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United We Stand |
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Brainerd Area Amateur Radio Club, Inc. |
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"Ham Tips" Front End Overload |
Situation: You are trying to talk from your car to another car via a 2-meter repeater. You hear an apparent weak signal, or no signal, from the other operator. He may or may not have the same problem hearing you. Other stations can hear the two of you just fine. Answer: You are too close to the other car and the other
operator’s transmitter is overloading the front end of your receiver. How can this be? Well, when using a two-meter repeater, the other operator is transmitting at a frequency 600 KHz away from the frequency you receive on. The strong carrier causes your receiver to more-or-less “blank out” because the local transmitter may be 100 dB or more higher in level than the repeater’s output signal at that location. The problem is worst when the repeater is a long ways away and the vehicles are close together.The answer is for both operators to run less power. Just because you have a 50 watt transmitter does not mean that it needs to run at that power level, especially when you are within 20 miles of the repeater. I typically run just 2 watts when I am within 20 miles of town. This is “good operating practice.” You use the minimum amount of power required to get the job done. It reduces, but does not always eliminate, the front end overload problem. A lot of it has to do with the design of the receivers involved. The other answer, of course, is to switch to simplex on a non-repeater channel such as 146.52 MHz, which is the National Calling Channel. There are plenty of other channels, like 146.58 MHz, which are less used.
Story by Mark Persons WØMH 
