TRX-1: some loss of signal when headphones are used

[kmartin]

I have noticed some loss of signal when i use headphones or external speaker on my TRX-1 or at least when monitoring
P25 trunk systems i get full bars when monitoring systems with the built in speaker and display shows "T" when monitoring
but if i plug anything into the headphone jack the T disappears ! and when i monitor the control channel by its self i get full
bars even with Attenuator on, but if i plug in my headphone or external speaker i loose 1 to 2 bars on signal strength meter !
has anyone else had this problem or know what causes this to happen ?

 

[tvengr]

With the headphone or speaker cable in close proximity to the antenna, it may be detuning the antenna or making it directional. Try using a short antenna extension cable between the antenna jack on the scanner and the antenna. I suspect there will be no difference with the antenna at a distance away from the cables. For optimal results, there should be no conductive objects close to the antenna. It is also possible that the cables can be acting as an antenna with the signal arriving out of phase with the antenna signal producing a cancellation effect.

 

[kmartin]

With the headphone or speaker cable in close proximity to the antenna, it may be detuning the antenna or making it directional. Try using a short antenna extension cable between the antenna jack on the scanner and the antenna. I suspect there will be no difference with the antenna at a distance away from the cables. For optimal results, there should be no conductive objects close to the antenna. It is also possible that the cables can be acting as an antenna with the signal arriving out of phase with the antenna signal producing a cancellation effect.

i forgot to mention i have 2 antennas hooked up at different sides of the room 800mhz verticals equal gain , about 10 feet apart so there is cable hooked up to a BNC T on the scanner as well as equal lengths of cable to each antenna i think its just the unit's design because simulcast distortion

 

[tvengr]

There are 2 problems with your antenna system. With 2 antennas in parallel with the T connector, you have an impedance mismatch. Depending on the wavelength and the direction of the signal you are monitoring, the signals could be in phase and additive or out of phase and subtractive. If the signal arrives at both antennas 180 degrees out of phase with each other, there can be a complete cancellation and loss of signal. Your antenna setup is definitely directional. Try eliminating the T connector and use a single antenna.

 

[slicerwizard]

The headphone cable is adding a counterpoise - i.e. the ground side of your antenna system, and that can change tuning, polarization, directionality, ...

 

[kmartin]

ok thanks