a green RX light and/or you do not have an SNR value of 6 or greater (as displayed in iDModTool):

• if SNR is a positive number greater than 2 then look to trees or other obstructions, snow on the dish, condensation in the feed horn and the usual things that limit signal quality.
• If the SNR is -100 indicating that the iDirect modem does not see the satellite at all, then check the configuration of the positioner and verify correct satellite and polarization. If uncertain try vertical transmit and horizontal receive.
• Check the back of the iDirect modem for red lights. Cycle power if any red lights are seen.
• Now check the configuration of the modem. From the iDmodTool, lower center of the screen, check the Rx Freq and compare this to what you had when you last got the system working. If you don’t have that number, call your service provider and ask for the outbound carrier frequency. If it is incorrect then ask your provider to e-mail a fresh option file to you. You will need the iSite program to install it.
• Turn off the power on the positioner and verify the LNB indicator is still on. If not, check cabling to the modem. Verify that the two coaxial cables on the back of the positioner are not reversed. Check also that the cable from the positioner is plugged into the modem’s Rx input. Not to be confused with the Rx output that should have a silver cap on it.
• Finally, disconnect the coaxial cable that leads to the roof from the back of the positioner and connect that directly to the modem Rx input. If this works then a defective positioner is indicated.

Troubleshooting a solid RX lock that won’t transmit: TX should be blinking green. The iDmodTool is helpful here because it will adjust transmit power until you are connected. Assuming the hardware is working, there are only three reasons that you cannot connect.

• The account is disabled at the NOC.
• The transmitter power is too high or too low. iDmodTool will continue to adjust both up and down until you are connected. Again, check the back of modem for red lights. If any, reset power. If red light persists, then check transmitter and cable.

The latitude and longitude, while not important for receive lock, is critical for transmit. If this is a fixed site or you have used manual override, then check setting. Degrees and at least two decimal positions are required. Some versions of the positioner firmware would allow the positioner to begin pointing using the last known position after a timeout. This is okay if you have not moved.

After all this, and 20 min. of watching iDmodTool adjust your Tx power, then you must consider hardware. The easiest way to check the transmitter, if you have Rx lock, is to call your provider and ask him to command a CW test signal and watch for it on a spectrum analyzer. It takes about 10 minutes, and verifies transmitter operation from modem to BUC. While you are there, he might want to do a 1db compression test. Some older BUC’s like the NJT5017(f) are subject to drastically reduce power if driven by excessive power from the modem. Simply, the modem calls for a little more power and gets a lot less. Your provider can set your MaxTxPwr if this is the case.

If you are having trouble staying online, check all the above. On the iDModTool, if the TxPwr bar graph display stays all the way to the right, max power, then consider a bigger dish, bigger BUC or lower bandwidth uplink connection. Your provider may move you to a different in-route.

Troubleshooting

 What do the LED Indicators mean on the iDirect modem?

On initial Power up the PWR and STATUS led’s will be on. After a while the STATUS led will go out and the NET and RX will flash Yellow.

The LEDS should go solid green in the following order RX > TX > NET.

PWR should be on at all times and STATUS will be off except after initial Power up.

Troubleshooting issues on the iDirect Modem  (Active site)

• Check the LED status at front panel of the iDirect modem with the technician (Rx, Tx & NET).
• Are the TX, RX and LAN cables connected to the iDirect modem?
• Try to Ping the modem remotely.
• If you can ping the modem, then Telnet into the modem & check the Rx SNR value along with ARP Table (to check if LAN is connected to the iDirect modem).
• If PC is not connected to the modem, then the ARP Table command will not show any IP address in the list. If this is the case, then ask the technician to check the LAN cable at his end.
• If you are NOT able to Ping, the modem then ask the technician to Ping the modem from his end. If he is able to Ping the modem, then ask him to telnet into the modem & check the Rx SNR value.
• If not ask to check IP settings, router, LAN cable and ports.
• If the Rx LED is Amber, then you need to ask the technician to fine tune the antenna & get the Rx lock. Check to see that the coaxial connector is clean and free from any corrosion. If there are signs of corrosion, it is recommended that the LNB be replaced.
• Once he gets the Rx lock then check with the service provider what could be the issue. If everything is good from the service provider’s end, then ask the technician to swap the cables & check the LED again.
• If all the LED’s are Green and still customer is not able to browse the internet, then connect the iDirect modem directly to the PC without any router or a switch and then ask to browse.
• Simultaneously ask Teleport to check for routing issues.
• If still he is not able to browse, then check the DNS/IP configuration and make sure that he have entered the right DNS.

