The 2 large blips, in the first division on the left, are PCS Blocks "A" and "B." They are about -38 dbm at the receiver, and about -10 db at the output of the LNA. The antenna is pointed away from the Wireless Cable site, but it can still be seen in the last 3 divisions (columns) on the right. 2.5 Ghz ENG channels 8 & 9 can be seen at the start of the eighth division, with channel nine to the right. This is all coming from an Ultrascan Antenna. When the Ultrascan's LNA is put in the "high gain" position, lines appear through the picture, so it is kept in the "low gain" position. This rural site is generally useable, but many broadcasters are not so lucky!
This screen is divided into 10 vertical divisions (columns).
Use the chart below to identify the signals in each column.
These measurements were taken before XM-Radio @ ~2.34 GHz
Frequency SPAN in MHz
Service & FREQUENCY in MHZ
signal at Receiver Mixer
|TYPICAL Attenuation for State of the Art LNA
Cell Relay: 2110-2130
A : -35 db
|4||2140-2220||MMDS:2150-65||-60 dbm||-1 db||~110 db|
|- 60 dbm below 2450 MHz
-60 dbm above 2485 Mhz
|-1 db @ 2440 MHz
Wireless Cable/ ITFS / MDS: above 2500
|>50 db@ 2440 MHz|
|8||2460-2540||>90 db@ 2500 MHz|
|9||2540-2620||-60 dbm||-2 db||>160 db|
|10||2620-2700||-60 dbm||-6 db||>160 db|
If you are experiencing loss of range, noisy audio and video, or other interference to your ENG or STL Receiver, disconnect the antenna line to your receiver, and connect it to a spectrum analyzer.
You will need a Spectrum Analyzer that covers up to 2700 MHz.
Take a look at the frequencies around 1930-1945 Mhz (PCS Block "A"), 1945-1950 (Block "D"), 1950-1965 Mhz (PCS Block "B"), 1965 to 1970 Mhz (Block "E"), 1970 to 1975 Mhz (Block "F"). and 1975-1990 Mhz (Block "C")
The signal level(s) you are seeing is the output of your LNA, MINUS the line loss of the coax bringing your signal down the tower. It is important to look at the width of the PCS signal. If it appears to be 1.25 MHz wide, you are dealing with a CDMA System. CDMA uses Spread Spectrum Technology, and the amplitude you see, is only a fraction of the actual power! Pan your antenna 360 degrees, and measure some of the signals above -40 dbm. that you see from 1900 to 2700 Mhz. Please keep in mind that your Antenna System's amplifier may already be producing "false signals," which are the result of moderate and high level signals being amplified non-linearly (intermodulation, or "intermod").
If you have a state of the art receiver, it does not want to see MULTIPLE SIGNALS HIGHER THAN -36 dbm, and less for receivers with LNAs made prior to ~1990. Modern receivers usually have 20 db typical LNA gain built in.
When you have multiple signals that are raised 20 db, and then fed to a typical mixer at a level of -16 dbm each, the mixer will produce a tremendous amount of mixes. When this mixing of undesired signals raises the noise floor, your range is cut. When the products of this RF mixing appear at your receiver's IF frequency (the frequency that it uses to amplify and process your STL or ENG signals), your range is drastically cut!
Your LNA must have headroom to cleanly handle signals, without mixing them. To determine if your LNA is cleanly handling signals, you need to know the loss of the transmission line you are using between your LNA, at the top of your tower, and your receiver. Determine the loss of the line, and add this line loss to the highest level signal you see on the screen of your spectrum analyzer. This is the actual level at the output of you LNA! Modern LNAs can only produce about +10 dbm power output, but at this level, they are compressing signals, and mixing them together!. The level you calculated must never exceed -10 dbm, if you want clean audio and video. Older LNAs, such as found in the NURAD 20QP1 Horn Antenna System, can cleanly handle only -25 dbm. You must maintain RF headroom. There are many other signals in the spectrum waiting to mix with moderate level signals. Our Hi-Power SuperFilter/LNA can handle a power output level in excess of 1 watt.
You should never apply a signal greater than -36 dbm to a receiver with a -80 dbm threshold (ie: MILLENNIUM).
You should never apply a signal greater than -26 dbm to a receiver with a -70 dbm threshold (ie: MA2G)
But wait! Every signal that appears at the receiver's mixer, adds to the noise floor, and adds noise to your picture and audio subcarriers, or helps to corrupt your digital data stream. And, if you are seeing strong PCS, it's also at the image frequency of most 2 GHz ENG and STL channels (rec. LO minus 70 MHz = IF Frequency), and will degrade video and audio to some degree, in virtually all receivers with a single 70 Mhz I.F! An easier way is to add 140 MHz to the PCS frequency you see on your spectrum analyzer, and see if the answer falls within plus or minus 10 Mhz of your ENG or STL channel. If you can't get in from those old reliable places, or your audio subcarriers are noisy, or your STL lost it's fade margin, you now know why! Call us if you don't like what you see.
If you don't see any PCS signals, one of three things is possible: 1) You are using our SuperFilter/LNA, 2) PCS has not come to your area yet! 3) Your LNA is DEAD!! More PCS Information
6/25/97: Jim Barger, WCAU-TV, Philadelphia, PA, has the honor of being the first to contact us regarding "C Block" PCS Interference! Our predictions were right on schedule!
When you need equipment that has to work the first time, equipment that will still be working after an electrical storm, and equipment that will give you many years of trouble-free service, WE ARE THE ONLY GAME IN TOWN. We set the standards that others TRY to copy!
It's your choice. You can read articles on "Living with PCS', or you can Upgrade to our SuperFilter/LNA.