ok so my 148 gtl side mike and cobra 2000 gtl both have exit13 NPC mod
they sound good when monitoring on another radio all limiters are intact mike gain I've always run them at 1 or 2 o'clock position while I was on the 148 on channel 8 I can hear splatter on channel 9 but not on channel 7
then I switch over to the 2000 and the same scenario 1 channel up yes 1 channel down no issue also it doesn't matter what channel you use it's always 1 up with this issue I went from 12 o'clock on the AMC pot to close and it fades away maybe because the radios are only 3 feet away from each other 1 on an antenna other on a dummy load. thanks
Not to get too technical, but you may hear terminology like...
- 60dB down at 3kHz...
Or...
Image Rejection - 65dB
These refer to a way the receiver responds to the noise present on frequencies close to and near the frequency you're tuning into.
Your Cobra 2000 has this to say about it (Its' on Page 7 of your owners manual)
In trying to get good SENSITIVTY and good SELECTIVITY - they tend to "Walking Contradictions" you can't have both without one them interfering with the other...
So along comes RF Gain, the "Great Equalizer" - its' concern is to allow one method, to achieve it's goals and yet allow the other to do some work to help it achieve it's own goals.
Referring to -
Selectivity - your bandwidth to receive a signal depends on how good the steps of filtering is.
The more steps or stages of filtering, the greater the level of attenuation around and AT the frequency of interest.
As a level of caution:
- You can have too many stages of filtering - where even the signals you want to receive can't get thru all the stages no matter how much amplification is applied to the original signal arriving to the antenna - including all the noise around it and embedded in it.
This is Reciprocal - it affects another approach, or aspect:
- You can also have Sensitivity problems - for then the signal and its' noise the receiver "captures" together with it, then is amplified together, along with any other signals that are strong yet not exactly on the frequency.
- The radio processes the RF signal as a method of mixing the received signal to a local signal to make an IMAGE of the ORIGINAL signal - but at a different - lower frequency that can be amplified to a higher degree of accuracy than your RF signal can be if left alone.
- Mixing to get an IMAGE inherits the problems the original signal had - it's noise, any interference from frequencies close to the selected frequency - SEE ABOVE - will also be included.
So what you're hearing, is the "bleedover" you have as a factor of overload. You can swamp the receiver close by with the images as well as the sheer strength of RF signal present at the other radio - into the radio you're monitoring - thru several methods listed above and then others that are more related to a "rectification" of the signal thru the Monitors radios own Audio Amplifier circuitry.
You can determine the path or method used by simply moving or separating the radios apart and use a dummy load on the monitor radio to help balance out currents that can form thru it's shell, or skin - that can interfere of generate the effect because the shielding the case provides is simply overloaded and can't isolate the receiver from it.
One other factor is the REJECTION - the ability of the Receiver to "knock down" the Gain that the RF Gain is not able to do, and attenuate ALL signals arriving to the radio's receiver (A figure of Merit as performed by the AGC) but in doing so, leaves behind an "image" itself - that being the received strong signal - mixing as an IF image because the AGC is working at rejecting the very signal causing the strong image to appear, as if it is mirroring the signal like an Echo.