Troubleshooting the Evolution X3 Receive Chain

1) Check to see that the LNB and feed horn match the Service ordered.
2) In case of interference, it is recommended to use a narrow frequency range LNB.
3) Is the coaxial connection correct and tight?
4) If you do not know, or are uncertain of any of these parameters, consult the receiver documentation.
5) Check to see that the coaxial connector is clean and free from any corrosion. If there are signs of corrosion, it is
recommended that the LNB be replaced.
6) Check to see that the feed is secured to the LNB using the screws provided with the LNB.
7) Check to see that the “O” ring is installed between the LNB and the feed horn flange to prevent water from
entering the input waveguide of the LNB.
8 ) Check for the presence of water or moisture in the input waveguide of the LNB. If there are signs of corrosion it
is recommended that the LNB be replaced.
9) Ensure that the condition of the outside cover of the coaxial cable is without breaks or cracks. Also make sure
that there are no sharp bends, pinch points or flattened sections of the cable.
10) Check that there are between +13 and +18 volts coming from the receiver to power the LNB.
11) If there is a signal from the LNB but no signal at the router, check the signal at the end of the cable before the
router with a spectrum analyzer.
12) In the Option File, under the MODEM PARAMETERS section, increase the rx acq_range to 2 million.
13) Change the LNB to one with a narrow frequency range which is preferable.

Troubleshooting the Evolution X3 Transmit Chain

1) Make sure that the BUC matches the antenna and the satellite router being used.
2) Are the input and output frequency ranges correct?
3) Is the 10 MHz reference signal present?
4) Is the DC power level around +24 volts at the router output and at the cable end on the roof?
5) Ensure that the coaxial connection is tight and that the connector is sealed against water. Connectors that
incorporate a separate center pin that is soldered in place are recommended for the best operation of the BUC.
6) Ensure that the directions of the feed waveguide and OMT are oriented correctly. Failure to do so will result in
improper operation of the BUC.
7) Ensure that the BUC is secured to the feed using the screws provided with the BUC.
8 ) Ensure that the “O” ring is installed between the BUC and the feed flange to prevent water from entering
the input waveguide of the BUC.
9) Ensure that all external BUC assemblies are properly grounded in accordance with grounding instructions
supplied by your antenna and receiver manufacturer’s manual. Grounding provides protection to the BUC against lightning and ESD damage.
10) For proper system operation consult your iDirect satellite router manual.
11) Ensure that the condition of the outside cover of the coaxial cable is without breaks or cracks. Also, make sure
that there are no sharp bends, pinch points or flattened sections in the cable.
12) Change the BUC, make sure the Local Oscillator frequency is the same. If not, change the Option File under
FREQUENCY TRANSLATION to the new L.O. frequ

Antenna Polarization

Antenna polarization is a very important consideration when choosing and installing an antenna. Most communications systems use either vertical, horizontal or circular polarization. Knowing the difference between polarizations and how to maximize their benefit is very important to the antenna user.

A Polarization Review

An antenna is a transducer that converts radio frequency electric current to electromagnetic waves that are then radiated into space. The electric field or “E” plane determines the polarization or orientation of the radio wave. In general, most antennas radiate either linear or circular polarization.

A linear polarized antenna radiates wholly in one plane containing the direction of propagation. In a circular polarized antenna, the plane of polarization rotates in a circle making one complete revolution during one period of the wave. If the rotation is clockwise looking in the direction of propagation, the sense is called right-hand-circular (RHC). If the rotation is counterclockwise, the sense is called left-hand-circular (LHC).

An antenna is said to be vertically polarized (linear) when its electric field is perpendicular to the Earth’s surface. An example of a vertical antenna is a broadcast tower for AM radio or the “whip” antenna on an automobile.

Horizontally polarized (linear) antennas have their electric field parallel to the Earth’s surface. Television transmissions in the USA use horizontal polarization.

A circular polarized wave radiates energy in both the horizontal and vertical planes and all planes in between. The difference, if any, between the maximum and the minimum peaks as the antenna is rotated through all angles, is called the axial ratio or ellipticity and is usually specified in decibels (dB). If the axial ratio is near 0 dB, the antenna is said to be circular polarized. If the axial ratio is greater than 1-2 dB, the polarization is often referred to as elliptical.

Important Considerations

Polarization is an important design consideration. The polarization of each antenna in a system should be properly aligned. Maximum signal strength between stations occurs when both stations are using identical polarization

When choosing an antenna, it is an important consideration as to whether the polarization is linear or elliptical. If the polarization is linear, is it vertical or horizontal? If circular, is it RHC or LHC?

On line-of-sight (LOS) paths, it is most important that the polarization of the antennas at both ends of the path use the same polarization. In a linearly polarized system, a misalignment of polarization of 45 degrees will degrade the signal up to 3 dB and if misaligned 90 degrees the attenuation can be 20 dB or more. Likewise, in a circular polarized system, both antennas must have the same sense. If not, an additional loss of 20 dB or more will be incurred.

