Many Modern Receivers use a 1st I.F. frequency near 744 MHz.
Great care must be taken to prevent R.F. signals around these
frequencies from entering the receiver. These pictures
are from WOFL's ENG Site at their Channel 35 UHF Transmitter.
The Signals are coming from another UHF Station, a short distance away.
This is the actual signal from WOFL-TV's new Ultrascan ENG antenna.
The interfering signal you are seeing here is UHF TV channel 65.
The signal level is -15.7 dbm, and is blasting through
the receiver's LNA and mixer, right into the
1st IF amplifier, at 744 MHz! Even the
LNA's noise floor is high, after going
through 1120' of 7/8" Heliax line.
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KCNC-TV in Denver Colorado had an even greater problem. Their "Code Runner" receiver has a first IF of 744 Mhz. 741.25 MHz is the Visual Carrier Frequency of the 5 Megawatt Channel 59 UHF transmitter, located on the same mountain-top, only a few hundred feet away. They used our SuperFilter/LNA to remove the interference from the receiver's input, but needed additional shielding to filter all video, audio, and power leads going to the receiver. An alternative would be to switch to a different receiver. |