Also, note that linearly polarized antennas will work with circularly polarized antennas and vice versa. However, there will be up to a 3-dB loss in signal strength. In weak signal situations, this loss of signal may impair communications.

Cross polarization is another consideration. It happens when unwanted radiation is present from a polarization which is different from the polarization in which the antenna was intended to radiate. For example, a vertical antenna may radiate some horizontal polarization and vice versa. However, this is seldom a problem unless there is noise or strong signals nearby.

Typical Applications

Vertical polarization is most often used when it is desired to radiate a radio signal in all directions such as widely distributed mobile units. Vertical polarization also works well in the suburbs or out in the country, especially where hills are present. As a result, nowadays most two-way Earth to Earth communications in the frequency range above 30 MHz use vertical polarization.

Horizontal polarization is used to broadcast television in the USA. Some say that horizontal polarization was originally chosen because there was an advantage to not have TV reception interfered with by vertically polarized stations such as mobile radio. Also, manmade radio noise is predominantly vertically polarized and the use of horizontal polarization would provide some discrimination against interference from noise.

In the early days of FM radio in the 88-108 MHz spectrum, the radio stations broadcasted horizontal polarization. However, in the 1960’s, FM radios became popular in automobiles which used vertical polarized receiving whip antennas. As a result, the FCC modified Part 73 of the rules and regulations to allow FM stations to broadcast RHC or elliptical polarization to improve reception to vertical receiving antennas if the horizontal component was dominant.

Circular polarization is most often use on satellite communications. This is particularly desired since the polarization of a linear polarized radio wave may be rotated as the signal passes through any anomalies (such as Faraday rotation) in the ionosphere. Furthermore, due to the position of the Earth with respect to the satellite, geometric differences may vary especially if the satellite appears to move with respect to the fixed Earth-bound station. Circular polarization will keep the signal constant regardless of these anomalies.

What is Available

As stated earlier, for best performance, it is desirable to use an antenna with the same polarization on both ends of a communications path. If a system is already in place, all that is required is to find out what polarization is presently being used and match it.

Most base station antenna providers will supply either vertical or horizontal polarized antennas. They are the most economical types. Furthermore, vertically polarized antennas seem to be the most popular for two-way communications, as stated above, while horizontal polarization is most predominant in broadcast communications such as TV and FM.

Circularly polarized antennas are normally more costly than linear polarized types since true circular polarization is difficult to attain. An example of a true circularly polarized antenna is the helix.

However, the most common circularly polarized antenna uses crossed Yagi’s for “near circular” or elliptical polarization. Elliptical polarization can be generated by placing two identical linear polarized Yagi’s at right angles (90-degree phase differential) to each other and then feeding them with equal power and a phasing network. A well-made antenna of this type will have a typical axial ratio of +/-1 to 3 dB. In special applications, crossed Yagi antennas can be configured to accept either RHC or LHC by a selection relay.

Other Considerations

If your antenna is to be located on an existing tower or building with other antennas in the vicinity, try to separate the antennas as far as possible from each other. In the UHF range, increasing separation even a few extra feet may significantly improve performance from problems such as desensitization.

When setting up your own exclusive communications link, it may be wise to first test the link with vertical and then horizontal polarization to see which yields the best performance (if any). If there are any reflections in the area, especially from structures or towers, one polarization may outperform the other. Furthermore, if there are other RF signals in an area, using a polarization opposite the predominant high-level signals will give some isolation as discussed earlier.

On another note, when radio waves strike a smooth reflective surface, they may incur a 180-degree phase shift, a phenomenon known as specular or mirror image reflection. The reflected signal may then destructively or constructively affect the direct LOS signal. Circular polarization has been used to an advantage in these situations since the reflected wave would have a different sense than the direct wave and block the fading from these reflections.

Diversity Reception

Even if the polarizations are matched, other factors may affect the strength of the signal. The most common are long and short-term fading. Long term fading results from changes in the weather (such as barometric pressure or precipitation) or when a mobile station moves behind hills or buildings. Short term fading is often referred to as “multipath” fading since it results from reflected signals interfering with the LOS signal.

Some of this fading phenomenon can be decreased using diversity reception. This type of system usually employs dual antennas and receivers with “voting” system to choose the busiest signal. However, for best results, the antennas should be at least 20 wavelengths apart so that the signals are no longer correlated. This would be 20-25 feet at 880 MHz, quite a structural problem.

Nowadays we are inundated with mobile radios and cellular telephones. The polarization on handheld units is often random depending on how they are held by the user. This has led to new studies which have found that polarization diversity can be an advantage. The most important breakthrough in this area is that the antennas at the base station do not have to be separated physically as described above. They can be collocated if they are orthogonal and well isolated from each other. Only time will tell if these systems are truly cost effective.